Question

What mass (in kg) of $K_{2}O$ contains the same number of moles of $K$ atoms as in $1.0$ kg $KCl$?

• A. $0.158$ kg
• B. $0.315$ kg
• C. $1.262$ kg
• D. $0.631$ kg

Answer 1

Answer: (D)

$0.631$ kg

Molecular weight of $KCl$ $=39+35.5=74.5$ g/mol
Thus, the number of moles in $1$ kg or $1000$ g of $KCl$ $=\frac{1000}{74.5}=13.4228$ moles.
Number of moles of $K=13.4228$ moles
$1$ mol of $K_{2}O$ contains $2$ moles of $K$.
Thus, number of moles of $K_{2}O=\frac{13.4228}{2}=6.711$ moles.
Molecular weight of $K_{2}O$ $=32\times 2+16=94$ g/mol
Thus, mass of $K_{2}O$ $=6.711\times 94=630.834$ g $=0.631$ kg.