4 (a) Acids are used to remove scale - AQA - GCSE Chemistry - Question 4 - 2014 - Paper 3
Question 4
4 (a) Acids are used to remove scale.
4 (a) (i) Give the name of a carbonate in scale.
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Worked Solution & Example Answer:4 (a) Acids are used to remove scale - AQA - GCSE Chemistry - Question 4 - 2014 - Paper 3
Step 1
4 (a) (i) Give the name of a carbonate in scale.
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Answer
One example of a carbonate found in scale is calcium carbonate (CaCO₃).
Step 2
4 (a) (ii) What is the name of the gas?
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Answer
The gas produced when acids react with scale is carbon dioxide (CO₂).
Step 3
4 (b) Complete the displayed structure of ethanoic acid (CH₃COOH).
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Answer
The displayed structure of ethanoic acid is:
H
|
H ─ C ─ C
|
O
||
O
The structure must correctly show the -COOH group.
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Answer
Hydrochloric acid reacts faster than ethanoic acid because it is a stronger acid. This means that it has a lower pH and dissociates more completely in solution, producing more hydrogen ions (H⁺).
Step 5
4 (c) (ii) Suggest why hydrochloric acid should not be used to dissolve scale in kettles.
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Answer
Hydrochloric acid is corrosive; it can damage the kettle's metal components and may lead to leaks or other structural issues.
Step 6
4 (d) Calculate the concentration of the hydrochloric acid.
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Answer
To find the concentration of the hydrochloric acid, we can use the titration formula:
the moles of NaOH used = concentration × volume = 0.200 moles/dm³ × (28.60 cm³ / 1000) = 0.00572 moles.
Since the reaction ratio of HCl to NaOH is 1:1, moles of HCl = 0.00572 moles.
Now calculate the concentration:
Concentration of HCl = moles of HCl / volume of HCl in dm³ = 0.00572 moles / (25.00 cm³ / 1000) = 0.2288 moles/dm³.
