STOICHIOMETRY

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Example 1:2Mg + O2 2MgO

0.025 mol 0.025 mol

What is the mass of the oxide formed if 0.6 g of magnesium is burnt in excess oxygen?

Number of moles of Mg = =0.025 mol

0.6

24

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Stoichiometry:

From the equation :2 moles of magnesium, Mg produce 2 moles of magnesium oxide, MgO

From the calculation :0.025 mole of magnesium, Mg produce 0.025 mole of magnesium oxide, MgO

Therefore, mass of MgO Mass = 0.025 x 40 = 1.0 g

n =_mass___ molar mass

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Example 2:CaCO3 + 2HCl CaCl2 + H2O + CO2

0.05 mol 0.05 mol

What is the volume of carbon dioxide released when 5 g of calcium carbonate reacts with hydrochloric acid at room condition?

Number of moles of CaCO3 = =

5.0

1000.05 mol

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Stoichiometry:

From the equation :1 mole of calcium carbonate, CaCO3 produce

1 mole of carbon dioxide, CO2

From the calculation :0.05 mole of calcium carbonate, CaCO3 produce0.05 mole of carbon dioxide, CO2

Therefore, volume of CO2: Volume = 0.05 x 24

= 1.2 dm¯³

n =_volume__ molar volume

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Example 3:5.0 g of hydrated copper(II) sulphate, CuSO4.5H2O is heated to remove its water vapour. Calculate the mass of water vapour removed.

CuSO4.5H2O CuSO4 + 5H2O

Number of moles of CuSO4.5H2O = =

6

Stoichiometry:

From the equation :

..................................................................................

..................................................................................

..................................................................................

.................................From the calculation :

………………………………………………………………………………………………………………………………………………………………………………………………………………

Therefore, mass of water vapour : Mass == 7

Example 4

3.1 g of sodium oxide is formed when the sodium metal is burnt completely in oxygen at STP. Calculate the volume used.

4Na + O2 2Na2O

Number of moles of Na2O = =

8

Stoichiometry:

From the equation :

………………………………………………………………………………………………………………………………………………………………………………

From the calculation :.………..……………………………………………………………………………………………………………………………………………………………………Therefore, volume of oxygen:

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