Citric acid was found to contain 37.51% C, 4.20% H, and 58.29% O by mass. What is the simplest formula for citric acid?

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justaguide | College Teacher | (Level 2) Distinguished Educator

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Citric acid has 37.51% carbon, 4.2% hydrogen and 58.29% oxygen by mass. The molar mass of carbon is 12 g/mole. The molar mas of hydrogen in 1 g/mole and the molar mass of oxygen is 16 g/mole. Dividing the percentage mass of the elements in citric acid by their molar mass gives 3.12 C, 4.2 H and 3.643 O. To determine the empirical formula of citric acid, the numbers have to be expressed in an integral ratio. Dividing 3.12 by 4.2 gives 0.742 ~~ 0.75. Dividing 3.643 by 4.2 gives 0.867 ~~ 0.865

The ratio is 0.75 : 1 : 0.875

multiply all the terms by 8

=> 0.75*8 : 8 : 0.875*8

=> 6 : 8 : 7

The empirical formula of citric acid is C6H8O7

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