Q: A chemist calculates that 1.20 g of $$P_4$$ can be produced from a reaction, but only 0.90 g is actually obtained. What is the percentage yield?

$$\frac{0.90}{1.20} \times 100 = 75\%$$

Q: A chemist wants to prepare 0.500 L of 0.100 mol L$$^{-1}$$ $$K_2CrO_4$$ from a stock solution of 1.75 mol L$$^{-1}$$ $$K_2CrO_4. $$What volume of the stock solution is required?

$$V_i = \frac{M_f V_f}{M_i} = \frac{0.100 \times 0.500}{1.75} = 0.0286\ \mathrm{L}$$

Q: A chemist needs to prepare 250 mL of 0.200 mol L$$^{-1}$$ $$NaCl$$ solution from a 1.00 mol L$$^{-1}$$ stock solution. What volume of the stock solution should be used?

$$V_i = \frac{M_f V_f}{M_i} = \frac{0.200 \times 0.250}{1.00} = 0.050\ \mathrm{L}$$

Q: A chemist purchases 12 mol L$$^{-1}$$ HCl and wants to prepare 1.0 L of 1.0 mol L$$^{-1}$$ HCl. What volume of the concentrated acid should be used?

$$V_i = \frac{1.0 \times 1.0}{12} = 0.083\ \mathrm{L}$$

Question 1

A chemist calculates that 1.20 g of $$P_4$$ can be produced from a reaction, but only 0.90 g is actually obtained. What is the percentage yield?

Accepted Answer

$$\frac{0.90}{1.20} 	imes 100 = 75\%$$

Question 2

Which of the following best describes the difference between theoretical yield and actual yield in a chemical reaction?

Accepted Answer

Theoretical yield is the maximum amount of product predicted by stoichiometry, while actual yield is the amount actually obtained from the experiment.

Question 3

A solution is prepared by dissolving 0.150 mol of $$AgNO_3 in $$enough water to make 1.00 L of solution. What is the molarity of the solution?

Accepted Answer

$$M = \frac{0.150}{1.00} = 0.150\ \mathrm{mol\ L$$^{-1}$$}$$

Question 4

Which of the following statements about dilution is correct?

Accepted Answer

Dilution does not change the number of moles of solute present in the solution.

Question 5

A chemist wants to prepare 0.500 L of 0.100 mol L$$^{-1}$$ $$K_2CrO_4$$ from a stock solution of 1.75 mol L$$^{-1}$$ $$K_2CrO_4. $$What volume of the stock solution is required?

Accepted Answer

$$V_i = \frac{M_f V_f}{M_i} = \frac{0.100 	imes 0.500}{1.75} = 0.0286\ \mathrm{L}$$

Question 6

Which of the following best represents the correct order of increasing concentration for the beakers shown (A, B, C, D) containing the same solute?

Accepted Answer

C \u003c D \u003c A \u003c B

Question 7

A 1 mol L$$^{-1}$$ solution of $$Ca(NO_3$)_2$$ contains which of the following ion concentrations?

Accepted Answer

1 mol L$$^{-1}$$ $$Ca^{2+}$$ and 2 mol L$$^{-1}$$ $$NO_3$$^-$$

Question 8

A chemist needs to prepare 250 mL of 0.200 mol L$$^{-1}$$ $$NaCl$$ solution from a 1.00 mol L$$^{-1}$$ stock solution. What volume of the stock solution should be used?

Accepted Answer

$$V_i = \frac{M_f V_f}{M_i} = \frac{0.200 	imes 0.250}{1.00} = 0.050\ \mathrm{L}$$

Question 9

If 5.00 mL of 0.0985 mol L$$^{-1}$$ $$NaOCl$$ reacts with excess butanethiol ($$C_4H_9SH$$), how many grams of butanethiol can be deodorized? (Molar mass of $$C_4H_9SH = 90.18 g $$mol$$^{-1}$$, reaction: $$2C_4H_9SH + NaOCl \rightarrow C_4H_9S-SC_4H_9 + NaCl + H_2O)$$

Accepted Answer

$$0.0888\ \mathrm{g}$$

Question 10

Which equation correctly relates the initial and final concentrations and volumes during a dilution?

Accepted Answer

$$M_i V_i = M_f V_f$$

Question 11

A solution is made by mixing 0.0500 L of 0.100 mol L$$^{-1}$$ $$Ca(NO_3$)_2$$ and 0.0750 L of 0.250 mol L$$^{-1}$$ $$NaNO_3. $$What is the final concentration of $$NO_3$$^-$$ ions in the 0.1250 L solution?

Accepted Answer

$$[NO_3$^-] = \frac{0.0288}{0.1250} = 0.230\ \mathrm{mol\ L$$^{-1}$$}$$

Question 12

Which of the following is a correct unit for molarity?

Accepted Answer

$$\mathrm{mol\ L$$^{-1}$$}$$

Question 13

A chemist purchases 12 mol L$$^{-1}$$ HCl and wants to prepare 1.0 L of 1.0 mol L$$^{-1}$$ HCl. What volume of the concentrated acid should be used?

Accepted Answer

$$V_i = \frac{1.0 	imes 1.0}{12} = 0.083\ \mathrm{L}$$

Question 14

Which of the following best explains why the concentration of a solution decreases when it is diluted?

Accepted Answer

The volume of solvent increases while the number of moles of solute remains constant.

Question 15

A 1 mol L$$^{-1}$$ $$KCl$$ solution contains:

Accepted Answer

1 mol L$$^{-1}$$ $$K^+$$ and 1 mol L$$^{-1}$$ $$Cl^-$$

Question 16

Which of the following is the correct formula for calculating molarity?

Accepted Answer

$$M = \frac{n}{V}$$

Question 17

A student adds 25.5 g of $$AgNO_3 ($$molar mass = 169.88 g mol$$^{-1}) to $$water to make 1.00 L of solution. What is the molarity of the solution?

Accepted Answer

$$M = \frac{25.5}{169.88} = 0.150\ \mathrm{mol\ L$$^{-1}$$}$$

CH 4-4: Chemical Reactions and Stoichiometry: Yields, Concentration, Dilution, and Solution Stoichiometry

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