MOLES
WORKSHEET
Senior-I
1. A compound X contains carbon, hydrogen and oxygen only.
X contains 54.54% of carbon by mass, 9.09% of hydrogen by mass and 36.37% of oxygen by
mass.
(i) Calculate the empirical formula of compound X.
(ii) Compound X has a relative molecular mass of 88.
Deduce the molecular formula of compound X
2. This question is about some compounds of sulfur.
(a) The concentration of sodium chlorate(I) in a solution can be found by reacting sodium
chlorate(I) with excess acidified potassium iodide and then titrating the iodine liberated
with aqueous sodium thiosulfate, Na2S2O3.
I2 + 2Na2S2O3 bbbbbbbbbbbbb 2NaI + Na2S4O6
A solution of sodium thiosulfate contains 12.4g of sodium thiosulfate, Na2S2O3.5H2O, in
1.00 dm3 of solution.
(i) Calculate the concentration of the sodium thiosulfate solution in mol / dm3.
(ii) 23.6 cm3 of this sodium thiosulfate solution reacts with exactly 12.5 cm3 of aqueous
iodine.
Calculate the concentration, in mol / dm3, of the aqueous iodine.
3. (a) Dilute ethanoic acid reacts with sodium carbonate.
2CH3COOH + Na2CO3 mmmm 2CH3COONa + H2O + CO2
a. Calculate the volume, measured at r.t.p., of carbon dioxide produced, in cm3, when 3.18g of
sodium carbonate reacts with excess dilute ethanoic acid.
b. Concentrated sulfuric acid oxidises arsenic to arsenic(III) oxide.
c. Complete the equation for this reaction.
......As + …...H2SO4 mmmmmmmAs4O6 + .....H2O + 6SO2[3]
4. Calculate the mass of oxygen in the 11.5 dm3 sample at room temperature and pressure.
5. A sample of clean, dry air contains 0.0400% carbon dioxide by volume.
Calculate the number of molecules of carbon dioxide in 480dm3 of clean, dry air at room
temperature and pressure.
One mole of any gas contains 6.02 × 1023 molecules.
6. Hydrogen fluoride, HF, has a simple molecular structure. It is soluble in water.
(a) Aqueous hydrogen fluoride is a weak acid.
Write an equation to show the dissociation of hydrogen fluoride.
(b) Explain why is aqueous hydrogen sulfide described as a weak acid.
(c) Dilute hydrofluoric acid reacts with aqueous calcium hydroxide.
2HF(aq) + Ca(OH)2(aq) CaF2(aq) + 2H2O(l)
What is the minimum volume, in cm3, of 0.150 mol / dm3Ca(OH)2 required to react completely
with a solution containing 0.200 g of HF?
(c) Calculate the volume, in dm3, of 19.2g of nitrogen at room temperature and pressure.
Give your answer to two significant figures.
7. (a) A sample of 2.34g of aluminium is reacted with 50.0cm3 of 2.00mol/dm3 sulfuric acid.
2Al(s) + 3H2SO4(aq) Al2(SO4)3(aq) + 3H2(g)
Show by calculation that the aluminium is in excess in this reaction.
8. Concentrated aqueous ammonia is used to make fertilisers such as ammonium phosphate,
(NH4) 3PO4. Calculate the percentage by mass of nitrogen in ammonium phosphate.
9. How many atoms are there in each of the following:
a. 2 mol of ammonia gas
b. 64 g of sulfur
10. Calculate the percentage of water in copper(II) sulfate crystals. (CuSO4.5H2O).
11. A bottle of medicine contains 120 mg of paracetamol in 5 cm3 of solution. What is the
concentration , in g/dm3 of paracetamol in the medicine?
12. Calculate the mass of the solid obtained when 16.5 g of sodium hydrogen carbonate is heated
strongly until there is no further change. The equation for the reaction is:
NaHCO3(s) Na2CO3(s) + CO2(g) + H2O(g)
13. Iron reacts with dilute hydrochloric acid to form iron(II) chloride.
Fe(s) + 2HCl (aq) FeCl 2(aq) + H2(g)
A student added 2.1 g of iron to 50 cm3 of 0.10 mol / dm3 hydrochloric acid.
(i) Calculate the amount, in moles, of iron present.
(ii) Calculate the amount, in moles, of hydrochloric acid present.
(iii) Calculate the volume of hydrogen formed in this reaction, measured at room temperature and
pressure
14. 40 cm3 of 0.2 mol/dm3 solution of hydrochloric acid just neutralised 20 cm3 of sodium hydroxide
solution in a titration. What is the concentration of sodium hydroxide solution in g/dm3 used in
this neutralisation reaction?
15. A compound of carbon, hydrogen and chlorine contains 0.48 g of carbon, 0.08 g of hydrogen and 1.42
g of chlorine. Deduce the empirical formula of this compound.
16. A student titrated a metal hydroxide with 0.200 mol/dm3 hydrochloric acid. It required 12.5 cm3 of
hydrochloric acid to neutralise 25.0 cm3 of 0.0500 mol / dm3 metal hydroxide solution.
(i) Calculate the amount, in moles, of hydrochloric acid used.
(ii) Calculate the amount, in moles, of metal hydroxide present
17. Cyclohexane can be manufactured from hexane as shown in the equation.
C6H14 C6H12 + H2
Calculate the mass of cyclohexane that can be made from 258 g of hexane.
[Mr of cyclohexane = 84].
18. Dilute nitric acid reacts with aqueous barium hydroxide
2HNO3(aq) + Ba(OH)2(aq) Ba(NO3)2(aq) + 2H2O(l)
A student titrates 25.0cm3 of dilute nitric acid with 0.0450mol/dm3 barium hydroxide using
methyl orange as an indicator.
A volume of 34.0cm3 of aqueous barium hydroxide reacts exactly with the dilute nitricacid.
Calculate the concentration of the dilute nitric acid.
19. Dilute hydrochloric acid reacts with aqueous sodium carbonate.
2HCl + Na2CO32NaCl + H2O + CO2
A student titrates 20.0cm of 0.0250mol/dm3 aqueous sodium carbonate with dilute
3
hydrochloric acid using methyl orange as an indicator. A volume of 15.5cm3 of dilute
hydrochloric acid reacts exactly with the 0.0250mol/dm3 aqueous sodium carbonate.
Calculate the concentration, in mol/dm3, of the dilute hydrochloric acid.
