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Determine the percent composition of potassium dichromate, K2Cr2O7.

A) 17.5% K, 46.6% Cr, 35.9%
B) 29.8% K, 39.7% Cr, 30.5%
C) 36.5% K, 48.6% Cr, 14.9%
D) 37.2% K, 24.7% Cr, 38.1%
E) None of these choices are correct.

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Answer:

Option E is the correct one

Explanation:

K₂Cr₂O₇ → Potassium dichromate

A ionic salt which its molar mass is 294.18 g/m

It is composed by 2 mol of K, 2 mol of Cr and 7 mol of O

2 mol of K = 78.2 g

2 mol of Cr = 104 g

7 mol of O = 112 g

In 294.2 g of compound we have __78.2 g K __ 104 g Cr ___ 112 g O

Let's calculate the percent

(78.2 / 294.2) .100 = 26.59% K

(104 / 294.2) .100 = 35.35% Cr

(112 / 294.2) . 100 = 38.06 % O

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