Question

Write the formula by criss-cross method of Ammonium arsenate.

Answer 1

The formula of ammonia is ‘NH₄’, having a valency of 1⁺.

The formula of arsenate is ‘AsO₄’ with valency 3^-.

Step 1 –

Write the formula of ammonium arsenate:

Symbol Valency

Ammonia NH₄ 1⁺

Arsenate AsO₄ 3^-

Step 2 –

Write each symbol with its valency:

NH₄¹⁺ AsO₄^3-

Step 3 –

Interchanging the valences:

$$\begin{gathered} {\mathrm{NH}}_4{\mathrm{AsO}}_4 \\ \searrow \swarrow \\ {1}^{+}{3}^{-} \end{gathered}$$

The formula of the compound Aluminium sulphate is (NH₄)₃AsO₄.