INSTRUCTIONS TO CANDIDATES
- Answer ALL questions in the spaces provided in each question.
- Mathematical tables and electronic calculators may be used for calculations.
- all working must be clearly shown where necessary.
FOR EXAMINERS ONLY
QUESTION |
MAXIMUM SCORE |
CANDIDATES SCORE |
1 |
15 |
|
2 |
13 |
|
3 |
12 |
|
Total |
40 |
|
QUESTIONS
- You are provided with
- 2.0M NaoH solution labelled B
- Sulphuric(VI) acid solution labelled A `
You are to:
- Prepare a dilute solution of NaoH solution.
- Determine the concentration of in moles per litre.
PROCEDURE 1
- Using a pipette 25.0cm3 of solution B and place it into 250cm3 volumetric flask.
- Add about 200cm3 of distilled water and share well.
- Add more water to make up to 250cm3mark. Label this solution C
- Calculate the concentration of the dilute solution C in moles per litres. [2mks]
PROCEDURE 2
- Fill the burette with solution A and record the readings in the table below.
- Pipette 25cm3 of dilute solution C and place it into 250ml conical flask.
- Add 2-3 drops of phenolphthalein indicator.
- Titrate with solution A.
- Record your results in the table below.
- Repeat the titration two or more times and complete the table.
I |
II |
III |
|
Final burette reading (cm3) |
|||
Initial burette reading(cm3) |
|||
Volume of solution A(cm3) |
[4mks]
- Determine average volume of the acid (solution A) used. [1mk]
- Determine moles of dilute solution C in the volume used. [2mks]
- Write an equation for the reaction taking place. [1mk]
- Determine the number of moles of A used. [2mks]
- Determine the concentration of A in moles per litre. [2mks]
2. You are provided with the following
- 2M sodium hydroxide solution, solution B
- 2M hydrochloric acid, solution D
You are required to determine the molar enthalpy of neutralization of the acid using sodium hydroxide.
PROCEDURE
- Measure out 20cm3 of acid into a clean plastic beaker.
- Record the temperature of this solution in the table below
- Measure 5cm3 of sodium hydroxide and add it to the hydrochloric acid.
- Stir with the thermometer and record the maximum temperature reached.
- Repeat the above procedure adding 5cm3 portions of sodium hydroxide until the total volume of the solution is 50cm3.
Volume of acid(cm3) | 20 | 20 | 20 | 20 | 20 | 20 | 20 |
Volume of NaoH added cm3 | 0 | 5 | 10 | 15 | 20 | 25 | 30 |
Temperature(ºC)of solution |
[3mks]
You are required to:
- Plot a graph of temperature rise against sodium hydroxide added. [3mks]
- From your graph determine:
- maximum temperature change. [1mk]
- the volume of NaOH that is required for complete neutralization [1mk]
- Calculate the molar enthalpy of neutralization for this reaction. (C=4.2J/g/K) assume density of solution is 1gcm-3) [2mks]
- The theoretical molar heat of neutralization is -57.2kj/mol-1.Compare your value in [ii] above with the theoretical value. Give the reasons for any differences noted between these two values. [2mks]
3. You are provided with solid N carry out the tests below and record your observations and inferences.
- Place a spatula of N in a test tube and add 5cm3 of water and shake well divide the solution in to three portions.
OBSERVATION (1mk) INFERENCE (1mk) - Add sodium hydroxide to the first portion drop wise while observing till in excess
OBSERVATION (1mk) INFERENCE (1mk) - Add ammonia solution to the second portion drop wise until in excess.
OBSERVATION (1mk) INFERENCE (1mk) - Add four drops of potassium iodide solution to the third portion.
OBSERVATION (1mk) INFERENCE (1mk) - Add three drops of acid barium nitrate to the fourth followed by 5 drops of nitric acid
OBSERVATION (1mk) INFERENCE (1mk)
MARKING SCHEME
PROCEDURE 1
1.
- 2 moles →1000cm3 25 × 1=0.05 moles
1000
? 25cm3
0.05 moles-250cm3 0.05 × 1000=0.2m
250
PROCEDURE II
- Complete table 1
- Decimal 1
- Arithmetic 1
- Accuracy 1=0.2
- 12.5 +12.5 + 12.5 =12.5cm3
3 - 0.2 moles→1000cm3 0.2m × 25=0005 moles
1000
25cm3 - 2NaoH [aq]+H2SO4[aq]→NaSO4[aq]+2H2O[l]
- Mole ratio
A:C C=0.0025moles
1:2 A= 0.005 =0.0025 moles
2 - 0.0025→answer a= 0.0025 × 1000
answer a
1000
- 12.5 +12.5 + 12.5 =12.5cm3
2. Table
- Complete table 1
- Decimal point 1
- Trend 1
- Graph
Axis 1/2 - Mk each
Scale 1/2 Mk each
Plotting 1 mk
Curve 1 mk -
- answer from the graph
- Use MCDθ
Mass=50 × 1=50g.
From MCDθ→50g × 4.2J/g/ºC answer in b [i] above.
g - Theoretical value is higher than the obtained value
Heat lost to the surrounding[1mk]
Heat absorbed by the apparatus[1mk]
- Graph
3.[a]
OBSERVATION (1mk) | INFERENCE (1mk) |
It dissolves into a colourless solution | Soluble salt[ NoCu2+,Fe2+ or Fe3+ |
[b]
OBSERVATION (1mk) | INFERENCE (1mk) |
White precipitate soluble in excess [1mk] | Pb2+,Zn2+,Al3+ ions present[ 2mks] for the 3 1mk for 2 0 mk for less than 2 |
[c]
OBSERVATION (1mk) | INFERENCE (1mk) |
White precipitate insoluble in excess[1mk] | Pb2+,Al3+ ions present[1mk] |
[d]
OBSERVATION (1mk) | INFERENCE (1mk) |
No Yellow precipitate formed[1mk] | Pb 2+ ions absent/ Al3+ present[1mk] |
[e]
OBSERVATION (1mk) | INFERENCE (1mk) |
White precipitate [1mk] | SO42- ions[1mk] |
Don’t dissolve on adding nitric acid | |
CONFIDENTIAL
- Burette
- Pipette
- 2 conical flasks
- 120cm3 of 2.0M NaoH labelled B
- 100cm3 0f 0.2M H2SO4 labelledA
- 250cm3 volumetric flask
- A label
- Pipette filter
- Stand and clamp
- 500cm3 distilled water
- Phenolphthalein indicator
- 100cm3 plastic beaker
- Thermometer
- 10cm3 measuring cylinder
- 100cm3 measuring cylinder
- 50cm3 2.0M HCl , Solution D
- 50cm3 2.0M NaoH
- 6 test tubes in a test tube rack
- 0.2g of solid N (Al2(SO4)3]
REAGENTS
- 2M NaoH
- 2M NH4OH
- Ba (NO3) 2solution
- 2M nitric acid
- Potassium iodide solution
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