# 3. Stoichiometry questions

1. Balance the following equations:
1. C2H5OH + O → CO2 + H2O
2. BCl3 + H2O → B(OH)3 + HCl
3. NiS + O2 → NiO + SO2
4. NH4VO3 → V2O5 + NH3 + H2O
5. N2O5 + H2O → HNO3
6. Ca3(PO4)2 + SIO2 + C → P4 + CaSiO3 + CO
2. Methane burns with oxygen according to the equation
CH4 + 2O2 → CO2 + 2H2O
How many moles of oxygen are required per mole of methane? How many kilograms of oxygen are required per kilogram of methane?  [2, 3.99]
3. A sample of a mixture of barium salts and sodium salts was completely dissolved in nitric acid.  Upon adding dilute sulfuric acid to the solution, virtually all the barium was precipitated as white BaSO4, which was filtered, dried and weighed.  If the mass of the original sample was .2270 g and the mass of the precipitate was 0.0235 g, calculate the mass fraction of barium in the mixture.  [0.0609]
4. Equal masses of sodium metal and water are reacted to form hydrogen gas, H2, and sodium hydroxide, NaOH. Write a balanced chemical equation for the reaction.  Which of the reactants is in excess if the reaction goes to completion? what fraction of the reactant remains unreacted? [H2O,.216]
5. Making powder is a mixture of sodium bicarbonate and a solid state acid.  When dissolved in water, carbon dioxide gas is rleased. Some 3examples of the reactions found in different brands of baking powders are shown below:
KH2PO4 + NaHCO3 → CO2 + KNaHPO4 + H2O
Na2Al2(SO4)4 + 6 NaHCO3 → 6 CO2 + 4 Na2SO4 + 2Al(OH)3
If each of the powders represented by these reactions consists of a stoichiometric mixture (meaning all reactants are exactly used up together), calculate the amount of CO2 (in moles) which would be released by 1.00 g of each kind of baking powder. [4.5×10-3 mol, 6.07×10-3 mol]
6. For the following reactions in acidic aqueous solution, balance the reactions. Remember, these are REDOX reactions
1. Fe2+ + O2 → Fe3+
2. H2O2 + Sn2+ → Sn4+ + H2O
3. H2O2 → H2O + O2
4. SbCl4 + SO42- + Cl → SbCl6 + H2SO3
5. PbS + H2O2 → PbSO4 + H2O
6. Mn2+ + BiO3 → MnO4 + Bi3+
7. NO + NO3 → N2O4
8. CS(NH2)2 + BrO3 → CO(NH2)2 + SO42- + Br
7. For the following reactions in basic aqueous solution, write the balanced reaction.
1. C2H4 + MnO4 → CH3COO + MnO2
2. ClO → ClO3 + Cl
3. Al(s) + NO3 → Al(OH)4 + NH3
4. Bi(OH)3 + Sn(OH)42- → Bi + Sn(OH)62-
5. MnO4 + CN → MnO2 + CNO
6. S + HO2 → SO42- + OH
8. A sample of seawater is titrated with an aqueous solution of silver nitrate, taking advantage of the reaction in which silver ion reacts with chloride ion to precipitate insoluble silver chloride (AgCl).  What is the concentration of chloride ion in the seawater if it takes 19.7 mL of 0.100 M AgNO3 solution to precipitate all the chloride ion from a 10.0 mL sample of seawater? What is the mass of AgCl precipitated? [0.197 mol/L, 0.282 g]
9. A sample of a mixture of KBr and NaBr weighing 0.5605 g was treated with AgNO3 and all the bromide ion was precipitated as AgBr(s).  When dried, the AgBr weighed 0.9702g. What was the mass percent of the KBr in the original sample?
10. What is the volume o fa 0.563 M solution of NaOH that is required to react completely with 10.0 mL of a 0.255 M solution of HNO3? [4.53 mL]
11. What volume of the same solution of NaOH is required to react completely with  10.0 mL of a .255 M solution of acetic acid?
12. What volume of the same solution of NaOH is required to react completely with 10.0 mL of a .255 M solution of H2SO4? 