AP Chemistry Quiz: Ph And Pk

What this quiz covers

This quiz focuses on Ph And Pk, giving you a quick way to practice the rules, question types, and explanations that matter most for AP Chemistry.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. $pK_a=\log(K_a)$
2. $pK_a=-\log(K_a)$ (correct answer)
3. $pK_a=\dfrac{1}{K_a}$
4. $pK_a=\log\left(\dfrac{1}{K_a}\right)+1$
5. $pK_a=-\log([\text{H}^+])$

Question 2

1. 1
2. 10
3. $5.0\times10^{-1}$
4. $1.0\times10^{-5}$
5. 5 (correct answer)

Question 3

1. $K_b=4.0\times10^{-4}$
2. $K_b=1.0\times10^{-4}$ (correct answer)
3. $K_b=1.0\times10^{4}$
4. $K_b=4.0\times10^{4}$
5. $K_b=1.0\times10^{-10}$

Question 4

1. The claim is correct because $pK_b$ equals the pH of any solution of that base.
2. The claim is correct because $pK_b$ equals $-\log[\text{OH}^-]$ for any solution.
3. The claim is incorrect because $pK_b$ is a property of the base, whereas pH depends on the extent of reaction and the solution concentration. (correct answer)
4. The claim is incorrect because $pK_b$ is defined as $\log(K_b)$, not $-\log(K_b)$.
5. The claim is incorrect because $pK_b$ must always be greater than 7.

Question 5

1. $pK_a = -\log(K_a)$, so $pK_a = 7.00$. (correct answer)
2. $pK_a = \log(K_a)$, so $pK_a = -7.00$.
3. $pK_a = -\log([\text{H}^+])$, so $pK_a$ equals the pH of the solution.
4. $pK_a = -\log([\text{HA}])$, so $pK_a$ depends on the initial acid concentration.
5. $pK_a = 1/K_a$, so $pK_a = 1.0\times 10^{7}$.

Question 6

1. Base 2 produces the more basic solution because its $pK_b$ is larger.
2. Base 1 produces the more basic solution because its $pK_b$ is smaller. (correct answer)
3. Both solutions have the same pH because both are weak bases.
4. Base 1 is the weaker base because its $pK_b$ is smaller.
5. Both solutions must have $\text{pH}=10$ because $pK_b$ values are given.

Question 7

1. Solution 1 has a higher pH because $K_a$ is larger.
2. Solution 2 has a lower pH because $K_a$ is smaller.
3. Both solutions have the same pH because both are $0.10\,\text{M}$.
4. Both solutions have pH $=4$ because $K_a$ values are powers of ten.
5. Solution 1 has a lower pH because HX is the stronger acid (larger $K_a$) at the same concentration. (correct answer)

Question 8

1. Because $pK_a = 5.00$, the solution must have $\text{pH} = 5.00$.
2. A smaller $pK_a$ would indicate a stronger acid and thus a more acidic solution (lower pH), assuming the same initial concentration. (correct answer)
3. A larger $pK_a$ indicates a stronger acid and thus a lower pH, assuming the same initial concentration.
4. $pK_a$ is the negative logarithm of the initial acid concentration, so changing concentration changes $pK_a$.
5. Because $K_a$ is less than 1, HA is a strong acid and the solution will have a very low pH.

Question 9

1. The claim is correct because p$K_a$ is defined as the pH of the acid solution.
2. The claim is incorrect because p$K_a$ is a measure of acid strength, not the actual pH of a particular solution. (correct answer)
3. The claim is correct because p$K_a$ equals $-\log[\text{H}^+]$ for any acid solution.
4. The claim is incorrect because p$K_a$ must always be greater than 7 for a weak acid.
5. The claim is correct because p$K_a$ depends only on the initial concentration of HA.

Question 10

1. $pK_b(\text{NH}_3) > pK_b(\text{B})$ because $\text{NH}_3$ has the smaller $K_b$. (correct answer)
2. $pK_b(\text{NH}_3) = pK_b(\text{B})$ because both are weak bases.
3. $pK_b(\text{NH}_3) > pK_b(\text{B})$ because $\text{NH}_3$ has the larger $K_b$.
4. $pK_b(\text{NH}_3) < pK_b(\text{B})$ because $\text{NH}_3$ has the smaller $K_b$.
5. $pK_b(\text{NH}_3) < pK_b(\text{B})$ because $\text{NH}_3$ has the larger $K_b$.

Question 11

1. The pH increases because the acid is weaker.
2. The pH decreases because the acid is stronger. (correct answer)
3. The pH stays the same because $K_a$ does not affect pH.
4. The pH increases because $pK_a$ increases.
5. The pH stays the same because the concentration is fixed.

Question 12

1. The HA solution has a lower pH than the HB solution. (correct answer)
2. The HA solution has a higher pH than the HB solution.
3. The two solutions have the same pH because both are weak acids.
4. The two solutions have the same pH because both solutions have the same initial concentration.
5. The HB solution has a lower pH than the HA solution because HB has the smaller $K_a$.

Question 13

1. Because $pK_b = 3.00$, the solution must have $\text{pOH} = 3.00$.
2. A larger $pK_b$ would indicate a stronger base and a higher pH, assuming the same initial concentration.
3. A smaller $pK_b$ would indicate a stronger base and thus a higher pH, assuming the same initial concentration. (correct answer)
4. $pK_b$ increases when more base is added because $pK_b$ depends on concentration.
5. Because $K_b < 1$, B is a strong base and the pH will be close to 14.

Question 14

1. Acid 2 produces the lower pH because its $K_a$ is smaller.
2. Acid 1 produces the lower pH because its $K_a$ is larger. (correct answer)
3. Both produce the same pH because both $K_a$ values are less than 1.
4. Acid 1 produces the higher pH because a larger $K_a$ means less ionization.
5. Both solutions must have $\text{pH} = 5$ because one $K_a$ is $10^{-5}$.

Question 15

1. $\text{HB}$ is the stronger acid because it has the larger $pK_a$
2. $\text{HA}$ is the stronger acid because it has the smaller $pK_a$ (correct answer)
3. They are equally strong because both are weak acids
4. $\text{HB}$ is the stronger acid because $pK_a$ equals the pH
5. They must have the same pH because $pK_a$ is independent of acid strength

Question 16

1. Replacing HA with an acid that has $pK_a = 7.00$.
2. Replacing HA with an acid that has a larger $pK_a$ than 5.00.
3. Replacing HA with an acid that has $K_a = 1.0\times 10^{-7}$.
4. Replacing HA with an acid that has the same $K_a$ but a different initial concentration does not affect pH.
5. Replacing HA with an acid that has $K_a = 1.0\times 10^{-3}$. (correct answer)

Question 17

1. The $\text{HB}$ solution has lower pH because $pK_a$ is larger
2. The $\text{HA}$ solution has lower pH because $pK_a$ is smaller (correct answer)
3. The solutions have the same pH because both are weak acids
4. The $\text{HB}$ solution has lower pH because $pK_a$ equals $[\text{H}^+]$
5. The solutions have the same pH because $pK_a$ depends only on concentration

Question 18

1. The pH increases because the base produces more $\text{OH}^-$. (correct answer)
2. The pH stays the same because $K_b$ does not affect equilibrium.
3. The pH decreases because a larger $K_b$ means a weaker base.
4. The pH decreases because the base produces more $\text{H}^+$.
5. The pH increases because $pK_b$ increases.

Question 19

1. Acid X is stronger than acid Y, so the solution of X has the lower pH. (correct answer)
2. Acid Y is stronger than acid X, so the solution of Y has the lower pH.
3. Acid X is stronger than acid Y, so the solution of X has the higher pH.
4. Acid Y is stronger than acid X, so the solution of Y has the higher pH.
5. The acids have equal strength because their $pK_a$ values differ by 2.0.

Question 20

1. $pK_a(\text{HJ}) > pK_a(\text{HK})$ because HJ has the larger $K_a$.
2. $pK_a(\text{HJ}) < pK_a(\text{HK})$ because HJ has the larger $K_a$. (correct answer)
3. $pK_a(\text{HJ}) = pK_a(\text{HK})$ because both are acids.
4. $pK_a(\text{HJ}) > pK_a(\text{HK})$ because HJ has the smaller $K_a$.
5. $pK_a(\text{HJ}) < pK_a(\text{HK})$ because HJ has the smaller $K_a$.