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Practice each question, then open the answer or worked solution.
Write down the formulae of
(i) sodium oxide
(ii) aluminium chloride
(iii) sodium sulphide
(iv) magnesium hydroxide
The following are the formulae:
(i) sodium oxide – Na2O
(ii) aluminium chloride – AlCl3
(iii) sodium sulphide – Na2S
(iv) magnesium hydroxide – Mg (OH)2
Write down the names of compounds represented by the following formulae:
(i) Al2(SO4)3
(ii) CaCl2
(iii) K2SO4
(iv) KNO3
(v) CaCO3.
Listed below are the names of the compounds for each of the following formulae:
(i) Al2(SO4)3 – Aluminium sulphate
(ii) CaCl2 – Calcium chloride
(iii) K2SO4 – Potassium sulphate
(iv) KNO3 – Potassium nitrate
(v) CaCO3 – Calcium carbonate
What is meant by the term chemical formula?
Chemical formulas are used to describe the different types of atoms and their numbers in a compound or element. Each element’s atoms are symbolised by one or two letters. A collection of chemical symbols that depicts the elements that make up a compound and their quantities.
For example, the chemical formula of hydrochloric acid is HCl.
How many atoms are present in a
(i) H2S molecule and
(ii) PO43- ion?
The number of atoms present is as follows:
(i) H2S molecule has 2 atoms of hydrogen and 1 atom of sulphur hence 3 atoms in total.
(ii) PO43- ion has 1 atom of phosphorus and 4 atoms of oxygen hence 5 atoms in total.