Terence Pang

# O Level Chemistry Paper 1: A quick 3 step method to solving simple mole questions

Below is a sample question of O Level Chemistry Paper 1 MCQ

Mole questions can be easily solved with 3 steps

Find no. of moles from given information. Since 147 g is given, we find no. of moles using mass/molecular mass which can be found from periodic table. In this case, the relative molecular mass of potassium chlorate is 39 + 35.5 + 16x3

Find no. of moles of unknown using mole ratio. In this case, the mole ratio of potassium chlorate to oxygen is 2:3. So we take 1.2 x 3/2 to get 1.8 mols

Use the relevant formula to find the final answer. In this case, we are finding volume of gas, so the formula is no. of moles = vol of gas / 24 dm^3 .

With these 3 steps, we can arrive at the ans of 43.2 dm^3. As a benchmark, you should be able to solve this question in no more than a minute.

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