Q: A student dissolves 60 g of NaOH in 250 mL of water. What is the molarity of the solution? (Molar mass of NaOH = 40 g/mol)

$$M = \frac{60\ \text{g}}{40\ \text{g/mol} \times 0.250\ \text{L}} = 6.0\ \text{M}$$

Q: A solution is prepared by dissolving 15 mL of 4.0 M NaCl into enough water to make 1.5 L of solution. What is the final concentration?

$$M_1V_1 = M_2V_2$$ $$4.0\ \text{M} \times 0.015\ \text{L} = M_2$ \times 1.5\ \text{L}$$ $$M_2 = 0.040$$\ \text{M}$$

Q: Which of the following is a correct balanced chemical equation for the reaction between HNO$$_3(aq) $$and NaOH(aq)?

$$\text{HNO}_3(\text{aq}) + \text{NaOH}(\text{aq}) \rightarrow \text{NaNO}_3(\text{aq}) + \text{H}_2\text{O}(\ell)$$

Q: Given the chemical equation $$2\text{C}_6\text{H}_{12} + 11\text{O}_2 \rightarrow 8\text{CO}_2 + 6\text{H}_2\text{O}$$, how many moles of C$$_6H$_{12}$$ are needed to produce 14.4 moles of CO$$_2$$?

$$\frac{2\ \text{mol}\ \text{C}_6\text{H}_{12}}{8\ \text{mol}\ \text{CO}_2} \times 14.4\ \text{mol}\ \text{CO}_2 = 3.6\ \text{mol}\ \text{C}_6\text{H}_{12}$$

Q: What is the pH of a $$3.6 \times 10$$^{-5}$$ M HNO_3$ solution?

$$\text{pH} = -\log[\text{H}^+] = -\log(3.6 \times 10$$^{-5}$$) = 4.44$$

Q: A mixture of gases contains 2 atm of O$$_2$$, 1 atm of N$$_2$$, and 3 atm of CO$$_2. $$What is the total pressure?

$$P_{\text{total}} = P_{O_2$} + P_{N_2$} + P_{CO_2$} = 2 + 1 + 3 = 6\ \text{atm}$$

Q: What is the percent by mass (%m/m) of a solution made by dissolving 10 g of NaCl in 90 g of water?

$$\%m/m = \frac{10\ \text{g}}{100\ \text{g}} \times 100 = 10\%$$

Q: How many moles of C$$_6H$_6$$ are present in 0.56 g of C$$_6H$_6$$? (Molar mass = 78 g/mol)

$$\text{moles} = \frac{0.56\ \text{g}}{78\ \text{g/mol}} = 0.019\ \text{mol}$$

Q: Which formula is used to calculate the molarity of a solution?

$$M = \frac{\text{moles of solute}}{\text{L of solution}}$$

Question 1

A student dissolves 60 g of NaOH in 250 mL of water. What is the molarity of the solution? (Molar mass of NaOH = 40 g/mol)

Accepted Answer

$$M = \frac{60\ 	ext{g}}{40\ 	ext{g/mol} 	imes 0.250\ 	ext{L}} = 6.0\ 	ext{M}$$

Question 2

Which of the following statements about saturated solutions is correct?

Accepted Answer

If more solute is added to a saturated solution, it will precipitate out and the concentration will remain the same.

Question 3

A solution is prepared by dissolving 15 mL of 4.0 M NaCl into enough water to make 1.5 L of solution. What is the final concentration?

Accepted Answer

$$M_1V_1 = M_2V_2$$ 
 $$4.0\ 	ext{M} 	imes 0.015\ 	ext{L} = M_2$ 	imes 1.5\ 	ext{L}$$ 
 $$M_2 = 0.040$$\ 	ext{M}$$

Question 4

Which of the following is a correct balanced chemical equation for the reaction between HNO$$_3(aq) $$and NaOH(aq)?

Accepted Answer

$$	ext{HNO}_3(	ext{aq}) + 	ext{NaOH}(	ext{aq}) ightarrow 	ext{NaNO}_3(	ext{aq}) + 	ext{H}_2	ext{O}(\ell)$$

Question 5

Given the chemical equation $$2	ext{C}_6	ext{H}_{12} + 11	ext{O}_2 ightarrow 8	ext{CO}_2 + 6	ext{H}_2	ext{O}$$, how many moles of C$$_6H$_{12}$$ are needed to produce 14.4 moles of CO$$_2$$?

Accepted Answer

$$\frac{2\ 	ext{mol}\ 	ext{C}_6	ext{H}_{12}}{8\ 	ext{mol}\ 	ext{CO}_2} 	imes 14.4\ 	ext{mol}\ 	ext{CO}_2 = 3.6\ 	ext{mol}\ 	ext{C}_6	ext{H}_{12}$$

Question 6

What is the pH of a $$3.6 	imes 10$$^{-5}$$ M HNO_3$ solution?

Accepted Answer

$$	ext{pH} = -\log[	ext{H}^+] = -\log(3.6 	imes 10$$^{-5}$$) = 4.44$$

Question 7

Which of the following solutions is basic?

Accepted Answer

$$	ext{pH} = 9.3$$

Question 8

A mixture of gases contains 2 atm of O$$_2$$, 1 atm of N$$_2$$, and 3 atm of CO$$_2. $$What is the total pressure?

Accepted Answer

$$P_{	ext{total}} = P_{O_2$} + P_{N_2$} + P_{CO_2$} = 2 + 1 + 3 = 6\ 	ext{atm}$$

Question 9

Which of the following is a strong electrolyte?

Accepted Answer

NaCl (aq)

Question 10

What is the percent by mass (%m/m) of a solution made by dissolving 10 g of NaCl in 90 g of water?

Accepted Answer

$$\%m/m = \frac{10\ 	ext{g}}{100\ 	ext{g}} 	imes 100 = 10\%$$

Question 11

Which of the following is a constitutional isomer of hexane?

Accepted Answer

2-methylpentane

Question 12

How many moles of C$$_6H$_6$$ are present in 0.56 g of C$$_6H$_6$$? (Molar mass = 78 g/mol)

Accepted Answer

$$	ext{moles} = \frac{0.56\ 	ext{g}}{78\ 	ext{g/mol}} = 0.019\ 	ext{mol}$$

Question 13

Which formula is used to calculate the molarity of a solution?

Accepted Answer

$$M = \frac{	ext{moles of solute}}{	ext{L of solution}}$$

Question 14

Which of the following is the correct relationship for the ion product of water at 25°C?

Accepted Answer

$$[	ext{H}^+][	ext{OH}^-] = 1.0 	imes 10$$^{-14}$$

Question 15

A student needs to prepare 360 mL of 0.50 M Ca(OH)$$_2$$ solution. How many grams of Ca(OH)$$_2$$ are required? (Molar mass = 74 g/mol)

Accepted Answer

$$0.50\ 	ext{mol/L} 	imes 0.360\ 	ext{L} = 0.18\ 	ext{mol}$$ 
 $$0.18\ 	ext{mol} 	imes 74\ 	ext{g/mol} = 13.3\ 	ext{g}$$

Question 16

Which of the following is NOT a property of acids?

Accepted Answer

Acids produce OH$$^-$$ ions in water.

Question 17

Which of the following is an example of a mole-to-mass conversion?

Accepted Answer

Calculating the grams of NaCl needed to provide 2.0 moles of NaCl.

Question 18

Which of the following best describes a supersaturated solution?

Accepted Answer

A solution that contains more solute than it can theoretically hold at a given temperature.

Introduction to Chemistry: Key Concepts and Practice Problems (Chapters 5, 6, 7, 8, 10)

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