Home Teachers' Resources CHEMISTRY PRACTICAL GUIDE- KCSE CHEMISTRY PAPER 3 BEST GUIDE

CHEMISTRY PRACTICAL GUIDE- KCSE CHEMISTRY PAPER 3 BEST GUIDE

CHEMISTRY PRACTICAL GUIDE

SPECIFIC OBJECTIVES OF CHEMISTRY PRACTICAL;
i. To test if the student is able to select & handle apparatus for use in an experimental work
ii. To test if the student is able to use his/her theoretical understanding of chemistry to make
accurate observations and draw conclusions from those observations
iii. To test if the student is able to make accurate measurements
AREAS COMMONLY TESTED IN PRACTICAL;
1. Qualitative analysis (organic & inorganic)
2. Quantitative analysis
3. Graphical work
A) QUALITATIVE ANALYSIS
Refers to the process of carrying out chemical tests on substances with the sole aim of
identifying them
TO BE ABLE TO GET GOOD RESULTS;
a) Accurately identify the test reagents
b) Identify what these reagents test
c) Predict the expected results
I. INORGANIC
Test for cations (12 cations involved; Na+, K+, NH4
+, Ca2+, Ba2+, Mg2+, Al3+, Zn2+,
Pb2+, Cu2+, Fe2+ & Fe3+)
1) Addition of NaOH drop wise until in excess
Observation Inference
 White precipitate, soluble in excess
OR
 White precipitate, insoluble in excess
OR
 No white precipitate
OR
Zn2+, Al3+, Pb2+ ZAP
Mg2+, Ca2+
Na+, K+, NH4
2
 Blue precipitate, insoluble in excess
OR
 Green precipitate, insoluble in excess
OR
 Brown precipitate, insoluble in excess
Cu2+
Fe2+
Fe3+
2) Addition of aq. Ammonia drop wise, until in excess
Observation
Inference
 White precipitate, soluble in excess
OR
 White precipitate, insoluble in excess
OR
 No white precipitate formed
OR
 Light blue precipitate, soluble in excess to give a deep blue solution
OR
 Green precipitate, insoluble in excess
OR
 Brown precipitate, insoluble in excess
Zn2+
Al3+, Pb2+, Mg2+
Na+, K+, Ca2+
Zn2+, Al3+, Pb2+, Mg2+ Absent
Cu2+
Fe2+
Fe3+
3) Dip a nichrome wire into the solution and burn in a non luminous flame (Flame test for cations)
Observation
Inference
 Burns with a yellow flame
OR
Na+
3
 Burns with a red flame
OR
 Burns with a purple flame
OR
 Burns with a white flame
Ca2+
K+
Mg2+
4) Addition of three drops of H2SO4/Na2SO4/K2SO4
Observation
Inference
 White precipitate
Ca2+, Ba2+, Pb2+
5) Addition three drops of HCl/NaCl/KCl
Observation
Inference
 White precipitate
Pb2+, Ag+
6) Addition of two drops of potassium iodide
Observation
Inference
 Yellow precipitate
Pb2+
4
TEST FOR ANIONS (SIX ANIONS; SO42-, SO32-, CO32-, Cl-, NO3- & HCO3-)
1) Addition of two drops of barium nitrate
Observation
Inference
 White precipitate
SO42-, SO32-, CO32-
2) Addition of two of drops of barium nitrate followed by five drops of nitric (V) acid
Observation
Inference
 White precipitate, dissolves upon addition of nitric (V) acid
 Bubbles of colourless gas produced
OR
 White precipitate, insoluble upon addition of nitric (V) acid
SO32-, CO32-
SO42-
3) Addition of two drops of acidified barium nitrate
Observation
Inference
 White precipitate.
SO42-
5
4) Addition of three drops of lead (II) nitrate
Observation
Inference
 White precipitate.
SO42-, SO32-, CO32-, Cl-
5) Addition of two drops of lead (II) nitrate followed by five drops of nitric (V) acid
Observation
Inference
 White precipitate, soluble on addition of nitric (V) acid.
 Bubbles of colourless gas
OR
 White precipitate, insoluble upon addition of nitric (V) acid
SO32-, CO32-
SO42-, Cl-
6) Addition of two drops of lead (II) nitrate, followed by worming
Observation
Inference
 White precipitate, soluble upon worming
OR
 White precipitate, insoluble upon worming
Cl-
SO42-, SO32-, CO32-
6
7) Addition of two drops of acidified lead (II) nitrate
Observation
Inference
 White precipitate
SO42-, Cl-
8) Addition of two drops of acidified potassium dichromate (VI)
Observation
Inference
 Bubbles of colourless gas,
 Colour of H+/K2Cr2O7 turns from orange to green
OR
 Bubbles of colourless gas
 H+/K2Cr2O7 retains its orange colour
SO32-
CO32-
7
9) Take about ½ of the solid provided into a dry test tube and heat it gently then strongly
Observation
Inference
 Colourless liquid formed on upper cooler parts of the test tube
 Blue litmus paper turns red and red litmus paper remains red
 Red litmus paper turns blue & blue litmus paper remains blue
 Bubbles of colourless gas that blows of a burning splint
 Brown fumes
 Relights a glowing splint
 Residue white when cold & yellow when hot
 White solid formed on cooler parts of test tube
The solid is hydrated
Acidic gas produced
NH4+
CO32-/HCO3-
NO3-
NO3-
ZnO formed
Contains a solid that sublime
10) Put the solid into a boiling tube, add about 10ml of distilled water and shake
Observation
Inference
 Dissolves to form a colourless solution
The solid is soluble in water
Cu2+, Fe2+, Fe3+ absent
8
11) Put the solid into a boiling tube, add water, shake then filter
Observation
Inference
 Partially dissolves to form a white residue and a Colourless filtrate
The solid is a mixture of soluble and insoluble salts.
Cu2+, Fe2+, Fe3+ absent both in the residue & in the filtrate
12) Transfer the residue from filter paper using a spatula into a boiling tube, add about 2 ml of nitric (V) acid
Observation
Inference
 Bubbles of colourless gas
 The solid dissolves
SO32-, CO32-
II. ORGANIC
1) Put the solid in a metallic spatula and burn it in a Bunsen burner flame
Observation
Inference
 Melts,
 Burns with a blue non sooty flame
OR
 Melts,
 Burns with a yellow/sooty flame
NB; Melts is not a must to be observed, only if it is observed
C=C / C= C absent
C=C / C= C
9
2) Put 4 drops of the liquid on a watch glass and burn it
3) Put the liquid in a boiling tube, add water then shake
Observation
Inference
 Miscible, forming uniform solution
Polar organic compound
4) Put the solid into a boiling tube, add about 10 ml of distilled water and shake
Observation
Inference
 Dissolves to form a colourless solution
Polar organic compound
5) Put the solid into a boiling tube, add ethanol & shake
Observation
Inference
 Dissolves to form a colourless liquid
Polar organic compound
Observation
Inference
 Burns with a blue non sooty flame
OR
 Burns with a yellow sooty flame
C=C / C= C absent
C=C / C= C
10
6) Determine the pH of the solution provided (Use of universal indicator)
Observation
Inference
 pH=6.5
OR
 pH=7
OR
 pH=2
OR
 pH=8
OR
 pH=14
Weakly acidic
Neutral
Strongly acidic
Weakly alkaline
Strongly alkaline
NB; 4 to 6.5 is weakly acidic, 1 to 3 is strongly acidic, 8 to 10 is weakly alkaline & 11 to 14 is strongly alkaline. This will help you with other pH values that have not been included under the observation column
7) Add 4 drops of acidified potassium manganate (VII)
Observation
Inference
 Purple potassium manganate (VII) is decolorized
C=C / C= C , R-OH
11
8) Add 4 drops of acidified potassium dichromate (VI)
Observation
Inference
 Potassium dichromate (VI) turns from orange to green
R-OH
NB; used for testing for R-OH, not for double and triple bonds
9) Addition of 4 drops of bromine water
Observation
Inference
 Bromine water is decolorized
C=C / C= C
10) Add the solid Na2CO3/NaHCO3 provided into the solution
Observation
Inference
 Bubbles of colourless gas produced
H+/R-COOH
12
CURRENT TRENDS IN SETTING
1) (Compiled from Nyakach girls Chemistry contest 2018 edition)
You are provided with;
o Solid Q suspected to be Zinc Sulphate
o 2 M Sodium hydroxide solution
o 2 M Aqueous ammonia
o 2 M Nitric (V) acid
o 0.5 M Barium Chloride solution
o Distilled water
(a) Using the provided chemicals, write down three tests and expected observations to completely confirm the identity of solid Q
(i) Test 1 Expected observation(s)
Put solid Q into a boiling tube, add
10 ml of distilled water, then shake White precipitate, soluble in excess
to dissolve solid Q. Divide the solution
formed into 3 portions; To the 1st portion,
add sodium hydroxide drop wise until in
excess
(ii) Test 2 Expected observation(s)
To the 2nd portion, add aqueous White precipitate, soluble in excess
ammonia drop wise until in excess
(iii) Test 3 Expected observation(s)
To the 3rd portion, add two drops of White precipitate formed upon adding
barium chloride, followed by about barium chloride, the white precipitate
10 ml of nitric (V) acid do not dissolve when acid is added
2) You are provided with;
o Solid R suspected to be Aluminium Chloride
o 2 M Sodium hydroxide solution
o Sodium Carbonate solution
o 0.5 M Lead (II) nitrate
o 0.2 M Barium Nitrate
o Distilled water
(b) Using the provided chemicals, write down four tests and expected observations to completely confirm the identity of solid R
(i) Test 1 Expected observation(s)
Put solid R into a boiling tube, add
10 ml of distilled water, then shake White precipitate, soluble in excess
to dissolve solid R. Divide the solution
formed into 4 portions; To the 1st portion,
add sodium hydroxide drop wise until in
excess
13
(ii) Test 2 Expected observation(s)
To the 2nd portion, add two drops of No white precipitate formed
Sodium carbonate
(iii) Test 3 Expected observation(s)
To the 3rd portion, add two drops of White precipitate is formed
Lead (II) nitrate
(iv) Test 4 Expected observation(s)
To the 4th portion, add two drops of No white precipitate is formed
barium nitrate
3) You are provided with;
o Solid S suspected to be Zinc Sulphate
o 2 M Aqueous ammonia
o Lead (II) nitrate solution
o 2 M Nitric (V) acid
o Barium Nitrate solution
o Distilled water
(a) Using the provided chemicals, write down three tests and expected observations to completely confirm the identity of solid S
(i) Test 1 Expected observation(s)
Put solid S into a boiling tube, add
10 ml of distilled water, then shake White precipitate, soluble in excess
to dissolve solid S. Divide the solution
formed into 3 portions; To the 1st portion,
add aqueous ammonia drop wise until in
excess
(ii) Test 2 Expected observation(s)
Add two drops of lead (II) nitrate White precipitate
(iii) Test 3 Expected observation(s)
Add two drops of barium nitrate followed White precipitate, insoluble when
by about 10 ml of nitric (V) acid acid is added
4) You are provided with;
o Solid T suspected to be Lead (II) nitrate
o 2 M Sodium hydroxide solution
o Sodium Chloride solution
o Aluminium foil
o Red and blue litmus papers
o Distilled water
o Test tube holder
o Source of heat
14
(a) Using the provided chemicals, write down three tests and expected observations to completely confirm the identity of solid T
(i) Test 1 Expected observation(s)
Put solid T into a boiling tube, add
10 ml of distilled water, then shake White precipitate, soluble in excess
to dissolve solid T. Divide the solution
formed into 3 portions; To the 1st portion,
add sodium hydroxide drop wise until in
excess
(ii) Test 2 Expected observation(s)
To the 2nd portion, add two drops White precipitate formed
of sodium chloride
(iii) Test 3 Expected observation(s)
To the 3rd portion, add 6 drops of Bubbles of colourless gas. Red
NaOH, drop a piece of aluminium litmus paper turns blue and blue
foil into the mixture then heat to boil litmus remains blue
and test any gas produced using litmus papers
NB; The theory behind test 3; aluminium foil reduces NO3- to NH4+ then NH4+ formed reacts with NaOH to produce NH3 (KCSE 2012)
5) You are provided with;
o Solid U suspected to be Magnesium Sulphate
o 2 M Sodium hydroxide solution
o 2 M Aqueous ammonia
o 0.5 M Barium Nitrate solution
o 2 M Nitric (V) acid
o Distilled water
(a) Using the provided chemicals, write down three tests and expected observations to completely confirm the identity of solid U
(i) Test 1 Expected observation(s)
Put solid U into a boiling tube, add
10 ml of distilled water, then shake White precipitate, insoluble in excess
to dissolve solid U. Divide the solution
formed into 3 portions; To the 1st portion,
add sodium hydroxide drop wise until in
excess
(ii) Test 2 Expected observation(s)
To the 2nd portion, add aqueous White precipitate, insoluble in excess
ammonia drop wise until in excess
15
(iii) Test 3 Expected observation(s)
To the 3rd portion, add 2 drops of barium White precipitate formed which do not
nitrate followed by addition of about dissolve when the acid is added
10 ml of nitric (V) acid
NB; Forget about barium when using NaOH and aqueous ammonia drop wise until in excess, a mention of Ba2+ will be treated as a contradictory ion (Refer KCSE 2015). This will help test 1 be easier to understand.
6) (Compiled from KCSE 2017)
You are provided with;
o Solid V suspected to be Lead (II) carbonate
o Aqueous sodium sulphate
o 2 M Aqueous ammonia
o 2 M Nitric (V) acid
o Wooden splint
(a) Using the provided chemicals, write down three tests and expected observations to completely confirm the identity of solid V
(i) Test 1 Expected observation(s)
To solid V in a boiling tube, add about Bubbles of colourless gas produced,
5 ml of nitric (V) acid and test for any Burning splint goes off
gas produced using a burning splint. Divide
the solution formed into 2 portions for
tests 2 and 3 below
(ii) Test 2 Expected observation(s)
To the 1st portion, add ammonia solution drop White precipitate insoluble in
wise until in excess excess
(iii) Test 3 Expected observation(s)
To the 2nd portion, add 2 drops of sodium White precipitate formed
sulphate
7). (An exam sample; for inorganic compounds)
You are provided with
 Solid Y, 0.5 g
 Sodium hydroxide
 Aqueous ammonia
 Solution F; aqueous lead (II) Nitrate
 Distilled water in wash bottle
 Source of heat
a) Describe the appearance of solid Y (1 mk)
 Colourless crystals
16
b) Add about 10 cm3 distilled water to substance Y in a boiling tube and shake
Observation
Inference
Dissolves to form a colourless solution
(
Solid Y is soluble in water
(
c) Substance Y is suspected to be calcium chloride
From the reagents provided and results in procedure (b) above select and describe three tests that could be carried out consecutively to confirm whether substance Y is indeed calcium chloride. Write the tests and expected observations in the spaces provided.
Test 1
Description of test
Expected observation
Divide the solution formed in (b) into 3 portions; To the 1st portion, add sodium hydroxide drop wise until in excess
(1mk)
White precipitate, insoluble in excess
(1mk)
Test 2
Description of test
Expected observation
To the 2nd portion, add ammonia solution drop wise until in excess
(1mk)
No white precipitate is formed
NB; Don’t think about barium ions when using NaOH & Aq. Ammonia solutions until in excess
(1mk)
Test 3
Description of test
Expected observation
To the 3rd portion, add 2 drops of lead (II) nitrate followed by warming
(1mk)
White precipitate that dissolves upon warming
(1mk)
17
d) Carry out the tests described in (c) above using substance Y and record the observations and inferences in the spaces provided.
NB; Remember that you were told that the solid is suspected to be CaCl2, this gives room for it to be something else as well. Let’s therefore assume that the actual salt that was provided was MgCl2
i) Test 1
Observation
Inference
White precipitate, insoluble in excess
(1 mk)
Mg2+, Ca2+
(1mk)
ii) Test 2
Observation
Inference
White precipitate, insoluble in excess
(1 mk)
Mg2+
(1mk)
iii) Test 3
Observation
Inference
White precipitate that dissolves upon warming
(1mk)
Cl-
(1mk)
8). You are provided with the following to use in this question;
o Solid X
o Bromine water
o Distilled water
o Acidified potassium dichromate (VI) solution
Solid X is suspected to be a polar saturated alkanol
a) Describe three consecutive tests you would carry out to confirm whether solid X is a polar saturated alkanol
18
(i) Test 1 Expected observation(s)
Place solid X into a boiling tube, add Solid X dissolves forming a colourless
5ml of distilled water and shake solution
(ii) Test 2 Expected observation(s)
To a portion of the solution formed in Bromine water is not decolorized
test 1, add 4 drops of bromine water
(iii) Test 3 Expected observation(s)
To another portion of the solution formed Acidified potassium dichromate (VI)
in test 1, add 4 drops of acidified potassium solution turns from orange to green
dichromate (VI) solution
9). You are provided with the following to use in this question;
o Solid W
o Bromine water
o Distilled water
o Solid sodium carbonate
Solid W is suspected to be a polar unsaturated alkanoic acid
b) Describe three consecutive tests you would carry out to confirm whether solid W is a polar unsaturated alkanoic acid.
(i) Test 1 Expected observation(s)
Place solid W into a boiling tube, add Solid W dissolves forming a colourless
5ml of distilled water and shake solution
(ii) Test 2 Expected observation(s)
To a portion of the solution formed in Bromine water is decolorized
test 1, add 4 drops of bromine water
(iii) Test 3 Expected observation(s)
To another portion of the solution formed Bubbles of colourless gas produced
in test 1, add solid sodium carbonate
10). (Full exam format. Compiled from KISIOMI Chemistry joint examinations; 2018)
You are provided with the following to use in this question;
o Solid Z
o Bromine water
o Distilled water
o Acidified Potassium manganate (VII) solution
Solid Z is suspected to be a polar unsaturated organic compound
19
(a) Describe three consecutive tests you would carry out to confirm whether solid Z is polar and unsaturated.
i) Test I
Description of Test
Expect Observation
Place solid Z into a boiling tube, add Solid X dissolves forming a colourless
5ml of distilled water and shake solution
(½mk)
Solid Z dissolves forming a colourless
solution
(½mk)
ii) Test 2
Description of Test
Expect Observation
To a portion of the solution formed in
test 1, add 4 drops of acidified potassium decolorized
manganate (VII)
(1mk)
potassium manganate (VII) is deolourized
(1mk)
iii) Test 3
Description of Test
Expect Observation
To another portion of the solution formed
in test 1, add 4 drops of bromine water
(½mk)
Bromine water is decolourized
(½mk)
(b) Carry out the tests outlined in part (a) and record the observations and inferences
i)
Test I
Observation
Inferences
Solid Z dissolves forming a colourless solution
(½mk)
Polar organic compound
(½mk)
(ii)
Test 2
Observation
Inferences
Potassium manganate (VII) decolourizes
(½mk)
C=C / C= C , R-OH
(1mk)
20
(iii)
Test 3
Observation
Inferences
Bromine water decolourized
(1mk)
C=C / C= C
(1mk)
QUANTITATIVE ANALYSIS
CALCULATIONS
CONDITIONS;
 Students MUST transfer the values intact, that is, if the answer above is to 4 d.p. and should be used in the subsequent working, therefore the student cannot round it off in the air and use it when it is now 3 d.p
 Answers to at least 4 decimal places is OK either rounded off or truncated (chopped off)
 Presenting two different workings attracts full penalty on that particular question
 RAM & RFM should not have units on the answer
GRAPH WORK
CONDITIONS;
 The scale chosen should be able to accommodate all the points in the table and it should have consistent scale intervals
 Label, units are not necessary as units would attract penalties e.g., just stating Time is sufficient, not a must to state Time (seconds)
 Scale should be big enough to cover at least ½ of the grid provided, that is, the student should ensure that he/she uses at least ½ of the big boxes on the vertical & on the horizontal axes
 Students should avoid committing zero at the origin; it is safer that way
 Total coincidence of ruler with grid lines when doing y- and x-axes lines, extra keenness.
 Points should be plotted intact ie, as they appear on the table
 The curve/line should pass through the initial plot, as this was the first experiment done under a lot of purity.
 Use broken lines when reading from a graph
 Temperature graphs (temperature axis) are normally broken but not ΔT graphs.
21
SOLUBILITY & SOLUBILITY CURVES
Solubility; Maximum mass of solute required to saturate 100 g of solvent at a given temperature
Solubility curve; a graph of solubility against temperature for a particular solute
EXPECTED SHAPES FOR SOLUBILITY CURVES;
NB;
i. Do a curve of best fit, don’t use a ruler & don’t look for points
ii. No extrapolation of a curve (don’t extend a curve)
iii. Temperature values in the table of whole numbers are better than 1dp
ENERGY CHANGES (THERMOCHEMISTRY)
TABLE FOR THERMOMETER READINGS
o Thermometer readings of whole numbers are convenient and safe
1) ENTHALPY OF SOLUTION
Definition; the enthalpy change that occurs when one mole of a substance completely dissolves in water
22
EXPECTED SHAPES FOR ENTHALPY OF SOLUTION
a) For exothermic processes
When no break in temperature readings When there is break in temperature readings
TABLE WITH A BROCKEN READING
TABLE WITHOUT A BROCKEN READING
b) For endothermic processes
When no break in temperature readings When there is a break in temperature readings
2) ENTHALPY OF DISPLACEMENT
Definition; the enthalpy change that occurs when one mole of a substance is displaced from a solution of its ions
23
EXPECTED SHAPES FOR ENTHALPY OF DISPLACEMENT
a) For exothermic processes
When no break in temperature readings When there is break in temperature readings
b) For endothermic processes
When no break in temperature readings When no break in temperature readings
3) ENTHALPY OF NEUTRALIZATION
Definition; the enthalpy change that occurs when one mole of H+ ion from an acid is completely neutralized by an alkali to form one mole of water
EXPECTED SHAPES FOR ENTHALPY OF NEUTRALIZATION
24
For exothermic processes For endothermic processes
NB; V1 is the volume of the acid/base that completely neutralize the other
ΔH= mcΔT
RATES OF REACTION;
Definition; Change in concentration of reactants/products per unit time
RATES TABLE
 Time readings of whole numbers are better than 1 or 2 dp readings
 values should be to 3 dp & consistent unless for cases where values work out to less than 3 dp
 Temperature or time readings in the table must either increase or decrease continuously
EXPECTED SHAPES FOR RATES
The shape can either be a straight line or a smooth curve depending on the quantities being plotted
e.g,
(i) Effect of concentration on the rate of reaction is a straight line from origin
(ii) Effect of temperature on the rate of reaction is a smooth curve
COMPILED BY ABUNA O. D

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