Question 1

A weak acid, HA, dissociates in water according to the equation $$\mathrm{HA} + \mathrm{H_2O} \rightleftharpoons \mathrm{H_3O^+} + \mathrm{A^-}. $$Which of the following is the correct equilibrium constant expression for this dissociation?

Accepted Answer

$$K_a = \dfrac{[\mathrm{H_3O^+}][\mathrm{A^-}]}{[\mathrm{HA}]}$$

Question 2

Which of the following pairs is a correct example of a conjugate acid-base pair?

Accepted Answer

$$\mathrm{H_2O}$$ / $$\mathrm{OH^-}$$

Question 3

A student mixes $$0.10 M $$acetic acid ($$K_a = 1.8 	imes 10$$^{-5}$$) with water. What is the pH of the solution? (Assume x$$ \ll 0.10$$)

Accepted Answer

pH $$\approx 3.38$$

Question 4

Which of the following reactions represents a Bronsted-Lowry acid-base reaction?

Accepted Answer

$$\mathrm{NH_3$} + \mathrm{H_2O} \rightarrow \mathrm{NH_4$^+} + \mathrm{OH^-}$$

Question 5

Given the $$K_a$$ values for two acids, which statement is correct?

Accepted Answer

The acid with the higher $$K_a is $$the stronger acid.

Question 6

A buffer solution is prepared by mixing $$0.20$$ mol of acetic acid and $$0.10$$ mol of sodium acetate in $$1.0 L of $$water. What is the pH of the buffer? ($$K_a = 1.8 	imes 10$$^{-5}$$)

Accepted Answer

pH $$= 4.74 + \log \left( \dfrac{0.10}{0.20} \right)$$

Question 7

During the titration of $$50.0 mL of$$ $$0.100 M $$acetic acid with $$0.100 M $$NaOH, what is the pH at the equivalence point? ($$K_a = 1.8 	imes 10$$^{-5}$$)

Accepted Answer

pH $$\approx 8.72$$

Question 8

Which indicator would be most suitable for marking the endpoint of a titration between a weak acid and a strong base?

Accepted Answer

Phenolphthalein (pH range 8.2–10.0)

Question 9

Given the formula $$\mathrm{$$CaF_2$$}$$, what is the correct expression for its solubility product constant ($$K_{sp}$$)?

Accepted Answer

$$K_{sp} = [\mathrm{Ca$$^{2+}$$}][\mathrm{F^-}]^2$$

Question 10

A saturated solution of $$\mathrm{Ag_2CO_3}$$ has a $$K_{sp} of$$ $$8.1 	imes 10$$^{-12}$$. What is the concentration of $$\mathrm{Ag^+}$$ ions in the solution?

Accepted Answer

$$[\mathrm{Ag^+}] = 2x$$, where $$K_{sp} = 4x^3$

Question 11

Which salt will have the lowest solubility in water if their $$K_{sp}$$ values are as follows: $$\mathrm{$$BaSO_4$$}$$ ($$1.1 	imes 10$$^{-10}$$), $$\mathrm{AgCl}$$ (1.8$$ 	imes $$10^{-10}$$), $$\mathrm{$$PbI_2$$}$$ ($$7.1 	imes 10$$^{-9}$$), $$\mathrm{$$CaF_2$$}$$ (3.2$$ 	imes $$10^{-11}$$)?

Accepted Answer

$$\mathrm{$$BaSO_4$$}$$

Question 12

If $$Q$$ for a salt solution is greater than $$K_{sp}$$, what will happen?

Accepted Answer

A precipitate will form until $$Q = K_{sp}.$$

Question 13

Which of the following best distinguishes the Bronsted-Lowry acid-base definition from the Lewis acid-base definition?

Accepted Answer

Bronsted-Lowry acids donate protons, while Lewis acids accept electron pairs.

Question 14

A solution contains $$0.050 M$$ $$\mathrm{Mg$$^{2+}$$}$$ and $$0.020 M$$ $$\mathrm{Ca$$^{2+}$$}. If$$ $$K_{sp}$$ for $$\mathrm{Mg(OH)_2} is$$ $$1.8 	imes 10$$^{-11}$$ and for $$\mathrm{Ca(OH)_2}$$ is 5.5$$ 	imes $$10^{-6}$$, which hydroxide will precipitate first upon addition of $$\mathrm{OH^-}$$?

Accepted Answer

$$\mathrm{Mg(OH)_2}$$

Question 15

Which of the following is the correct net ionic equation for the reaction between $$\mathrm{NaOH}$$ and $$\mathrm{HCl}$$ during a titration?

Accepted Answer

$$\mathrm{OH^-} + \mathrm{H^+} \rightarrow \mathrm{H_2O}$$

Question 16

A buffer is made by mixing $$0.25$$ mol of ammonia ($$\mathrm{NH_3$}) $$and $$0.15$$ mol of ammonium chloride ($$\mathrm{NH_4Cl}) in$$ $$1.0 L of $$water. What is the pH of the buffer? ($$K_b = 1.8 	imes 10$$^{-5}$$)

Accepted Answer

pH $$= 14 - [4.74 + \log(0.25/0.15)]$$

Question 17

Which of the following statements about selective precipitation is correct?

Accepted Answer

Selective precipitation separates ions based on their different $$K_{sp}$$ values.

Question 18

A solution is prepared by mixing $$0.10 M$$ $$\mathrm{Ba$$^{2+}$$}$$ and $$0.10 M$$ $$\mathrm{SO_4$^{2-}}. If$$ $$K_{sp}$$ for $$\mathrm{$$BaSO_4$$} is$$ $$1.1 	imes 10$$^{-10}$$, will a precipitate form?

Accepted Answer

Yes, because $$Q \u003e K_{sp}.$$

General Chemistry Study Guide: Acids, Bases, Buffers, and Solubility

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