Q: A solution contains 0.01 M CaCl$_2$ and 0.07 M F$^-$. A solution containing copper (II) ions is added to selectively precipitate one of the ions. At what concentration of copper (II) will a precipitate begin to form? (Ksp(CaF$_2$) = $1.0 \times 10^{-10}$, Ksp(CuF$_2$) = $5.1 \times 10^{-5}$)

$2.0 \times 10^{-8}\ \text{M}$, CaF$_2$

Question 1

A 250 mL solution is made of 0.10 M HClO and 0.14 M its conjugate base. What mass of HClO (MM = 52.5 g/mol) in grams can the buffer absorb before one of the components is no longer present?

Accepted Answer

0.88 g

Question 2

Which of the following best describes the equivalence point in a titration of a weak acid with a strong base?

Accepted Answer

The equivalence point is greater than 7 because only the conjugate base remains.

Question 3

If 0.10 mol of NaF (pKa = 3.18) is added to water to make a 1.00 L solution, what is the $[	ext{F}^-]$ concentration of the resultant solution in molarity?

Accepted Answer

$0.10\ 	ext{M}$

Question 4

What is the pH of a buffer solution that contains 1.0 L of 0.40 M CH3COOH and 1.00 mol NaCH3COO (Ka = $1.8 	imes 10^{-5}$)?

Accepted Answer

5.02

Question 5

A solution begins with 0.10 M NaF dissolved in water. What is the concentration in molarity of $	ext{OH}^-$ ions in the solution? ($K_b$ for F$^-$ = $2.9 	imes 10^{-11}$)

Accepted Answer

$1.7 	imes 10^{-6}\ 	ext{M}$

Question 6

To create a buffer that maintains a pH around 5, which substance would you choose? (Use close values for Ka.)

Accepted Answer

CH3COOH and KCH3COO

Question 7

A 250 mL solution of 0.10 M HClO is titrated with 0.200 M NaOH. What is the expected pH of the resulting solution once 50.0 mL of the NaOH solution has been added to the HClO solution? (Assume no change in total volume.)

Accepted Answer

5.20

Question 8

Benzene has a $\Delta H_{	ext{vap}} = 33.9\ 	ext{kJ/mol}$ and a $\Delta S_{	ext{vap}} = 94.4\ 	ext{J/(mol\cdot K)}$. What is the boiling point of benzene in Celsius?

Accepted Answer

$80.1^\circ 	ext{C}$

Question 9

Balance the following reaction and then solve for the $\Delta S^\circ$ in J/(mol·K) for this reaction.

Li(s) + H2O(l) $\rightarrow$ LiOH(aq) + H2(g)

Given: $S^\circ$ [Li(s)] = 29.1, $S^\circ$ [H2O(l)] = 69.9, $S^\circ$ [LiOH(aq)] = 50.0, $S^\circ$ [H2(g)] = 130.6 (all in J/(mol·K))

Accepted Answer

$81.6$

Question 10

The following reaction is exothermic and spontaneous at 25°C:

$	ext{C}_2	ext{H}_5	ext{OH}(l) + 3	ext{O}_2(g) ightarrow 2	ext{CO}_2(g) + 3	ext{H}_2	ext{O}(l)$

Which of the following statements correctly describes the spontaneity?

Accepted Answer

The reaction is spontaneous at all temperatures.

Question 11

Which answer below is the best description for 'microscopic' entropy?

Accepted Answer

The number of possible microstates

Question 12

What is the $\Delta G^\circ$ (in kJ/mol) for a reaction at 25°C that has a $\Delta H = 110\ 	ext{kJ/mol}$ and a $\Delta S$ of $65.5\ 	ext{J/(mol·K)}$?

Accepted Answer

$90.5$

Question 13

How many of the following processes represent an increase in entropy?
I. Water is heated and evaporates from 25°C to 100°C
II. The sublimation of I$_2$
III. CO$_2$ is dissolved in water to make a carbonated beverage
IV. NO$_2$(g) $\rightarrow$ N$_2$O$_4$(g)

Accepted Answer

Two

Question 14

If $\Delta G$ is 0, what must be true regarding $\Delta G$?

Accepted Answer

The system is at equilibrium

Question 15

Which of the following is true regarding a spontaneous process?
I. $\Delta G$ is negative
II. $\Delta S$ is positive
III. $\Delta H$ is negative

Accepted Answer

Only I

Question 16

Which of the following is/are always true for spontaneous processes?
I. $\Delta G < 0$
II. $\Delta S > 0$
III. $\Delta H < 0$

Accepted Answer

Only I

Question 17

A solution contains 0.01 M CaCl$_2$ and 0.07 M F$^-$. A solution containing copper (II) ions is added to selectively precipitate one of the ions. At what concentration of copper (II) will a precipitate begin to form? (Ksp(CaF$_2$) = $1.0 	imes 10^{-10}$, Ksp(CuF$_2$) = $5.1 	imes 10^{-5}$)

Accepted Answer

$2.0 	imes 10^{-8}\ 	ext{M}$, CaF$_2$

Question 18

Which answer describes how HF is both a Brønsted-Lowry acid and a Lewis acid?
I. HF donates an H$^+$ ion to a Brønsted-Lowry base
II. HF donates an H$^+$ ion to a Lewis base
III. HF accepts an electron pair from a Lewis base

Accepted Answer

I and III

Question 19

Which of the following statements is most true about a buffer?
I. The addition of acid to the buffer is a reversible process
II. The buffer always contains equal concentrations of acid and base
III. The addition of 0.01 mol of NaOH to a 1.0 M HF solution makes a buffer (if pH is within 1 unit of pKa)

Accepted Answer

Only I

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