Question 1

How would acidification of seawater affect marine organisms?

Accepted Answer

Acidification of seawater would decrease the concentration of dissolved carbonate ions, which are essential for calcification in many marine organisms like corals and shell-building animals. This can lead to slower growth rates, weaker skeletons, and potential population declines.

Question 2

If acid rain has lowered the pH of a particular lake to pH 4.0, which of the following statements about this lake is true?

Accepted Answer

The pH of a solution is a measure of its acidity or basicity. The pH scale ranges from 0 to 14, with 7 being neutral. A pH below 7 indicates an acidic solution, while a pH above 7 indicates a basic solution.The hydrogen ion concentration is a measure of the amount of hydrogen ions (H+) in a solution. The hydroxyl ion concentration is a measure of the amount of hydroxyl ions (OH-) in a solution.The pH of a solution is inversely related to the hydrogen ion concentration. The higher the hydrogen ion concentration, the lower the pH. The lower the hydrogen ion concentration, the higher the pH.In this case, the pH of the lake is 4.0. This means that the hydrogen ion concentration is 1 × 10-4 moles per liter of lake water. The hydroxyl ion concentration is 1 × 10-10 moles per liter of lake water.

Question 3

Increased atmospheric CO₂ concentrations will have what effect on seawater?

Accepted Answer

Increased atmospheric CO₂ concentrations will lead to an increase in dissolved CO₂ in seawater, leading to a decrease in pH and an increase in acidity. This increase in acidity will cause carbonate ions to combine with hydrogen ions to form bicarbonate ions, resulting in a decrease in carbonate concentrations.

Question 4

If the cytoplasm of a cell is at pH 7, and the mitochondrial matrix is at pH 8, this means that

Accepted Answer

The pH scale is logarithmic, so a difference of one pH unit corresponds to a tenfold difference in hydrogen ion concentration. A pH of 7 is more acidic than a pH of 8, meaning the cytoplasm has a tenfold higher concentration of hydrogen ions than the mitochondrial matrix.

Question 5

CO₂ absorbed by the oceans combines with water to form H2CO3. Which of the following will result from increasing the concentration of H2CO3 in the oceans?

Accepted Answer

When CO2 is absorbed by the oceans, it forms carbonic acid (H2CO3) which can lower the pH of the water. Therefore, increasing the concentration of H2CO3 in the oceans will cause the pH to decrease even more. This is because carbonic acid is a weak acid, and it will dissociate into hydrogen ions (H+) and bicarbonate ions (HCO3-), thereby increasing the concentration of H+ and decreasing the pH. As the pH decreases, the concentration of carbonate ions (CO32-) will also decrease, because they will combine with H+ ions to form bicarbonate ions (HCO3-).

Question 6

Carbonic acid (H2CO3) serves as a buffer in human blood. Carbonic acid is a weak acid that dissociates into a bicarbonate ion (HCO3-) and a hydrogen ion (H+). Thus,
H2CO3 ↔ HCO3- + H+
A decrease in blood pH would result in

Accepted Answer

A decrease in blood pH indicates an increase in H+ concentration. To counteract this, the equilibrium shifts to the left, increasing H2CO3 and decreasing HCO3-.

Question 7

A beaker contains 100 mL of NaOH solution at pH = 13. A technician carefully pours into the beaker 10 mL of HCl at pH = 1. Which of the following statements correctly describes the results of this mixing?

Accepted Answer

When NaOH and HCl are mixed, they undergo a neutralization reaction to form NaCl and H2O. The reaction can be represented as follows:
NaOH (aq) + HCl (aq) → NaCl (aq) + H2O (l)
Since HCl is a strong acid, when it is added to the solution of NaOH (a strong base), it will completely neutralize the NaOH. The pH of the beaker's contents will decrease because H+ ions will be produced. Thus, the correct statement is E. The concentration of Na+ ion will not rise significantly since NaOH is a strong base and its dissociation is complete. Similarly, the concentration of Cl- ion will not be 0.1 M, but it will be the same as the concentration of Na+ ion, which is 1 M. The concentration of undissociated H2O molecules will remain unchanged since they are not involved in the reaction.

Question 8

Buffers are substances that help resist shifts in pH by

Accepted Answer

Buffers are substances that can either donate or accept protons (H+). When an acid is added to a solution, the buffer accepts the H+ ions, thereby prevent any drastic changes in pH. Similarly, when a base is added to a solution, the buffer donates H+ ions to counteract the effects of the added OH-. Choice D is the correct answer because it describes the mechanism by which a buffer resists a shift in pH - accepting H+ when acids are added.

Question 9

One proposal to mitigate the effects of burning fossil fuels on atmospheric CO₂ concentrations is to pipe liquid CO₂ into the ocean at depths of 2,500 feet or greater. At the high pressures at such depths, CO₂ is heavier than water. What potential effects might result from implementing such a scheme?

Accepted Answer

Piping liquid CO₂ into the ocean at depths of 2,500 feet or greater may lead to changes in the growth of deep sea-dwelling organisms with calcium carbonate shells. This is because the added CO₂ could result in a decrease in pH and an increase in acidity, which can make it more difficult for these organisms to build and maintain their calcium carbonate shells.

Question 10

Research indicates that acid precipitation can damage marine corals by

Accepted Answer

Acid precipitation can decrease the concentration of carbonate ions in oceans, which are important for the formation and maintenance of corals' hard structures. This can lead to coral bleaching and decline in coral populations.

Question 11

Approximately what percentage of human-generated atmospheric CO₂ is absorbed by the oceans?

Accepted Answer

The oceans absorb about 25% of human-generated atmospheric CO₂, playing a significant role in mitigating climate change.

Question 12

Consider two solutions: solution X has a pH of 4; solution Y has a pH of 7. From this information, we can reasonably conclude that

Accepted Answer

The pH scale is logarithmic, so each whole number change represents a tenfold change in hydrogen ion concentration. A pH of 4 means the hydrogen ion concentration is 10^-4 M, and a pH of 7 means it is 10^-7 M. Therefore, solution X has 1,000 times more hydrogen ions than solution Y.

Question 13

One liter of a solution of pH 4 has how many more hydrogen ions (H+) than 1 L of a solution of pH 9?

Accepted Answer

The pH scale is logarithmic, meaning that a solution with a pH of 4 has 10 times more hydrogen ions than a solution with a pH of 5, and 100 times more hydrogen ions than a solution with a pH of 6, and so on. Thus, a solution with a pH of 4 has 10,000 times more hydrogen ions than a solution with a pH of 9 (10^(-4) versus 10^(-9)), which means that one liter of a solution of pH 4 has 100,000 times more hydrogen ions than one liter of a solution of pH 9. Therefore, the answer is E.

Question 14

Carbon dioxide (CO₂) is readily soluble in water, according to the equation CO₂ + H₂O ↔ H2CO3. Carbonic acid (H2CO3) is a weak acid. Respiring cells release CO₂ into the bloodstream. What will be the effect on the pH of blood as that blood first comes in contact with respiring cells?

Accepted Answer

As respiring cells release CO₂, it diffuses into the bloodstream and reacts with water to form carbonic acid (H2CO3), which is a weak acid. This reaction releases hydrogen ions (H+) into the blood, thus decreasing the blood pH slightly. Therefore, the best answer is A, blood pH will decrease slightly.

Question 15

Figure 2.1
Which of the following best describes the relationship between the atoms described in Figure 2.1?

Accepted Answer

The answer of  Figure 2.1
Which of the following best...

Question 16

An equal volume (5 mL) of milk of magnesia from a freshly opened bottle is added to each of the following solutions. After complete mixing, which of the mixtures will have the lowest pH?

Accepted Answer

Lemon juice is acidic, with a pH range of around 2-3. When milk of magnesia, which is basic, is added to it, the resulting mixture will have a pH closer to neutral, but still on the acidic side. Therefore, the mixture with lemon juice will have the lowest pH compared to the other options.

Question 17

One liter of a solution of pH 8 has how many more hydroxyl ions (OH-) than 1 L of a solution of pH 4?

Accepted Answer

A solution with pH 8 has a hydroxyl ion concentration of 10^-6 M, while a solution with pH 4 has a hydroxyl ion concentration of 10^-10 M. The difference in hydroxyl ion concentration is 10^4, or 100,000 times more.

Question 18

Which of the following statements about buffer solutions is true?

Accepted Answer

Buffer solutions can resist changes in pH when either an acid or a base is added to them. This is because buffer solutions contain both a weak acid and its conjugate base (or a weak base and its conjugate acid), which can neutralize any added acid or base and prevent large changes in pH.

Question 19

One of the buffers that contributes to pH stability in human blood is carbonic acid (H2CO3). Carbonic acid is a weak acid that, when placed in an aqueous solution, dissociates into a bicarbonate ion (HCO3-) and a hydrogen ion (H+). Thus,
H2CO3 ↔ HCO3- + H+
If the pH of the blood increases, one would expect

Accepted Answer

An increase in pH indicates a decrease in H+ concentration. To restore pH to its optimal level, the concentration of H+ must increase. This can be accomplished by the reaction shifting left, forming H2CO3 and increasing the concentration of H+ ions. In turn, this will decrease the concentration of HCO3- ions, which will act as a base to neutralize the excess H+ ions.

Question 20

An equal volume (5 mL) of vinegar from a freshly opened bottle is added to each of the following solutions. After complete mixing, which of the mixtures will have the highest pH?

Accepted Answer

Household cleanser containing 0.5 M ammonia will have the highest pH since ammonia is a base and will react with the acidic vinegar to form a less acidic solution. The other options either contain no acidic or basic components or contain acidic components that will react with the vinegar to form more acidic solutions.

Quiz 2: The Chemical Context of Life