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The concentration of hydrochloric acid in a solution was determined by an acid base titration using a standard solution of sodium carbonate - HSC - SSCE Chemistry - Question 29 - 2018 - Paper 1
Question 29
The concentration of hydrochloric acid in a solution was determined by an acid base titration using a standard solution of sodium carbonate. (a) Explain why sodium ... show full transcript
Worked Solution & Example Answer:The concentration of hydrochloric acid in a solution was determined by an acid base titration using a standard solution of sodium carbonate - HSC - SSCE Chemistry - Question 29 - 2018 - Paper 1
Step 1
Explain why sodium carbonate is a suitable compound for preparation of a standard solution.
Answer
Sodium carbonate (Na₂CO₃) is a stable compound that does not readily absorb moisture from the air. This property makes it an ideal candidate for the preparation of standard solutions because it allows for accurate weighing without additional variables affecting the mass.
Step 2
Using the data from the table, calculate the concentration of the hydrochloric acid.
Answer
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Calculate the average titre:
Average titre = (22.00 + 21.65 + 21.70 + 21.60) / 4 = 21.7625 mL
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Convert volume from mL to L:
Average titre in L = 21.7625 mL × (1 L / 1000 mL) = 0.0217625 L
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Calculate moles of sodium carbonate (Na₂CO₃):
Moles of Na₂CO₃ = concentration × volume = 0.1050 mol L⁻¹ × 0.02500 L = 0.002625 mol
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Determine moles of hydrochloric acid (HCl) using the reaction stoichiometry (1 Na₂CO₃ : 2 HCl):
Moles of HCl = 0.002625 mol Na₂CO₃ × 2 = 0.005250 mol HCl
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Calculate concentration of HCl:
Concentration of HCl (C) = moles / volume = 0.005250 mol / 0.0217625 L ≈ 0.2418 mol L⁻¹