2020 P1 Q9 - Determine Empirical Formula of Boron Carbide

Let's take a look at 2020 A Levels H2 Chemistry Paper 1 Question 9.

2020 p1 q9 question

We are required to determine the empirical formula of boron carbide given the mass analysis of its combustion to form boron oxide and carbon dioxide.

2020 p1 q9 combustion of boron carbide

Notice all the boron in boron carbide is transferred to B2O3 hence the amount of boron in 1.00g of boron carbide is equal to the amount of boron in 2.50g of B2O3.

Similarly all the carbon is transferred to CO2 and the amount of carbon in 1.00g of boron carbide is equal to the amount of carbon in 0.80g of CO2.

We can use the following formula to find out the mass of an element in a known mass of compound.

2020 p1 q9 mass ratio equal molar mass ratio

Therefore we can find the mass of boron in boron oxide and mass of carbon in carbon dioxide.

We can then calculate the moles of boron and carbon present.

2020 p1 q9 calculate moles of B and C

Finally we can compare the mole ratio for B to C.

2020 p1 q9 calculate B to C mole ratio

Since there are 4 B to every C, the empirical formula for boron carbide must be B4C.

2020 p1 q9 answer

So the answer to this question will be option D.

Topic: Mole Concept, Physical Chemistry, A Level Chemistry, Singapore

Back to list of questions for 2020 A Level H2 Chemistry Paper 1.

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