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This question is about acids - AQA - GCSE Chemistry - Question 9 - 2021 - Paper 1
Question 9
This question is about acids. Hydrogen chloride and ethanoic acid both dissolve in water. All hydrogen chloride molecules ionise in water. Approximately 1% of ethan... show full transcript
Worked Solution & Example Answer:This question is about acids - AQA - GCSE Chemistry - Question 9 - 2021 - Paper 1
Step 1
Step 2
Step 3
Suggest two improvements to the method that would increase the accuracy of the result.
Answer
- Use a digital burette: This allows for more precise measurement of the liquid being titrated, reducing human error in reading the scale.
- Increase the number of trials: Performing more titrations and averaging the results can give a more accurate concentration value.
Step 4
Calculate the mass of ethanoic acid (H₂C₂O₄) needed to make 250 cm³ of a solution with concentration 0.0480 mol/dm³.
Answer
To find the mass, we use the formula:
Substituting in the values:
ext{Mass} = 0.0480 ext{ mol/dm}^3 imes rac{250 ext{ cm}^3}{1000} imes 90
This results in a mass of:
.
Step 5
Calculate the concentration of the sodium hydroxide solution in mol/dm³.
Answer
From the balanced equation, 1 mole of H₂C₂O₄ reacts with 2 moles of NaOH.
The moles of H₂C₂O₄ used are calculated as follows:
ext{moles H₂C₂O₄} = 0.0480 ext{ mol/dm}³ imes rac{15.00 ext{ cm}^3}{1000} = 0.00072 ext{ mol}
Thus, moles of NaOH = 0.00072 × 2 = 0.00144 mol.
Now, using the volume of NaOH (25.0 cm³ or 0.025 dm³):
ext{Concentration of NaOH} = rac{0.00144 ext{ mol}}{0.025 ext{ dm}^3} = 0.0576 ext{ mol/dm}^3.