Page 25 - Q & A STPM 2022 Chemistry

Chemistry Term 1 STPM Chapter 1 Atoms, Molecules and Stoichiometry
Section C Essay Questions

Question 14
Titanium carbide, TiC, is the hardest of the known metal carbides. It can be made
by heating titanium(IV) oxide, TiO 2 , with carbon black to 2200°C. When 4.00 g of
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TiO 2 is heated with excess carbon, 2.8 g carbon monoxide gas is formed.
[Relative atomic mass: C = 12, O = 16, Ti = 47.8]
(a) Calculate the number of moles of titanium(IV) oxide and carbon monoxide
gas formed in the reaction.
(b) Construct an equation for the reaction of titanium(IV) oxide and carbon.
(c) If 5 kg of titanium(IV) oxide is reacted with 10 kg of carbon, what is the
Term
mass of titanium carbide formed?
1
Answer:
(a) Molar mass of TiO 2 = 47.8 + 2(16) = 79.8
Mass
4.00
The number of moles of TiO 2 = ——–——– = ——– = 0.050
Molar mass 79.8
Molar mass of CO = 12 + 16 = 28
Mass 2.8
The number of moles of CO = ——–——– = —— = 0.100
Molar mass 28
(b) 0.050 mol of TiO 2 produces 0.100 mol of CO.
1 mol of TiO 2 produces 2 mol of CO.
TiO 2 + 3C : TiC + 2CO
Mass 5000
(c) The number of moles of TiO 2 = ——–——– = ——– = 62.7
Molar mass
79.8
Mass 10 000
The number of moles of C = ——–——– = ——–– = 833.33 (in excess)
Molar mass
12
When determining the amount of product, carbon is disregarded because
the amount of carbon used is in excess.
Since one mole titanium(IV) oxide produces one mole titanium carbide,
the number of moles of titanium carbide formed = 62.7
Molar mass of titanium carbide, TiC = 47.8 + 12 = 59.8
Mass of TiC formed = 62.7 mol × 59.8 = 3749 g = 3.75 kg

Common Errors
Students did not change the mass of the substances from kilogram to gram
when they determine the number of moles of the substances.

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