Q: A solution contains 0.059 mol L$$^{-1} Mg$^{2+}$$ and 0.011 mol L$$^{-1} Ca$^{2+}. $$What is the minimum [OH$$^-$$] required to begin precipitating Mg(OH)$$_2$$? ($$K_{sp} Mg(OH$$)$$_2$$ = $$2.06 \times 10$$^{-13}$$)

$$1.9 \times 10$$^{-6}$$ mol L$$^{-1}$$

Question 1

Which of the following best describes a buffer solution?

Accepted Answer

A solution containing a weak acid and a salt of its conjugate base

Question 2

A buffer is most effective when the concentrations of acid and conjugate base differ by no more than what factor?

Accepted Answer

A factor of 10

Question 3

Calculate the pH of a buffer solution containing 0.20 mol L$$^{-1}$$ HCN and 0.30 mol L$$^{-1}$$ NaCN. $$K_a of $$HCN = $$3.5 	imes 10$$^{-4}$$. Use the Henderson-Hasselbalch equation.

Accepted Answer

$$pH = 4.99$$

Question 4

Which of the following statements about the common ion effect is correct?

Accepted Answer

The common ion effect decreases the solubility of an ionic compound

Question 5

A buffer solution is prepared by mixing 0.100 mol CH$$_3$$COOH and 0.100 mol CH$$_3$$COONa in 1.00 L of water. What is the initial pH? ($$K_a$$ = $$1.8 	imes 10$$^{-5}$$)

Accepted Answer

$$pH = 4.74$$

Question 6

Which of the following buffer mixtures is most effective at resisting pH change?

Accepted Answer

0.100 mol L$$^{-1} CH$_3$$COOH and 0.100 mol L$$^{-1} CH$_3$$COONa

Question 7

What is the pH of a buffer solution (100 mL) containing 0.50 mol L$$^{-1}$$ pyruvic acid ($$K_a = 4.1 	imes 10$$^{-3}$$) and 0.35 mol L$$^{-1}$$ sodium pyruvate?

Accepted Answer

$$pH = 2.97$$

Question 8

Which of the following indicators would NOT be suitable for a titration with an equivalence point at pH 6.24?

Accepted Answer

Cresol purple, pH transition range 7.6–9.2

Question 9

During the titration of a weak acid with a strong base, what is the pH at the equivalence point?

Accepted Answer

Greater than 7.00

Question 10

A solution contains 0.059 mol L$$^{-1} Mg$^{2+}$$ and 0.011 mol L$$^{-1} Ca$^{2+}. $$What is the minimum [OH$$^-$$] required to begin precipitating Mg(OH)$$_2$$? ($$K_{sp} Mg(OH$$)$$_2$$ = $$2.06 	imes 10$$^{-13}$$)

Accepted Answer

$$1.9 	imes 10$$^{-6}$$ mol L$$^{-1}$$

Question 11

Which compound will be more soluble in acid than in base, FeCO$$_3 or $$PbBr$$_2$$, and why?

Accepted Answer

FeCO$$_3$$, because CO$$_3$$^{2-}$$ is a basic anion that reacts with acid

Question 12

A 25.0 mL sample of 0.150 mol L$$^{-1} HI is $$titrated with 0.100 mol L$$^{-1}$$ NaOH. What is the volume of NaOH needed to reach the equivalence point?

Accepted Answer

37.5 mL

Question 13

Which of the following best explains why the solubility of Mg(OH)$$_2$$ increases in acidic solution?

Accepted Answer

H$$_3O$^+$$ neutralizes OH$$^-$$, shifting equilibrium to dissolve more Mg(OH)$$_2$$

Question 14

What is the pH at the equivalence point when titrating a weak base with a strong acid?

Accepted Answer

Less than 7.00

Question 15

Which of the following best describes the buffer capacity?

Accepted Answer

The amount of acid or base that can be added to a buffer without destroying its effectiveness

Question 16

A solution is 0.085 mol L$$^{-1} in Pb$^{2+}$$ and 0.025 mol L$$^{-1} in Ag$^+. If $$selective precipitation is to be achieved using NaCl, which ion will precipitate first?

Accepted Answer

Ag$$^+$$

Question 17

Which of the following is true about the Henderson-Hasselbalch equation?

Accepted Answer

It can only be used when the percent ionization is less than 5%

Aqueous Ionic Equilibrium: Buffers, Titrations, and Solubility

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