The World of Astoria Bob

Reaction Stoichiometry

To do these problems, you need to set up a proportion between the moles of given material to the moles of that material in the reaction equation. So if they said how many moles of a product B could be made from 0.2046 moles of reactant A, and the reaction was 2A → B, you'd set up a proportion where 0.2046/2 = (moles of B)/1, and solve for moles of B. If they ask for molecules, you need to use Avogadro's Number x moles in the proportion, and if they ask for mass, then you have to include molecular weight (or molar mass) in the calculation.

  1. How many moles of I2 are required to react with 0.429 mol of Al according to the following equation:
    2Al + 3I2 → 2AlI2
  2. How many moles of Ca(OH)2 are required to react with 1.36 mol of H3PO4 to produce Ca3(PO4)2 according to the equation:
    3Ca(OH)2 + 2H3PO4 → Ca3(PO4)2 + 6H2O
  3. How many carbon dioxide molecules are produced when 0.75 mol of propane is combusted according to this equation?
    C3H8 + 5O2 → 3CO2 + 4H2O
  4. How many NH3 molecules are produced by the reaction of 4.0 mol of Ca(OH)2 according to the following equation:
    (NH4)2SO4 + Ca(OH)2 → 2NH3 + CaSO4 + 2H2O
  5. What mass of sodium hydroxide, NaOH, would be required to produce 16 g of the antacid milk of magnesia [magnesium hydroxide, Mg(OH)2] by the following reaction?
    MgCl2(aq) + 2NaOH(aq) → Mg(OH)2(s) + 2NaCl(aq)
  6. What mass of gallium oxide, Ga2O3, can be prepared from 29.0 g of gallium metal?
    The equation for the reaction is: 4Ga + 3O2 → 2Ga2O3
  7. What mass of oxygen gas, O2, from the air is consumed in the combustion of 702 g of octane, C8H18, one of the principal components of gasoline?
    2C8H18 + 25O2 → 16CO2 + 18H2O
  8. What mass of CO is required to react with 25.13 g of Fe2O3 according to the equation:
    Fe2O3 + 3CO → 2Fe + 3CO2

Reaction Yields

For this section, very important in chemistry lab experiments and research (I did this sort of research for years and needed to make these calculations), you need to determine the limiting reagent, then calculate the amount of moles of product expected, and then find the fraction of what you got over what was expected, all determined by the balanced equation. It's one of my favorite chemistry calculations.

  1. Upon reaction of 1.274 g of copper sulfate with excess zinc metal, 0.392 g copper metal was obtained according to the equation:
    CuSO4(aq) + Zn(s) → Cu(s) + ZnSO4(aq)
    What is the percent yield?
  2. What is the percent yield of a reaction that produces 12.5 g of the gas Freon CF2Cl2 from 32.9 g of CCl4 and excess HF?
    CCl4 + 2HF → CF2Cl2 + 2HCl