Question 1

Determine the pH of a $$0.22\ \mathrm{M}$$ NaF solution at $$25^\circ\mathrm{C}. $$The $$K_a of HF is$$ $$3.5 	imes 10$$^{-5}$$. (Notice this is a salt)

Accepted Answer

10.20

Question 2

Calculate the pH of a buffer that is $$0.225\ \mathrm{M}\ \mathrm{HC_2H_3O_2}$$ and $$0.162\ \mathrm{M}\ \mathrm{NaC_2H_3O_2}. $$The $$K_a$$ for $$\mathrm{HC_2H_3O_2} is$$ $$1.8 	imes 10$$^{-5}$$.

Accepted Answer

4.89

Question 3

Consider a buffer composed of an acid HA and its conjugate base $$A^-. $$Which solution would make the most effective buffer?

Accepted Answer

0.500\ \mathrm{M}\ \mathrm{HA};\ 0.500\ \mathrm{M}\ \mathrm{A^-}$

Question 4

Which of the following best explains why a buffer is most effective when the concentrations of the weak acid and its conjugate base are equal?

Accepted Answer

Because the buffer can neutralize equal amounts of added acid and base, maximizing its capacity.

Question 5

A buffer solution is prepared by mixing $$0.300\ \mathrm{mol} of $$acetic acid ($$\mathrm{HC_2H_3O_2}) $$and $$0.300\ \mathrm{mol} of $$sodium acetate ($$\mathrm{NaC_2H_3O_2}) in $$enough water to make $$1.0\ \mathrm{L} of $$solution. What is the pH of the buffer? ($$K_a$$ for acetic acid $$= 1.8 	imes 10$$^{-5}$$)

Accepted Answer

4.74

Question 6

If $$0.01\ \mathrm{mol} of $$HCl is added to $$1.0\ \mathrm{L} of $$the buffer solution in the previous question, what will happen to the pH?

Accepted Answer

The pH will decrease slightly, but remain close to the original value.

Question 7

Which of the following salts will produce a basic solution when dissolved in water?

Accepted Answer

NaF

Question 8

A solution is made by dissolving $$0.10\ \mathrm{mol} of $$NaF in $$1.0\ \mathrm{L} of $$water. What is the main chemical reaction that occurs in the solution?

Accepted Answer

$$\mathrm{F^-} + \mathrm{H_2O} \rightleftharpoons \mathrm{HF} + \mathrm{OH^-}$$

Question 9

Which of the following statements about buffer solutions is correct?

Accepted Answer

A buffer resists changes in pH when small amounts of acid or base are added.

Question 10

A buffer is prepared using $$0.100\ \mathrm{M}$$ formic acid ($$\mathrm{$$HCHO_2$$}) $$and $$0.100\ \mathrm{M}$$ sodium formate ($$\mathrm{$$NaCHO_2$$}). If $$the $$K_a$$ for formic acid is $$1.8 	imes 10$$^{-4}$$, what is the pH of the buffer?

Accepted Answer

3.74

Acid-Base Equilibria, Buffers, and Salt Solutions Study Guidance

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