Everything Science Grade 10

2.4 CHAPTER 2. CLASSIFICATION OF MATTER

Example 5: Writing chemical formulae 3

QUESTION

Write the chemical formula for magnesium oxide.

SOLUTION

Step 1:List the ions involved.

Mg2+and O^2 −

Step 2:Find the right combination

Mg2+: 2

O^2 −: 2

If you use the cross method, you will get a ratio of2 : 2. This ratio must

always be in simplest form, i.e.1 : 1.

Step 3:Write down the formula

MgO (notMg 2 O 2 )

Example 6: Writing chemical formulae 4

QUESTION

Write the formula for copper(II) nitrate.

SOLUTION

Step 1:List the ions involved

Cu2+(the questions asks for copper(II) not copper(I))

NO− 3

Step 2:Find the right combination

40 Chemistry: Matter and Materials