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Homework: Stoichiometry

Answer the following questions using complete sentences.

  1. Do the coefficients in a balanced chemical equation express a ratio in terms of the masses of the substances? Explain.
  2. Is the molar mass of salt (NaCl) different when it appears in a balanced chemical equation with a coefficient of 2? (For example: 2NaCl → 2Na + Cl2). Explain.
  3. Some elements are written as molecular formulas, rather than as single atoms. Consult your notes about naming chemicals and write the formulas for all of the elements that always appear as diatomic molecules. As a bonus, find two other non-metals which appear in molecular formulas but which are not diatomic.
  4. The Law of Conservation of Matter requires that the mass of all reactants must equal the mass of all products. Does it also require that there be the same number of moles of chemicals on both sides of a chemical equation? Why or why not?
  5. How is stoichiometry like building a bicycle from parts such as a frame, wheels, and a handlebar?
  6. Describe in words how you find the mass of a chemical product in a reaction given the mass of a reactant and the balanced chemical equation. Use the following example as a starting point: 35.0 g NaCl in the decomposition equation given in a previous problem.
  7. Write a balanced chemical equation for the combustion of methane (CH4) in oxygen to produce water and carbon dioxide.
  8. Find each of the following numbers of moles based on the equation you wrote in the previous problem:
    1. Moles of CO2 when 40 mol O2 are consumed:
    2. Moles of CH4 needed to form 200 mol H2O:
    3. Moles of O2 needed to combine with 0.050 mol CH4:

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Show work for all calculations. You will need a calculator and a periodic table to complete them. You may also use your ions reference sheet.

  1. The hydrochloric acid (HCl) secreted in your stomach can be neutralized by antacid products which contain aluminum hydroxide:
    3HCl + Al(OH)3AlCl3 + 3H2O
    1. How many grams of aluminum hydroxide are required to neutralize 0.220 mol of stomach acid?
    2. How many moles of water would be produced by the reaction? How many grams of water is that?
  2. Octane (C8H18) is one of several components in gasoline. If a car engine burns 500. g of octane while idling for one hour, how many grams of carbon dioxide are produced? (The reaction is much like the one for the combustion of methane given earlier in this homework assignment).
    2C8H18 + 25O2 → 16CO2 + 18H2O
  3. Write and balance a chemical equation showing the combustion of pentane (C5H12). How many grams of oxygen are required to completely burn 9.88 g of pentane?
  4. When a solution of silver nitrate is mixed with a solution of calcium chloride a fine, white solid forms. The solid is called a precipitate and in this reaction is silver chloride. The calcium and nitrate ions form a calcium nitrate solution. Write a balanced chemical equation for this reaction before beginning to work on the calculations required to answer the following questions.
    1. Fill in the formulas in the blanks below and then balance the chemical equation:
        Silver(I)   +   Calcium       Caclium    +     Silver(I)
        Nitrate         Chloride        Nitrate         Chloride
       __________   +  __________     __________   +  __________ 
    2. If 3.45 g of silver chloride is produced, how many grams of calcium chloride were used?
    3. How many grams of calcium nitrate would be produced from 11.36 grams of silver nitrate if it were reacted with enough calcium chloride?

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  1. When sodium bicarbonate (also called sodium hydrogen carbonate or baking soda) is used in the lab to neutralize sulfuric acid it produces sodium sulfate, water, and carbon dioxide. Usually, the baking soda is a solid in powder form and the acid is present as a solution in water. The carbon dioxide has limited solubility in water and so it bubbles away into the air. How many grams of baking soda are required to neutralize 2.50 mol of sulfuric acid according to the balanced chemical equation?
    2NaHCO3 + H2SO4Na2SO4 + 2CO2 + 2H2O
  2. The mass of the solution that contained the 2.50 mol of sulfuric acid in the previous problem was 980.8 g.
    1. Find the total mass of the sulfuric acid solution and the baking soda you added to it to neutralize it.
    2. Using the law of conservation of mass, what is the total mass of the products once the reaction is complete?
    3. In practice, the actual mass of the solution will be less than the mass you calculated in the previous question. This does not involve a violation of the law of conservation of mass but instead is a result of the properties of one of the chemical products. Explain and calculate the actual mass that you would measure on a lab balance.
  3. Optional Problem: Hydrogen reacts with oxygen to produce water (2H2 + O2 → 2H2O).
    You have 5.0 mol H2 and 2.0 mol O2.
    1. If you actually had an unlimited amount of oxygen (but only 5.0 mol hydrogen), how many moles of water could you make?
    2. If you actually had an unlimited amount of hydrogen (but only 2.0 mol oxygen), how many moles of water could you make?
    3. Given the amounts actually present in the problem as stated above, how much water would you actually be able to make?
    4. One of the reactants will have some material left over. Which one and how much?
This homework belongs with the Stoichiometry Group Activity.
See also some additional problems for Stoichiometry.
The next activity and homework in this unit are the Limiting Reagent and Percent Yield Activity and Homework.
Credit for some problem set-ups is due to Nathan Guerin.
Last updated: May 06, 2020       Home