# Stoichiometry Extra Practice Problems

NOTE:  All scientific notation is written in the following manner:  (Coefficient)E(Exponent).  For example, 6.00 x 101 is written as 6.00E1, and 2.01 x 10-5 is written as 2.01E-5.

Many of these problems involve equations that you previously balanced in the "Reactions" Extra Practice Problems.  Also, please be aware that small differences between your answers and mine are most likely due to using differently rounded values for molar masses, etc.  (But please let me know if I’ve made errors with typos, calculations, sig figs, etc.)

1. Magnesium carbonate decomposes to magnesium oxide and carbon dioxide.  How many grams of carbon dioxide are produced when 6.0 mol of magnesium carbonate decomposes?

2.  How many moles of NaOH are required to react completely with 0.50 mol of H3PO4 according to the unbalanced reaction:

H3PO4  +  NaOH  →   Na3PO4  +  H2O

3.  Iron(III) hydroxide reacts with sulfuric acid.  a) What type of reaction is this?  b) What are the products of this reaction?  c) Suppose that 1.6 mol of the iron-containing product are produced by this reaction. How many moles of the other product are produced?

4.  Consider the reaction from problem 2.  If 9.00 moles of each reactant was used in the reaction, then how many moles of the excess reactant would be left over?

5.  How many grams of KMnO4 are needed to react completely with 100.0 g of Fe according to the balanced reaction:

3 KMnO4  +  5 Fe  +  24 HCl  →  5 FeCl3  +  3 MnCl2  +  3 KCl  + 12 H2O

6. Sand consists primarily of silicon dioxide, SiO2. Pure elemental silicon for use in the semiconductor industry can be produced by reaction of sand with elemental carbon at high temperatures. Carbon monoxide gas (CO) is also a product of the reaction. a) Write the balanced chemical equation for the reaction of silicon dioxide with carbon.  b) How many atoms of Si will be formed from the complete reaction of 34.5 kg of SiO2?  c) How many grams of CO will be formed?  d) How many moles of carbon will be necessary to ensure a complete reaction?

7.  Aluminum metal can react with iron(III) oxide by a single displacement reaction.  a) What are the products?  b) How many grams of the aluminum-containing product are produced by the complete reaction of 0.20 moles of aluminum?

8.  Two moles of potassium permanganate reacts with 5 moles of oxalic acid and 6 moles of hydrochloric acid to produce 2 moles of manganese(II) chloride, 10 moles of carbon dioxide, 2 moles of potassium chloride, and 8 moles of water. When 0.45 moles of carbon dioxide are produced by this reaction, how many grams of water are also produced?

9.  Sodium metal reacts with chlorine gas to form NaCl.  The complete reaction of 4.6 g of sodium metal yields how many grams of sodium chloride?

10.  How many moles of KClO3 are needed to prepare 7.1 mol of O2 according to the unbalanced reaction:

KClO3 →  KCl  +   O2

11.  Refer to the reaction from example 1.  According to this reaction, how many grams of carbon dioxide should result from the reaction of 4.0 kg of magnesium carbonate?

12.  You need to make 20.0 g of silver chloride from silver nitrate and sodium chloride.  How much silver nitrate, in kilograms, do you require?

13.  How many kilograms of the aluminum-containing product would be produced by the complete reaction of 27.0 g of Al(OH)3 with excess sulfuric acid?

14.  Refer to the reaction from example 9.  What mass, in grams, of chlorine gas does it take to react completely with 4.6 g of sodium metal?  What mass of sodium metal does it take to completely react with 1.42 g of chlorine?

15.  Refer to the reaction from example 9.  If we started with exactly 10 g of sodium metal and 10 g of chlorine gas, would either of these elements be left over at the end of the reaction?  Which one?  Which is the limiting reagent?

16. Sulfur trioxide reacts with water in air to produce sulfuric acid (a component of acid rain).  a) How many molecules of water must react when 8.0 g of sulfur trioxide reacts?  b) What mass, in ng, of sulfuric acid is formed?

17.  Urea has the formula (NH2)2CO and is used as a fertilizer because it reacts with water to form ammonia and carbon dioxide.  The ammonia provides nitrogen to the plant.  a) If 300. g of urea and 100. g of water react, how many grams of ammonia and carbon dioxide will be produced?  b) How many grams of the excess reagent actually reacts?

18.  Silicon carbide, SiC, is an important abrasive made by the high temperature reaction of SiO2 with carbon.  CO is the other product.  If 5.00E3 g SiO2 and 5.00E3 g of carbon react:  a) What is the maximum amount (in grams) of SiC that can be formed?  b) How many moles of the excess reactant react?   c) How many moles of the excess reactant remain after the reaction is complete?

19. Consider the reaction from problem 3, for which 10.00 moles of each reactant was used.  How many moles of the excess reactant will be left over, if 20.00 moles of water were formed?

20.  Carbon disulfide combusts to form carbon dioxide and sulfur dioxide as products.  A mixture of 3.5 g carbon disulfide and 1.75 g of oxygen react.  What is the maximum number of grams of sulfur dioxide that can be formed?

21.  Aspirin (C9H8O4) is formed by the following reaction:

 C7H6O3 salicylic acid +     C4H6O3 acetic anhydride → C9H8O4 aspirin +   CH3COOH       acetic acid

a) How many grams of acetic anhydride are needed to react with 4.50 g of salicylic acid?

b) Determine the mass of aspirin that results from the reaction.

c) How many grams of acetic acid will also be formed?

22. Consider the reaction from problem 13, starting with 2.34 mg of aluminum hydroxide and 2.94 mg of sulfuric acid.  a) How much aluminum-containing product is formed, in mg?  b) How much, in mg, of each reactant will be left over?

23.  Hydrogen gas and chlorine gas react to yield HCl gas as the only product.  a) If you react 3.56 grams of H2 with 8.94 grams of Cl2, which reactant is limiting?  Which reagent is in excess?   b) How many grams of HCl are formed?

24.  a)  How many grams of ethylene chloride, C2H4Cl2, can be prepared by reacting 15.4 g of C2H4 with 37.4 g Cl2?    b) How many moles of the excess reagent will be left over?

*25. Zinc undergoes a single displacement reaction with silver nitrate solution.  When 25.0 g of zinc is added to the solution, the percent yield of silver is 72.3%.  What mass of silver was actually formed?

*26. If you react 0.503 g of LiOH and 0.784 g of phosphoric acid, and 0.378 g of water is formed, how many grams of the limiting reactant was used up? How many grams of the excess reactant will be left over?

1. 2.6E2 g (6.0 mol) CO2

2. 1.5 mol

3. a) Neutralization (acid-base) reaction, a kind of double replacement reaction b) products are iron(III) sulfate and water c) 9.6 mol water

4.  9.00 mol H3PO4 (at start) - 3.00 mol H3PO4 (consumed) = 6.00 mol H3PO4 left over

5.  169.8 g  KMnO4

6. a) SiO2 + 2 C →  Si  +  2 CO   b) 3.45E26 atoms of Si  c) 32200 g of CO  d) 1150 moles of C

7.  a) aluminum oxide (Al2O3) and iron metal (Fe)  b) 10. g

8.  6.5 g H2O

9.  12 g NaCl

10.  4.7 moles KClO3

11.  2.1E3 g CO2

12.  2.37E-2 kg AgNO3

13. 0.0592 kg of Al2(SO4)3

14.  7.1 g Cl2, 0.921 g Na

15.  Na would be left over, Cl2 is the LR

16.  a)  6.0E22 molecules H2O  b) 9.8E9 ng H2SO4

17.  a) 170. g NH3 and 220. g CO2 are formed (Urea is the LR)   b) 90.1 g of water reacts

18.  a) 3.34E3 g SiC  (unbalanced equation is  SiO2 + C → SiC + CO)   b) 250. mol C react   c) 166. mol C left over

19. 3.33 mol iron(III) hydroxide

20.  2.34 g SO2, O2 is the LR

21.  a) 3.33 grams of acetic anhydride      b)  5.87 grams of aspirin        c)  1.96 grams of acetic acid

22. a) 3.42 mg aluminum sulfate   b) 0.78 mg aluminum hydroxide, 0 mg sulfuric acid

23.  a)  H2  +  Cl2  →  2 HCl, Limiting reactant = Cl2 , excess reactant = H2    b)  9.19 grams of HCl

24.  a)  52.2 grams C2H4Cl2  (Limiting reagent is Cl2)      b)  0.022 moles C2H4 (0.549 moles at start – 0.527 moles reacted)

25. 59.6 g Ag (actual yield)

26. LR = LiOH, 0.503 g consumed.  ER = H3PO4, 0.0980 g left over