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A student attempted to determine the concentration of a hydrochloric acid solution - HSC - SSCE Chemistry - Question 28 - 2013 - Paper 1
Question 28
A student attempted to determine the concentration of a hydrochloric acid solution. The following steps were performed. Step 1: A conical flask was rinsed with wate... show full transcript
Worked Solution & Example Answer:A student attempted to determine the concentration of a hydrochloric acid solution - HSC - SSCE Chemistry - Question 28 - 2013 - Paper 1
Step 1
Identify the mistake the student made in step 4 and propose a change that would improve the validity of the result.
Answer
The mistake made in step 4 was that the student blew through the pipette to transfer the sodium carbonate solution. Instead of blowing through the pipette, the student should have touched the end of the pipette to the surface of the conical flask to allow the liquid to flow out naturally, ensuring all of the solution is transferred without introducing air bubbles.
Step 2
Explain the effect of the mistakes made in steps 2 and 3 on the calculation of the concentration of the hydrochloric acid solution.
Answer
In step 2, rinsing the pipette with water would decrease the number of moles of sodium carbonate it contains, as it dilutes the solution. In step 3, not filling the pipette correctly leads to the addition of an incorrect volume of sodium carbonate. Consequently, the titration would yield a lower amount of hydrochloric acid reacting with the sodium carbonate, resulting in an inaccurately higher calculated concentration of the hydrochloric acid solution, since the student would assume a greater volume of Na2CO3 was present than was actually there.