Lecture problems - stoichiometry PDF

Preview

Summary

lecture problem...

Description

CHE 112F - Chemistry Sample Problems for the Lecture Stoichiometry (note: problems are taken from a variety of sources)

1)

A 73.3 ml sample of a slurry of impure zinc sulfide ore has an average density of 1.365 g/ml and contains 50.5% by mass of the impure zinc sulfide ore. The sample was reacted with concentrated nitric acid and all of the sulfur in the zinc sulfide was converted to sulfuric acid. The resulting sulfate was completely precipitated as barium sulfate, which, when recovered and dried, had a mass of 58.4 g. Calculate the percentage of zinc sulfide in the impure ore. ZnS + 10 HNO3 à Zn(NO3)2 + H2SO4 + 8 NO2 + 4 H2O H2SO4 + BaCl2 à BaSO4 + 2 HCl

Answer: 48.3%

2)

The complete combustion of a 1.005 g mixture of ethyl alcohol [C2H5OH] and diethyl ether [(C2H5)2O] yields 1.963 g of CO2. What must be the percent, by mass, of C2H5OH in this sample?

Answer: 91% 3)

A drop (0.05 mL) of 12.0 M HCl is spread over a sheet of Al foil 0.10 mm thick. Assuming that all of the acid is consumed while eating through the foil, derive a formula for the area of the hole. Al (s) + 3HCl (aq) à AlCl3 (aq) +

3 H2 (g) 2

4) 4) A 2.05 g sample of an iron-aluminum alloy (ferroaluminum) is dissolved in excess HCl (aq) producing 0.105g of H2(g). What is the percent composition, by mass, of iron and aluminum in the ferroaluminum? The appropriate equations are given below. Fe(s) + 2 HCl (aq) à FeCl2 (aq) + H2 (g) 2 Al(s) + 3 HCl (aq) à 2 AlCl3(aq) + 3/2 H2 (g)...