# 2021 P1 Q10 - Determining Greatest Number of Molecules

Let's take a look at 2021 A Levels H2 Chemistry Paper 1 Question 10. We are required to determine which option contains the greatest number of molecules. Since number of molecules is directly related to number of moles, we can just calculate the moles for each option instead.

Option A - 2.00g of ethyl methanoate The molar mass for ethyl methanoate, C3H6O2, is 74.0.

Number of moles will be mass over molar mass = 2.70 x 10-2

Option B - 4.00g of liquid bromine Molar mass for bromine, Br2, is 159.8.

Number of moles will be mass over molar mass = 2.50 x 10-2

Option C - 550 cm3 of hydrogen measured at rtp Molar volume of a gas at room temperature and pressure is 24.0 dm3.

Number of moles will be volume in dm3 over molar volume = 2.29 x 10-2

Option D - 1.55 x 1022 molecules of water Number of moles will be number of molecules over Avogadro constant L = 2.57 x 10-2

We can now compare all the options to determine which has the greatest moles (and greatest number of molecules). The answer to this question is option A (2.70 x 10-2).

This question is not difficult but can be pretty tedious.

Hence we have to be familiar with our mole concept calculations to attempt this question efficiently.

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

Back to list of questions for 2021 A Level H2 Chemistry Paper 1.

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