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} |
- 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 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
|
TEST |
OBSERVATIONS |
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 |
|
|
SOLID R
|
TEST |
OBSERVATIONS |
INFERENCES |
(a) |
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 3cm3of 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 |
|
|
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 -
- Average volume / final accuracy 1(tied to school value)
-
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
- Graph
- Solid Q
Observation
inferences
i)
No white ppt formed ½ mk
Ca 2+ Mg2+, Pb2+, Al3+ Zn2+ Absent 1mk
ii)
Burns with a golden yellow flame ½ mk
Na+ confirmed 1mk
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 =@1/2 mks
B(i)
Dissolves½ mk forming a colorless solution½ mk
Polar substance½ mk
ii)
KMNO4 decolorized½ mk
ROH, =C = C =, = C = C =1mk
ii)
Effervescence½ mk
H+ or RCOOH1mk
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