Formulae for ionic compounds

2 marks · Normal

Write the formula for these ionic compounds:

(a)

sodium phosphate

[1 mark]

(b)

calcium carbonate

[1 mark]

Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.

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(a) Na3PO4

(b) CaCO3

Common mistakes: not balancing charges; not using brackets for phosphate

Show mark scheme and worked solution

Marking points

A1 (a) · 1 mark · Correct formula for sodium phosphate: Na3PO4.

A2 (b) · 1 mark · Correct formula for calcium carbonate: CaCO3.

Worked solution

a) Sodium is Na+, phosphate is PO4^3–; need 3 sodium to balance 1 phosphate: Na3PO4. b) Calcium is Ca2+, carbonate is CO3^2–; one of each balances charges: CaCO3.