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Complete combustion of 0.0100 mol of an organic acid produced 0.0200 mol of carbon dioxide - AQA - A-Level Chemistry - Question 7 - 2022 - Paper 3
Question 7
Complete combustion of 0.0100 mol of an organic acid produced 0.0200 mol of carbon dioxide. The same amount of the acid required 20 cm³ of 1.00 mol dm⁻³ NaOH (aq) f... show full transcript
Worked Solution & Example Answer:Complete combustion of 0.0100 mol of an organic acid produced 0.0200 mol of carbon dioxide - AQA - A-Level Chemistry - Question 7 - 2022 - Paper 3
Step 1
Calculate moles of the organic acid
Answer
From the balanced equation of combustion, 1 mol of the organic acid produces 1 mol of carbon dioxide.
Given that 0.0100 mol of the organic acid produced 0.0200 mol of carbon dioxide, we can conclude that the molar ratio of the acid to carbon dioxide is 1:2. Therefore, the organic acid has 2 carboxylic acid groups (COOH).
Step 2
Determine the total moles of NaOH used for neutralisation
Answer
To find the moles of NaOH used, we use the formula:
[ ext{Moles} = ext{Concentration} \times ext{Volume} ]
The concentration is 1.00 mol dm⁻³ and the volume is 20 cm³. First, convert the volume to dm³:
[ 20 \text{ cm}^3 = 0.020 \text{ dm}^3 ]
Now, calculate the moles of NaOH: [ ext{Moles NaOH} = 1.00 \times 0.020 = 0.0200 \text{ mol} ]
Step 3
Identify the formula of the acid
Answer
Since 0.0200 mol of NaOH is required to neutralise the acid which produces 0.0100 mol of the organic acid and demonstrates the presence of 2 carboxylic acid groups, the only formula that matches this profile is C (HOOCCH₂COOH). This acid can release 2 protons in solution, corresponding to the 0.0200 mol of NaOH needed for complete neutralisation.