Two samples of calcium fluoride are decomposed into their constituent elements. The first sample produced 0.154 g of calcium and 0.146 g of fluorine. If the second sample produced 294 mg of fluorine, how many grams of calcium were formed? A) 0.280 g B) 3.09 × 10² g C) 3.13 g D) 0.310 g E) 2.80 × 10² g

Question

Quizplus · Accepted Answer

First sample:
The molar ratio of CaF2 to Ca is 1:1, so 0.154 g of Ca means 0.154/40.08 = 0.003847 mol of Ca.
The molar ratio of CaF2 to F2 is also 1:1, so 0.146 g of F2 means 0.146/37.99 = 0.003847 mol of F2.
Therefore, the chemical equation for the decomposition is: CaF2 -> Ca + F2
And 0.003847 mol of Ca is formed.

Second sample:
From the chemical equation: CaF2 -> Ca + F2
The molar ratio of CaF2 to F2 is 1:2, so 294 mg of F2 means 294/37.99/2 = 0.003072 mol of F2.
Therefore, 0.003072 mol of Ca is formed.

Adding the two samples together:
0.003847 mol + 0.003072 mol = 0.006919 mol of Ca
So, the total mass of Ca formed is 0.006919 mol x 40.08 g/mol = 0.277 g.
Round to the nearest hundredth gives the answer D: 0.310 g.

Two Samples of Calcium Fluoride Are Decomposed into Their Constituent