Q: Which of the following equations correctly represents the calculation for parts per billion (ppb)?

$$ppb = \frac{\text{mass of solute}}{\text{mass of solution}} \times 10^9$

Q: Which of the following is the correct formula for calculating mass percentage?

$$\text{Mass percentage} = \frac{\text{mass of one component}}{\text{mass of whole solution}} \times 100$$

Question 1

A chemist wants to produce water by reacting hydrogen gas with oxygen gas according to the balanced equation: $$2H_2(g) + O_2$(g) \rightarrow 2H_2O(g). If $$the chemist starts with 10.0 g of $$H_2$$ and 80.0 g of $$O_2$$, what is the limiting reagent?

Accepted Answer

Hydrogen gas ($$H_2)$$

Question 2

In the combustion of octane, $$2C_8H_{18}(l) + 25O_2(g) \rightarrow 16CO_2(g) + 18H_2O(g)$$, how many grams of $$CO_2$$ are produced from 5.00 moles of $$C_8H_{18}$$? (Molar mass of $$CO_2 = 44.01$ g/mol)

Accepted Answer

$$1.76 	imes 10^3$ g

Question 3

A plant consumes 44.0 g of $$CO_2 in $$photosynthesis. Using the balanced equation $$6CO_2(g) + 6H_2O(g) \rightarrow C_6H_{12}O_6$(aq) + 6O_2(g)$$, what mass of glucose ($$C_6H_{12}O_6$) can be synthesized? (Molar masses: CO_2$ = 44.01 g/$$mol, $$C_6H_{12}O_6$ = 180.2 g/$$mol)

Accepted Answer

30.0 g

Question 4

If you have 0.500 mol of $$KClO_3$$ and it decomposes according to $$2KClO_3(s) \rightarrow 2KCl(s) + 3O_2(g)$$, how many moles of $$O_2$$ are produced?

Accepted Answer

0.750 mol

Question 5

A solution is prepared by dissolving 5.00 g of NaCl in enough water to make 250.0 mL of solution. What is the molarity of the solution? (Molar mass of NaCl = 58.44 g/mol)

Accepted Answer

$$0.342 M$$

Question 6

You have a 0.250 M solution of $$H_2SO_4$$ and want to prepare 100.0 mL of a 0.0500 M solution. What volume of the original solution should you use? (Use $$M_1V_1 = M_2V_2)$$

Accepted Answer

20.0 mL

Question 7

A 200.0 g sample of solution contains 390 mg of sodium ion. What is the concentration of sodium ion in ppm?

Accepted Answer

$$1.95 	imes 10^3$ ppm

Question 8

In the reaction $$2NO(g) + 5H_2(g) \rightarrow 2NH_3(g) + 2H_2O(g)$$, if you start with 86.3 g of NO and 25.6 g of $$H_2$$, what is the theoretical yield of $$NH_3 in $$grams? (Molar mass of $$NO = 30.01 g/$$mol, $$H_2 = 2.02$ g/mol, NH_3$ = 17.03 g/$$mol)

Accepted Answer

49.0 g

Question 9

A reaction produces 72.3 g of Fe from 167 g of $$Fe_2O_3$$ and 85.8 g of CO. The balanced equation is $$Fe_2O_3(s) + 3CO(g) \rightarrow 2Fe(s) + 3CO_2(g). $$What is the percent yield of Fe? (Molar masses: $$Fe_2O_3 = 159.7 g/$$mol, $$CO = 28.01 g/$$mol, $$Fe = 55.85 g/$$mol)

Accepted Answer

63.5%

Question 10

Which of the following best explains why the actual yield of a chemical reaction is often less than the theoretical yield?

Accepted Answer

Side reactions and incomplete reactions reduce the actual yield

Question 11

A solution is made by mixing 30.0 mL of ethanol with enough water to make 100.0 mL of solution. What is the volume percent of ethanol in the solution?

Accepted Answer

30.0%

Question 12

If you have 5 molecules of $$CH_4$$ and 8 molecules of $$O_2$$ reacting according to $$CH_4 + 2O_2$$ \rightarrow $$CO_2 + 2H_2O$, what is the limiting reagent and how many molecules of CO_2$ can be formed?

Accepted Answer

$$O_2 is $$limiting; 4 molecules of $$CO_2$$ can be formed

Question 13

A chemist wants to prepare a solution with a mass percent of 10% NaCl. If she dissolves 5.0 g of NaCl in water, what should be the total mass of the solution?

Accepted Answer

50 g

Question 14

Which of the following equations correctly represents the calculation for parts per billion (ppb)?

Accepted Answer

$$ppb = \frac{	ext{mass of solute}}{	ext{mass of solution}} 	imes 10^9$

Question 15

A 0.500 L solution contains 0.0250 mol of $$KNO_3. $$What is the molarity of the solution?

Accepted Answer

0.0500 M

Question 16

Which of the following is the correct formula for calculating mass percentage?

Accepted Answer

$$	ext{Mass percentage} = \frac{	ext{mass of one component}}{	ext{mass of whole solution}} 	imes 100$$

Question 17

A reaction mixture contains 3.00 mol of $$N_2$$ and 6.00 mol of $$H_2$$ for the synthesis of ammonia: $$N_2 + 3H_2$$ \rightarrow 2NH_3$$. What is the limiting reagent and how many moles of NH_3$ can be formed?

Accepted Answer

$$H_2 is $$limiting; 2.00 mol $$NH_3$$ can be formed

Question 18

A 100.0 mL solution contains 0.500 g of glucose ($$C_6H_{12}O_6$). What is the mass/volume percent of glucose in the solution?

Accepted Answer

0.500%

Question 19

Which of the following best describes the concept of stoichiometry in chemical reactions?

Accepted Answer

It is the calculation of quantitative relationships between reactants and products using balanced chemical equations

Question 20

A chemist needs to dilute 25.0 mL of a 2.00 M $$NaOH$$ solution to a final concentration of 0.500 M. What will be the final volume after dilution?

Accepted Answer

100.0 mL

Stoichiometry and Solution Concentrations: Mass Relationships in Chemical Reactions

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