Experimental Setup

Question 1

Why is the solid added to distilled water?

Answer 1

To avoid contamination

Question 2

Explain why mean titre is used in titration by repeating the experiments.

Answer 2

To obtain a more reliable value

Question 3

Improve the titration experiment. (5 ways)

Answer 3

1. Rinse the apparatus and pour the washings in the conical flask
   - ensure no acid left in the beaker
2. Use larger mass of acid
   - reduce percentage error
3. Crush the solid
   - speed up reaction
4. Weigh by difference
5. Add less water initially but add water in the volumetric flask up to the mark

Question 4

Outline a suitable method with apparatus for carrying out an experiment. Decomposition of hydrogen peroxide with metal oxide catalyst. (5 marks)

Answer 4

1. Use weighing scales to weigh the metal oxide (1)
2. Use measuring cylinder to pour hydrogen peroxide solution and water into a conical flask
3. Immerse flask in water bath at 35 ̊C
4. Add oxide to flask and connect flask to gas syringe
5. Measure volume of oxygen every minute for 10 minutes at regular time intervals

Question 5

How to perform titration? (4 marks)

Answer 5

add few drops of indicator (1)
take initial and final reading on burette (1)
swirl the conical flask (1)
add acid until the indicator changes colour (1)

Question 6

Advantages of using volumetric pipettes and measuring cylinder respectively.

Answer 6

volumetric pipette
more accurate / more precise / lower percentage error (1)
measuring cylinder
faster /easier / more convenient (1)