How to determine Empirical Formula of Compound
2015/P1/Q15; 2008/P1/13

GCE O level, Singapore, 2015/P1/Q15 & 2008/P1/13

The formula of an oxide of element Y is Y2O3. 8.0 g of Y2O3 contains 5.6 g of Y. How many moles of Y does 5.6 g of the element contain?

When we do chemical calculations, very often, we will be given the mass of each element in the compound, and then asked to determine the empirical formula of a compound.

We will go through the following example before tackling the actual question tested in 2008 and 2015.

Common Example

Chemical Analysis shows that a compound contains 79.9% by mass of carbon and 20.1% by mass of hydrogen. Calculate the empirical formula of the compound.

Examination Question 2015/P1/Q15 & 2008/P1/13

The question, which appeared in both 2008 and 2015, is pretty special. Firstly, students may not be aware that they can actually adopt the familiar 4-step table used to determine empirical formula. Many stumbled at this question and were unsure how to proceed. Using the same 4-step table, we are going to determine the moles of Y in this compound.

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How to determine Empirical Formula of Compound2015/P1/Q15; 2008/P1/13