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ICSE Class 10 Chemistry Question 20 of 23

Solved Sample Paper 3 — Question 19

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19
Question

Question 7(iii)

Concentrated nitric acid oxidises phosphorus to phosphoric acid according to the following equation:

P + 5HNO3 ⟶ H3PO4 + 5NO2 + H2O

(a) What mass of phosphoric acid can be prepared from 3.1 g of phosphorus?

(b) What mass of nitric acid will be consumed at the same time?

Answer

P+5HNO3⟶H3PO4+H2O+5NO231 g5[(1)+14+3(16)]3(1)+31=5[63]+4(16)=315g=98 g\begin{matrix} \text{P} & + & 5\text{HNO}_3 & \longrightarrow & \text{H}_3\text{PO}_4 & + & \text{H}_2\text{O} & + & 5\text{NO}_2 \\ 31 \text{ g} & & 5[(1)+14+3(16)] & & 3(1) + 31 \\ & &= 5[63] & & + 4(16) \\ & & = 315 g & & = 98 \text{ g} \\ \end{matrix}

(a) 31 g of P forms 98 g of phosphoric acid

∴ 3.1 g will form 9831\dfrac{ 98}{31} x 3.1 = 9.8 g.

Hence, 9.8 g of phosphoric acid is formed

(b) 31 g of P consumes 315 g of nitric acid.

∴ 3.1 g will consume = 31531\dfrac{315}{31} x 3.1 = 31.5 g