Chapter 7. Stoichiometry of Chemical Reactions

# 7.6 End of Chapter Problems

1. How many molecules of O2 will react with 6.022 × 1023 molecules of H2 to make water?

The reaction is 2 H2(g) + O2(g) $\longrightarrow$ 2 H2O(ℓ).

2. How many moles are present in 6.411 kg of CO2? How many molecules is this?

3. What is the mass in milligrams of 7.22 × 1020 molecules of CO2?

4. What is the mass in grams of 1 molecule of H2O?

5. What is the volume of 3.44 mol of Ga if the density of Ga is 6.08 g/mL?

6. For the chemical reaction

2 C4H10(g) + 13 O2(g) $\longrightarrow$ 8 CO2(g) + 10 H2O(ℓ)

assume that 13.4 g of C4H10 reacts completely to products. The density of CO2 is 1.96 g/L. What volume in liters of CO2 is produced?

7. Calculate the mass of each product when 100.0 g of CuCl react according to the reaction

2 CuCl(aq) $\longrightarrow$ CuCl2(aq) + Cu(s)

What do you notice about the sum of the masses of the products? What concept is being illustrated here?

8. What mass of CO2 is produced from the combustion of 1 gal of gasoline? The chemical formula of gasoline can be approximated as C8H18. Assume that there are 2,801 g of gasoline per gallon.

9. A chemical reaction has a theoretical yield of 19.98 g and a percent yield of 88.40%. What is the actual yield?

10. Given the initial amounts listed, what is the limiting reagent, and how much of the other reactants are in excess?

2 P4 +  6 NaOH +  6 H2O  $\longrightarrow$  3 Na2HPO4  +  5 PH3

Initial amounts used: P= 35.0 g; NaOH = 12.7 g; H2O = 9.33 g

11. Verify that it does not matter which product you use to predict the limiting reagent by using both products in this combustion reaction to determine the limiting reagent and the amount of the reactant in excess. Initial amounts of each reactant are given.

12. Chlorine can be produced by the reaction of hydrochloric acid with excess manganese(IV) oxide according to the following reaction: 4HCl(aq) + MnO2(s) $\longrightarrow$ Cl2(g) + 2H2O(l) + MnCl2(aq). How many moles of HCl are needed to form 12.5 mol Cl2?

13. How many moles of aluminum oxide will be produced by reacting 9.5 mol of Al with O2?
How many moles of O2will react?

14. Nitrogen monoxide is oxidized in air to give brown nitrogen dioxide:

2NO(g) + O2(g) $\longrightarrow$ 2NO2(g)
Starting with 2.2 mol NO, how many moles and how many grams of Oare required for complete reaction? What mass of NO2, in grams, is produced?

15. How many grams of Mg will react with 7.5 grams of H2SOin the reaction:
Mg +  H2SO4  $\longrightarrow$  MgSO4  +  H2

16. Zinc will react with hydrochloric acid producing hydrogen gas and zinc chloride:
Zn +  2HCl  $\longrightarrow$  ZnCl2  +  H2
How many grams of Hwill be produced if 5.0 grams of zinc are used?

17. The final step in the manufacture of platinum metal (for use in automotive catalytic converters and other products) is the reaction: 3(NH4)2PtCl6(s) $\longrightarrow$ 3Pt(s) + 2NH4Cl(s) + 2N2(g) + 16HCl(g)
How many grams of Pt can be produced by decomposing 12.35 g (NH4)2PtCl6?

18. How many kilograms of NHwill be produced when 25.0 kg of Hreacts with excess N2?

19. A 3.00 cmpiece of aluminum reacts with a solution of HCl and produces Hgas and AlCl3. Determine the mass of Hformed. (Al has a density of 2.70 g/cm3)

20. One of the most important commercial reactions is the “Haber” production of ammonia:
3H2(g)  +  N2(g)  $\longrightarrow$  2NH3(g)
Chiefly by this reaction, the industrial “fixation” of nitrogen now accounts for about one-third of all the nitrogen fixed on our planet. If 3.0 kg of Hand 1.0 kg of Nare mixed and allowed to react until one or both of the reactants is used up,
a)   how many moles of the NHmolecules are produced?
b)   how many moles of the Hare left?
c)   how many moles of the Nare left?

21. Iron reacts with chlorine to produce FeClas:  2Fe +  3Cl2  $\longrightarrow$  2FeCl3
If 10.6 grams of iron are mixed with 18.9 grams of chlorine and allowed to react,
a)   how many grams of FeClwill be produced?
b)   how many grams of excess reactant will be left after the reaction is complete?

22. Silver tarnishes in the presence of hydrogen sulfide in the following reaction:
4Ag  +  2H2S  +  O2  $\longrightarrow$  2Ag2S  +  2H2O
How many grams of Ag2S can be obtained by this reaction from a mixture of 0.950 g Ag, 0.140 g H2S, and 0.0800 g O2?

23. 11.92 g of Pb(NO3)and 20.31 g of KI react as:  Pb(NO3)2+ 2 KI  $\longrightarrow$  PbI2  +  2 KNO3
How many grams of PbIare produced if the yield of the reaction is 81%?

24. Reaction of Hand Nproduces ammonia (NH3) with 65.5%yield. If 30.0 g of NHare required, how many grams of Nand how many of Hmust be used?

25. Solid calcium carbonate dissolves in a solution of hydrochloric acid and reacts to form a solution of calcium chloride and water, and bubbles of carbon dioxide.

How many grams of calcium chloride will form if 40.0 g of CaCOis mixed with 0.500 mol of HCl?
How many grams of calcium carbonate, if any, will remain unreacted?

26. Freon-12 (CCl2F2) is a gas that has been used as a refrigerant. It is prepared by the reaction between carbon tetrachloride and antimony trifluoride. The other product that is produced is SbCl3. If the percent yield is 72.0%, how many grams of antimony trifluoride must be treated with excess carbon tetrachloride to obtain an actual yield of 25.0 grams of Freon-12?

27. Aluminum chloride (Al2Cl6) can be made by the following reaction: 2Al(s) + 3Cl2(g) $\longrightarrow$ Al2Cl6(s)
a)  which reactant is limiting if 2.70 g Al and 4.05 g Clare mixed?
b)  what mass of Al2Clcan be produced?
c)  What mass of the excess reactant will remain when the reaction is complete?

28. Iron oxide can be reduced to the metal as follows: Fe2O3(s) + 3CO(g) $\longrightarrow$ 2Fe(s) + 3CO2(g)
How many grams of iron can be obtained from 1.00 kg of the iron oxide?
If 654 g Fe was obtained from the reaction, what was the percent yield?

29. Disulfur dichloride can be prepared by the following reaction:
3SCl2(l) + 4NaF(s) $\longrightarrow$ SF4(g) + S2Cl2(l) + 4NaCl(s)
What mass of SCl2is needed to react with excess NaF to prepare 1.19 g S2Cl2, if the yield is 51%?

30. You have a 0.12 M solution of BaCl2. What ions exist in the solution, and what are their concentrations?

31. Assume that 6.73 g Na2CO3is dissolved in enough water to make 250. mL of solution,
a) what is the molarity of the sodium carbonate?
b) What are the concentrations of the Na+and CO32-ions?

32. What is the mass, in grams, of solute in 250. mL of a 0.0125 M solution of KMnO4?

33. What volume of 0.123 M NaOH, in mL, contains 25.0 g NaOH?

34. What is the maximum mass, in grams, of AgCl that can be precipitated by mixing 50.0 mL 0.025 M AgNO3solution with 100.0 mL of 0.025 M NaCl solution? Which reactant is in excess? What is the concentration of the excess reactant remaining in solution after the AgCl has precipitated?

35. How many moles of NaOH react with 7.80 mol of the acid H2SO4?

36. How many mL of 0.512 M NaOH is required to react completely with 25.0 mL of 0.234 M H2SO4?

37. What mass, in grams, of Na2CO3is required for complete reaction with 25.0 mL of 0.155 M HNO3?      Na2CO3(aq)+ 2HNO3(aq) $\longrightarrow$ 2NaNO3(aq)+ CO2(g)+ H2O(l)

1. 3.011 × 1023 molecules of O2

2. 145.7 mol; 8.77 × 1025 molecules

3. 52.8 mg

4. 2.99 × 10−23 g

5. 39.4 mL

6. 20.7 L

7. 67.91 g of CuCl2; 32.09 g of Cu. The two masses add to 100.0 g, the initial amount of starting material, demonstrating the law of conservation of matter.

8. 8633 g

9. 17.66 g

10. The limiting reagent is NaOH; 21.9 g of P4 and 3.61 g of H2O are left over.

11. Both products predict that O2 is the limiting reagent; 20.3 g of C3H8 are left over.

12.   50.0 mol HCl

13.   4.8 mol Al2O3    7.1 mol O2

14.   1.1 mol O2    35 g O2    1.0 x 102g NO2

15.   1.9 g Mg

16.  0.15 g H2

17.  5.428 g Pt

18.  141 kg NH3

19.  0.908 g H2

20.  71 mol NH3    1.4 x 103mol H2    0 mol N2

21.  28.8 g FeCl3    0.7 g Fe

22.  1.02 g Ag2S

23.  13 g PbI2

24.  37.7 g N2    8.13 g H2

25.  Must use a balanced equation to solve this:

1 CaCO3(s)  +  2 HCl(aq) $\longrightarrow$ 1 CaCl2(aq) + 1 H2O(l) + 1 CO2(g)

27.7g CaCl2    15.0g CaCOunreacted

26.  34.2 g SbF3

27.  a) Clis limiting  b) 5.08 g Al2Cl6   c) 1.67 g Al unreacted

28.  699 g 93.5%

29.  5.3 g SCl2

30.  0.12 M Ba2+, 0.24 M Cl

31.  a) 0.254 M Na2CO3   b) 0.508 M Na+, 0.254 M CO32-

32.  0.494 g KMnO4

33.  5.08 x 103mL

34.  0.18 g AgCl, NaCl, 0.0083 M NaCl

35.  15.6 mol NaOH

36.  22.9 mL NaOH solution

37.  0.205 g Na2CO3