3. Water

In a neutral solution, the concentration of __________.

A base _______:

Which of the following statements about buffers is true?

Measurements show that the pH of a particular lake is 4.0. What is the hydrogen ion concentration of the lake?

a. 4.0 M

b. 10¹⁰M

c. 10⁴M

d. 10⁴M

What is the hydroxide ion concentration of the lake described in question 3?

a. 10⁻¹⁰ M

b. 10⁻⁴ M

c. 10⁻⁷ M

d. 10.0 M

A solution at pH 6 contains _________ H+ than the same amount of a solution at pH 8.

a. 20 times more

b. 100 times more

c. 2 times less

d. 100 times less

A can of cola consists mostly of sugar dissolved in water, with some carbon dioxide gas that makes it fizzy and makes the pH less than 7. In chemical terms, you could say that cola is an aqueous solution where water is the _________, sugar is a _________, and carbon dioxide makes the solution _________.

a. solvent . . . solute . . . basic

b. solute . . . solvent . . . basic

c. solvent . . . solute . . . acidic

d. solute . . . solvent . . . acidic

If you were given a solution that has a pH of 8.5, what would be its concentration of protons? What is the difference in proton concentration between this solution and one that has a pH of 7?

A recent experimental study looked at the combined effects of ocean acidification and increased ocean temperatures, both aspects of climate change, on the growth of polyps, juvenile coral animals. Researchers reported the average polyp biomass (in μg/polyp) after 42 days of growth under four treatments: a control with pH and temperature maintained close to normal reef conditions, a pH lowered by 0.2 units, a temperature raised by 1°C, and a combined lower pH and higher temperature. The results showed that polyp biomass was reduced somewhat in both the low-pH and high-temperature treatments, but the combined treatment resulted in a reduction in growth by almost a third—a statistically significant result. Experiments often look at the effects of changing one variable at a time while keeping all other variables constant.

Explain why this experiment considered two variables—both a higher temperature and a lower pH—at the same time.

Consider the reaction between carbon dioxide and water to form carbonic acid (CH2O3):

CO2(𝑔)+H2O(𝑙)⇌CH2O3(𝑎𝑞)

In the ocean, carbonic acid immediately dissociates to form a proton and bicarbonate ion, as follows:

CH2O3(𝑎𝑞)⇌CHO3−(𝑎𝑞)+H+(𝑎𝑞)

As atmospheric CO2 increases, the ocean absorbs more of the gas. Would this sequence of reactions be driven to the left or the right? How would this affect the pH of the ocean?

Stony corals secrete thin layers of calcium carbonate (CaCO3) to build the foundation of coral reefs. The relationship between calcium carbonate, carbonic acid, and calcium bicarbonate (Ca(HCO3)2) is shown below:

CH2O3(𝑎𝑞)+CaCO3(𝑠) ⇌ Ca(HCO3)2(𝑎𝑞)

Predict what will happen to the calcium carbonate foundation of reefs as CO2 levels rise in the oceans.

The current average pH of our oceans is 8.1. What is the concentration of protons in the oceans? How has the proton concentration changed in our oceans when compared to before the industrial revolution, when the average pH was 8.2? Express this change as a percentage increase.