Questions
Instructions to the candidates:-
- Answer all the questions
- Mathematical tables and electronic calculators may be used.
- All working MUST be clearly shown where necessary.
- Use the first 15 minutes of the 2 ¼ hours to ascertain you have all the chemicals and apparatus that you may need.
QUESTION 1
- You are provided with solution K and L
- Solution K is 1M H2SO4
- Solution L contains 8.7g of the hydroxide of metal M {with formulae MOH] in 600cm3 of the solution
- You are required to carry out the experiment to determine;
- Concentration of solution L
- R.A.M of metal M
Procedure
- Measure 75cm3 of solution K and put into a clean 250cm3 volumetric flask and add distilled water up to the mark
-label this solution W - Fill a clean burette with solution W
- Pipette 25cm3 of solution L into a clean conical flask and add 2 drops of phenolphthalein indicator
- Titrate the solution W in the burette against solution L in the conical flask and record the results in the table below
- Repeat {3} and {4} above as you fill the table below.
TABLE 1
I | II | III | |
Final burette reading {cm3} | |||
Initial burette reading {cm3} | |||
Volume of solution W used {cm3} |
[4mks]
- Calculate the;
- Average volume of solution W used [1mk]
- Concentration of solution W [1mk]
- Number of moles of solution W that reacted with each 25cm3 portion of solution L {2mks]
- Calculate the;
- Number of moles of the metal hydroxide {MOH} in solution L that reacted with each portion of solution W [2mks]
- Concentration of solution L [1mk]
- Number of moles of the metal hydroxide [MOH]in 600cm3 of solution L [2mks]
- R.A.M of metal M [2mks]
[0=16, H=1]
QUESTION 2
You are provided with solution N and P
- Solution N is 2M HCl
- Solution P is 0.16M sodium thiosulphate
- You are required to carry out the experiment below to determine how concentration affects the rate of reaction between HCl and sodium thiosulphate solutions
PROCEDURE
- Fill a clean burette with solution P.
- Measure 25cm3 of the solution P from the burette into a clean 100cm3 glass beaker and place on a white piece of paper with a cross[x] marked on it
- Add 10cm3 of solution N into it and immediately start a stop watch and note the time taken for the cross beneath the mixture to become invisible
- Clean the 100cm3 beaker and measure into it 20cm3 of solution P form the burette, and add 5cm3 of distilled water into the solution solution
- Repeat step [2] above and note the time taken for the cross to become invisible
- Repeat the experiment using volumes indicated on the table below and as you record the results
TABLE 2
Expt | 1 | 2 | 3 | 4 | 5 |
Volume of solution p(cm3) | 25 | 20 | 15 | 10 | 5 |
Volume of water added to solution p{cm3} | 0 | 5 | 10 | 15 | 20 |
Volume of solution N | 10 | 10 | 10 | 10 | 10 |
Time taken for the cross to become invisible [in seconds] | |||||
1/t S-1 |
(4mks)
- plot a graph of 1/t against volume of solution P on the grid provided [3mk]
- From the graph
- Determine the time taken for the cross to become invisible when 12.5cm3 of solution P is used [2mks]
- Explain the effect of concentration on the rate of reaction between HCl and sodium thiosulphate solution [2mks]
QUESTION 3
- You are provided with solids Q and R
- You are required to carry out the tests below as you record your observations and inferences
- SOLID Q
-Add about 5cm3 of distilled water to solid Q, shake the mixture thoroughly for a while and then filter it
NOTE: Retain both the filtrate and the residue for the tests below
- SOLID Q
TEST | OBSERVATION | INFERENCES | ||
A | i | Divide the filtrate into 4 portion To the first portion, add 4 drops of NaOH |
||
ii | Scoop the 2nd portion on a metallic spatula and ignite on a non-luminous flame |
|||
iii | To the 3rd portion, add 2 drops of Pb{NO3}[aq] | |||
iv | To the 4th portion ,add acidified KmnO4 | |||
B | i | Put the residue in a test tube and add about 2cm3 of HNO3 | ||
ii | To the mixture in b{i} above, add 2 drops of KI solution | |||
ii | SOLID R | |||
TEST | OBSERVATION | INFERENCES | ||
A | i | Scoop a portion of solid R on a Metallic spatula and burn on a Non-luminous flame |
||
B | i | Put the remaining portion of solid R into a clean test tube and add about 3cm3 of distilled water, shake and divide into 2 portions |
||
ii | To the 1st portion, add 2 drops of acidified KMnO4 and warm | |||
iii | To the 2nd portion add NaCO3 |
Confidential
- Each student should be supplied with the following
- Burette
- Pipette
- Pipette filler
- Filter funnel
- White tile
- Clamp and stand
- 2 conical flask
- 100cm3 glass Beaker (empty)
- Stop watch
- 100cm3 measuring cylinder
- 10cm3 measuring cylinder
- 250cm3 volumetric flask
- Metallic spatula
- 6 clean test tubes
- Test tube holder
- 500ml distilled water
- White piece of paper or filter paper
- 1 filter paper
- 1 labelling paper
- Phenolphthalein indicator
- About 90cm3 solution K
- About 100cm3 solution L
- About 70cm3 solution N
- About 90cm3 solution P
- About 0.5gNaHCO3
- About 1.0g solid Q
- About 0.5g solid R
- Each student should have access to the following solutions:
- Mean of heating
- 2M NaOH
- 2M HNO3
- Pb(NO3)
- Acidified KMNO4
- Potassium iodide solution
NB: the above solutions should be supplied with a dropper each.
- SOLUTIONS PREPARATION AND SOLID MEASUREMENTS
- SOLUTION K IS 1M H2SO4
- SOLUTION L IS 0.36 M NaOH CONTAINING 14.4g OF NAOH IN 1 LITRE OF THE SOLUTION
- SOLUTION N IS 2M HCl
- SOLUTION P IS 0.16 M Na2S2O3(SODIUM THIOSULPHATE)
- SOLID Q IS A MIXTURE OF SODIUM SULPHITE(Na2SO3) AND LEAD (II) CARBONATE (PbCO3) MIXED IN THE RATIO 1:1 (should be thoroughly mixed)
- SOLID R IS MALEIC ACID
Marking Scheme
QUESTION 1
TABLE 1
- complete table CT 1 mk
- decimal point D 1 mk
- accuracy A (tied to school value)1 mk
- principal of averaging 1 mk
-
- Average volume / final accuracy 1(tied to school value)
NB theoretically expected value = 15.0 cm3 - 1M x 75 cm3 ½ mk
250cm3
= 0.3M ½ mk - Ans in (ii)above X ans in (i)above½ mk = ans ½ mk
1000
2MOH(aq) + H2SO4 (aq) → M2SO4(aq) + H2O(l) 1mk
Mole ratio = 2:1 ½ mk
- Average volume / final accuracy 1(tied to school value)
-
- Moles of solution W = 2 x ans in a(iii) ½ mk
- ans in b(i)x 1000½ mk = ans ½mk
25 - ans in (i)x 600 = ans½ mk
25½ mk - 8.7/½ mk= RFM OF MOH½ mk
ans in b (iii)
RAM of metal M = RFM -(16+1) ½ mk= ans½ mk
QUESTION 2
TABLE 2
- complete table CT1mk
- decimal point D 1mk
- trend (increasing time )1mk
- 1/t row completed 1mk
- Graph
Plotting 1mk
Scale 1mk
Straight line touching origin (0,0) 1mk - Correctly read value from the graph 1mk
- Correct reciprocal of value read from the graph 1mk
- Rate at reaction increase with increase in concentration of the sodium thiosulphate because increase in concentration increases number of successfulcollisions
QUESTION 3
- Solid Q
-
Observation inferences A i No white ppt formed ½ mk Ca2+ Mg2+, Pb2+, Al3+ Zn2+ Absent ii Burns with a golden yellow flame Na+ confirmed iii White ppt formed ½ mk Cl-, SO42-, SO32-,CO32-1mk iv KMNO4 decolorized½ mk SO32-, Confirmed1mk B i Effervescence occurs ½ mk CO32-, SO32-1mk ii Yellow ppt formed½ mk
Pb2+ confirmed1mk
-
-
- Solid R
Observation inferences A Burns with a yellow sooty flame½ mk =C = C = , = C = C B i Dissolves½ mk forming a colorless solution½ Polar substance½ mk ii KMNO4 decolorized½ mk ROH, =C = C =, = C = C = ii Effervescence½ mk H+ or RCOOH1mk
- Solid R
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