Question

Oxides and peroxides are not the only types of compounds that metals can make with oxygen, superoxides are also possible. 1.15 g of sodium on reaction with oxygen at high pressure gives 2.75 g of a white powder, sodium superoxide. What mass of oxygen was combined with the sodium?

• A. $1.3g$
• B. $1.5g$
• C. $1.6g$
• D. $1.9g$

Answer 1

Answer: (C)

$1.6g$

$\begin{array}{ccccc}Na& +& O_2& \to & Na{O}_2\\ & & & & Superoxide\\ \text{1 mol}& & \text{1 mol}& & \text{1 mol}\\ \text{23 g}& & \text{32 g}& & \text{55 g}\end{array}$
$1.15g=0.05mol0.05mol$
$2.75g=\frac{2.75}{55}=0.05mol$
So the mass of oxygen was combined with the sodium
$\left(i\right)O_2$ combined = 0.05 mol = 1.6 g
$\left(ii\right)O_2$ = 0.05 mol = 0.10 mol O-atoms
$\left(iii\right)$ Sodium used = 0.05 mol
$\left(iv\right)$ Superoxide = $Na{O}_2$
So the mass of oxygen was combined with the sodium is 1.6grams
Hence option C is correct.