Question

A sample of magnesium phosphate contains 0.25 moles of oxygen atomsthen find how many moles of magnesium phosphate Mg₃(PO₄)₂ are present in the sample.

• A. $0 \text{.} 2 \times 1 0^{- 2}$
• B. $1 \text{.} 2 5 \times 1 0^{- 2}$
• C. $2 \text{.} 5 \times 1 0^{- 2}$
• D. $3 \text{.} 1 2 5 \times 1 0^{- 2}$

Answer 1

Answer: (D)

Mg₃ (PO₄ )₂ One mole of salt has 8 moles of O atoms i.e., 8 moles of O atoms $\equiv$ 1 mole salt
0.25 moles of O atoms $\equiv$ $\frac{1}{8} \times 0 \text{.} 2 5$
= $\frac{2 5 \times 1 0^{- 2}}{8}$
= $3 \text{.} 1 2 5 \times 1 0^{- 2}$ moles.