Exercise 2

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Solutions, hints and answers can be found in the Solutions Page. It is strongly recommended that students do not look at the solutions until after completing or attempting to complete the problems. Going straight to the solutions will reduce the point of the exercises.

4.1

The Haber Process combines nitrogen from the air with hydrogen derived mainly from natural gas (methane) into ammonia, which is important in the production of fertilizer. The unbalanced chemical reaction is

\[N_2(g)+H_2(g) \rightleftharpoons NH_3(g)\]

Under certain conditions, 50.0 grams of nitrogen are converted to ammonia, and the process has a 66.0% yield of ammonia. What mass of ammonia is produced?

4.2

Vinegar, an aqueous solution of acetic acid, \(HC_2H_3O_2\), can be used to remove the calcium carbonate scale (\(CaCO_3\)) left on pots and pans when hard water has been used for cooking. If you use 65.5 g of acetic acid, how many moles of calcium carbonate can you dissolve?

\[HC_2H_3O_2 + CaCO_3 \rightarrow Ca(C_2H_3O_2) + CO_2 + H_2O \; \rm{(unbalanced)}\]

4.3

Aluminum and sulfur react to form aluminum sulfide.

\[2 Al + 3 S \rightarrow Al_2S_3\]

If 6.75 g aluminum and 9.25 g sulfur are mixed, how much aluminum sulfide can be produced?
Which react is the limiting reagent?
How much of the other reagent is left after the reaction is complete?

4.4

Acetylsalicylic acid (\(C_9H_8O_4\)), or aspirin, can be made from acetic anhydride and salicylic acid.

\[C_7H_6O_3 + C_4H_6O_3 \rightarrow C_9H_8O_4 + C_2H_4O_2\]

Salicylic acid + acetic anhydride → acetylsalicylic acid + acetic acid

How much C₉H₈O₄ and C₂H₄O₂ will be produced if 5.32 g of \(C_7H_6O_3\) reacts with 5.11 g of \(C_4H_6O_3\)? Assume 100% yield.

4.5

Baking soda (sodium bicarbonate) has a variety of uses, including cleaning, dental care (toothpastes), cooking, and neutralizing acid spills on highways. When it reacts with sulfuric acid, it produces carbon dioxide.

\[2 NaHCO_3 + H_2SO_4 \rightarrow Na_2SO_4 + 2 H_2O + 2 CO_2\]

A chemistry student reacts 375 g \(NaHCO_3\) with 225 g \(H_2SO_4\).

How much \(CO_2\) forms? (Assume 100% yield)
Identify the limiting and excess reagents.
How much excess reagent is left after the reaction is complete?
What is the percent yield if 150 g of \(CO_2\) is produced?

4.6

Para-dichlorobenzene, which is frequently used to repel moths as mothballs, has a percentage composition of 49.0% C, 2.7% H, and 48.3% Cl. It has a molecular weight of 147.0 g/mol. Find its empirical and molecular formulas.

4.7

Balance the following reactions.

NaHCO₃(s) → Na₂CO₃(s) + CO₂(g) + H₂O(g)
FeSO₄(aq) + Ag(s) ® Ag₂SO₄(s) + Fe(s)
CaCl₂(aq) + K₂CO₃(aq) → CaCO₃(s) + KCl(aq)
C₂H₅OH(l) + O₂(g) → CO₂(g) + H₂O(l)
FeCl₃(aq) + NaOH(aq) → Fe(OH)₃(s) + NaCl(aq)
CS₂(s) + Cl₂(g) ® CCl₄(l) + SCl₂(s)
Na₃PO₄(aq) + CrCl₃(aq) ® CrPO₄(s) + NaCl(aq)

4.8

Give the balanced equation for each of the following.

HClO₄(aq) + Mg(OH)₂(s) → Mg(ClO₄)₂(aq) + H₂O(l)
H₂SO₄(aq) + Pb(NO₃)₂(aq) → PbSO₄(s) + HNO₃(aq)
NaOH(aq) + AlCl₃(aq) → Al(OH)₃(s) + NaCl(aq)

4.9

Please give the balanced equation for each of the following.

\(Na(s)+H_2O(l) \rightarrow NaOH(aq)+H_2(g)\)
\(H_2(g) +O_2(g) \rightarrow H_2O(g)\)
\(AgNO_3+CaCl_2 \rightarrow AgCl+Ca(NO_3)_2\)