e) chemical formulae and chemical equations

Question 1

1.21- write word equations and balanced chemical equations to represent the reactions studied in this specification.

Answer 1

A chemical equation which is expressed by using word is called word equation.

Eg: Carbon + oxygen => carbon dioxide

A chemical equation which is expressed by using symbols is called chemical equation.

Eg: C(s) + O2 (g ) => CO2(g)

Question 2

1.22 use the state symbols (s), (l), (g) and (aq) in chemical equations to represent solids, liquids, gases and aqueous solutions respectively

Answer 2

(s) for solids
(l) for liquids
(g) for gases
(aq) for aqueous solution

Question 3

1.23 understand how the formulae of simple compounds can be obtained experimentally, including metal oxides, water and salts containing water of crystallisation

Answer 3

Finding the n in BaCl2.nH2O
Mass of crucible- 30.00g, Mass or crucible + barium chloride crystals, BaCl2.nH2O
= 32.44g
Mass or crucible + anhydrous barium chloride, BaCl2
= 32.08g

=32.08-30.00
Mass of BaCl2= 2.08g

Mass of water:
32.44-32.08= 0.36g

BaCl2 - mass 20.8 
H20- mass 0.36
Number of moles:
1) 2.08/208 
2) 0.36/18
Ratio of moles 1:2
Simplest (empirical formula) BaCl2.2H2O.

Question 4

1.24 calculate empirical and molecular formulae from experimental data

Answer 4

Carbon and Hydrogen
Carbon - 85.7g 
Hydrogen- 14.3g
1- (85.7/12)
2- (14.3/1)
= 
1) 7.14
2) 14.3
Ratio: 1.2
SEF- CH2

Converting empirical formulae into molecular formulae-

Relative formula mass of the compound was 56. (56 / 14 = 4)

So you need four lots of CH2 The molecular formula is C4H8.

Question 5

1.25 calculate reacting masses using experimental data and chemical equations

Answer 5

Calculate the mass of magnesium oxide that can be made by completely burning 6g of magnesium in oxygen.

Equation for reaction: 2Mg + O2 => 2MgO

1. Calculate the amount, in moles, of magnesium reacted

Ar of Mg is 24

Amount of magnesium = (6 / 24) = 0.25mol

2. Calculate the amount of magnesium oxide formed

The equation tells us that 2 mol of Mg for 2 mol of MgO, hence the amount of MgO formed is the same as the amount of

Mg reacted.

Amount of MgO formed is 0.25 mol

3. Calculate the mass of MgO formed

Mr of MgO = (24 + 16) = 40

Mass of magnesium oxide = (0.25 x 40) = 10g

Question 6

1.27 carry out mole calculations using volumes and molar concentrations.

Answer 6

Mole = Volume x Concentration