Question 1

Which of the following statements best describes a polyprotic acid?

Accepted Answer

A polyprotic acid can donate more than one proton per molecule, but does so one proton at a time.

Question 2

Which of the following is an example of a polyprotic acid?

Accepted Answer

$$\mathrm{H_2SO_4}$$

Question 3

Consider the dissociation of sulfuric acid ($$\mathrm{H_2SO_4}) in $$water. Which equation correctly represents the first step of its ionization?

Accepted Answer

$$\mathrm{H_2SO_4} + \mathrm{H_2O} \rightarrow \mathrm{$$HSO_4$$^-} + \mathrm{H_3O^+}$$

Question 4

A student is titrating a solution of a polyprotic acid with a strong base. Which observation would most likely indicate the presence of more than one acidic proton?

Accepted Answer

The titration curve displays multiple buffer regions and equivalence points.

Question 5

Which of the following best explains why polyprotic acids lose one proton at a time?

Accepted Answer

The removal of each proton requires a different amount of energy, so they are lost sequentially.

Question 6

Which of the following is the correct sequence of dissociation for carbonic acid ($$\mathrm{H_2CO_3}) in $$water?

Accepted Answer

$$\mathrm{H_2CO_3} \rightarrow \mathrm{$$HCO_3$$^-} + \mathrm{H^+}$$, then $$\mathrm{$$HCO_3$$^-} \rightarrow \mathrm{CO_3$^{2-}} + \mathrm{H^+}$$

Question 7

During the Green Crystal lab, a student observes that the solution changes color as acid is added. Which explanation best fits this observation if the acid is polyprotic?

Accepted Answer

Each proton lost by the acid causes a stepwise change in pH, which can affect the color of pH-sensitive indicators.

Question 8

Which of the following acids is NOT polyprotic?

Accepted Answer

$$\mathrm{$$HNO_3$$}$$

Question 9

If a polyprotic acid has $$K_{a1} = 1.0 	imes 10$$^{-3}$$ and K$$_{a2} = 1.0 	imes $$10^{-6}$$, what does this indicate about the acid's dissociation?

Accepted Answer

The first proton is lost much more easily than the second.

Question 10

A solution contains $$0.10 M$$ $$\mathrm{H_2CO_3}. $$After the first dissociation, what is the major species present in solution?

Accepted Answer

$$\mathrm{H_2CO_3}$$ and $$\mathrm{$$HCO_3$$^-}$$

Question 11

Which of the following best describes the titration curve of a diprotic acid?

Accepted Answer

It has two distinct buffer regions and two equivalence points.

Question 12

In the context of the Green Crystal lab, why is it important to know whether the acid used is polyprotic?

Accepted Answer

Because the number of protons donated affects the stoichiometry and the interpretation of experimental results.

Question 13

Which of the following equations represents the second dissociation of phosphoric acid ($$\mathrm{H_3PO_4}$$)?

Accepted Answer

$$\mathrm{H_2PO_4^-} \rightarrow \mathrm{$$HPO_4$$^{2-}} + \mathrm{H^+}$$

Question 14

A student adds a strong base to a solution of $$\mathrm{H_2SO_4}. $$Which of the following best describes the neutralization process?

Accepted Answer

The base neutralizes one proton at a time, first forming $$\mathrm{$$HSO_4$$^-}$$, then $$\mathrm{SO_4$^{2-}}.$$

Question 15

Which of the following is a correct statement about the $$K_a$$ values of polyprotic acids?

Accepted Answer

The first $$K_a is $$always larger than the second $$K_a.$$

Polyprotic Acids and Laboratory Practice

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