Question

An emerald gemstone is an impure form of the mineral beryl, Be3Al2Si16O18. What is the percentage of silicon in the mineral?

a. 6.59%
b. 54.9%
c. 35.2%
d. 3.30%
e. 3.43%

Answer 1

b. 54.9%

Step-by-step explanation:

An emerald gemstone has the formula Be₃Al₂Si₁₆O₁₈. We can find the mass of each element in 1 mole of Be₃Al₂Si₁₆O₁₈ by multiplying the molar mass of the element by its atomicity.

Be: 3 × 9.01 g = 27.03 g

Al: 2 × 26.98 g = 53.96 g

Si: 16 × 28.09 g = 449.4 g

O: 18 × 16.00 g = 288.0 g

Total mass = 818.4 g

The mass percentage of silicon is:

(449.4 g / 818.4 g) × 100% = 54.91%