Question

12g of X2O5 , an oxide of element X contains 7.2g of X. How many moles of X does 7.2g of the element contain?

Answer 1

We have 12 g of X2O5 with 7.2 g of X

%X = 7.2 / 12 = 60.0%

for oxygen 5 x 16 = 80 g/ mole

% O = 40 %

so molar mass of X2O5 = 80 x 100 / 40 = 200 g / mole

mass of X2 in a mole = 120 g

X has Molar mass 60 g / mole

7.2 g has 7.2 / 60 moles = .12 moles

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