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2.5: Buffers, pH, Acids, and Bases - Biology

2.5: Buffers, pH, Acids, and Bases - Biology


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Learning Objectives

  • Identify the characteristics of acids
  • Identify the characteristics of bases
  • Define buffers and discuss the role they play in human biology

The pH scale ranges from 0 to 14. The pH of a solution is a measure of its acidity or alkalinity (base). You have probably used litmus paper, paper that has been treated with a natural water-soluble dye so it can be used as a pH indicator, to test how much acid or base (alkalinity) exists in a solution. You might have even used some to make sure the water in an outdoor swimming pool is properly treated.

This pH test measures the amount of hydrogen ions that exists in a given solution. High concentrations of hydrogen ions yield a low pH (acidic substances), whereas low levels of hydrogen ions result in a high pH (basic substances). The overall concentration of hydrogen ions is inversely related to its pH and can be measured on the pH scale (Figure 1). Therefore, the more hydrogen ions present, the lower the pH; conversely, the fewer hydrogen ions, the higher the pH. A change of one unit on the pH scale represents a change in the concentration of hydrogen ions by a factor of 10, a change in two units represents a change in the concentration of hydrogen ions by a factor of 100. Thus, small changes in pH represent large changes in the concentrations of hydrogen ions. Pure water is neutral. It is neither acidic nor basic, and has a pH of 7.0. Anything below 7.0 (ranging from 0.0 to 6.9) is acidic, and anything above 7.0 (from 7.1 to 14.0) is alkaline. The blood in your veins is slightly alkaline (pH = 7.4). The environment in your stomach is highly acidic (pH = 1 to 2). Orange juice is mildly acidic (pH = approximately 3.5), whereas baking soda is basic (pH = 9.0).

Acids are substances that provide hydrogen ions (H+) and lower pH, whereas bases provide hydroxide ions (OH) and raise pH. The stronger the acid, the more readily it donates H+. For example, hydrochloric acid and lemon juice are very acidic and readily give up H+ when added to water. Conversely, bases are those substances that readily donate OH. The OH ions combine with H+ to produce water, which raises a substance’s pH. Sodium hydroxide and many household cleaners are very alkaline and give up OH rapidly when placed in water, thereby raising the pH.

Buffers

Most cells in our bodies operate within a very narrow window of the pH scale, typically ranging only from 7.2 to 7.6. If the pH of the body is outside of this range, the respiratory system malfunctions, as do other organs in the body. Cells no longer function properly, and proteins will break down. Deviation outside of the pH range can induce coma or even cause death.

So how is it that we can ingest or inhale acidic or basic substances and not die? Buffers are the key. Buffers readily absorb excess H+ or OH, keeping the pH of the body carefully maintained in the aforementioned narrow range. Carbon dioxide is part of a prominent buffer system in the human body; it keeps the pH within the proper range. This buffer system involves carbonic acid (H2CO3) and bicarbonate (HCO3) anion. If too much H+ enters the body, bicarbonate will combine with the H+ to create carbonic acid and limit the decrease in pH.

Likewise, if too much OH is introduced into the system, carbonic acid will rapidly dissociate into bicarbonate and H+ ions. The H+ ions can combine with the OH ions, limiting the increase in pH. While carbonic acid is an important product in this reaction, its presence is fleeting because the carbonic acid is released from the body as carbon dioxide gas each time we breathe. Without this buffer system, the pH in our bodies would fluctuate too much and we would fail to survive.

Learning Objectives

The pH of a solution is a measure of the concentration of hydrogen ions in the solution. A solution with a high number of hydrogen ions is acidic and has a low pH value. A solution with a high number of hydroxide ions is basic and has a high pH value. The pH scale ranges from 0 to 14, with a pH of 7 being neutral. Buffers are solutions that moderate pH changes when an acid or base is added to the buffer system. Buffers are important in biological systems because of their ability to maintain constant pH conditions.

Practice Question

Using a pH meter, you find the pH of an unknown solution to be 8.0. How would you describe this solution?

  1. weakly acidic
  2. strongly acidic
  3. weakly basic
  4. strongly basic

[reveal-answer q=”596748″]Show Answer[/reveal-answer]
[hidden-answer a=”596748″]This solution is weakly basic. Remember, a pH of 7.0 is neutral. Anything above that (7–14) is acidic, and anything below that (0–6) is basic.[/hidden-answer]

The pH of lemon juice is about 2.0, whereas tomato juice’s pH is about 4.0. Approximately how much of an increase in hydrogen ion concentration is there between tomato juice and lemon juice?

  1. 2 times
  2. 10 times
  3. 100 times
  4. 1000 times

[reveal-answer q=”835678″]Show Answer[/reveal-answer]
[hidden-answer a=”835678″]Lemon juice is 100 times as acidic as tomato juice. Remember, each step in the pH scale represents a change in concentration by a factor of 10. Since tomato juice has a pH of 4.0, and lemon juice has a pH of 2.0, the concentration would change by 10 times 10.[/hidden-answer]


The acidity of the solution

The number of hydrogen ions present in a solution is a measure of the acidity of the solution. All acids do not ionize completely when dissolved in water, i.e., all the molecules of acid do not ionize and exist in the solution as electrically-charged particles. The hydrogen ion concentration is a measure, therefore, of the amount of dissociated acid rather than of the an amount of acid present. Strong acids dissociate more freely than weak acids hydrochloric acid, for example, dissociates freely into H+ and Cl− whereas carbonic acid, a weak acid, dissociates much less freely into H+ and CO3–. The number of free hydrogen ions is a measure of its acidity rather than an indication of the type of molecule from which the hydrogen ions originated.


Ionic Product of Water Kw

Water can act as an acid or a base. And the following equilibrium exists in water:


This can be expressed as an equilibrium constant using the concentrations. However, the equilibrium lies very far to the left. This means that very few hydrogen and hydroxide ions are produced and the concentration of water can be taken to be constant. Therefore we get a different expression that is called Kw.


Now that we have this information it is possible to calculate the pH of strong bases, by a very simple process have a look at the following example.


Multiple Choice Questions on pH and Buffer

26. The Henderson-Hasselbalch equation:

a) allows the graphic determination of the molecular weight of a weak acid from its pH alone.
b) does not explain the behavior of di- or tri-basic weak acids
c) employs the same value for pKa for all weak acids.
d) is equally useful with solutions of acetic acid and of hydrochloric acid.
e) relates the pH of a solution to the pKa and the concentrations of acid and conjugate base.

27. Consider an acetate buffer, initially at the same pH as its pKa (4.76). When sodium hydroxide (NaOH) is mixed with this buffer, the:
a) pH remains constant.
b) pH rises more than if an equal amount of NaOH is added to an acetate buffer initially at pH 6.76.
c) pH rises more than if an equal amount of NaOH is added to unbuffered water at pH 4.76.
d) ratio of acetic acid to sodium acetate in the buffer falls.
e) sodium acetate formed precipitates because it is less soluble than acetic acid.

28. A compound is known to have a free amino group with a pKa of 8.8, and one other ionizable group with a pKa between 5 and 7. To 100 mL of a 0.2 M solution of this compound at pH 8.2 was added 40 mL of a solution of 0.2 M hydrochloric acid. The pH changed to 6.2. The pKa of the second ionizable group is:
a) The pH cannot be determined from this information.
b) 5.4
c) 5.6
d) 6.0
e) 6.2

29. Three buffers are made by combining a 1 M solution of acetic acid with a 1 M solution of sodium acetate in the ratios shown below.

1 M acetic acid 1 M sodium acetate

Buffer 1: 10 mL 90 mL
Buffer 2: 50 mL 50 mL
Buffer 3: 90 mL 10 mL
Which of these statements is true of the resulting buffers?
a) pH of buffer 1 < pH of buffer 2 < pH of buffer 3
b) pH of buffer 1 = pH of buffer 2 = pH of buffer 3
c) pH of buffer 1 > pH of buffer 2 > pH of buffer 3
d) The problem cannot be solved without knowing the value of pKa.
e) None of the above.

30. A 1.0 M solution of a compound with 2 ionizable groups (pKa’s = 6.2 and 9.5 100 mL total) has a pH of 6.8. If a biochemist adds 60 mL of 1.0 M HCl to this solution, the solution will change to pH:
a) 5.60
b) 8.90
c) 9.13
d) 9.32
e) The pH cannot be determined from this information.

Answers:
26. e) relates the pH of a solution to the pKa and the concentrations of acid and conjugate base.
27. d) ratio of acetic acid to sodium acetate in the buffer falls.
28. c) 5.6
29. b) pH of buffer 1 = pH of buffer 2 = pH of buffer 3
30. a) 5.60

Reference: Lehninger Principles of Biochemistry Lecture Notebook 4th Revised Edition


2.5: Buffers, pH, Acids, and Bases - Biology

PART II. CORNERSTONES: CHEMISTRY, CELLS, AND METABOLISM

Acids, bases, and salts are three classes of biologically important compounds (table 2.3). Their characteristics are determined by the nature of their chemical bonds. Acids are ionic compounds that release hydrogen ions in solution. A hydrogen atom without its electron is a proton. You can think of an acid, then, as a substance able to donate a proton to a solution. Acids have a sour taste, such as that of citrus fruits. However, tasting chemicals to see if they are acids can be very hazardous, because many are highly corrosive. An example of a common acid is the phosphoric acid—H3PO4—in cola soft drinks. It is a dilute solution of this acid that gives cola drinks their typical flavor. Hydrochloric acid is another example:

Acids are ionically bonded molecules, which when placed in water dissociate, releasing hydrogen (H + ) ions.

TABLE 2.3. Some Common Acids, Bases, and Salts

Weak acid found in vinegar

Weak acid of carbonated beverages that provides bubbles or fizz

Weak acid found in sour milk, sauerkraut, and pickles

Weak acid used in cleaning solutions, added to carbonated cola beverages for taste

Strong acid used in batteries

Strong base also called lye or caustic soda used in oven cleaners

Strong base also known as caustic potash used in drain cleaners

Weak base also known as milk of magnesia used in antacids and laxatives

Found in medicine, canning, and baking powder

Used in fire extinguishers, antacids, baking powder, and sodium bicarbonate

Used in laxatives and skin care

Used in water softeners, fertilizers, and cleaning agents

A base is the opposite of an acid, in that it is an ionic compound, which, when dissolved in water, removes hydrogen ions from solution. Bases, or alkaline substances, have a slippery feel on the skin. They have a caustic action on living tissue by converting the fats in living tissue into a water-soluble substance. A similar reaction is used to make soap by mixing a strong base with fat. This chemical reaction gives soap its slippery feeling. Bases are also used in alkaline batteries. Weak bases have a bitter taste—for example, the taste of broccoli, turnip, and cabbage. Many kinds of bases release a group of hydrogen ions known as a hydroxide ions, or an OH - group. This group is composed of an oxygen atom and a hydrogen atom bonded together, but with an additional electron. The hydroxide ion is negatively charged therefore, it will remove positively charged hydrogen ions from solution. A very strong base used in oven cleaners is sodium hydroxide, NaOH. Notice that ions that are free in solution are always written with the type and number of their electrical charge as a superscript.

Basic (alkaline) substances are ionically bonded molecules, which when placed in water dissociate, releasing hydroxide (OH - ) ions.

Acids and bases are also spoken of as being strong or weak (Outlooks 2.2). Strong acids (e.g., hydrochloric acid) are those that dissociate nearly all of their hydrogens when in solution. Weak acids (e.g., phosphoric acid) dissociate only a small percentage of their hydrogens. Strong bases dissociate nearly all of their hydroxides (NaOH) weak bases, only a small percentage. The weak base sodium bicarbonate, NaHCO3, will react with acids in the following manner:

Notice that sodium bicarbonate does not contain a hydroxide ion but it is still a base, because it removes hydrogen ions from solution.

The degree to which a solution is acidic or basic is represented by a quantity known as pH. The pH scale is a measure of hydrogen ion concentration (figure 2.15). A pH of 7 indicates that the solution is neutral and has an equal number of H + ions and OH - ions to balance each other. As the pH number gets smaller, the number of hydrogen ions in the solution increases. A number higher than 7 indicates that the solution has more OH - than H + . Pure water has a pH of 7. As the pH number gets larger, the number of hydroxide ions increases.

The concentration of acid (proton donor or electron acceptor) is greatest when the pH number is lowest. As the pH number increases, the concentration of base (proton acceptor or electron donor) increases. At a pH of 7, the concentrations of H + and OH - are equal. As the pH number gets smaller, the solution becomes more acidic. As the pH number gets larger, the solution becomes more basic, or alkaline.

It is important to note that the pH scale is logarithmic—that is, a change in one pH number is actually a 10-fold change in real numbers of OH - or H + . For example, there is 10 times more H +

When water dissociates, it releases both hydrogen (H + ) and hydroxide (OH - ) ions. It is neither a base nor an acid. Its pH is 7, neutral.

in a solution of pH 5 than in a solution of pH 6 and 100 times more H + in a solution of pH 4 than in a solution of pH 6.

Salts are ionic compounds that do not release either H + or OH - when dissolved in water thus, they are neither acids nor bases. However, they are generally the result of the reaction between an acid and a base in a solution. For example, when an acid, such as HCl, is mixed with NaOH in water, the H + and the OH - combine with each other to form pure water, H2O. The remaining ions (Na + and Cl - ) join to form the salt NaCl:

The chemical reaction that occurs when acids and bases react with each other is called neutralization. The acid no longer acts as an acid (it has been neutralized) and the base no longer acts as a base.

As you can see from figure 2.15, not all acids or bases produce the same pH. Some compounds release hydrogen ions very easily, cause low pHs, and are called strong acids. Hydrochloric acid (HCl) and sulfuric acid (H2SO4) are strong acids (figure 2.16a). Many other compounds give up their hydrogen ions grudgingly and therefore do not change pH very much. They are known as weak acids. Carbonic acid (H2CO3) and many organic acids found in living things are weak acids. Similarly, there are strong bases, such as sodium hydroxide (NaOH) and weak bases, such as sodium bicarbonate—Na + (HCO3) - .

FIGURE 2.16. Strong Acid and Strong Base

(a) Hydrochloric acid (HCl) has the common name of muriatic acid. It is a strong acid used in low concentrations to clean swimming pools and brick surfaces. It is important that you wear protective equipment when working with a solution of muriatic acid. (b) Liquid-Plumr ® is a good example of a drain cleaner with a strong base. The active ingredient is NaOH.

Maintaining Your pH —How Buffers Work

Acids, bases, and salts are called electrolytes, because, when these compounds are dissolved in water, the solution of ions allows an electrical current to pass through it. Salts provide a variety of ions essential to the human body. Small changes in the levels of some ions can have major effects on the functioning of the body. The respiratory system and kidneys regulate many of the body's ions. Because many kinds of chemical activities are sensitive to changes in the pH of the surroundings, it is important to regulate the pH of the blood and other body fluids within very narrow ranges. Normal blood pH is about 7.4. Although the respiratory system and kidneys are involved in regulating the pH of the blood, there are several systems in the blood that prevent wide fluctuations in pH.

Buffers are mixtures of weak acids and the salts of weak acids that tend to maintain constant pH, because the mixture can either accept or release hydrogen ions (H + ). The weak acid can release hydrogen ions (H + ) if a base is added to the solution, and the negatively charged ion of the salt can accept hydrogen ions (H + ) if an acid is added to the solution.

One example of a buffer system in the body is a phosphate buffer system, which consists of the weak acid dihydrogen phosphate (H2PO4 - ) and the salt of the weak acid monohydrogen phosphate (HPO4 - ).

(The two arrows indicate that this is in balance, with equal reactions in both directions.) The addition of an acid to the mixture causes the equilibrium to shift to the left.

Notice that the arrow pointing to the right is shorter than the arrow pointing to the left. This indicates that H+ is combining with HPO4 - and additional H2PO4 - is being formed. This removes the additional hydrogen ions from solution and ties them up in the H2PO4 - , so that the amount of free hydrogen ions in the solution remains constant.

Similarly, if a base is added to the mixture, the equilibrium shifts to the right, additional hydrogen ions are released to tie up the hydroxyl ions, and the pH remains unchanged.

Seawater is a buffer solution that maintains a pH of about 8.2. Buffers are also added to medicines and to foods. Many lemon-lime carbonated beverages, for example, contain citric acid and sodium citrate (salt of the weak acid), which forms a buffer in the acid range. The beverage label may say that these chemicals are to impart and regulate "tartness." In this case, the tart taste comes from the citric acid, and the addition of sodium citrate makes it a buffered solution.

24. What does it mean if a solution has a pH of 3, 12, 2, 7, or 9?

25. If the pH of a solution changes from 8 to 9, what happens to the hydroxide ion concentration?

The study of life involves learning about the structure and function of organisms. All organisms display the chemical and physical properties typical of all matter and energy. The two kinds of energy used by organisms are potential and kinetic. The kinetic molecular theory states that all matter is made up of tiny particles, which are in constant motion.

Energy can be neither created nor destroyed, but it can be converted from one form to another. Potential energy and kinetic energy can be interconverted. The amount of kinetic energy that the molecules of various substances contain determines whether they are solids, liquids, or gases. Temperature is a measure of the average kinetic energy of the molecules making up a substance. Heat is the total internal kinetic energy of molecules. The random motion of molecules, which is due to their kinetic energy, results in their being distributed throughout available space, forming mixtures.

There are many kinds of atoms, whose symbols and traits are described by the periodic table of the elements. These atoms differ from one another by the number of protons and electrons they contain. Each is given an atomic number, based on the number of protons in the nucleus, and an atomic weight, an average of all the isotopes of a particular element. The mass number is the sum of the number of protons and neutrons in the nucleus of an atom.

All matter is composed of atoms, which are composed of an atomic nucleus and electrons. The atomic nucleus can contain protons and neutrons, whereas the electrons encircle the nucleus at different energy levels. Atoms tend to seek their most stable configuration and follow the octet rule, which states that they all seek a filled outermost energy level.

Atoms may be combined by chemical reactions into larger units called molecules. There are many kinds of molecules. Two kinds of chemical bonds allow molecules to form—ionic bonds and covalent bonds. A third bond, the hydrogen bond, is a weaker bond that holds molecules together and may help large molecules maintain a specific shape. Molecules are described by their chemical formulas, which state the number and kinds of components of which they are composed.

An ion is an atom that is electrically unbalanced. Ions interact to form ionic compounds, such as acids, bases, and salts. Compounds that release hydrogen ions when mixed in water are called acids those that remove hydrogen ions are called bases. A measure of the hydrogen ions present in a solution is the pH of the solution.

Water is one of the most important compounds required by all organisms. This polar molecule has many unique properties, which allow organisms to survive and reproduce. Without water, life as we know it on Earth would not be possible.

How atoms achieve stability is the nature of chemical reactions. Five of the most important chemical reactions that occur in organisms are (1) oxidation-reduction, (2) dehydration synthesis, (3) hydrolysis, (4) phosphorylation, and (5) acid-base reactions.

Acids, bases, and salts are three classes of biologically important molecules. The hydrogen ion releasing or acquiring properties of acids and bases make them valuable in all organisms.

Salts are a source of many essential ions. Although acids and bases may be potentially harmful, buffer systems help in maintain pH levels.

1. _____ is the total internal kinetic energy of molecules.

2. The atomic weight of the element sodium is

3. Which is not a pure substance?

c. a mixture of milk and honey

d. the compound table salt

4. When a covalent bond forms between two kinds of atoms that are the same, the result is known as a

c. dehydration chemical reaction.

5. In this kind of chemical reaction, two molecules interact, resulting in the formation of a molecule of water and a new, larger end product.

6. Which of the following is an acid?

7. Salts are compounds that do not release either _____ or _____ ions when dissolved in water.

8. This intramolecular force under the right conditions can result in a molecule that is coiled or twisted into a complex, three-dimensional shape.

9. A triple covalent bond is represented by which of the following?

a. a single, fat, straight line

b. a single, thin, straight line

c. three separate, thin lines

d. three thin, curved lines

10. Electron clouds, or routes, traveled by electrons are sometimes drawn as spherical or _____ shapes.

11. Atoms of the same element differ from ions of that element because

a. they have different numbers of electrons.

b. their proton numbers are not the same.

c. their neutrons numbers are not the same.

d. there is no difference between an atom and an ion of the same element.

12. When someone uses the expression “you’re full of hot air,” he is referring to which phase of matter?

13. When a person is “running a fever,” she is experiencing an increase in her body’s _____.

14. Ions that are bonded together and form a threedimensional structure are called a _____.

15. A bottle of soda or pop is best described as

a. a heterogeneous mixture.

1. Heat 2. a 3. c 4. d 5. b 6. a 7. H + , OH - 8. C 9. c 10. hourglass 11. a 12. c 13. temperature 14. crystal 15. C

Chemicals Around the House

Sodium bicarbonate (NaHCO3) is a common household chemical known as baking soda, bicarbonate of soda, or bicarb. It has many uses and is a component of many products, including toothpaste and antacids, swimming pool chemicals, and headache remedies. When baking soda comes in contact with hydrochloric acid, the following reaction occurs:

What happens to the atoms in this reaction? In your description, include changes in chemical bonds, pH, and kinetic energy. Why is baking soda such an effective chemical in the previously mentioned products? Try this at home: Place a pinch of sodium bicarbonate (NaHCO3) on a plate. Add two drops of vinegar. Observe the reaction. Based on the previous reaction, can you explain chemically what has happened?

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Acid-Base Balance

Ventilatory Parameter: Arterial PCO2

The Henderson-Hasselbalch equation ( Equation 7 ) indicates that pH can be calculated from two variables, P co 2 and , without consideration of other acid-base pairs in the plasma (isohydric principle). Arterial P co 2 can be interpreted as a “ventilatory” parameter that reflects the adequacy of ventilation relative to the rate of carbon dioxide production. If arterial P co 2 exceeds the normal range (35 to 45 mm Hg), then the patient is hypoventilating, and, conversely, if the arterial P co 2 is lower, the patient is hyperventilating. These terms should be distinguished from hyperpnea and hypopnea, which refer to the increases or decreases of ventilation to meet respiratory requirements, as, for example, the hyperpnea during exercise, and from tachypnea and bradypnea, which indicate rapid and slow respiratory rates. Furthermore, the key parameter that determines arterial P co 2 at any rate of carbon dioxide production is alveolar ventilation, because ventilation of dead space does not lead to the loss of carbon dioxide. Arterial P co 2 is determined by the rate of carbon dioxide production, the ratio of the dead space to tidal volume, and minute ventilation.

The utility of arterial P co 2 as a ventilatory parameter is readily illustrated by a few brief examples. Arterial P co 2 is usually normal during moderate exercise, and the subject is neither hyperventilating nor hypoventilating, despite obvious hyperpnea and tachypnea. Patients with severe lung disease frequently hypoventilate despite both hyperpnea and tachypnea at rest, because much of the inhaled air is delivered to an enlarged physiologic dead space as a result of both shunting and regions of low ratio. An increase in carbon dioxide production may be caused by an increased metabolic rate (e.g., exercise or fever) or occasionally by an acute release of carbon dioxide from stores due to a severe, acute metabolic acidosis (e.g., during and after cardiopulmonary arrest or a grand mal seizure, when large amounts of lactic acid are produced and is converted to carbon dioxide). Regardless of the reason that ventilation fails to keep pace with carbon dioxide production, the concomitant increase in arterial P co 2 is classified as hypoventilation. Conversely, hyperventilation is frequently seen as a respiratory compensation for metabolic acidosis, or in response to hypoxia, anxiety, or other conditions that stimulate the carotid bodies and respiratory centers.


ACIDS AND BASES WITHIN THE BODY

In modern chemistry, we have a sound understanding of acids and bases (also called alkalis). Acids and bases pervade our lives, from the laboratory to the kitchen, and these crucial substances are used as laboratory reagents, industrial catalysts, food additives, and in cleaning products. However, over the course of the history of chemistry, it took centuries to understand these substances fully.

ANCIENT SCIENCE-VINEGAR AND SOAP

During the time of the Ancient Greeks, the properties of acids and bases were only vaguely understood. During their attempts to categorize substances and try to bring balance, harmony, and perfection to the universe, they used a variety of tests to distinguish compounds. One of these was taste, and they divided substances according to whether they were sour, bitter, salty or sweet. As the Greek influence waned and their knowledge passed on to the Romans, they began to refer to sour substances, such as vinegar or lemon juice, as acids.

ACIDS AND BASES – THE PLAYTHINGS OF ALCHEMISTS

As science moved on through the Islamic Golden Age and the Renaissance, alchemists started to understand more about acids, discovering that stronger solutions could speed up the corrosion of metal and dissolve certain rocks. Medieval and Islamic alchemists had a range of acids and alkalis to choose from:

  • Soda (sodium carbonate)
  • Potash (Potassium carbonate)
  • Ammonia
  • Hydrochloric acid
  • Sulfuric acid
  • Acetic acid
  • Citric acid
  • Sulfuric acid
  • Aqua regia, a mixture of nitric and hydrochloric acid that could even dissolve gold

In about 1300, a Spanish scholar, Arnaldus de Villa Nova, began to use litmus for

studying acids and bases. This compound, extracted from a lichen, had been used as a dye since at least the time of the Vikings, but he was the first known scholar to use it as a test of acidity. This idea was expanded by Robert Boyle (25 January 1627 – 31 December 1691), who found that certain plant derived substances changed color in the presence of acids or bases. One example was syrup of violets, which is blue in a pH neutral environment but turns green when exposed to bases, and red when mixed with acid.

THE ENLIGHTENMENT – CLASSIFYING ACIDS AND ALKALIS

It was not until the time of Antoine Lavoisier (26 August 1743 – 8 May 1794), a brilliant French chemist who attempted to classify elements and understand the nature of heat, that a more systematic study of acids and bases took place. At this time, chemists began to define bases as substances that could neutralize acids to form water and a salt. In 1776, influenced by studies into the properties of gases, Lavoisier tried to isolate the compound in acids responsible for their unique properties. Incorrectly, he proposed that a substance called oxygen was responsible, but his observations led to further studies. The British scientist, Humphrey Davy (1778-1829), better known for his studies into gases, tested the theories of Lavoisier and discovered that oxygen was not the element responsible for the properties of acids. Many acids did not contain oxygen, so he proposed that something else must be responsible, reasoning that it was the only element common to all acids. The Swedish chemist, Svante Arrhenius (1859-1927), was the next chemist to study acids and bases, proposing that acids and bases gained their properties because of the action of ions in the solution.

According to Arrhenius, the definition of acids and bases went like this:

Acids are substances delivering hydrogen cations (positively charged hydrogen, often simply called proton or abbreviated H + ) to the solution (water).

HCl and H2SO4 (cf. footnote 3 ) which form H + and Cl – or SO4 2- , respectively, dissolved in water.

Bases are substances delivering hydroxyl anions (OH – ) to the solution (water).

NaOH and Ca(OH)2 (cf. footnote 4 ) which form OH – Na + and Ca 2+ , respectively, dissolved in water.

Acids and bases react in a neutralisation reaction to form water (where H + reacts with OH – to form H2O) and the corresponding salt (In the examples: NaCl, Na2SO4, CaCl2 or CaSO4).

Brønsted and Lowry

Inspired by the work of Arrhenius, a Danish fellow named Johannes Nicolaus Brønsted and, independently, an Englishman by the name of Thomas Martin Lowry extended the acid-base theory to what is nowadays being taught in school, the Brønsted-Lowry concept. Here are the definitions according to those august gentlemen:

Acids are substances from which a proton (H + ) can be removed.

Bases are substances that bind protons.

These definitions mutated somewhat to become the slightly less accurate school-book-definition, in which acids are proton ‘donors’ and bases proton ‘acceptors’.

THE PH

pH stands for potential hydrogen, and is defined as the Negative logarithm of the concentration of hydrogen ions. pH is measured on a pH scale ranging from 0 to 14. 0 is considered highly acidic, while a pH of 14 is very basic, and a pH of 7 is neutral. Since pH is measured on a log scale, this means a pH of 9 is ten times more basic than a pH of 8. This alone gives you an idea of how important acid base balance in the human body is.

HOW TO CALCULATE PH AND [H + ]

The equilibrium equation yields the following equation for pH:

Calculate the pH for a specific [H + ]. Calculate pH given [H + ] = 1.4 x 10 -5 M

pH = -log10[H + ]
pH = -log10(1.4 x 10 -5 )
pH = 4.85

Calculate [H + ] from a known pH. Find [H + ] if pH = 8.5

[H + ] = 10 -pH
[H + ] = 10 -8.5
[H + ] = 3.2 x 10 -9 M

ACIDS AND BASES IN THE BODY

Three types of reactions can be distinguished from point of view of the acid-base balance. (1) proton-productive, (2) proton-consumptive, (3) proton-neutral. Examples follow:

1) Proton-productive reactions

a) Anaerobic glycolysis in muscles and erythrocytes

Glucose → 2 CH3CHOHCOO – + 2 H +

b) Ketogenesis – production of ketone bodies

Fatty acids → ketone bodies + n H +

c) Lipolysis

TAG → 3 FA + glycerol + 3 H +

d) Ureagenesis

2) Proton-consumptive reactions

a) Gluconeogenesis

2 lactate + 2 H + → Glc

b) Neutral and dicarboxylic amino acids oxidation

3) Proton-neutral reactions

a) Complete glucose oxidation

b) Lipogenesis from glucose

Human organism (healthy or not) every day produces great quantities of acids – source of protons. Organism is acidified by these processes:

1) Complete oxidation
2) Incomplete oxidation

Carbohydrates → glucose → pyruvate, lactate + H +

Triacylglycerol → fatty acids, ketone bodies + H +

Phospholipids → phosphate + H +

Proteins → amino acids→ sulphate, urea + H +

FACTORS THAT AFFECT PH LEVELS

The average pH in human blood is about 7.4, and narrowly ranges from 7.35 to 7.45. A slight change outside of this range can be devastating to cells and the entire body. Normal day to day activity affects our pH on a continual basis. This includes the air we breathe, the food we eat, and our urine that is excreted. Something as simple as washing your hands affects the pH on your skin.

Diet, however, plays a major role in acid base balance in the human body. A healthy diet should consist of about 75% alkaline foods such as vegetables, fruits and non animal proteins. The other 25% of a healthy diet includes acidic foods such as animal proteins (meat), grains, and dairy products.


Acids And Bases Worksheet Ph : Acids And Bases Assignment 1 2 Pdf Aleena Azam Biology 1406 P01 Name Course And Section Chapter 3 Acids Bases Ph And Buffer Worksheet 15pts Hydrogen Course Hero / Imagine you have two beakers

Acids And Bases Worksheet Ph : Acids And Bases Assignment 1 2 Pdf Aleena Azam Biology 1406 P01 Name Course And Section Chapter 3 Acids Bases Ph And Buffer Worksheet 15pts Hydrogen Course Hero / Imagine you have two beakers. Calculate the ph of a buffer solution prepared by dissolving 0.20 mole of cyanic acid (hcno) and When dissolved in water, there are no action on litmus ph. Some of the worksheets for this concept are lesson 8 acids bases and the ph scale time ii, inquiry and assessment unit, acids bases practice work, acids bases work, work 10 1 acid base and ph pdf, strong acids and bases work, calculating ph and poh work, acid and base ph calculations supplemental work key. Displaying top 8 worksheets found for this concept. Complete the following table by filling in the empty spaces.

A solution of glycolic acid (hg) has a ph of 2.00. C) a solution has a ph of 7, it's neutral. Grade 7 acids and bases worksheet from files.liveworksheets.com chemists use strong acids and bases to get chemical reactions in the lab. Naming acids worksheets key from www.unmisravle.com neutralization doc 24 kb ph indicators doc 33 kb reactions of acids and bases doc 37 kb electrolytes. Browse ph acids and bases chemistry resources on teachers pay teachers, a marketplace trusted by millions of teachers for original educational resources.

Acids And Bases Worksheet from s3.studylib.net Acids bases and ph worksheet. A solution of glycolic acid (hg) has a ph of 2.00. Introduce or review acids, bases, and the ph scale using the printable worksheets or digital distance learning activity. (all work above must be complete before attempting the bonus) you are stuck with a problem. Acid base ms beaucage from msbeaucage.weebly.com worksheets are acidsbases ph work, name date strong acids and bases, acids bases and solutions answer key, acid base practice work, 3719 acids and bases work, acids bases work, acids bases calculations practice work, calculating ph and poh work. If ph is less than 7, the substance is if the ph is 7, the substance is if ph is more than 7, the substance is most substances are (acid, base, neutral) 10. Acids/bases & ph worksheet contact detail: Some of the worksheets for this concept are acids bases and a base r, 11 0405 acids bases salts wkst, acids and bases chapter 14 15, lesson 8 acids bases and the ph scale time ii, acid base practice test, acids bases and solutions answer key, acidsbases ph work.

Ph measure for precise measurements.

Step 2 choose the species that can produce h+, and write balanced equations for the reactions producing h+. Worksheet 24 buffers 2 what is the ph of a buffer formed from 50 from acids and bases worksheet , source: Fill in the blanks with suitable words. E) a ph greater than 7 is a basic. Acids/bases & ph worksheet contact detail: Naming acids worksheets key from www.unmisravle.com neutralization doc 24 kb ph indicators doc 33 kb reactions of acids and bases doc 37 kb electrolytes. (all work above must be complete before attempting the bonus) you are stuck with a problem. Difference between essential and nonessential amino acids. Substance ph value acid or base ph indicator colour of ph indicator black coffee 5 litmus milk of magnesia 10. Greenbowe has a solutions of acids, bases, and salts simulation. Acids bases and ph worksheet. Acids and bases other contents: Be sure to write a chemical equation(s) for each problem.

Grade 7 acids and bases worksheet from files.liveworksheets.com chemists use strong acids and bases to get chemical reactions in the lab. Effect on ph of mixing aqueous solutions of strong acid with a strong base. (all work above must be complete before attempting the bonus) you are stuck with a problem. An introduction to acids, bases, and the ph scale. E) a ph greater than 7 is a basic.

Ppt Worksheet Acids Bases Ph Key Powerpoint Presentation Free Download Id 5491032 from image3.slideserve.com Effect on ph of mixing aqueous solutions of strong acid with a strong base. The equilibrium constant for a. Out of these, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website. Some of the worksheets for this concept are 11 0405 acids bases salts wkst, chapter 14 creative commons license acidsbases and salts, acids bases and salts, acid base reactions the ph, name ap chem chapter 14 outline acids and bases the, week 8 work chapter 10 acids and bases, bronsted. Worksheet 24 buffers 2 what is the ph of a buffer formed from 50 from acids and bases worksheet , source: Worksheet doc 25 kb titration problems doc 62 kb solution ph meter ph paper estimate ph value not. Showing 8 worksheets for acids and bases and the ph scale. Worksheet to accompany the lesson acids, bases and ph.

C) a solution has a ph of 7, it's neutral.

Acids bases and ph worksheet. Download the report sheet, complete it, and then submit it via canvas as an for example a substance with ph = 8 is a very weak. Browse ph acids and bases chemistry resources on teachers pay teachers, a marketplace trusted by millions of teachers for original educational resources. Identify whether the substance is an acid or a base and indicate what colour the ph indicator will turn. Imagine you have two beakers Some of the worksheets for this concept are acids bases and a base r, 11 0405 acids bases salts wkst, acids and bases chapter 14 15, lesson 8 acids bases and the ph scale time ii, acid base practice test, acids bases and solutions answer key, acidsbases ph work. Step 2 choose the species that can produce h+, and write balanced equations for the reactions producing h+. Acids bases and ph worksheet answers | akademiexcel.com from akademiexcel.com acids and bases pogil awesome weak acid base and salt problems key 1 from acids bases and ph worksheet answers , source:alisonnorrington.com. Complete the following table by filling in the empty spaces. Originally the terms acid and base referred to taste. Ph and h+ calculations for strong acids and bases by definition, strong acids and bases are 100% ionized in water solution. Worksheet doc 25 kb titration problems doc 62 kb solution ph meter ph paper estimate ph value not. Effect on ph of mixing aqueous solutions of strong acid with a strong base.

Acids bases and ph worksheet answers | akademiexcel.com from akademiexcel.com acids and bases pogil awesome weak acid base and salt problems key 1 from acids bases and ph worksheet answers , source:alisonnorrington.com. Worksheet 24 buffers 2 what is the ph of a buffer formed from 50 from acids and bases worksheet , source: Ph and h+ calculations for strong acids and bases by definition, strong acids and bases are 100% ionized in water solution. D) a ph less than 7 is an acid, with lower numbers indicating stronger acids. Worksheets labeled with are accessible to pro subscribers only.

Acids Bases And Ph Worksheet By Good Science Worksheets Tpt from ecdn.teacherspayteachers.com Ph practice (), ph calcuations (), and ph review problems ().all mr. Showing 8 worksheets for acids and bases and the ph scale. Acids/bases & ph worksheet (continued). Worksheet doc 25 kb titration problems doc 62 kb solution ph meter ph paper estimate ph value not. Introduce or review acids, bases, and the ph scale using the printable worksheets or digital distance learning activity. Imagine you have two beakers A) the ph scale measures how acidic or basic a substance is. Worksheet 24 buffers 2 what is the ph of a buffer formed from 50 from acids and bases worksheet , source:

Complete the following table by filling in the empty spaces.

Acids bases and ph worksheet. Imagine you have two beakers Acids bases and ph worksheet answers | akademiexcel.com from akademiexcel.com acids and bases pogil awesome weak acid base and salt problems key 1 from acids bases and ph worksheet answers , source:alisonnorrington.com. Can calculate from ph for example: Acids bases and ph worksheet answers | akademiexcel.com from akademiexcel.com acids and bases pogil awesome weak acid base and salt problems key 1 from acids bases and ph worksheet answers , source:alisonnorrington.com. Worksheet to accompany the lesson acids, bases and ph. Difference between essential and nonessential amino acids. A solution of glycolic acid (hg) has a ph of 2.00. E) a ph greater than 7 is a basic. Be sure to write a chemical equation(s) for each problem. Acids and bases the degree of acidity or alkalinity (basic) is important in organisms. Acids and bases worksheet ph : Greenbowe has a solutions of acids, bases, and salts simulation.

Source: 0.academia-photos.com

Worksheet 24 buffers 2 what is the ph of a buffer formed from 50 from acids and bases worksheet , source: Worksheet to accompany the lesson acids, bases and ph. Some of the worksheets for this concept are 11 0405 acids bases salts wkst, chapter 14 creative commons license acidsbases and salts, acids bases and salts, acid base reactions the ph, name ap chem chapter 14 outline acids and bases the, week 8 work chapter 10 acids and bases, bronsted. Complete the following table by filling in the empty spaces. Originally the terms acid and base referred to taste.

Source: www.goodscience.com.au

Introduce or review acids, bases, and the ph scale using the printable worksheets or digital distance learning activity. The equilibrium constant for a. D) a ph less than 7 is an acid, with lower numbers indicating stronger acids. Identify whether the substance is an acid or a base and indicate what colour the ph indicator will turn. C) a solution has a ph of 7, it's neutral.

As the ph increases the hydronium ion concentration decreases. Be sure to write a chemical equation(s) for each problem. Worksheet doc 25 kb titration problems doc 62 kb solution ph meter ph paper estimate ph value not. Acids/bases & ph worksheet (continued). B) ph scale ranges from 0 to 14.

Source: cdn.theworksheets.com

Calculate the ph of a buffer solution prepared by dissolving 0.20 mole of cyanic acid (hcno) and Difference between essential and nonessential amino acids. (weak acids, weak bases, salts, and buffers) name:_____ work on separate paper. Acids bases and ph worksheet. A) the ph scale measures how acidic or basic a substance is.

Source: image.slidesharecdn.com

The equilibrium constant for a. A) the ph scale measures how acidic or basic a substance is. Browse ph acids and bases chemistry resources on teachers pay teachers, a marketplace trusted by millions of teachers for original educational resources. Worksheet to accompany the lesson acids, bases and ph. Acids/bases & ph worksheet contact detail:

When dissolved in water, there are no action on litmus ph. Acids and bases worksheet ph : Worksheet doc 25 kb titration problems doc 62 kb solution ph meter ph paper estimate ph value not. (all work above must be complete before attempting the bonus) you are stuck with a problem. When do you use indicators and a ph meter to measure ph?

Ph practice (), ph calcuations (), and ph review problems ().all mr. Acids, bases, and ph worksheets are the core elements of any diet and nutrition plan. When do you use indicators and a ph meter to measure ph? Acids/bases & ph worksheet contact detail: What is the formula for a hydronium ion?

Worksheet 24 buffers 2 what is the ph of a buffer formed from 50 from acids and bases worksheet , source: Substance ph value acid or base methyl red phenolphthalein indigo carmine tomato oven cleaner egg 3. Effect on ph of mixing aqueous solutions of strong acid with a strong base. (weak acids, weak bases, salts, and buffers) name:_____ work on separate paper. D) a ph less than 7 is an acid, with lower numbers indicating stronger acids.

A) the ph scale measures how acidic or basic a substance is. When dissolved in water, there are no visible. Step 2 choose the species that can produce h+, and write balanced equations for the reactions producing h+. Complete the following table by filling in the empty spaces. Browse ph acids and bases chemistry resources on teachers pay teachers, a marketplace trusted by millions of teachers for original educational resources.

Source: wsk.westfieldrepeatedly.site

Some of the worksheets for this concept are lesson 8 acids bases and the ph scale time ii, inquiry and assessment unit, acids bases practice work, acids bases work, work 10 1 acid base and ph pdf, strong acids and bases work, calculating ph and poh work, acid and base ph calculations supplemental work key.

Some of the worksheets displayed are acidsbases ph work, strong acids and bases work, acid and base ph calculations supplemental work key, calculating ph and poh work, lesson 8 acids bases and the ph scale time ii, name date strong acids and bases, work 22 titrations key, acids bases practice work.

Source: content.lessonplanet.com

Browse ph acids and bases chemistry resources on teachers pay teachers, a marketplace trusted by millions of teachers for original educational resources.

Worksheet 24 buffers 2 what is the ph of a buffer formed from 50 from acids and bases worksheet , source:

Source: middleschoolscienceblog.files.wordpress.com

Indicators for small volume samples.

Grade 7 acids and bases worksheet from files.liveworksheets.com chemists use strong acids and bases to get chemical reactions in the lab.

Source: worksheets.helpteaching.com

Acids/bases & ph worksheet (continued).

Source: calamityjanetheshow.com

Some of the worksheets displayed are acidsbases ph work, strong acids and bases work, acid and base ph calculations supplemental work key, calculating ph and poh work, lesson 8 acids bases and the ph scale time ii, name date strong acids and bases, work 22 titrations key, acids bases practice work.

Source: ecdn.teacherspayteachers.com

B) ph scale ranges from 0 to 14.

Some of the worksheets for this concept are acidsbases ph work, strong acids and bases work, lesson 8 acids bases and the ph scale time ii, acids bases work, acids bases practice work, name date strong acids and bases, calculating ph and poh work, chapter 14 creative.

Some of the worksheets for this concept are acids bases and a base r, 11 0405 acids bases salts wkst, acids and bases chapter 14 15, lesson 8 acids bases and the ph scale time ii, acid base practice test, acids bases and solutions answer key, acidsbases ph work.

The equilibrium constant for a.

A solution of glycolic acid (hg) has a ph of 2.00.

Naming acids worksheets key from www.unmisravle.com neutralization doc 24 kb ph indicators doc 33 kb reactions of acids and bases doc 37 kb electrolytes.

Source: d1e4pidl3fu268.cloudfront.net

You have a 1.5 m solution of hcl.

(all work above must be complete before attempting the bonus) you are stuck with a problem.

Source: files.liveworksheets.com

Ph practice (), ph calcuations (), and ph review problems ().all mr.

Worksheet 24 buffers 2 what is the ph of a buffer formed from 50 from acids and bases worksheet , source:

Acids bases and ph worksheet answers | akademiexcel.com from akademiexcel.com acids and bases pogil awesome weak acid base and salt problems key 1 from acids bases and ph worksheet answers , source:alisonnorrington.com.

Complete the following table by filling in the empty spaces.

The equilibrium constant for a.

(weak acids, weak bases, salts, and buffers) name:_____ work on separate paper.

Be sure to write a chemical equation(s) for each problem.

Source: calamityjanetheshow.com

This lesson includes three packets for students to read to understand and identify the properties of an acid or base.

Some of the worksheets for this concept are lesson 8 acids bases and the ph scale time ii, inquiry and assessment unit, acids bases practice work, acids bases work, work 10 1 acid base and ph pdf, strong acids and bases work, calculating ph and poh work, acid and base ph calculations supplemental work key.


MCQ on Water: Physical and Chemical Properties pH and Buffer Systems Part 3 (Biochemistry MCQ-13)

(1). What is the molecular weight of water?
a. 10 g/mol
b. 15 g/mol
c. 18 g/mol
d. 20 g/mol

(2). What is the H + ion concentration in pure water?
a. 1 X 10 -7 m
b. 1 X 10 7 m
c. 1 X 10 -14 m
d. 1 X 10 14 m

(3). The equilibrium constant of ionization reaction of pure water is:
a. 1.8 X 10 -14 M
b. 1.8 X 10 -16 M
c. 1.8 X 10 -7 M
d. 1.8 X 10 -7 M

(4). The pH of pure water is neutral, the best explanation for this is:

a. The pH of pure water is 7
b. In pure water the concentration of H + and OH – are same
c. Water do not contain free H + or OH – ions
d. What will never ionize

(5). What is the concentration of OH – ions in a solution with an H + ion concentration of 1.3 X 10 -4 M?

a. 7.7 X 10-11 M
b. 7.7 X 10-10M
c. 1.4 X 10-11M
d. 1.4 X 10-10 M

(6). As the pKa of an acid increases, the acid will be:

a. More weaker
b. More stronger
c. Converted to neutral solution
d. Converted to basic solution

(7). Buffers are mixtures of:

a. Strong acid and strong base
b. Strong acid and weak base
c. Weak acid and their conjugate base
d. Weak base and their conjugate acid

(8). If a solution has to be a buffer, its pH should be

a. At its pKa value
b. At is Ka value
c. At 7
d. At 14

(9). The most important peculiarity of water when compared to other solvents is that water has:

a. High boiling point, high melting point and high heat of vaporization
b. High boiling point, low melting point and low heat of vaporization
c. Low boiling point, high melting point and low heat of vaporization
d. Low boiling point, low melting point and low heat of vaporization

(10). Which of the following is the correct representation of Henderson-Hasselbalch equation?

(11). According to Henderson-Hasselbalch equation, when the pH of a solution becomes equal to its pKa, the solution becomes a buffer. This condition is achieved when _____

a. The concentration of proton donor equals the concentration of proton acceptor
b. Concentration of proton donor become zero
c. Concentration of proton acceptor become zero
d. The concentration of proton donor become log 1/10th of concentration of proton acceptor

(12). Normal pH of blood is

(13). The heat of vaporization of water molecule at atmospheric temperature is:

a. 2260 J/g
b. 1260 J/g
c. 2260 k.cal
d. 1260 k.cal

(14). The water level in the human body is regulated by the hormone _____

a. ACTH
b. Oxytocin
c. FSH
d. Epinephrine

(15). The polarity of water molecule is due to

a. Difference in electronegativity of oxygen and hydrogen atoms in water
b. The readily ionizing behavior of water
c. The positive charge of water molecule
d. The negative charge of water molecule

(16). The van der Waals radius of hydrogen atom in water molecule is

a. 1.2 Å
b. 1.4 Å
c. 1.6 Å
d. 1.8 Å

Biology / Life Sciences MCQ: Biochemistry MCQ -11: (Multiple Choice Questions / Model Questions / Sample Questions in Biochemistry: Water and pH Part 3 with detailed answer key, explanations and references for preparing CSIR JRF NET Life Science Examination and also for other competitive examinations in Life Science / Biological Science such as ICMR JRF Entrance Exam, DBT BET JRF Exam, GATE (XL) Life Science Exam, GATE (BT) Biotechnology Exam, ICAR JRF Exam, University PG Entrance Exam, JAM Exam, GS Biology Exam, GRE, Medical Entrance Examination etc. This set of practice questions will help to build your confidence in Biochemistry to face the real examination. A large quantum of questions in our practice MCQ is taken from previous year question papers of various national and international Biology / Life Sciences competitive examinations. Please take advantage of our Lecture Notes, PPTs, Previous Year Questions, Mock Tests , and Video Tutorials for your preparation. You can download all these questions papers and study materials as PDF from our Slidesha reaccount absolutely free

Answer Key, Explanations and References

(1). Ans. (c). 18 g/mol

Exactly the molecular weight of water is 18.01528 g/mol

(2). Ans. (a). 1 X 10 -7 m

(3). Ans. (b). 1.8 X 10 -16 M

(4). Ans. (b). In pure water the concentration of H+ and OH- are same

(5). Ans. (a). 7.7 X 10 -11 M

Use the equation of ion product of water

(6). Ans. (a). More weaker

pKa is the negative log of Ka. Strong acids will have higher Ka values where as weak acids will have lower Ka values.

(7). Ans. (c). Weak acid and their conjugate base

(8). Ans. (a). at its pKa value

(9). Ans. (a). High boiling point, high melting point and high heat of vaporization

(10). Ans. (d). all the above

(11). Ans. (a). The concentration of proton donor equals the concentration of proton acceptor

(12). Ans. (d). 7.4

(13). Ans. (a). 2260 J/g

(14). Ans. (b). Oxytocin

(15). Ans. (a). Difference in electronegativity of oxygen and hydrogen atoms in water

(16). Ans. (a). 1.2 Å

Reference: (1). Lehningers Principles of Biochemistry: Chapter: Water
(2). Fundamentals of Biochemistry by Voet and Voet: Chapter: Water

The answer key is prepared with best of our knowledge.
Please feel free to inform the Admin if you find any mistakes in the answer key..

MCQ on Water, pH and Buffer | Part – 2 | Part – 1 |


Acid and Base Lab with Report

Day 1: After completing the pH Gizmo and preparing red cabbage indicator solution, students were formally introduced to acids and bases via a lab. Having just learned about indicators (chemical solutions that change color in response to changes in pH, Lesson 117) we reviewed Day 1 of the Acid and Base Lab Report Packet. and then students had the remainder of the day to work through the Day 1 worksheet and prepare for the lab.

Day 2: For Day 2 of the Acid and Base Lab, students used their red cabbage juice indicator solution to measure the pH of eight different solutions (comparing the color of the indicator to a color chart for red cabbage indicator). Students repeated the process using universal indicator. Finally, students evaluated the effect of sodium bicarbonate (baking soda) on the pH of the solutions, as determined by the indicator colors. Students should carefully document all steps of the lab, taking pictures of the indicator solutions before and after addition of sodium bicarbonate. Indicator Solution Charts are provided below:

Universal Indicator Chart

Red cabbage indicator chart

Days 3+: Students will work with their assigned lab groups to write a lab report for the Acid and Base Lab. The lab report will consist of:

  • Introduction – a paragraph explaining the purpose of the lab
  • Safety Concerns – list all safety concerns associated with working with acids and bases, along with required precautions for the lab (explain why each piece of personal protective equipment is required)
  • Procedure – an ordered list of steps explaining:
    • how the red cabbage indicator solution was prepared
    • pH evaluation of all samples in universal indicator and red cabbage juice indicator solutions
    • pH evaluation of all samples after calcium carbonate added
    • pH measurement with pH probe
    • pH determined with red cabbage indicator solution
    • pH determined with universal indicator solution
    • pH determined with pH probe
    • pH determined after addition of calcium carbonate
    • The effectiveness and consistency of indicator solutions, relative to the two indicator solutions compared with the pH probe
    • An explanation of how calcium carbonate affected pH
    • Bonus: An explanation of why the indicator solutions changed color (with sources cited)
    • Bonus: An explanation of why calcium carbonate affected pH (with sources cited)

    Day 4: After a much-need 4-day weekend, we began class with the Lesson 84 PowerPoint which included a starter question helping students connect acid/base chemistry with the biology of heartburn. For the lab last week, students observed the effect of sodium bicarbonate (NaHCO3, or baking soda) on acids and bases. For the ChemCatalyst, students made the connection of acid neutralization with the related compound calcium carbonate (CaCO3, commonly found in antacids). Students have the remainder of the short week to complete the lab report from the lab last week. The group lab report packet is due at the end of school Friday, and the lab report must be shared with the teacher by midnight Friday. Late work will receive a maximum of 60% credit.

    Groups who finished early will be provided with a variety of learning enrichment options related to our work thus far during the unit, including:


    Watch the video: oxea vaseis kai alata (January 2023).