Download PS 1 chem 121

1. How many zinc atoms are present in 20.0 g Zn?
2. How many molecules of ethane (C2H6) are present in 50.3 g of ethane?
3. Calculate the mass of carbon in 125.0 grams of aniline, C6H7N. This compound is the starting
material for many dyes.
4. What is the empirical formula of the compound with the following composition:
32.79% Na, 13.02% Al, 54.19% F.
5. An organic compound (0.1014 g) which contains only carbon, hydrogen and oxygen, was
combusted to give 0.1486g of carbon dioxide and 0.0609 g of water. Find the empirical formula
of the compound
6. Balance the following equations:
N2O5(g) + H2O(l) → HNO3(aq)
Mg2C3(s) + H2O(l) → Mg(OH)2(s) + C3H4(g)
PCl5(l) + H2O(l) → H3PO4(aq) + HCl(aq)
Cr(s) + S8(s) → Cr2S3(s)
Au2S3(s) + H2(g) → Au(s) + H2S(g)
NH4ClO4(s) + Al(s) → Al2O3(s) + N2(g) + HCl(g) + H2O(g)
6. Balance the reaction in which sodium metal, reacts with bromine molecules, to make ionic
sodium bromide, NaBr.
7. Write and balance the equation for the complete combustion of butane, C4H10, a common
fuel.
8. The solid fuel in the booster stage of the space shuttle is a mixture of ammonium perchlorate
and aluminium powder, which react as follows:
NH4ClO4(s) + Al(s) → Al2O3(s) + N2(g) + HCl(g) + H2O(g)
Balance the equation.
What mass of aluminium should be mixed with 5.0 x 103 kg of ammonium perchlorate?
9. Camels store the fat tristearin (C57H110O6) in the hump. As well as being a source of energy
the fat is a source of water, because when it is used the reaction below takes place. What mass of
water is available from 1.0 kg of fat? The equation is not balanced.
C57H110O6(s) + O2(g) → CO2(g) + H2O(l)
10. Ammonia reacts with oxygen to produce nitrogen oxide and water, according to the
following unbalanced equation:
NH3 (g) + O2(g) → NO(g) + H2O(l)
If 2.00 g of ammonia is reacted with 4.50 g of oxygen
a) which is the limiting reagent?
b) how much NO is formed?
c) what mass of the excess reagent remains at the completion of the reaction?
11. Magnesium sulfate forms a hydrate, MgSO4 . nH2O, which is 51.2 % water by mass.
Calculate the number of water molecules in the molecular formula (find the value of n).
12. The theoretical yield of sodium perxenate (Na4XeO6) in a reaction was 1.25 g, but only 1.21
g was obtained. What was the percentage yield of the reaction?
13. In the reaction of 4.0 moles of nitrogen with 6.0 moles of hydrogen, a chemist obtained 1.6
moles of ammonia. What is the percent yield of ammonia?