Problem Set 4.7: Unit 4 Review Complete each question. Show your work for all calculations.

Part A. Chemical Reactions.

Write complete balanced equations including phase subscripts. Classify each.

1. Lead and phosphorus powders are added and react.

synthesis 6 Pb _(s) + P_{4 (s)} à 2 Pb₃P_{2 (s)}

2. Calcium metal reacts with fluorine gas.

synthesis Ca _(s) + F_{2 (g)} à CaF_{2 (s)}

3. Methane is decomposed.

decomposition CH_{4 (g)} à C_(s) + 2 H_{2 (g)}

4. Potassium reacts with liquid sulphur.

synthesis 16 K _(s) + S_{8 (l)} à 8 K₂S _(s)

5. Iron (III) bromide is reacted to isolate bromine.

decomposition 2 FeBr_{3 (s)} à 3 Br_{2 (l)} + 2 Fe _(s)

6. Propane C₃H_{8 (l)} is burned as a fuel.

combustion C₃H_{8 (l)} + 5 O_{2 (g)} à 3 CO_{2 (g)} + 4 H₂O _(g)

7. A solution of lead (II) nitrate is added to the solution of sodium carbonate.

double replacement Pb(NO₃)_{2 (aq)} + Na₂CO_{3 (aq)} à 2 NaNO_3(aq) + PbCO_{3 (s)}

8. Magnesium is added to hydrochloric acid.

single replacement Mg _(s) +2 HCl _(aq) à MgCl_{2 (aq)} + H_{2 (g)}

9. Iron (II) acetate solution is added to a solution of barium chloride.

double replacement Fe(CH₃COO)_{2 (aq)} + BaCl_2(aq) à FeCl_2(aq) + Ba(CH₃COO)_{2 (aq)}

10. Sulphur is obtained from gaseous sulphur trioxide.

decomposition 8 SO_{3 (g)} à S_{8 (s)} + 12 O_{2 (g)}

11. Aqueous iodine is reacted with a solution of potassium chloride.

single replacement I_{2 (aq)} + KCl _(aq) à N.R.

12. Iron ore (iron (III) oxide) is reacted with carbon to refine iron. Carbon dioxide gas is produced.

single replacement 2 Fe₂O_{3 (s)} + 3 C _(s) à 3 CO_2(g) + 4 Fe _(s)

13. Potassium is added to water. The resulting chemical solution is basic and the gas produced “pops” with a lit splint.

single replacement 2 K _(s) + 2 HOH_(l) à 2 KOH _(aq) + H_{2 (g)}

14. A gas that will re-ignite a glowing splint is reacted with liquid octane C₈H₁₈.

combustion 2 C₈H_{18 (l)} + 25 O_{2 (g)} à 16 CO_{2 (g)} + 18 H₂O _(g)

15. A solution of nickel (III) nitrate is added to a solution of phosphoric acid.

double replacement Ni(NO₃)_{3 (aq)} + H₃PO_{4 (aq)} à 3 HNO_{3 (aq)} + NiPO_{4 (s)}

Part B. Mole Calculations

1. How many atoms of oxygen are there in 105.3 g of glucose? 2.114 x 10²⁴ atoms O

105.3g x 1 mol x 6.02 x 10²³ molecules x 6 atoms

180.18g 1mol 1 molecule

2. What volume would 16.2 g of nitrogen gas occupy at STP? 13.0 L N₂

16.2g x 1 mol x 22.4 L = 13.0L

28.02 g 1 mol

3. How many atoms would 2.35 L of neon have? 6.32 x 10²² atoms Ne

2.35 L x 1 mol x 6.02 x 10²³ atoms

22.4 L 1 mol

4. If a sample of disulphur hexabromide had 6.99 x 10²³ atoms of bromine what mass would the sample have? 105 g S₂Br₆

6.99 x 10²³ atoms x 1molecule x 1mol x 543.52g

6 atoms Br 6.02 x 10²³ 1 mol

5. Find the total number of atoms in 7.67 g of sodium phosphide. 1.85 x 10²³ atoms

6. How many carbon atoms in 60.5 g of ethanol? 1.58 ^x 10²⁴ atoms C

7. How many molecules in

a) 7.56 g of bromine gas?. 2.85 ^x 10²² molecules Br₂

b) 88.55 g of carbon monoxide gas?. 1.903 ^x 10²⁴ molecules CO

c) 18.6 L of chlorine gas (at STP)? 5.00 ^x 10²³ molecules Cl₂

d) 1.56 x 10³ L of methane gas at STP? 4.19 ^x 10²⁵ molecules CH₄

8. What volume, at STP, would

a) 6.85 x 10²² molecules of sulphur dioxide take up. 2.55 L SO₃

b) 68.7 g of helium take up. 385 L He

Part C. Empirical and Molecular Formula/Percent Composition

1. A sample is made of 5.87 g Ni and 10.64 g Cl. Determine the empirical formula of this compound.

NiCl₃

2. A 5.38 g sample is made of 4.44 g C and the rest hydrogen. Determine the empirical formula of this compound.

C₂H₅

3. A compound is made of 5.89 g cobalt, 2.80 g nitrogen and 9.60 g oxygen. Determine the empirical formula of this compound.

CoN₂O₆

4. A sample is made of 4.30 g carbon and 0.723 g hydrogen. Determine the molecular formula of this compound if its molar mass is 168.36 ^g/_mol.

C₁₂H₂₄

5. A sample is made of 16.3 g carbon, 2.75 g hydrogen and 25.8 g fluorine. Determine the molecular formula of this compound if its molar mass is 66.06 ^g/_mol.

C₂H₄F₂

6. Determine the % composition of copper in Cu₃BO₃

76.43%

7. Determine the % composition of each atom in PbCr₂O₇

48.96% Pb, 24.58% Cr, 26.47% O

Part D. Stoichiometry

A balanced equation reveals mole ratios, which can be converted, as needed, into information in grams, and used to solve stoichiometry problems.

1. What mass of fluorine will react with 105.3 g of aluminum ?

222.5 g

2. What volume of carbon dioxide would be produced when 26.2g of methane gas is combusted (burned) ?

36.6 L

3. What mass of lithium metal is needed to react with 8.35 L of nitrogen gas ?

15.5 g

4. If 12.3 g of lead (II) nitrate reacts with silver bromide, what mass of silver nitrate is made ?

12.6 g

5. Determine the number of molecules of ammonia made when 7.65 g of hydrogen gas reacts with excess nitrogen.

1.52 x 10²⁴ molecules

6. How many moles of hydrogen gas are needed to react with 15.1 L chlorine gas to produce hydrogen chloride gas?

0.674 moles

7. How many litres of oxygen gas are needed to react completely with 16.2 g of hydrogen gas to produce water?

89.8 L

8. How many moles of calcium oxide are produced when 36.4 g of calcium reacts completely with oxygen gas?

0.908 mol

9. How many grams of aluminum are required to produce 41.70 g of aluminum oxide, through the reaction of aluminum with oxygen gas?

22.07 g

10. How many grams of solid iodine are produced by the decomposition of 2.54 x 10²⁴ molecules of hydrogen iodide gas?

535 g

11. How much energy is released when 235.6 g of Na metal reacts with chlorine gas?

2 Na + Cl₂ à 2 NaCl ∆H = -36.5 kJ

187 kJ

12. How energy will be required to complete the reaction of 12.2 g of sodium to produce sodium oxide?

4 Na + O₂ + 124.7 kJ à 2 Na₂O

16.5 kJ

Part E. Limiting Reactant And Percent Yield

A substance that is not present in sufficient quantities to react with all of another substance present is called a limiting reactant; the other substance is said to be in excess.

1. In the reaction 2 H₂ + O₂ à 2 H₂O, exactly 8.51 g H₂ is combined with 9.25 g O₂ and a reaction occurs. Determine the

a) limiting reactant: oxygen

b) amount of the product in moles. 0.578 mol

2. If 0.143 g K and 0.236 g Cl₂ are reacted in the reaction 2 K + Cl₂ à 2 KCl, determine the:

a) limiting reactant: potassium

b) mass of the product in grams. 0.273 g

3. In the reaction of 7.45 g N₂ and 4.20 g O₂ to form dinitrogen monoxide, determine the

a) limiting reactant oxygen

b) mass of excess reactant 0.004 mol or 0.112 g

c) mass of dinitrogen monoxide produced 11.5 g

4. If 80.0 g of bromine is added to 40.0 g of sodium,

a) what is the limiting reactant? bromine

b) what is the excess mass of the reactant? 17.0 g Na

c) what is the mass of product? 103 g NaBr

5. If 72.5 g of copper is reacted with 30.0 L of chlorine gas, determine the

a) limiting reactant? copper

b) excess mass of the reactant? 14 g Cl₂

c) mass of product (CuCl₂)? 153 g CuCl₂

6. Answer the following questions based on this reaction:

Pb(NO₃)_{2 (aq)} + 2 NaCl _(aq) à PbCl_{2 (s)} + 2 NaNO_{3 (aq)}

a) If 225 mL of 12.95 M Pb(NO₃)_2(aq) are reacted with a solution made with 5.05 g of NaCl _(aq), how many grams of lead (II) chloride will be precipitated? 12.0 g

b) If the actual yield of lead (II) chloride is 1.06 g, what is the percent yield? 8.83 %

7. Ca + Cl₂ à CaCl₂

1.00 mole of Ca and 1.00 mole of Cl₂ were present as reactants. Only 106 g of CaCl₂ is produced. What is the percent yield? 95.5 %

8. N₂ + 3 H₂ à 2 NH₃

Exactly 0.600 mole of N₂ and 1.80 mole of H₂ were reacted (i.e. no excess reactant). Only 14.5 g of NH₃ is produced. What is the percent yield? 70.9 %