Worksheet Set B
Worksheet B002
(K. Nel - 2012)
A. Physical and Chemical change
1. Write equations for the following reactions:
a. 2 moles of copper atoms combine with 2 moles of sulfur atoms to form 2 moles of
copper(II) sulphide
2𝐶𝑢 + 2𝑆 → 2𝐶𝑢𝑆
b. 1 mole of iron(III) oxide (Fe2O3) reacts with 3 moles of hydrogen molecules to form 2
moles of iron atoms and 3 moles of water molecules.
𝐹𝑒2 𝑂3 + 3𝐻2 → 2𝐹𝑒 + 3𝐻2 𝑂
c. 1 mole of ethanol molecules (C2H5OH) burns in 3 moles of oxygen molecules to form 2
moles of carbon dioxide molecules and 3 moles of water molecules.
𝐶2 𝐻5 𝑂𝐻 + 3𝑂𝐻2 → 2𝐶𝑂2 + 3𝐻2 𝑂
2. Balance the following equations:
a. 1Cl2(g) + 2KBr(aq) → 2KCl(aq) + 1Br2(aq)
b. 1Zn(l) + 1F2O3(l) → 2Fe(l) + 3ZnO(s)
c. 1Pb(NO3)2(s) → 1PbO2(s) + 2NO2(g) + O2(g)
d. 1C2H5OH(l) + 1O2(g) → 1CO2(g) + 1H2O(l)
e. 2Al(s) + 6HCl(aq) → 2AlCl3(aq) + 3H2(g)
3. When calcium carbonate is heated strongly, the following change occurs:
CaCO3(s) → CaO(s) + CO2(g)
a. Write a word equation for this change
Calcium Carbonate  Calcium Oxide + Carbonate
b. How many moles of CaCO3 are there in 75g of calcium carbonate?
Ca40g
O=16g
C=12g
𝐶𝑎𝐶𝑂3 → 40𝑔 + 12𝑔 + 16,3𝑔
= 100g
75 g of 𝐶𝑎𝐶𝑂3 = 0,75 mole
c. What mass of calcium oxide is obtained from the thermal decomposition of 75g of
calcium carbonate? Assume a 45% yield.
Ca=40g
O=16g
(40𝑔+16𝑔)𝑥75
100
= 42𝑔
d. What mass of carbon dioxide will be given off simultaneously (at the same time)?
75g – 42g = 33g
e. What volume will this gas occupy at rtp?
1 mole of gas = 24𝑑𝑚3
0,75 mole of gas = 18𝑑𝑚3
4. 8g of impure magnesium carbonate reacts with an excess of hydrochloric acid as shown below:
MgCO3(s) + 2HCl(aq) → MgCl2(aq) + H2O + CO2(g)
1325 cm3 of carbon dioxide is collected at rtp.
a. How many moles of carbon dioxide are produced?
1 mole of 𝐶𝑂2 = 24000𝑐𝑚3
= 1025 𝑐𝑚3
1325𝑐𝑚3
24000𝑐𝑚3
= 0,05 𝑚𝑜𝑙𝑒 of 𝐶𝑂2 released.
b. What mass of pure magnesium carbonate would give this volume of carbon dioxide?
1 mole of MgCO3 = Mg = 24g
C = 12g
24g + 12g +(16g x3)
= 84g
O = 16g
84g x 5/100 = 4,2g (Pure MgCO3)
c. Calculate the %purity of this magnesium carbonate.
4,2𝑔
𝑥100 = 52,5% 𝑖𝑠 𝑝𝑢𝑟𝑒 𝑜𝑓 MgCO3
8𝑔
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