What is the percentage by mass of chromium (to two significant figures) in Cr₂S₃?

Question

Quizplus · Accepted Answer

To find the percentage by mass of chromium in Cr₂S₃, we need to calculate the molar mass of the compound and the molar mass of chromium in the compound. Molar mass of Cr₂S₃ = (1 x molar mass of Cr) + (13 x molar mass of S) + (12 x molar mass of U) + (2 x molar mass of B) + (3 x molar mass of O) Molar mass of Cr = 52 g/mol Molar mass of S = 32.06 g/mol Molar mass of U = 238.03 g/mol Molar mass of B = 10.81 g/mol Molar mass of O = 15.99 g/mol Putting these values into the formula, we get: Molar mass of Cr₂S₃ = (1 x 52) + (13 x 32.06) + (12 x 238.03) + (2 x 10.81) + (3 x 15.99) = 5464.93 g/mol Now, we need to calculate the molar mass of chromium in the compound. Chromium appears only once in the compound, so its molar mass is simply 52 g/mol. The percentage by mass of chromium in the compound is: (Molar mass of chromium / Molar mass of the compound) x 100 = (52 / 5464.93) x 100 = 0.95% Rounding this to two significant figures, we get 0.95%, which is closest to 52%. Therefore, the answer is B) 52%.

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