Q: Given the following $$K_a$$ values, which acid is the strongest?

Nitrous acid ($$K_a = 4.6 \times 10$$^{-4}$$)

Question 1

Which of the following combinations would form a buffer solution when mixed in water?

Accepted Answer

0.10 M NaCN and 0.10 M HCN

Question 2

Calculate the pH of a buffer solution prepared by dissolving 13.02 g of sodium acetate ($$\mathrm{NaC_2H_3O_2}$$, molar mass = 82.03 g/mol) and 15.40 g of acetic acid ($$\mathrm{HC_2H_3O_2}$$, molar mass = 60.05 g/mol) in water to make 500 mL of solution. The $$K_a of $$acetic acid is $$1.8 	imes 10$$^{-5}$$.

Accepted Answer

$$pH = 4.53$$

Question 3

You need to prepare 1.00 L of a buffer solution with a pH of 5.02. Which acid/conjugate base pair is most appropriate to use?

Accepted Answer

Acetic acid/acetate ($$pK_a = 4.74)$$

Question 4

Given the following $$K_a$$ values, which acid is the strongest?

Accepted Answer

Nitrous acid ($$K_a = 4.6 	imes 10$$^{-4}$$)

Question 5

A solution contains 0.0010 moles of $$\mathrm{Ba$$^{2+}$$}$$ and 0.00010 moles of $$\mathrm{SO_4$^{2-}} in 1 L. $$The $$K_{sp}$$ for $$\mathrm{$$BaSO_4$$} is$$ $$1.0 	imes 10$$^{-10}$$. Will a precipitate form?

Accepted Answer

Yes, because $$PI \u003e K_{sp}$$

Question 6

Calculate the solubility (in mol/L) of $$\mathrm{$$CaF_2$$} if$$ $$K_{sp} = 4.0 	imes 10$$^{-8}$$.

Accepted Answer

$$s = 2.0 	imes 10$$^{-3}$$

Question 7

If you add $$\mathrm{$$AgNO_3$$} to a $$solution containing $$\mathrm{S$$^{2-}$$}$$, a precipitate of $$\mathrm{Ag_2S}$$ forms. Which of the following best explains why?

Accepted Answer

The ionic product $$[Ag^+]^2[S$$^{2-}$$]$$ exceeds $$K_{sp}$$ for $$\mathrm{Ag_2S}$$

Question 8

Which of the following will increase the solubility of $$\mathrm{AgCN} in $$water?

Accepted Answer

Adding a strong acid such as $$\mathrm{$$HNO_3$$}$$

Question 9

A student wants to prepare a buffer with pH = 6.78 using an acid with $$pK_a = 6.38. $$What should be the ratio $$\left( \frac{[A^-]}{[HA]} \right) in $$the buffer?

Accepted Answer

$$2.51$$

Question 10

The solubility of $$\mathrm{AgCl} at 25$$°C is $$0.00019 g $$per 100 mL. Calculate the $$K_{sp}$$ for $$\mathrm{AgCl} ($$molar mass = 143 g/mol).

Accepted Answer

$$1.8 	imes 10$$^{-10}$$

Question 11

Which of the following best describes the 'common ion effect'?

Accepted Answer

The decrease in solubility of a salt when a solution already contains one of its ions

Question 12

A solution contains $$1.0 	imes 10$$^{-4}$$ M $$\mathrm{$$Fe^{2+}$$}$$. What minimum concentration of $$\mathrm{$$S^{2-}$$}$$ is required to start precipitation of $$\mathrm{FeS}$$? (K$$_{sp} = 5.0 	imes $$10^{-18})$$

Accepted Answer

$$5.0 	imes 10$$^{-14}$$ M

Question 13

Which of the following statements about $$K_{sp} is $$correct?

Accepted Answer

$$K_{sp} is $$the equilibrium constant for the dissolution of a sparingly soluble salt

Question 14

If the ionic product ($$PI) $$for a salt is less than its $$K_{sp}$$, what will happen?

Accepted Answer

No precipitate will form

Question 15

Which of the following will NOT form a buffer solution?

Accepted Answer

0.10 M NaCl and 0.10 M HCl

Question 16

Which factor does NOT affect the solubility of a sparingly soluble salt?

Accepted Answer

The color of the salt

Question 17

A solution is prepared by mixing 0.50 mol of $$\mathrm{H_2CO_3}$$ and 0.50 mol of $$\mathrm{$$NaHCO_3$$} in 1.00 L. If 0.357 $$mol of NaOH is added, what is the new ratio $$\left( \frac{[$$HCO_3$$^-]}{[H_2CO_3]} \right)$$ after the reaction?

Accepted Answer

$$2.51$$

Question 18

Which of the following best explains why the solubility of $$\mathrm{AgCl}$$ decreases when $$\mathrm{NaCl} is $$added to the solution?

Accepted Answer

The common ion effect shifts the equilibrium toward the solid $$\mathrm{AgCl}$$

Question 19

Which of the following statements about buffer solutions is FALSE?

Accepted Answer

A buffer is formed by mixing a strong acid and its conjugate base

Buffer Solutions and Solubility Equilibria in Analytical Chemistry

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