ACSEE (Form 6) Gases — practice questions

Explore 4 free Gases questions in ACSEE (Form 6) Chemistry. Open each question or exercise to read its content, reference answers and available explanation.

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Gases questions and exercises with answers

Showing questions 1–4 of 4.

A compound of nitrogen and hydrogen is 87.4% nitrogen by mass. Its empirical formula is:Read the answer and worked solution →Order the formula methodRead the answer and worked solution →Correct for water vapourRead the answer and worked solution →Fix the gas law lineRead the answer and worked solution →

Worked practice questions

A compound of nitrogen and hydrogen is 87.4% nitrogen by mass. Its empirical formula is:

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Correct answer: B. NH2

1. Take 100 g: 87.4 g nitrogen and $100-87.4=12.6$ g hydrogen. 2. Divide by relative atomic masses: nitrogen $\dfrac{87.4}{14}=6.243$, hydrogen $\dfrac{12.6}{1}=12.6$. 3. Divide both by the smaller: nitrogen $1$, hydrogen $\dfrac{12.6}{6.243}=2.02$. 4. The simplest whole-number ratio is therefore $1:2$. 5. The empirical formula is NH₂. Forgetting to subtract from 100 to get the hydrogen percentage is the usual first slip. _Source: NECTA ACSEE 2023 Chemistry 132/1, Question 1: Gases_

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Order the formula method

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Steps

Take the percentage of each element
Divide each by its relative atomic mass
Divide all results by the smallest
Round to the simplest whole-number ratio
Write the empirical formula
Divide the molecular mass by the empirical mass
Multiply the empirical formula by that factor

Instructions

Tap the steps in the order you carry them out.

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Correct for water vapour

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Questions

Hint
total minus the vapour pressure
Unit
mmHg
Answer
742.5
Question
Total 760 mmHg, water vapour 17.5 mmHg. Dry gas pressure?
Hint
divide by 760
Unit
atm
Answer
0.934
Question
A gas is at 710 mmHg. In atmospheres, to 3 d.p.?

Instructions

Apply Dalton's law and key in the answer.

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