2021 P1 Q10 - Determining Greatest Number of Molecules

Let's take a look at 2021 A Levels H2 Chemistry Paper 1 Question 10.

2021 p1 q10 question

We are required to determine which option contains the greatest number of molecules.

2021 p1 q10 more moles equal more 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

2021 p1 q10 option a

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

2021 p1 q10 option b

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

2021 p1 q10 option c

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

2021 p1 q10 option d

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).

2021 p1 q10 answer

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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