Question

Hydrogen is generated by the action of steam with heated magnesium. Calculate the mass of magnesium which will produce just sufficient hydrogen to combine with all the oxygen that can be obtained by the complete decomposition of 24.5 g of $KCl{O}_3$.

• A. 4.8 g
• B. 14.4 g
• C. 7.2 g
• D. 28.8 g

Answer 1

The correct option is B

14.4 g

$Mg+H_{2}O\to MgO+H_2$

$2H_2+O_2\to 2H_{2}O$

$2KCl{O}_3\to 2KCl+3O_2$

i.e., $2KCl{O}_3=3O_2=6H_2=6Mg$

2 moles of KClO₃ correspond to 6 moles of Mg

Or 1 mole of $KCl{O}_3$ (122.5 g) corresponds to 3$\times$24 g of Mg

24.5 g of $KCl{O}_3$​ will correspond to $\frac{72}{122.5}\times 24.5$ = 14.4 g of Mg.