Q: Which equation is used to calculate the pH of a buffer solution containing a weak acid and its conjugate base?

$$pH = pK_a + \log \frac{[\text{base}]}{[\text{acid}]}$$

Q: A solution contains $$0.040\ M$$ $$Pb^{2+}$$ and $$0.25\ M$$ $$Cl^-. $$Will $$PbCl_2$$ precipitate? ($$K_{sp}($$PbCl_2$$) = 1.6 \times 10$$^{-5}$$)

Yes, because $$Q = [Pb$$^{2+}$$][Cl^-]^2 = 0.040 \times (0.25)^2$ = 0.0025 \u003e K_{sp}$$

Question 1

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

Accepted Answer

The addition of a strong electrolyte containing an ion in common with a dissolved weak electrolyte suppresses the ionization of the weak electrolyte.

Question 2

A buffer solution is prepared by mixing 0.50 mol of acetic acid ($$CH_3COOH) $$and 0.50 mol of sodium acetate ($$CH_3COONa) in 1.0 L of $$water. If $$K_a$$ for acetic acid is $$1.8 	imes 10$$^{-5}$$, what is the pH of the buffer? (Use pK_a$$ = -\log K_a$$)

Accepted Answer

$$pH = 4.74$$

Question 3

Which equation is used to calculate the pH of a buffer solution containing a weak acid and its conjugate base?

Accepted Answer

$$pH = pK_a + \log \frac{[	ext{base}]}{[	ext{acid}]}$$

Question 4

A buffer solution contains 0.75 M lactic acid ($$HC_3H_5O_3) $$and 0.75 M sodium lactate ($$C_3H_5O_3Na). $$What is the pH after adding 0.15 mol of HCl to 1.00 L of this buffer? ($$K_a = 1.4 	imes 10$$^{-4}$$ for lactic acid)

Accepted Answer

$$pH = 3.68$$

Question 5

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

Accepted Answer

$$pH = 7$$

Question 6

Which of the following statements about acid-base indicators is correct?

Accepted Answer

An indicator changes color at a pH equal to its $$pK_a.$$

Question 7

What is the solubility product constant ($$K_{sp}) $$expression for $$Ba_3$$($$PO_4)_2$?

Accepted Answer

$$K_{sp} = [Ba$$^{2+}$$]^3[PO_4$^{3-}]^2$$

Question 8

If the ion product $$Q$$ for $$Mg(OH)_2 is $$greater than its $$K_{sp}$$, what will happen?

Accepted Answer

A precipitate of $$Mg(OH)_2$$ will form.

Question 9

Which of the following will increase the solubility of $$Fe(OH)_2 in $$water?

Accepted Answer

Decreasing the pH of the solution.

Question 10

A solution contains $$0.040\ M$$ $$Pb^{2+}$$ and $$0.25\ M$$ $$Cl^-. $$Will $$PbCl_2$$ precipitate? ($$K_{sp}($$PbCl_2$$) = 1.6 	imes 10$$^{-5}$$)

Accepted Answer

Yes, because $$Q = [Pb$$^{2+}$$][Cl^-]^2 = 0.040 	imes (0.25)^2$ = 0.0025 \u003e K_{sp}$$

Question 11

Which of the following best explains why the addition of $$NaF to a $$saturated solution of $$CaF_2$$ decreases the solubility of $$CaF_2$$?

Accepted Answer

The common-ion effect shifts the equilibrium to the left, decreasing solubility.

Question 12

Which of the following is true about buffer capacity?

Accepted Answer

A buffer with higher concentrations of acid and base can neutralize more added acid or base before the pH changes significantly.

Question 13

Which of the following is the correct sequence for calculating the pH after adding a strong acid to a buffer?

Accepted Answer

1. Use stoichiometry to find new $$[HA]$$ and $$[A^-]$$; 2. Use Henderson-Hasselbalch equation to find pH.

Question 14

Which of the following is a real-world application of buffer solutions?

Accepted Answer

Maintaining blood pH in the human body.

Question 15

A polyprotic acid is titrated with a strong base. What is true about the titration curve?

Accepted Answer

There are multiple equivalence points, one for each dissociation.

Question 16

Which indicator would be most suitable for the titration of a weak acid with a strong base if the equivalence point is at pH 9?

Accepted Answer

Phenolphthalein (color change interval $$8.3 \u003c pH \u003c 10.0)$$

Question 17

Which of the following best describes selective precipitation in qualitative analysis?

Accepted Answer

Adding a reagent to a solution to precipitate one ion while leaving others in solution based on differences in $$K_{sp}.$$

Question 18

Which of the following statements about the effect of pH on solubility is correct?

Accepted Answer

A salt with a basic anion is more soluble in acidic solution.

Aqueous Equilibria: Buffers, Titrations, and Solubility (GOB Chemistry Study Notes)

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