Question

5 how many moles are in 3.3 grams of potassium sulfide, $\text{k}_2\text{s}$?

Explanation:

Step1: Calculate molar mass of $\text{K}_2\text{S}$

Molar mass of $\text{K} = 39.10\ \text{g/mol}$, molar mass of $\text{S} = 32.07\ \text{g/mol}$
$$\text{Molar mass of } \text{K}_2\text{S} = 2\times39.10 + 32.07 = 110.27\ \text{g/mol}$$

Step2: Moles from mass and molar mass

Use formula $n=\frac{m}{M}$, where $m=3.3\ \text{g}$, $M=110.27\ \text{g/mol}$
$$n=\frac{3.3}{110.27}$$

Answer:

$0.030$ moles (rounded to two significant figures)