Q: A solution is prepared by dissolving 24.5 g of NaCl in 150.0 mL of H$_2$O (density = 1.00 g/mL). What is the mass percent of NaCl in the solution?

$\frac{24.5}{24.5 + 150.0 \times 1.00} \times 100 = 14.0\%$

Q: A solution is prepared by mixing 25.6 mL of C$_2$H$_5$OH (density = 0.789 g/mL, molar mass = 46.1 g/mol) with enough water to produce 250.0 mL of solution. What is the molarity of ethanol in the solution?

$\frac{25.6 \times 0.789}{46.1} = 0.438$ mol; $M = \frac{0.438}{0.250} = 1.75$ M

Q: A sample of BaCO$_3$ (1.97 g) is dissolved in excess HCl. The CO$_2$ produced is absorbed by 22.46 mL of 0.1082 M NaOH. Determine the mass of BaCO$_3$ which was present in the sample. (BaCO$_3$ + 2HCl $\rightarrow$ BaCl$_2$ + CO$_2$ + H$_2$O; CO$_2$ + 2NaOH $\rightarrow$ Na$_2$CO$_3$ + H$_2$O)

Moles NaOH = $0.02246 \times 0.1082 = 0.00243$ mol; Moles CO$_2$ = $0.00243/2 = 0.001215$ mol; Mass BaCO$_3$ = $0.001215 \times 197.34 = 0.24$ g

Q: A 1.50 M NaHCO$_3$ solution is used to neutralize 78 mL of 2.6 M H$_2$SO$_4$ from a rebuilt auto battery. How many milliliters of NaHCO$_3$ must be used? (Balanced equation: $2\text{NaHCO}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{SO}_4 + 2\text{CO}_2 + 2\text{H}_2\text{O}$)

$2.6 \times 0.078 = 0.2028$ mol H$_2$SO$_4$; $0.2028 \times 2 = 0.4056$ mol NaHCO$_3$; $0.4056/1.5 = 0.2704$ L = 270 mL

Question 1

A solution is prepared by dissolving 24.5 g of NaCl in 150.0 mL of H$_2$O (density = 1.00 g/mL). What is the mass percent of NaCl in the solution?

Accepted Answer

$\frac{24.5}{24.5 + 150.0 	imes 1.00} 	imes 100 = 14.0\%$

Question 2

Which of the following best describes the equivalence point in a titration?

Accepted Answer

The point at which the acid and base have been consumed in exactly equivalent amounts.

Question 3

A 0.550 mol Ba(NO$_3$)$_2$ solution reacts with 325 mL of 0.250 M Al$_2$(SO$_4$)$_3$ solution to precipitate BaSO$_4$. The balanced equation is:

$3	ext{Ba(NO}_3	ext{)}_2 + 	ext{Al}_2(	ext{SO}_4)_3 ightarrow 3	ext{BaSO}_4 + 2	ext{Al(NO}_3	ext{)}_3$

How many grams of BaSO$_4$ are produced (theoretical yield)? (Molar mass BaSO$_4$ = 233 g/mol)

Accepted Answer

0.550 mol × $\frac{3}{3}$ × 233 g/mol = 128 g

Question 4

A solution is prepared by mixing 25.6 mL of C$_2$H$_5$OH (density = 0.789 g/mL, molar mass = 46.1 g/mol) with enough water to produce 250.0 mL of solution. What is the molarity of ethanol in the solution?

Accepted Answer

$\frac{25.6 	imes 0.789}{46.1} = 0.438$ mol; $M = \frac{0.438}{0.250} = 1.75$ M

Question 5

Which of the following statements about limiting reactants is correct?

Accepted Answer

The limiting reactant is the one that produces the least amount of product.

Question 6

A sample of BaCO$_3$ (1.97 g) is dissolved in excess HCl. The CO$_2$ produced is absorbed by 22.46 mL of 0.1082 M NaOH. Determine the mass of BaCO$_3$ which was present in the sample. (BaCO$_3$ + 2HCl $\rightarrow$ BaCl$_2$ + CO$_2$ + H$_2$O; CO$_2$ + 2NaOH $\rightarrow$ Na$_2$CO$_3$ + H$_2$O)

Accepted Answer

Moles NaOH = $0.02246 	imes 0.1082 = 0.00243$ mol; Moles CO$_2$ = $0.00243/2 = 0.001215$ mol; Mass BaCO$_3$ = $0.001215 	imes 197.34 = 0.24$ g

Question 7

Which of the following is a correct use of the dilution equation $M_1V_1 = M_2V_2$?

Accepted Answer

To calculate the volume of a concentrated solution needed to prepare a less concentrated solution.

Question 8

A 1.50 M NaHCO$_3$ solution is used to neutralize 78 mL of 2.6 M H$_2$SO$_4$ from a rebuilt auto battery. How many milliliters of NaHCO$_3$ must be used? (Balanced equation: $2	ext{NaHCO}_3 + 	ext{H}_2	ext{SO}_4 ightarrow 	ext{Na}_2	ext{SO}_4 + 2	ext{CO}_2 + 2	ext{H}_2	ext{O}$)

Accepted Answer

$2.6 	imes 0.078 = 0.2028$ mol H$_2$SO$_4$; $0.2028 	imes 2 = 0.4056$ mol NaHCO$_3$; $0.4056/1.5 = 0.2704$ L = 270 mL

Question 9

Which of the following is NOT a typical problem when using NaOH as a titrant for standardization?

Accepted Answer

NaOH is a weak base and does not fully dissociate.

Question 10

A sample of concentrated nitric acid has a density of 1.41 g/mL and contains 70.0% HNO$_3$ by mass. What is the molarity of the solution? (Molar mass HNO$_3$ = 63.0 g/mol)

Accepted Answer

1.41 g/mL × 1000 mL = 1410 g/L; 70% of 1410 g = 987 g HNO$_3$; $987/63.0 = 15.7$ mol; $M = 15.7$ M

Question 11

Which of the following best describes the difference between theoretical yield and actual yield?

Accepted Answer

Theoretical yield is the maximum possible amount of product, while actual yield is the amount actually obtained from the reaction.

Question 12

A mixture of KClO$_3$ and KCl with a mass of 9.000 g is heated to produce O$_2$. After heating, the mass of residue is 7.900 g. Assuming all the KClO$_3$ decomposed to KCl and O$_2$, what was the mass percent of KClO$_3$ in the original mixture? (KClO$_3$ $\rightarrow$ KCl + O$_2$)

Accepted Answer

Mass loss = 9.000 - 7.900 = 1.100 g (O$_2$); $\frac{1.100}{32.00} = 0.0344$ mol O$_2$; $0.0344 	imes 2 = 0.0688$ mol KClO$_3$; $0.0688 	imes 122.55 = 8.43$ g; $\frac{8.43}{9.00} 	imes 100 = 93.7\%$

Question 13

Which of the following is the correct formula for calculating percent yield?

Accepted Answer

$\frac{	ext{actual yield}}{	ext{theoretical yield}} 	imes 100$

Question 14

A 0.0652 g sample of pure strontium halide reacts with excess sulfuric acid, and the solid strontium sulfate formed is found to weigh 0.075 g. What is the formula of the original halide? (Molar mass Sr = 87.6 g/mol, SrSO$_4$ = 183.7 g/mol)

Accepted Answer

Moles SrSO$_4$ = $0.075/183.7 = 0.000408$ mol; Moles SrX$_2$ = $0.000408$ mol; Molar mass SrX$_2$ = $0.0652/0.000408 = 160$ g/mol; X = Cl

Question 15

Which of the following is the correct definition of molarity?

Accepted Answer

Moles of solute per liter of solution.

Question 16

A titration is performed using 0.250 M NaOH to neutralize 25.0 mL of 0.200 M HCl. What volume of NaOH is required? (Balanced equation: NaOH + HCl $\rightarrow$ NaCl + H$_2$O)

Accepted Answer

$0.200 	imes 0.0250 = 0.00500$ mol HCl; $0.00500/0.250 = 0.0200$ L = 20.0 mL

Question 17

Which of the following is a correct statement about an intermediate in a chemical reaction?

Accepted Answer

An intermediate is produced in one step and consumed in another, and does not appear in the overall reaction.

Solution Concentrations, Stoichiometry, and Titration in General Chemistry

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