Air or some like to call it Atmosphere is considered a ‘minor’ chapter in GCE O Levels Chemistry examination, so much so that many teachers do not emphasise on their existence, not to mention importance.
As described by my Sec 4 Chemistry students, many of their Chemistry School teachers:
- Ask the students to read textbook on their own
- Give them 1 page summary mindmap or worksheet and ask them to just memorise it
- Never even mention that Air is part of examination
Now, i beg to differ on this. If you are an educator (teacher, HOD or tutor) or even a parent that follows closely with Ten Years Series, you would realised that questions on Air have been appearing in recent year’s GCE O Levels Chemistry Examination.
Many a times, they appear in Section A (Short Questions) of Paper 2, and commonly in the form of Tables, Charts (Pie or Bar) or even Graphs. They are Application-Based questions and require the student to apply their concepts, rather than simply regurgitate what they memorise. TAKE NOTE especially if you are aiming to ACE your Chemistry!
Students must know the essential concepts of this topic well in order to be able to understand and comprehend these application fast, and solve them in limited time in examination conditions.
Let’s check out some questions on Air (Atmosphere):
Question 1:
Unpolluted rain water has a pH of about 6. Which of the following gas causes this pH?
A. Carbon Dioxide
B. Oxygen
C. Nitrogen Dioxide
D. Sulfur Dioxide
&
Question 2:
Which gas is NOT produced when hydrocarbons are burnt in the internal combustion engines?
A. Carbon dioxide
B. Carbon monoxide
C. Hydrogen
D. Oxide of nitrogen
&
Question 3:
Powdered calcium carbonate is commonly placed near the chimneys in coal-burning power station, in order to reduce atmospheric pollution by removing the waste gases. Which waste gas will not be removed by the powdered calcium carbonate?
A. Sulfur trioxide, SO3
B. Nitrogen dioxide, NO2
C. Carbon monoxide, CO
D. Phosphorous (V) oxide, P2O5
Now is your time to do some work. Try out the questions and see how much you know about this topic.
PS: Leave your answers and any suggested solutions in the “Leave a Reply” section below.
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1. D, 2. B, 3. D
I am unsure about qn3!
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sean Reply:
October 28th, 2010 at 3:05 am
See my response below.
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Easy
A – Corresponding acid carbonic acid is a weak acid
A – The rest are all produced except hydrogen (CO2 and CO from complete/incomplete combustion, N oxides from internal combustion engine where N2 and O2 react under high temp and pressure.
C – Calcium carbonate is a base, hence removes acidic oxides. CO is a neutral oxide and will not be removed.
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1. for question 1 hydrogen is answer
2. q-2 phosphorous penta oxide is answer
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sean Reply:
October 28th, 2010 at 3:06 am
Phosphorus penta oxide is considered an acidic oxide which will react with calcium carbonate. Thus it cant be the answer.
Regards,
Sean Chua
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A – carbon dioxide is naturally present in air and hence is not considered a “pollutant”.
c – hydrogen cannot be produced from the combustion of hydrocarbons.
c – carbon monoxide is neutral and as such will not react with carbonates.
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sean Reply:
October 28th, 2010 at 2:51 am
Good answers from you Fabian! Keep up the good work!
To Your Academic Success in Chemistry,
Sean Chua
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i think it’s A, D, D (:
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Sorry, I meant ACC, (mixed up with AAC) , explanations are still the same.
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sean Reply:
October 28th, 2010 at 2:52 am
=)
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A,C,D
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so carbon dioxide is acidic?
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sean Reply:
October 28th, 2010 at 2:53 am
Yes Max.
Carbon dioxide is considered an acidic oxide.
It dissolves in water to form carbonic acid, H2CO3 which is a weak acid.
Regards,
Sean Chua
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1. D -Since pH 6 is considered to be an acid, it is an acid rain. And sulfur dioxide is the main cause of an acid rain.
2. B
3. ? (I’m not sure).
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1. D – Since it has a pH of 6, it is an acid rain. Sulfur dioxide is the main cause of acid rain.
2. C
3. ? (I’m not sure).
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sean Reply:
October 28th, 2010 at 2:56 am
Hi.
Do note that rain water which is slightly acidic is due to the carbonic formed when carbon dioxide dissolves in water.
Carbonic acid is NOT CONSIDERED as acidic rain.
Normally, acidic rain refers to Sulfuric Acid (formed from Sulfur Dioxide) and Nitric Acid (formed from Nitrogen Dioxide).
As such, answer is A for Question 1.
PLEASE NOTE cos this is a major error made by most students.
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Ouestion 1: A
Question 2: D
Question 3: C
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sean Reply:
October 28th, 2010 at 3:04 am
See my response below.
=)
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Andrew is correct. With sulphur dioxide, pH of the rain will be closer to 3. For qn2, Hydrogen will undergo combustion to form steam/water, so hydrogen will not be present.
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sean Reply:
October 28th, 2010 at 3:05 am
Good to see you sharing with the rest. Keep sharing and learning at the same time.
Cheers!
Sean Chua
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C DD
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sean Reply:
October 28th, 2010 at 3:04 am
See my response and suggested solutions below.
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A – it’s always Carbonic Acid. Learnt in Geog class too. Cos H2CO3 is a weak acid, hence ph = 6, weak acid.
C – Hydrogen.
C- Carbon Monoxide (Im not too sure, anyone care to explain?)
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sean Reply:
October 28th, 2010 at 3:04 am
=) cool!
Sean Chua
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1. D
2. A
3. A
Please reply.
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sean Reply:
October 28th, 2010 at 3:03 am
See my response below. Let me know your thoughts.
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1) A – Carbon dioxide occurs naturally in *unpolluted air*, becoming carbonic acid
2) C – H2O, CO2, CO, but never H2.
3) C – All other polluting gases are acidic, and acids will react with carbonates. CO is a neutral but polluting gas.
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sean Reply:
October 28th, 2010 at 3:03 am
=) well done!
Sean Chua
Reply
Good to see all of you contributing and discussing.
The answers are A, C and C.
Q1: A
Reason: Carbon dioxide (never considered as a pollutant) in the air will dissolves in rain water to form carbonic acid which is a weak acid.
Q2: C
Reason: Carbon dioxide is produced due to complete combustion. Carbon monoxide might be produced due to incomplete combustion. Oxides of nitrogen is produced due to reaction between N2 and O2 in the air around the car’s engine which has high temp. Hydrogen is not produced by car’s engine.
Q3: C
Reason: Calcium carbonate is use to remove acidic oxides. Carbon monoxide (CO) is a neutral oxide and does not react with calcium carbonate.
Hope you are learning something here.
PS: Drop me a comment. I would love to hear from you.
May the Force be with you,
Sean Chua
Reply
Titus Reply:
November 11th, 2010 at 6:37 pm
for q2,
The question asked which gas is NOT produced when HYDROCARBONS are burnt in the internal combustion engines?
In your answer you said,
Oxides of nitrogen is produced due to reaction between N2 and O2 in the air around the car’s engine which has high temp
But, N2 and O2 are not HYDROCARBONS right?
Reply
For question 1:
Ans: A
Explanation: Carbon dioxide is an acidic gas which does not pollute waters. As given in the question, water is unpolluted, therefore oxides of nitrogen and Sulphur dioxide (which are pollutants) may be neglected
For question 2:
Ans: C
Explanation: Hydrogen is a gas which can never be produced in internal combustion chambers. only the gases such as carbon dioxide, carbon monoxide and oxides of nitrogen may be produced (besides, if hydrogen would be produced in the chambers it would burn so rapidly that the whole engine would blow up!)
For question 3:
Ans: C
Explanation: Calcium carbonate reacts and thus removes the gases which are acidic (acidic oxides). Carbon monoxide (CO) is not an acidic oxide (it is neutral) and therefore the Calcium Carbonate fails to react and remove the carbon monoxide from the polluted mixture.
Reply if any doubt =D
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