Self Test on Balancing Equations and Mass Calculations

Dr. Walt Volland, revised July 12, 2013 all rights reserved 2005-2013


1. Assign oxidation numbers to the "*" marked atoms in the following ions and molecules.
____Cl in
____O in
____S in



____N in
____H in
____C in



____C in
____N in
____C in



2. Balance and classify each of the following reactions. Acid-base, oxidation-reduction, precipitation. Use a solubility table to identify insoluble and soluble products. State the physical forms for each product. (l), liquid; (g), gas; (s), solid; (aq), aqueous.

C12H26(l) + O2(g) ----> CO2(g) + H2O(g)

Si2H6(g) + O2(g) ----> H2O(g) + SiO2(s)

Na2S(aq) + ZnCl2(aq) ----> ZnS(s) + NaCl(aq)

Na2CO3(aq) + HNO3(aq) ----> NaNO3(aq) + CO2(g) + H2O(l)


How many moles of H2 are needed to hydrogenate 10 moles of the unsaturated fatty acid         C14H26CO2H and form the saturated fatty acid C14H30CO2H ? Hint balance the equation first.

Show work

____C14H26CO2H     +     ____ H2 ----->   _____C14H30CO2H



What is the number of moles of product formed, when 825 grams of S8(s) reacts with unlimited grams of Cl2(g)?

S8(l) + 4 Cl2(g) -----> 4 S2 Cl2 (g)


Explain why reactions do not typically give 100% yields.

What is the percent yield for the production of diborane, B2H6? The predicted yield is 126 g and the actual yield was 81 g? The equation for the reaction is written below.

2 NaBH4(s) + I2(s) ----> B2H6(g) + 2 NaI(s) + H2(g)



Phosphoric acid is made in industry by reacting sulfuric acid with mineral phosphates. The reaction between the mineral apatite, Ca5(PO4)3F, and sulfuric acid is written below.

5 H2SO4(aq) + Ca5(PO4)3F + 10 H2O ----> HF + 3 H3 PO4 + CaSO4• 2 H2O


What is the actual yield for the reaction if the theoretical yield is 109 pounds of phosphoric acid, H3 PO4, and the percent yield normally is 83 %?


What is the limiting reagent if 100. moles of hydrogen sulfide, H2S, is mixed with 240. moles of sodium hydroxide, NaOH, according to the following reaction? Show work .

H2S+ 2 NaOH ----> Na2S + 2 H2O


What is the limiting reagent if 100. grams of carbon disulfide, CS2, is mixed with 120. grams of sodium hydroxide, NaOH, according to the following reaction? Show work .

3 CS2 + 6 NaOH ----> 2 Na2CS3 + Na2CO3 + 3 H2O