Chung Cheng High School (Main)
Pure Chemistry ANSWERS
(Acids, Bases & Salts)
25
Duration: 45 minutes
Name: _________________________ Class: ______ Index No.: ____
Date: _________
Section A (MCQ – 8 marks)
1
The pH scale below shows the position of five aqueous solutions P, Q, R and S of equal
concentrations.
P
Q
1
R
7
S
14
pH scale
What could the aqueous solutions be?
A
B
C
D
Ethanoic acid
P
Q
R
Q
Sulfuric acid
Q
P
S
P
Ammonia
S
R
P
S
Sodium Chloride
R
S
Q
R
(
D
)
2
A solution of sodium hydroxide containing universal indicator was bubbled with carbon
monoxide. What will be the colour of the indicator after a long period of time?
A Blue
B Green
C Purple
D Red
( C )
3
Which one of the following lists consists of an acid, a base and a salt?
A H2SO4, NaOH, ZnO
B HCl, HNO3, BaSO4
C HCl, MgO, Na2CO3
D K2SO4, H2O, NH4Cl
(
C
)
4
Which of the following oxides reacts with aqueous sodium hydroxide to give a salt?
A Zinc oxide
B Iron(II) oxide
C Copper(II) oxide
D Calcium oxide
( A )
5
Which of the following should not be used with hydrochloric acid to prepare zinc chloride?
A Zinc carbonate
B Zinc hydroxide
C Zinc metal
D Zinc nitrate
( D )
1
6
An experiment was conducted using the apparatus as shown below. Liquid X is an
aqueous solution which has the ability to conduct electricity.
Bulb
Platinum
Platinum
Liquid X
Which substance, when added into Liquid X, would cause the bulb to light up the
brightest?
A Ammonia
B Ethanoic acid
C Sulfuric acid
D Sugar
( C )
7
There are two unlabelled test-tubes. One contains sodium carbonate solution and the
other contains sodium chloride solution. Which test would you use to identify the
solutions?
A Add sodium hydroxide solution
B Add dilute hydrochloric acid
C Add aqueous ammonia
D Add lead(II) nitrate solution
( B )
8
What gas is produced when magnesium reacts with dilute hydrochloric acid?
A A gas that extinguish a lighted splint with a “pop” sound.
B A gas that forms white precipitate in limewater.
C A gas that turns moist blue litmus red.
D A gas that turns moist red litmus blue.
(
A
)
2
Section B (Structured Questions – 17 marks)
9
Answer the questions (a) to (d) using the list of substances below.
Ammonium chloride
Carbon dioxide
Dilute nitric acid
Copper(II) sulfate
Ammonia
Chlorine
Water
Silver chloride
Carbon monoxide
Dilute hydrochloric acid
Dilute sulfuric acid
Hydrogen
[A substance may be used once, more than once or not at all]
(a) An acid which reacts with lead(II) carbonate to give a gas and a soluble salt.
Dilute nitric acid
(b) A salt that can be prepared by precipitation.
Silver chloride
(c) An acidic oxide.
Carbon dioxide
(d) A gas that is produced when ammonium sulfate crystals is warmed gently with
aqueous sodium hydroxide.
Ammonia
[4]
10 Hydrochloric acid is a strong acid while ethanoic acid is a weak acid.
(a) Describe a simple test to show which is the strong acid and which is the weak acid.
Test the acids using pH meter/pH paper; a strong acid will
give a lower pH than a weak acid. OR
Add a few drops of universal indicator into each acid. A strong acid
will turn indicator red while a weak acid will turn indicator
orange/yellow
[2]
Note: Acid don’t change colour
(b) Describe the difference between strong and weak acids.
[2]
A strong acid is a compound that ionises completely in water to
form hydrogen ions while a weak acid is one that ionises partially
to form hydrogen ions.
Note: ions don’t ionize!
(c) Explain why hydrochloric acid should not be used for removing limescale from steel
pipes.
[1]
Being a strong acid, hydrochloric acid is more likely to react with
iron in the pipe.
3
11 Two investigations were made between Reaction A and B.
Reaction A: dilute sulfuric acid + magnesium ribbon
Reaction B: dilute sulfuric acid + platinum
(a) (i) Based on your knowledge in Chemistry, which reaction(s) will take place? Give a
reason for your choice.
[1]
Reaction A
Magnesium is a reactive metal but not platinum.
(ii) Describe your observation, if any, for Reaction A.
[2]
Effervescence, magnesium ribbon dissolves
(b) State one use of sulfuric acid.
[1]
Any one of the following
- Manufacture of fertilizers
- Manufacture of detergents
- As electrolyte inside car batteries
12 Describe how you will prepare and obtain pure dry sample of the following salts:
(Name the reagents used and describe the procedure)
(a) Lead(II) sulfate
[2]
Mix aqueous lead(II) nitrate with aqueous sodium sulfate
Filter the mixture
Wash the residue with distilled water
Dry the salt between filter papers
(b) Copper(II) sulfate
[2]
Add excess copper(II) oxide to sulfuric acid
Filter to remove excess copper(II) oxide
Heat filtrate till saturated. Allow the solution to cool
Filter to obtain crystals formed and dry between filter papers
4