Chemistry
PAPER 3
PRACTICAL
INSTRUCTIONS TO CANDIDATES
- Answer all the questions in the spaces provided in the question paper
- You are not allowed to start working with the apparatus for the first 15 minutes of the 21/4 hours allowed for this paper. This time is to enable you to read the question paper and make sure you have all the chemicals and apparatus required
- All working must be clearly shown where necessary
- Mathematical tables and electronic calculators may be used
Questions
- You are provided with:
- Solution B, containing 2MHCl
- Solid A, Magnesium ribbon
- Solution D, containing 0.2M NaOH
- Solution X, containing 0.15M Sodium thiosulphate
- You are required to: determine
- Molar heat of reaction between Magnesium and Hydrochloric acid
- Rate of reaction between Hydrochloric and Sodium thiosulphate
- PROCEDURE I
- Place 20cm3 of solution B into 50ml plastic beaker and measure the initial temperature of solution B
Initial temperature of solution B OC (1/2mk) - Add all the Solid A provided to solution B and stir the mixture with a thermometer, measure the maximum temperature of solution.
Maximum temperature of the solution OC (1/2mk) - Transfer the resulting solution formed into a 250ml volumetric flask, add distilled water upto the mark, shake the mixture well and label it as solution C
- Fill the burette with solution C upto 0.0mark, pipette 25cm3 of solution D into a clean conical flask and add 2-3 drops of phenolphthalein indicator.
- Titrate the two solutions until the pink colour turns colourless. Repeat the titration two more times and record the values in table I below
- Place 20cm3 of solution B into 50ml plastic beaker and measure the initial temperature of solution B
-
- Table I (4mks)
I II III Final burette reading Initial burette reading Volume of C used (cm3) - Calculate the average volume of solution C used (1mk)
- Calculate the number of moles of NaOH, Solution D used (1mk)
- Calculate the number of moles of Hydrochloric acid:
- In the average volume of solution C used (1mk)
- In 250cm3 of solution C (1mk)
- In original, 20cm3 of solution B (1mk)
- That reacted with solid A, Magnesium (1mk)
- Determine the molar heat of reaction between Hydrochloric acid, solution B and solid A, Magnesium (4.2Jg-1K-1, Density =1g/cm3) (2mks)
- Table I (4mks)
- PROCEDURE II
- Measure 30cm3 of solution X and transfer into a clean conical flask
- Place the conical flask containing solution to a white piece of paper marked X
- Add 10cm3 of solution B to the content of the conical flask swirl the flask and immediately start a stop watch, record the time taken for the mark X, to be invisible from above. Record the value in the table II below.
- Repeat the procedure (iii) above using the volumes of solution X and distilled water indicated in table II below
-
- Table II (6mks)
Experiment Volume of
solution X (cm3)Volume of
water (cm3)Time
(seconds)1/Time
( Sec-1)1 30 0 2 25 5 3 20 10 4 15 15 5 10 20 - Plot a graph of rate, 1/Time (sec-1) against volume of solution X (Horizontal axis) (3mks)
- From the graph, determine the time taken for mark X to be invisible when 18cm3 of water is used (1mk)
- Table II (6mks)
- You are required to: determine
- You are provided with solid K, which is a mixture of two salts, carry out the following tests on solid K and record observations and inferences in the spaces provided
Place all the solid K in a boiling tube and about 10cm3 of water and shake well, filter the content of the boiling tube into a clean test tube, keep the RESIDUE and FILTRATE for tests below.-
- To about 2cm3 of filtrate and add about 2M Sodium hydroxide until in excess
Observation Inference - Dip glass rod into about 2cm3 of the filtrate and place it in a Non-luminous flame
Observation Inference - To about 2 cm3 of filtrate add about five drops of hydrochloric acid, followed by 3 drops of Barium Chloride solution
Observation Inference
- To about 2cm3 of filtrate and add about 2M Sodium hydroxide until in excess
- Dry the residue between filter paper, Place half of it into a clean dry test tube and heat it strongly
Observation Inference -
- Place the remaining residue into another clean test tube and about 5cm3 of dilute Nitric (v) acid, shake the mixture and test any gases produced using a burning splint. Use the solution formed for tests below.
Observation Inference - To about 1cm3 of the solution add 2M Sodium hydroxide drop wise until in excess.
Observation Inference - To about 2cm3 of solution add 3 drops of Potassium Iodide solution.
Observation Inference
- Place the remaining residue into another clean test tube and about 5cm3 of dilute Nitric (v) acid, shake the mixture and test any gases produced using a burning splint. Use the solution formed for tests below.
-
- You are provided with solution Z in a test tube , use it to carry the tests below and record observations and inferences in the spaces provided.
Divide the solution into four portions.- To the 1st portion, add 2cm3 of water and let the mixture to stand for a minute.
Observation Inference - To the 2nd portion, add all the sodium Hydrogen carbonate provided.
Observation Inference - To the 3rd portion, add 3 drops of acidified Potassium Manganate VII and warm.
Observation Inference -
- Solution Z is suspected to be an Alkanoic acid, describe a test that can be carried out to confirm presence of alkanoic acid using Ethanol and any other necessary reagent and condition provided on the bench.
Test Expected observation - Carry out the test described in d(i) above.
Observation Inference
- Solution Z is suspected to be an Alkanoic acid, describe a test that can be carried out to confirm presence of alkanoic acid using Ethanol and any other necessary reagent and condition provided on the bench.
- To the 1st portion, add 2cm3 of water and let the mixture to stand for a minute.
Confidential
Each student will require: -
- 100cm3 of solution X
- 100cm3 of solution D
- 100cm3 of solution B
- 1g of solid K in stopped container
- 10cm3 of solution Z in a test tube
- 5cm3 of Ethanol in a test tube
- 3cm Mg ribbon (labeled solid A)
- 1 label
- 50ml Burette
- 25 ml pipette
- 2 conical flasks
- 50ml plastic beaker
- Thermometer
- 2 filter papers
- White tile
- Test tube rack with 6 test tubes
- Complete stand
- Test tube holder
- 250ml volumetric flask
- Stopwatch
- 0.5g of NaHCO3
- Wooden splint
- White piece of paper
- Distilled water in wash bottle
- Two boiling tubes
- 10ml measuring cylinder
- Glass rod
Access to:
- 2M NaOH with dropper
- Barium chloride solution with dropper
- Hydrochloric acid with dropper
- Nitric (V) acid with dropper
- Acidified potassium manganate VII with dropper
- Potassium iodide solution with dropper
- Concentrate sulphuric (VI) acid with dropper
- Source of heat
Identity of solutions and solids
- Solution X : - 0.15M Sodium thiosulphate
- Solution D : - 0.2M Sodium Hydroxide
- Solution B : -2M Hydrochloric acid
- Solution Z : - Acetic acid
- Solid K :- Mixture of 0.5g PbCO3 and 0.5g Na2SO4
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