The mole and chemical reactions
Threshold Questions
1 Determine the formula weight of
a copper(II) sulfate
b phosphorus trichloride
c ammonium chloride
2 Determine the molecular mass of
a ozone
b carbon dioxide
c sulfur trioxide
3 Calculate the mass of:
a 1.000 mol of silver metal
b 1.50 mol of oxygen gas
c 5.000 mol of carbon dioxide gas
d 5.00 mol of solid carbon dioxide
e 2.500 mol of sodium hydroxide
4 An Australian 50 cent coin minted in 2001 has a mass of 15.66 grams. It is made of 75.0
% copper and 25.0 % nickel. Calculate the number of moles of each metal in the coin.
5 Arrange the following in order of increasing mass: 1.0 mole of calcium carbonate, 2.0
moles of iron, 3.0 moles of ammonium fluoride, 4.0 moles of carbon monoxide, 5.0 moles
of neon, 6.0 moles of water.
6 Heating calcium carbonate in air forms calcium oxide. Write a chemical equation for this
reaction and calculate the mass of calcium oxide produced by completely converting 10.0
grams of calcium carbonate into calcium oxide.
7 Heating nickel(II) hydroxide in air forms nickel(II) oxide. Write a chemical equation for this
reaction and calculate the mass of nickel(II) oxide produced by completely converting 18.5
grams of nickel(II) hydroxide into nickel(II) oxide.
Intermediate Questions
8 Minerals are compounds that occur in rocks of the earth’s crust. The following list contains
the geological names and analyses by mass of ten minerals. Determine all their empirical
formulas and the chemical names of (a) to (e) inclusive.
a anglesite 68.3 % Pb, 10.6 % S, 21.1 % O
b brucite 41.7 % Mg, 54.9 % O, 3.4 % H
c siderite 48.2 % Fe, 10.4 % C, 41.4 % O
d fluorite 51.3 % Ca, 48.7 % F
e thenardite 32.4 % Na, 22.6 % S, 45.0 % O
9 How much does one scandium atom weigh:
a in atomic mass units (u)?
b in grams?
10 An atom of element X has a mass of 3.16 10–23 grams.
a Determine the atomic weight of X
b Write down the name of X.
11 The smelliest substance known is vanillin (formula C8H8O3). It is possible for the human
nose to smell 2.0 10–8 milligrams of vanillin in a litre of air. How many vanillin molecules
does this mass represent?
12 A certain water supply was found to be polluted by 0.10 mg/L of chloroform (CHCl3). How
many CHCl3 molecules are present in one drop (0.050 mL) of this water?
13 Analysis of 1.60 grams of an oxide of iron formed 1.12 grams of iron.
a What mass of oxygen was formed during the analysis?
b Evaluate the ratio: (number of moles of oxygen atoms) ÷ (number of moles of iron
atoms) in the compound.
c Write the empirical formula for the compound.
14 What is the empirical formula of:
a niobium oxide which contains 69.9 % of niobium by mass when analysed?
b scandium oxide which contains 65.3 % of scandium by mass when analysed?
c vanadium oxide which contains 61.4 % of vanadium by mass when analysed?
15 When analysed, a sample of a certain inorganic compound produced 0.010 moles of
calcium, 1.2 1022 carbon atoms and 0.64 grams of oxygen. What is the simplest
(empirical) formula of this compound?
16 The compound ethylene glycol has the following analysis:
38.7 % carbon, 9.7 % hydrogen and 51.6 % oxygen by mass.
a Determine the empirical formula of the compound.
b One mole of ethylene glycol has a mass of 62.0 grams. Write down the actual chemical
formula of the compound.
17 In an experiment to determine the formula of a hydrate of sodium carbonate Na2CO3·yH2O,
6.20 grams of the compound were heated until no further change in mass occurred. The
mass of anhydrous sodium carbonate Na2CO3 remaining was 5.30 grams.
Determine the value of "y".
18 An element X forms two oxides whose formulas are XO3 and X2O3. One of these oxides
contains 52.0 % of X by mass and has a molar mass of 100.0 g. Identify X.
19 A 1.00 g sample of zirconium metal reacted with fluorine gas to give 1.83 g of solid
zirconium fluoride. Determine the empirical formula of this compound and write a balanced
equation to represent this reaction.
20 1.00 g of titanium oxide, on reaction with hydrogen gas, yielded titanium metal and 0.45 g
of steam. Determine the empirical formula of titanium oxide and write a balanced equation
for the reaction.
21 Methane (CH4) burns in oxygen gas react forming steam and carbon dioxide. Write a
balanced equation for this reaction and determine which reactant will be in excess for this
reaction, and by how much, in a mixture of:
a 20.0 g of methane and 20.0 g of oxygen gas
b 25.0 g of methane and 100.0 g of oxygen gas
22 Propane (C3H8) burns in dinitrogen monoxide to produce nitrogen, steam and carbon
dioxide. If 5.0 g of propane and 100.0 g of dinitrogen monoxide reacted together as
completely as possible in this way, write a balanced equation for the reaction and
calculate:
a the mass of carbon dioxide produced
b the mass of the excess reactant remaining after the reaction was finished.
23 Aluminium and iodine react together forming aluminium iodide. If 1.35g of aluminium and
2.54g of iodine reacted together completely, which element is in excess, and what is the
maximum mass of the compound obtainable?
24 When magnesium and sulfur are heated together they form magnesium sulfide. If 50.0
grams of magnesium and 50.0 grams of sulfur were heated together:
a which element is the limiting reactant ?
b what is the maximum mass of magnesium sulfide which could be produced ?
c what mass of the excess reactant remains after all reaction has stopped?
25 Ammonia gas can be prepared by the reaction of ammonium chloride with calcium oxide.
Water and calcium chloride are also formed. If 112 grams of calcium oxide react with 224
grams of ammonium chloride:
a what is the maximum possible yield of ammonia?
b what mass of the excess reactant remains after the maximum amount of ammonia has
been produced?
26 A 0.250 g sample of a compound whose formula is M2SO4 (where M is a metallic element)
was reacted with barium chloride solution so that all the sulfate present was converted to
barium sulfate. If 0.161 g of barium sulfate was formed, identify the metal M.
27 When heated, potassium chlorate decomposes into solid potassium chloride and oxygen
gas. If 5.00 grams of potassium chlorate produced 3.04 grams of potassium chloride in
this way, determine the empirical formula of potassium chlorate and write a balanced
equation for the reaction.
Advanced Questions
28 Lithopone is an insoluble mixture of barium sulfate and zinc sulfide in 1:1 mole ratio. It is
made by reacting together solutions of zinc sulfate and barium sulfide.
a Write a balanced chemical equation to represent the reaction.
b Calculate the masses of zinc sulfate and barium sulfide that are required to make 1.00
tonne of lithopone.
29 1.00 g of the hydrocarbon butane produces 3.03 g of carbon dioxide and 1.55 g of water
when completely burned in oxygen.
a Determine the empirical formula of butane using the same procedure as was outlined
in the previous question.
b Determine its molecular formula if its molecular weight is known to be 58.0 u.
30 The empirical formulae of organic compounds composed of carbon and hydrogen can be
determined by combustion analysis. A measured amount of the compound is burned in
oxygen, thus completely changing it into carbon dioxide and steam. These 2 gases are
trapped by pre-weighed absorbers. The empirical formula is then calculated from the
masses of trapped H2O and CO2 in the absorbers (see the accompanying diagram). The
compound “limonene” is a hydrocarbon i.e. composed of C and H only. The combustion
analysis of 1.70 grams of limonene produced 5.50 grams of carbon dioxide and 1.80 grams
of water. To determine limonene’s empirical formula:
O2 in unreacted O2
HEAT water CO2 absorber
absorber
a Calculate the number of moles of carbon dioxide formed in the analysis
b Calculate the number of moles of C atoms that formed the carbon dioxide in (a)
c Calculate the number of moles of water formed (as steam) in the analysis
d Calculate the number of moles of H atoms that produced the water in (c)
e Evaluate the ratio (moles of C atoms) : (moles of H atoms) and convert this to the
simplest whole number ratio; hence write the empirical formula of limonene.
