Question

Magnesium hydroxide is 54.87% oxygen by
mass. How much oxygen is in 260 g of the
compound?
Answer in units of g
(part 2)
How many moles of oxygen is this?
Answer in units of mol

Answer 1

Magnesium hydroxide is 54.87% oxygen by mass. How much oxygen is in 260 g of the compound?

Answer in units of g

$$m = 260 \times \frac{54.87}{100} = 142.66\ \text{g}$$

(part 2)

How many moles of oxygen is this? Answer in units of mol

$$\nu = \frac{m}{M}$$ $$\nu = \frac{142.66}{16} = 8.92\ \text{mol}$$