Everything Science Grade 11

1.9 CHAPTER 1. ATOMICCOMBINATIONS

QUESTION

Write the chemical formula for sodium sulfate.

SOLUTION

Step 1 : Write down the ions that make up the compound.

Sodium sulfate containssodium ions and sulfateions.

Step 2 : Determine the valencyand charge of each ion.

Na+(valency = 1; charge = +1) and SO^24 −(valency = 2; charge =− 2 ).

Step 3 : Write the chemical formula.

Two sodium ions will be needed to balance thecharge of the sulfate ion. The

chemical formula for sodium sulfate is therefore:

Na 2 SO 4

Example 12: Formulae of ionic compounds

QUESTION

Write the chemical formula for calcium hydroxide.

SOLUTION

Step 1 : Write down the ions that make up the compound.

Calcium hydroxide contains calcium ions and hydroxide ions.

Step 2 : Determine the valencyand charge of each ion.

Calcium hydroxide contains the ions Ca2+(charge = +2) and OH−(charge =

− 1 ). In order to balance thecharge in a single molecule, two hydroxide ionswill

be needed for every ionof calcium.

Step 3 : Write the chemical formula.

The chemical formula for calcium hydroxide is therefore:

Ca(OH) 2

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