WAEC 2023 Chemistry 3 (Practical Alternative A) Legit Answers

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(1a)
Volume of pipette used, VA = 25.0cm³
Indicator Used = Methyl Orange

[TABULATE]

Burette Reading | Rough titre | 1st titre | 2nd titre |

Final Burette reading (cm³) | 25.60 | 32.80 | 26.40

Initial Burette reading (cm³) | 1.20 | 8.70 | 2.30

Volume of HCL used | 24.40 | 24.10 | 24.10

Average burette reading = (24.10 + 24.10)/2
volume of HCL used = 24.10cm³

3a.
When a few drops of NaOH solution are added to a 2 cm³ solution of Pb(NO3)2 (lead nitrate), the following observation would be made:

A white precipitate of lead(II) hydroxide (Pb(OH)2) would form. Lead(II) hydroxide is insoluble in water and appears as a white solid. The reaction can be represented as:

Pb(NO3)2 + 2NaOH -> Pb(OH)2 + 2NaNO3

The formation of a white precipitate indicates the presence of lead(II) ions in the solution, and the reaction between Pb(NO3)2 and NaOH results in the formation of lead(II) hydroxide.

3aii.
When a few drops of NaOH solution are added to a 2 cm³ solution of Fe2(SO4)3 (iron(III) sulfate), the following observation would be made:

A reddish-brown precipitate of iron(III) hydroxide (Fe(OH)3) would form. Iron(III) hydroxide is insoluble in water and appears as a reddish-brown solid. The reaction can be represented as:

Fe2(SO4)3 + 6NaOH -> 2Fe(OH)3 + 3Na2SO4

The formation of a reddish-brown precipitate indicates the presence of iron(III) ions in the solution, and the reaction between Fe2(SO4)3 and NaOH results in the formation of iron(III) hydroxide.

3b
To determine the melting point of benzoic acid in the laboratory, the following procedure can be followed:

1. Obtain a small amount of benzoic acid sample. Ensure that the sample is dry and free from any impurities.

2. Set up a melting point apparatus, such as a melting point apparatus or a capillary tube.

3. Clean and dry a capillary tube, which is a thin glass tube used to hold the sample. Fill the capillary tube with a small amount of powdered benzoic acid, ensuring it is compact and uniform.

4. Insert the capillary tube into the melting point apparatus, making sure it is secure.

5. Gradually heat the melting point apparatus while observing the benzoic acid sample through the magnifying lens.

6. As the temperature rises, observe the sample for any signs of melting. Initially, the powdered benzoic acid will remain solid, but at a specific temperature, the sample will start to melt and form a liquid phase.

7. Note the temperature at which the first signs of melting are observed.

8. Repeat the experiment at least two more times using fresh samples to ensure the accuracy and consistency of the obtained melting point values.

By following this procedure, the melting point of benzoic acid can be determined in the laboratory.