SSCE VCE Chemistry Practical Work: Some students were set the task

Question

Some students were set the task of determining the concentration of acetic acid in a particular brand of vinegar. An outline of the method they used is given below.

1. A burette is filled with a standard solution of sodium hydroxide.
2. The vinegar is diluted by a factor of 10 in a volumetric flask. A pipette is used to transfer 20.00 mL of diluted vinegar to a conical flask and a few drops of phenolphthalein indicator is added.
3. The diluted vinegar is titrated with the base. Titrations are repeated until three concordant results are obtained.

The equation for the reaction is

NaOH(aq) + CH₃COOH(aq) → CH₃COONa(aq) + H₂O(l)

a. The volumetric flask, the burette, the pipette and the conical flask are all rinsed before they are used. Indicate which solution should be used to finally rinse each of these pieces of glassware by ticking your responses in the appropriate boxes below.

| glassware used   | rinse with water | rinse with diluted vinegar solution | rinse with NaOH solution |
|------------------|-----------------|-----------------------------------|-------------------------|
| volumetric flask  |                 |                                   |                         |
| burette          |                 |                                   |                         |
| 20.00 mL pipette |                 |                                   |                         |
| conical flask    |                 |                                   |                         |

b. Why is the vinegar diluted before titrating?

c. Explain why titrations are repeated until three concordant results are obtained.

Some students were set the task of determining the concentration of acetic acid in a particular brand of vinegar - VCE - SSCE Chemistry - Question 6 - 2002 - Paper 1

Worked Solution & Example Answer:Some students were set the task of determining the concentration of acetic acid in a particular brand of vinegar - VCE - SSCE Chemistry - Question 6 - 2002 - Paper 1

a. glassware used

b. Why is the vinegar diluted before titrating?

c. Explain why titrations are repeated until three concordant results are obtained.

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glassware used	rinse with water	rinse with diluted vinegar solution	rinse with NaOH solution
volumetric flask	✔
burette			✔
20.00 mL pipette			✔
conical flask		✔