Chemistry - titration

kazinvictus

2010-02-14 7:18 pm

A concrete cleaning liquid consists essentially of a mixture of water, hydrochlororic acid and a small amount of detergent that has no acid-base properties. The concentration of HCL in the liquid may be determined by titrating it with a base. A chemist analyse the liquid using anhydrous sodium carbonate.

10.6 of anhydrous Na2CO3 is made up to 250mL of solution in a volumatric flask. After thorough mixing, 25.00 mL of this solution is pipetted into a dry conical flask. The concrete -cleaner is added slowly from a burette until the end point is reached, using methyl orange as the indicator. The volume of cleaning liquid required is 22.0 mL.

Q1: Use the data provided to calculate the concentration of HCl in the cleaing liquid.

Q2. Why Na2CO3. 10H2O is used instead of anhydrous sodium carbonate? Explain.

Thanks for help!

回答 (1)

六呎將軍

2010-02-14 7:38 pm

✔ 最佳答案

(1) From the given data, mass of Na2CO3 transferred to conical flask = 1.06g

With no. of moles = 0.01 mole

From equation: Na2CO3 + 2HCl → 2NaCl + CO2 + H2O

2 moles of HCl react with 1 mole of Na2CO3

So no. of moles of HCl = 0.02

With concentration = 0.02/0.022 = 0.909 M

(2) Since anhydrous sodium carbonate is hygroscopic (absorbing moisture from air), its mass may vary in the process of weighing, making an inaccurate result.

參考: Myself

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