Shanghai World Foreign Language Middle School
Chemistry Worksheet 5 – Calculations using Chemical Equations
Name: ______________________________________(
Date: ___________
Class: _____
1. A compound of magnesium and carbon contains equal percentages, by mass, of
each element. What is the empirical formula of the compound?
2. The reaction between hydrochloric acid and magnesium carbonate is shown below.
2HCl + MgCO3  MgCl2 + H2O + CO2
Which volume of 2.0 mol/dm3 hydrochloric acid is needed to react completely with
0.84 g of magnesium carbonate?
3. What volume of sulphur dioxide , measured at r.t.p., is produced on heating 9.1 g of
nickel sulphide, NiS, in oxygen?
2NiS + 3O2  2NiO + 2SO2
4. Excess steam and methane react together according to the equation below.
H2O(g) + CH4(g)  CO(g) + 3H2(g)
What volume of hydrogen can be obtained from 200 cm 3 of methane, measured at
the same temperature and pressure?
5. Iron carbonyl is a yellow liquid with formula Fe(CO)n. The relative molecular mass,
Mr, of iron carbonyl is 196.
a) (i) Calculate the value of n in the formula.
(ii) Iron carbonyl decomposes on heating to produce iron and carbon monoxide gas
(CO). Construct the equation, with state symbols, for the reaction.
b) Cobalt carbonyl has empirical formula Co(CO)4. The relative molecular mass, Mr, of
cobalt carbonyl is 342. Deduce the molecular formula of cobalt carbonyl.
6. In an experiment, 1.30 g of zinc granules and 100 cm 3 of 0.4 mol/dm3 sulfuric acid
were mixed so that they reacted together to produce aqueous zinc sulfate (ZnSO4)
and hydrogen gas.
a) Calculate the number of moles of zinc in 1.30 g.
b) Calculate the number of moles of sulfuric acid in 100 cm of 0.4 mol/dm solution.
c) Construct the equation, with state symbols, for the reaction.
7. When iron powder is heated in chlorine gas, brown crystals of iron chloride are
produced containing 65.5% by mass of chlorine.
a) Calculate the empirical formula of the chloride.
b) The relative molecular mass, Mr, of the chloride is 325. Deduce the molecular
formula of the chloride.
8. Carbon reacts with tungsten oxide according to the equation:
WO3(s) + 3C(s)  W(s) + 3CO(g)
Starting with 0.5 mol of WO3, calculate
a) The mass of carbon that reacts;
b) The volume of carbon monoxide produced at r.t.p.
9. Motorcars are often fitted with airbags which rapidly inflate during an accident, protecting
the driver and passengers. The bags are filled with nitrogen gas, which is produced from
the decomposition of sodium azide, NaN3, into its elements.
a) Construct the equation for the decomposition of sodium azide.
b) In a car crash, a typical airbag is filled with 84 dm3 of nitrogen, measured at r.t.p.
Calculate the mass of sodium azide needed to produce this amount of nitrogen.
c) Sodium azide reacts with dilute sulfuric acid to give sodium sulfate(Na2SO4) and
compound X. Compound X has the composition by mass, 97.7% nitrogen and 2.33%
(i) Calculate the empirical formula of compound X.
(ii) Construct the equation for the reaction of sodium azide with dilute sulfuric acid.
10. Sodium superoxide, NaO2, reacts with water according to the following equation.
4NaO2(s) + 2H2O(l)  4NaOH(aq) + 3O2(g)
1.10 g of sodium superoxide was reacted with excess water.
a) Calculate the volume of oxygen gas, measured at r.t.p., produced in the reaction.
b) The solution produced in the reaction had a volume of 50 cm . Calculate the
concentration of sodium hydroxide in the solution in mol/dm3.
11. A solution contains 15 g/dm3 of sodium carbonate crystals., Na2CO3.nH2O. Given that 25.0
cm3 of this solution requires 26.2 cm3 of 0.1 M hydrochloric acid for neutralisation using
methyl orange as an indicator , calculate the value of n.