Summary 'All the chemical reactions you have to learn in your specification for Cambridge IGCSE and O/Level

Chemistry summary and practice worksheets for Cambridge IGCSE and Cambridge O/L
examinations .



Summary and practice questions ( with answers) of all
Chemical reactions
1.Writing chemical formulae for ionic compounds 2. writing chemical formulae for
covalent compounds 3.writing word equations for the chemical reactions 4.writing
formula equations ( chemical equations) and Balancing chemical equations 5. Types
of chemical reaction 6.Writing ionic ( net ionic) equations 7. Writing and balancing
ionic half equations ( electron half equations) for redox reactions




1. Writing chemical formulae for ionic compounds
Ionic compounds are formed between metals and non-metals. To write the chemical formula
of ionic compounds, the group number on the periodic table can be used to determine the
ionic charges of elements in each group. Metal loses electrons and form +ve ions( cations )
and non-metals gain electrons to form anions( -ve ions).

For an ionic compound there is a rule for finding the correct formula. In every ionic formula the
cation is written
first and the anion written second. In the formula, the charge on one becomes the subscripts
of other.

Group I II III Iv V VI VII VIII
number
Valence 1 2 3 4 5 6 7 8
electrons
Ionic 1+ 2+ 3+ 4+ or 4- 3- 2- 1- none
charge
Combining 1 2 3 4 3 2 1 none
power

In an ionic formula, the total loss of electrons are equal to the total gain of electrons and the
overall net charge of the compound is zero.

Example 1: What is the chemical formula of calcium chloride

1. Write down the chemical symbols for the elements in the compound (Ca and
Cl)
2. Use the Periodic Table to find the combining power ( or ionic charge) of each element.
Ca 2+ Cl-

,Chemistry summary and practice worksheets for Cambridge IGCSE and Cambridge O/L
examinations .


3. If the numbers can be cancelled down, cancel them (they can’t be)
4. Swap over the combining powers. Write them below the symbols as a subscript.
5 If the number is one – please don’t write it!
The correct formula of calcium chloride is CaCl2

Ca2+ Cl- CaCl2

• Transition metals show multiple valencies and you should know few of these and the
charge of some complex ions are given in the paper

Examples
Cu2+, Cu+ ( CuO, Cu2O)
Fe2+ , Fe3+ ( FeO, Fe2O3)
Manganese (II) -Mn2+, Manganese(VI) -Mn6+ , Copper(II)- Cu2+
FeCO3 – Iron(II) carbonate
Cu(OH)2 – Copper(II) hydroxide

• Nitrogen, sulfur and phosphorous show multiple valencies ( you might have learned
this concept in redox reactions) .
Nitrogen and phosphorous show 3- when it joins with metals
Ca3P2
Na3N

• You can simplify the formulae, if ionic charges can be divided by the same figure.

Mg2+ O2- The chemical formula is MgO ( magnesium oxide)


Al3+ P-3 The chemical formula is AlP( aluminium phosphide)

Example 2: What is the chemical formula of magnesium oxide:
1. Write down the chemical symbols for the elements in the compound (Mg and
O)

2. Use the Periodic Table to find the ‘combining power’ of each element from the
table below. Write the combining power of each element under its symbol.
Mg2+ O2-)

4. If the numbers can be cancelled, cancel them (Mg O)

5. Swap over the combining powers and write down the symbols.

It is MgO

,Chemistry summary and practice worksheets for Cambridge IGCSE and Cambridge O/L
examinations .

, Chemistry summary and practice worksheets for Cambridge IGCSE and Cambridge O/L
examinations .


Example 3: Write the chemical formula of iron(III) sulfate

Fe3+ SO4 2-


Fe2( SO4) 3

Example 4: Write the chemical formula of potassium chromate.

K1+ Cr2O71-


KCr2O7
Practice Questions
Question 1
Name the following ionic compounds:
a) Na2SO4
b) MgF2
c) MgS
d) K3N
e) Ca3P2
f) AlCl3
g) Ag2O
h) Cu3PO4
i) Al(NO3)3
j) Na2CO3
k) Fe(HCO3)2
l) FeCO3
m) Cu(OH)2
n) Zn3(PO4)2
o) PbCl2


Question 2
Write the formulae for the given compounds
a) Sodium nitrate