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Form 4 Chapter 7 and 8
FORM 4 CHAPTER 7 ACIDS AND BASES
FORM 4 CHAPTER 8 SALTS
ANALYSIS OF PAST YEAR QUESTIONS FROM 2003 – 2008
Year
Paper No.
Type of
question
Question
No
2003
P2
2004
P3
S E
S
4
2
P2
E
S
2005
P3
E
S
P2
E
5
2006
P3
S
E
4
8
S
P2
E
S
2007
P3
E
S
4
P2
E
S
2008
P3
E
S
P2
E
7
S
P3
E
S
E
10
STRUCTURED QUESTIONS
1.
2004/P2/STRUCTURE/Q5
Table 5 shows Experiment I and II in the preparation of salt.
(a)
State one observation in Experiment I
(b)
……………………………………………………………………………………………………
[1 mark]
Based on Experiment II:
(i)
State the reason why copper(II) oxide powder is added in excess.
………………………………………………………………………………………….......
[1 mark]
(ii)
State how the excess
products.
copper(II) oxide powder can be separated from the
………………………………………………………………………………………….......
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(iii)
(iv)
Form 4 Chapter 7 and 8
State the chemical equation for the reaction that takes place in Experiment II.
………………………………………………………………………………………….......
[1 mark]
Calculate the maximum mass of the salt formed.
Use the information that the relative atomic mass of O =16, S = 32 and Cu = 64.
[2 marks]
(c)
Experiment I is repeated. Sulphuric acid is replaced by hydrochloric acid of the same
concentration. Predict the volume of hydrochloric acid required for a complete reaction.
…………………………………………………………………………………………………….
[1 mark]
(d)
There are several steps in the preparation of the salts in each of the Experiments I and
II. State one difference in the steps between the two experiments.
Experiment I
Experiment II
[1 mark]
2.
2005/P2/STRUCTURE/Q4
Table 4 shows the positive and negative ions in three salt solutions.
Name of Salt
Positive ion
Negative ion
Copper(II) sulphate
Cu2+
SO42-
Sodium sulphate
Na+
SO42-
Lead(II) sulphate
Pb2+
NO3-
Table 4
Use the information in Table 4 to answer the following questions.
(a) What is another name for a positively charged ion?
……………………………………………………………………………………………………
[1 mark]
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(b)
Form 4 Chapter 7 and 8
Name the ions in copper(II) sulphate solution.
………………………………………………………ion
………………………………………………………ion
[1 mark]
(c)
Write the formula for sodium sulphate.
…………………………………………………………………………………………………….
[1 mark]
(d)
When 10 cm3 of 0.5 mol dm-3 sodium sulphate solution is added to excess lead(II)
nitrate solution, a white precipitate is formed.
(i)
Write the chemical equation for the reaction.
………………………………………………………………………………………….......
[2 marks]
(ii)
Describe the chemical equation in (d)(i).
………………………………………………………………………………………….......
………………………………………………………………………………………………
[1 mark]
(iii)
Name the white precipitate
………………………………………………………………………………………………
[1 mark]
(iv)
Calculate the number of mole of sodium sulphate in the solution.
Use the formula : Number of mole = Volume x Concentration
[1 mark]
(v)
Calculate the mass of precipitate formed.
Given that the relative atomic mass of O = 16, S = 32, and Pb = 207.
Use the formula : Mass = Number of mole x Relative molecular mass
[2 marks]
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3.
Form 4 Chapter 7 and 8
2006/P2/STRUCTURE/Q4
(a)
8 g of solid sodium hydroxide, NaOH, is dissolved in distilled water to produce a solution
of 1000 cm3.
The NaOH solution produced has the concentration of 8 g dm-3 and molarity of 0.2
mol dm-3.
(i)
State the meaning of the concentration for the solution produced.
(Ii)
…………………………………………………………………………………………….
[1 mark]
State the meaning of the molarity for the solution produced.
…………………………………………………………………………………………….
[1 mark]
(iii)
(iv)
Write the formula that represents the relationship between the number of mole
(n), molarity (M) and volume (V) for the solution.
…………………………………………………………………………………………….
[1 mark]
Substitute the actual values of the number of mole, molarity and volume of the
NaOH solution into the formula in 3(a)(iii).
[Relative molecular mass of NaOH = 40]
……………………………………………………………………………………………
[1 mark]
(b)
Diagram 4.1 shows the precipitation of the standard solution of NaOH, 0.2 mol dm-3.
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(i)
Form 4 Chapter 7 and 8
What are the two parameters that should be measured accurately to prepare the
standard solution of NaOH?
Parameter I :…………………………………………………………………..……….
Parameter II :……………………………………………………………………………
[2 marks]
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(ii)
Form 4 Chapter 7 and 8
After all the NaOH solution is poured into the volumetric flask, the beaker and
the filter funnel must be rinsed several times with distilled water.
After each rinse, all of this water is transferred into the volumetric flask.
Give one reason for doing this.
……………………………………………………………………………………………
(iii)
(iv)
(v)
…………………………………………………………………………………………….
[1 mark]
What step should be taken to ensure that the meniscus level of the standard
solution is exactly in line with the graduation mark on the volumetric flask.
…………………………………………………………………………………………….
[1 mark]
A volumetric flask is more suitable to be used in the preparation of the standard
solution rather than a beaker.
Why?
…………………………………………………………………………………………….
[1 mark]
Why is the volumetric flask stoppered after the standard solution is prepared?
…………………………………………………………………………………………….
[1 mark]
4.
2003/P3/STRUCTURE/Q2
A student has carried out an experiment to construct an ionic equation for the formation of
lead(II) iodide. The experiment was carried out according to the following steps:
Step I
5.0 cm3 of potassium iodide solution 1.0 mol dm-3 was poured into each test
tube labeled P, Q, R, S, T, U, and V.
Step II
0.5 cm3 of lead(II) nitrate solution 1.0 mol dm-3 was added into test tube P.
Step III
Step II was repeated for test tubes Q, R, S, T, U, and V using the volumes
in Table 1.
Step IV
All the test tubes were put in the rack to allow lead(II) iodide to precipitate.
Test Tube
Volume of lead(II) nitrate
solution 1.0 mol dm-3/cm3
Height of lead(II) iodide
precipitate /cm
P
Q
R
S
T
U
V
Table 1
(a)
Figure 2 shows seven test tubes for the above experiment. Using the ruler given ,
measure the height of lead(II) iodide precipitate in test tubes P, Q, R, S, T, U, and V in
Figure 2. Record the height of the precipitate in Table 1.
[3 marks]
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Form 4 Chapter 7 and 8
(b)
Based on Table 1, draw a graph of the height of the precipitate against volume of
lead(II) nitrate solution on the graph paper on page .
[3 marks]
(c)
On the graph that you have drawn in (b),
(i)
Mark and write the minimum volume of lead(II) nitrate solution needed for
complete reaction with 5.0 cm3 of potassium iodide solution 1.0 mol dm-3.
[3 marks]
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(ii)
(iii)
(d)
Form 4 Chapter 7 and 8
Using the volume obtained in I(i), show the calculation for obtaining the number
of moles of Pb2+ and I- ions that are required for the formation of lead(II) iodide.
Then calculate the number of moles of I- ions that has reacted with 1 mol of Pb2+
ions.
[3 marks]
Write the ionic equation for the formation of lead(II) iodide.
……………………………………………………………………………………………..
[3 marks]
What can you observe about the height of the precipitate in Figure 2?
……………………………………………………………………………………………………..
……………………………………………………………………………………………………..
……………………………………………………………………………………………………..
[3 marks]
(e)
What is your inference based on your answer in (d)?
……………………………………………………………………………………………………..
……………………………………………………………………………………………………..
……………………………………………………………………………………………………..
[3 marks]
(f)
Categorise the ions found in the lead(II) nitrate solution and the potassium iodide
solution used in the experiment into positive and negative ions.
[3 marks]
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Form 4 Chapter 7 and 8
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Form 4 Chapter 7 and 8
FORM 4 CHAPTER ACIDS AND BASES
FORM 4 CHAPTER 8 SALTS
1
2
3
2004/P2/Q5
(a) From pink to colourless or intensity of the pink colour decreases or the container of the
mixture becomes warm or hot
(b) (i) To ensure all the the acid react completely with copper(II) oxide
(ii) By filtering
(iii) CuO + H2SO4
CuSO4 + H2O or
CuO +
2H+
Cu2+ + H2O
(iv) n(H2SO4) = 0.1 x 50/1000
Mass of Cu SO4 = 0.005 x 160
= 0.005
= 8.0 g
(c) 20.0 cm3 or twice the volume of sulphuric acid
(d)
Experiment I
Experiment II
 needs filtering
 no need filtering
 a mixture between two solutions
 a mixture between a solid and
solution
 need to add an indicator
 no need to add an indicator
 experiment is repeated without
 no need to repeat the experiment
using an indicator
 volume of sulphuric acid is added
 solute or CuO is added in excess
accurately
2005/P2/Q4
(a) cation
(b) Cu2+ ions & SO42- ions , H+ ions & OH- ions
(c) Na2SO4
(d) (i) Na2SO4 +
Pb (NO3)2
2NaNO3 +
PbSO4
(ii) I mol of lead(II) nitrate reacts with 1 mol of sodium nitrate to produce 1 mol of
lead(II) sulphate and 2 moles of sodium nitrate
(iii) Lead(II) sulphate
(iv) Number of mole = 10/1000 x 0.5 = 0.005
(v) Mass = 0.005 x (207 + 32 + 16 x 4) or 0.005 x 303 = 1.515 g
2006/P2/Q4
(a)
(i)
Concentration – the quantity or amount of solute (grams) dissolves in a
given volume(1 dm3) of solution
(b)
(Ii)
(iii)
(iv)
(i)
(ii)
(iii)
(iv)
(v)
Molarity – the number of moles of solutes that are present in 1 dm3 of solution.
n = MV(cm3) /1000 or n = MV(dm3)
n = 8/40 = 0.2 mole , M = 0.2 x 1000/1000, M = 0.2 mol dm-3
Parameter I : mass / moles of NaOH
Parameter II : volume of solution or distilled water
No traces of sodium hydroxide is left on the filter funnel or beaker for accurate
concentration or amount of solute used is accurate and not less
Add distilled water drop by drop until the meniscus is at the calibration mark
Measures the volume accurately
To prevent evaporation or evaporation of water can cause the changes in
concentration or easy to swirl the solution
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4
2003/P3/Q2
(a)
Test Tube
Volume of lead(II) nitrate
solution 1.0 mol dm-3/cm3
Height of lead(II) iodide
precipitate /cm
Form 4 Chapter 7 and 8
P
0.5
Q
1.0
R
1.5
S
2.0
T
2.5
U
3.0
V
3.5
1.1
2.2
3.4
4.4
5.5
5.5
5.5
Table 1
(The diagram given is not to scale - please refer to the original SPM question paper for
accuracy of readings)
(b)
(c)
1.
2.
3.
4.
5.
6.
(i)
label of the x-axis – volume(cm3)
label of the y-axis – height of precipitate(cm)
uniform scale
size of graph more than 50%
all points are transferred correctly
smooth graph
Suggested answer:
Height of precipitate
(cm)
Minimum volume- must be written on the graph
(2.5cm3)
Volume of lead(II) nitrate(cm3 )
(ii)
No. of mole (Pb2+) = 2.5 X 1.0 = 0.0025
1000
No. of mole (I-) = 5 X 1.0 = 0.005
1000
(d)
(e)
No. of mole of I- reacted with 1 mol of Pb2+ = 2 mole
(iii) Pb2+ + 2I- → PbI2
The height of precipitate increases gradually from test tubes P to S
The height of precipitate in test tubes T,U,V are the same
In test tubes P, Q, R, and S, more and more yellow precipitate of lead(II) iodide is
formed due to the increasing amount of lead(II) nitrate added to the test tubes or
potassium iodide has not completely reacted with lead(II) nitrate solution
In test tubes T,U,and V, potassium iodide/iodide ions have reacted completely or a
complete reaction has taken place
(f)
Solution
Lead(II) nitrate
Potassium iodide
Positive ions
Pb2+ , H+
K+ , H+
11
Negative ions
NO3- ,OHI-, OH-
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Form 4 Chapter 7 and 8
FORM 4 CHAPTER 7 ACIDS AND BASES
FORM 4 CHAPTER 8 SALTS
ANALYSIS OF PAST YEAR QUESTIONS FROM 2003 – 2008
Year
Paper No.
Type of
question
Question
No
1.
2003
P2
S
2004
P3
E
S
4
2
P2
E
S
2005
P3
E
5
S
P2
E
2006
P3
S
E
4
8
S
P2
E
S
2007
P3
E
4
S
P2
E
S
2008
P3
E
S
P2
E
S
7
P3
E
S
E
10
2003/P2/Q4/SECTION C
(a)
A farmer discovered that his vegetables were not growing well because the soil was
poor and acidic. As a chemistry student, you can help the farmer.
Suggest how the farmer can overcome the problem.
[2 marks]
(b)
Figure 7 shows an incomplete flow chart of cation and anion tests for salt X.
Use the reagents listed below and complete the flow chart to confirm that salt X
contains Pb2+ ions and CO32- ions. Include your observations.
REAGENTS
Dilute hydrochloric acid, dilute nitric acid and lime water
[8 marks]
(c)
You are required to prepare dry magnesium chloride salt. The chemicals supplied are
 magnesium sulphate solutions,
 dilute hydrochloric acid,
 potassium carbonate solution
Describe a laboratory experiment to prepare the salt. In your description, include the
chemical equations involved.
[10 marks]
2.
2005/P2/Q8/SECTION B
(a) The following information is about hydrochloric acid and ethanoic acid.


The pH of 1 mol dm-3 hydrochloric acid solution is 1
The pH of 1 mol dm-3 ethanoic acid solution is 4
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Form 4 Chapter 7 and 8
Explain why these two solutions have different pH values.
[4 marks]
(b)
Figure 8.1 shows two reagent bottles each containing an aqueous solution.
Qualitative analysis can be used to determine the presence of cations and anions in
solutions.
Describe chemical tests that can be used to verify the ions in each solution.
[10 marks]
(c)
A pupil carried out an experiment to investigate the chemical changes that occur to
copper(II) sulphate as a result of reaction P.
The result of the experiment is shown in Figure 8.2.
(i)
The chemical equation for reaction P is as follows:
CuCl2
+
Na2CO3
2NaCl
+ CuCO3
Excess sodium carbonate is added to 50cm3 of 0.5 mol dm-3 copper(II)
chloride.
Given that the relative molecular mass of CuCO3 = 124.
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Form 4 Chapter 7 and 8
Calculate the mass of copper(II) carbonate precipitate formed.
[2 marks]
(ii)
Name solid X and state its colour.
(iii)
Name gas Y and describe a method to verify its identity.
[2 marks]
[2 marks]
3.
2007/P2/Q7/SECTION B
(a)
(b)
(c)
The following are three examples of sulphate salts that can be prepared in the
laboratory.
 Potassium sulphate, K2SO4
 Lead(II) sulphate, PbSO4
 Zinc sulphate, ZnSO4
(i)
From these examples, identify the soluble and insoluble salts.
[2 marks]
(ii)
State the reactants for the preparation of the insoluble salt in 3(a)(i).
[2 marks]
With the aid of a labelled diagram, explain the crystallisation method for preparing a
soluble salt from its aqueous solution.
[6 marks]
Table 7 shows the observations from some tests carried out on salt X.
Test
I : Heating of salt X solid
Observation
A metal oxide is formed and a brown
gas is given off
II : Salt X solution is mixed with excess
A white precipitate which is insoluble in
aqueous ammonia
excess aqueous ammonia is formed
Table 7
Based on the information in Table 7:
(i)
Identify an anion that is present in Test I and describe a chemical test to verify
the anion.
[4 marks]
Identify two cations that are present in Test II and describe a chemical test to
(ii)
verify the cations
[6 marks]
4.
2008/P2/Q10/SECTION C
(a) Table 10 shows the pH values for solutions of acid A and acid B which have the
same concentration.
Acid
pH value
A
1
B
5
Table 10
By using one named example for each acid, explain why the pH values of the acids
are different.
[6 marks]
(b)
Lead(II) sulphate is insoluble in water.
Describe the preparation of lead(II) sulphate in the laboratory.
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Form 4 Chapter 7 and 8
In your description, include the chemical equations involved.
[10 marks]
(c)
The sting of a jelly-fish is alkaline and causes pain.
Suggest one substance that can be applied to the skin to relieve the pain without
causing further injury.
Give three reasons for your suggestions.
[4 marks]
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Form 4 Chapter 7 and 8
FORM 4 CHAPTER 7 ACIDS AND BASES
2003/P2/Q4/SECTION C
1 (a) By adding
- quick lime and slaked lime or calcium oxide and calcium hydroxide to the soil
- fertilizers or organic fertilizers or compost
[calcium phosphate or polyphosphate fertilizers or superphosphate fertilizers]
(b)
Salt X
Cation test
Anion test
Salt X + HNO3
Salt X + HNO3
heat
A colourless solution is formed
Gas evolved is flowed into lime water
Add hydrochloric acid into the colourless solution
Lime water turns chalky / milky
A white precipitate is formed
Confirmed the presence of carbonate ion, CO32-
heat
White precipitate dissolve
Confirmed the presence of lead(II) ions,Pb 2+
(c)
To prepare a dry magnesium chloride salt:Materials : magnesium sulphate solution, dilute hydrochloric acid, potassium
carbonate solution, filter papers, distilled water
Apparatus: 100 cm3 measuring cylinder, filter funnel, evaporating dish, Bunsen
burner, retort stand and clamp, beakers, glass rod,spatula and wire gauze
-
Measure required volume (50 -100 cm3) of molarity(0.5 - 1.0 mol dm-3)
magnesium sulphate solution by using a measuring cylinder and poured into a
beaker
Measure required volume (50 -100 cm3)of molarity(0.5 – 1.0 mol dm-3)
potassium carbonate solution by using a measuring cylinder and poured into
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-
Form 4 Chapter 7 and 8
another beaker
Mix the two solutions and a white precipitate ,magnesium carbonate,(MgCO3)
is formed
K2CO3 + MgCl2 → 2KCl + MgCO3
-
Filter out magnesium carbonate (MgCO3) to remove potassium sulphate or
impurities
-
Magnesium carbonate (MgCO3) is washed with a little cold distilled water
Measure required volume (50 -100 cm3) of molarity(0.5 – 1.0 mol dm-3 )of
hydrochloric acid solution by using a measuring cylinder and poured into a
beaker
Carefully warm the acid
Add magnesium carbonate powder bit by bit by using a spatula and stir using
a glass rod until some of it no longer dissolves
MgCO3 + 2HCl → MgCl2 + H2O + CO2
Remove the unreacted magnesium carbonate (MgCO3) by filtration
Pour the filtrate into an evaporating dish.
Gently heat the salt to produce a saturated solution
Cool the saturated solution until crystals are formed
Filter out the magnesium chloride, MgCl2 , crystals
Wash or rinse the crystals with distilled water
Press the crystals with a few pieces of filter paper to dry them
-
[refer to the Chemistry Practical Book on Page 114 – 115, 119]
2005/P2/Q8/SECTION B
2 (a)
- Hydrochloric acid(strong acid) ionises completely in water to produce a high
concentration of hydrogen ions
- if the concentration of H+ ions is high, the pH value is low
- Ethanoic acid (weak acid) ionises partially in water to produce low
concentration of hydrogen ions
- If the concentration of H+ ions is high, the pH value is high
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(b)
Form 4 Chapter 7 and 8
Test for Cl- in HCl
1. Pour 2 cm3 of hydrochloric acid into a test tube
2. Add nitric acid solution , then add silver nitrate solution
3. A white precipitate is formed, confirmed the presence of chloride ions
Test for NH4+ ions in ammonium chloride solution
1. Pour 2 cm3 of ammonium chloride solution into a test tube
2. Add Nessler’s reagent
3. A brown precipitate is formed, confirmed the presence of ammonium ions
OR
1. Pour 2 cm3 of ammonium chloride solution into a test tube
2. Add dilute sodium hydroxide solution and warm it
3. A colourless gas given off that change moist red litmus paper to blue
Test for Cl- ions in ammonium chloride solution
1. Pour 2 cm3 of hydrochloric acid into a test tube
2. Add nitric acid solution , then add silver nitrate solution
3. A white precipitate is formed, confirmed the presence of chloride ions
(c)
(i)
(ii)
(iii)
n = 0.5 x 50/1000
Mass of CuCl2 = 0.025 x 124
= 0.025
= 3.1 g
Solid X = Copper(II) oxide , black in colour
Carbon dioxide , flow the gas into lime water, lime water turns chalky
2007/P2/Q7/SECTION B
3 (a)
(i)
Soluble salt
Insoluble salt
Potassium sulphate, K2SO4
Lead(II) sulphate, PbSO4
Zinc sulphate, ZnSO4
(ii)
 lead(II) nitrate, Pb(NO3)2 or lead(II) ethanoate(CH3COO)2Pb and
 sodium sulphate or potassium sulphate or all soluble sulphate salt
(b)
The crystallisation method for preparing a soluble salt from its aqueous solution; Filter the solution to remove impurities and pour the filtrate into an
evaporating dish



Gently heat the solution to obtain a saturated solution
Cool the hot saturated solution to allow it to crystallise
Filter and wash or rinse the crystals using distilled water
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
Form 4 Chapter 7 and 8
Press the crystals with a few pieces of filter papers to dry them
[refer to the Chemistry Practical Book on Page 114]
(c)
(i)
Brown gas is nitrogen dioxide gas and the anion is nitrate
Test for nitrate ions
1. Pour 2 cm3 salt X solution into a test tube
2. Acidify the solution with about 2 cm3 of dilute sulphuric acid
3. Add 2 cm3 of iron(II) sulphate solution and shake to mix well
4. Slant the test tube and carefully add concentrated sulphuric acid down the
side of the test tube. Do not shake the test tube.
5. A brown ring is formed
[refer to the Chemistry Practical Book on Page 133]
(ii)
4
The cations :- Magnesium ions, aluminium ions and lead(II) ions (any two ions)
1. Pour 2 cm3 salt X solution into a test tube
2. Add sodium hydroxide solution into the test tube until in excess
3. A white precipitate is formed soluble in excess of NaOH, shows the present
of lead(II) ions or aluminium ions
4. A white precipitate is formed insoluble in excess of NaOH, shows the
present of magnesium ions
OR
1. Pour 2 cm3 salt X solution into a test tube
2. Add potassium sulphate solution or potassium chloride solution or
potassium iodide solution or sulphuric acid or hydrochloric acid into the test
tube
3. A white or yellow precipitate is formed, shows the present of lead(II) ions
4. If no precipitate is formed, indicates the presence of magnesium ions or
aluminium ions
2008/P2/Q10/SECTION C
(a)
Acid A
Hydrochloric acid or sulphuric acid or
nitric acid
Strong acid
Ionises completely in water
HCl → H+ + ClConcentration of H+ is high
(b)
Acid B
ethanoic acid or phosphoric acid
weak acid
Ionises partially in water
CH3COOH ↔ CH3COOConcentration of H+ is low
+ H+
To prepare lead(II) sulphate in the laboratory
Apparatus: beakers, filter funnel , retort stand, measuring cylinder, glass rod
Materials : lead(II) nitrate solution (1.0 – 2.0 mol dm-3), sodium sulphate solution or
any soluble sulphates (0.5 – 1.0 mol dm-3) or (0.5 – 1.0 mol dm-3)
sulphuric acid, filter paper, wash bottle
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Form 4 Chapter 7 and 8

Measure (20 - 100 cm3) of lead(II) nitrate , Pb(NO3) ,solution by using a
measuring cylinder and pour into a beaker
 Then, measure (20 - 100 cm3) of potassium sulphate, K2SO4 , solution by
using a measuring cylinder and pour into another beaker
 Pour the lead(II) nitrate solution into the sodium sulphate solution or
sulphuric acid and stir the mixture
 A white precipitate, PbSO4 , is formed
Pb(NO3)2 + K2SO4 → PbSO4 + 2KNO3 or Pb2+ + SO42- → PbSO4
 Filter the solution mixture
 Wash / rinse the residue/solid/salt with distilled water
 Press the crystals with a few pieces of filter papers to dry them
(c)
Substance that can be used – vinegar
- Vinegar is a weak acid
- vinegar will neutralise the sting of the jelly-fish which is alkali
- does not produce too much heat
- is less corrosive or do not harmful to the skin
20