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# GCE O Level 2011 Oct/Nov Chemistry 5072 (MCQ) Paper 1 Suggested Answers & Solutions

(102)
Tuition given in the topic of Little Miss Loi the Science Tutor (archived) from the desk of at 9:23 am (Singapore time)

Another morning, another booklet, another series of codes sent:

Note: After staring long and hard at the ang moh anomaly that is Q22, I’ve decided to change its answer to A. Reason being that scrap steel, containing a higher percentage (98%) of iron, will lead to a better yield and reduce mining wastes when iron is produced from it via recycling. The highlighted portion would definitely qualify as a correct reason if only it had been included in the original statement – instead of sparking intense debates like this 🙁

Do they tally with yours?

Update: Once again, the list of workings and explanations for each of the answers (where applicable) have been compiled (along with the questions at the end)!

You may access here by clicking the button (if you haven’t yet done so).

2011 O-Level October/November Chemistry 5072 Paper 1 Suggested Solutions

As usual, hopefully this will help in some way to settle some of the debates regarding some of the answers (and hopefully not create more in the process!)

### Revision Exercise

To show that you have understood what Miss Loi just taught you from the centre, you must:

1. Lucius commented in tuition class

2011
Nov
14
Mon
9:37am

1

Could you explain question 8, 22, 24 and 28? Lol

2. Gary Lee commented in tuition class

2011
Nov
14
Mon
9:39am

2

Can you kindly explain 9,22 and 35? Thanks!
Cheers!

3. Dannie commented in tuition class

2011
Nov
14
Mon
9:58am

3

dont agree with qn8; heres my working:
% of C= 72/222 x 100=32.4%
% of H = 18/222 x 100=8.1%
% of Si= 84/222 x 100=37.8%
% of O=48/222 x 100=21.6%
thus, Si has highest % by mass.
so answer should be D rite?

4. April Nguyen commented in tuition class

2011
Nov
14
Mon
10:05am

4

I think the answer for question 3 is B...I mean, ammonium salts are heated with alkalis will give off amonium gas, isnt it right?

• anonymous replied to April Nguyen’s comment

2011
Nov
14
Mon
10:45am

4.1

April Nguyen

question 3 should be D. This is because the question said that ammonia is "only" given off after aluminium foil is added to the hot solution. If the aqueous salt was ammonium nitrate, ammonia gas would have been given off the moment sodium hydroxide was added to it. ( This is QA). Thus, it can be seen that the aqeous salt has nitrate as it gives off ammonia when aluminium foil is added but cannot be ammonium nitrate because ammonia would already have been given off when sodium hydroxide was added. Hence, the only other possible nitrate would be sodium nitrate.

5. April Nguyen commented in tuition class

2011
Nov
14
Mon
10:14am

5

and isnt the answer for 17 is D? I mean, sure, metals from Group I have decreasing melting point down the group but not all alkali metals are from Group I?

6. anonymous commented in tuition class

2011
Nov
14
Mon
10:29am

6

my mark is 38/40 this time round but i think i might be in danger because alot of people found the paper quite easy. could you explain question 22 on the iron and steel thing. why is the answer not A? option 2 seems quite relevant. scrap steel does have a higher percentage of iron than iron ore and hence it has to be recycled to so call "conserve the iron" or something? can explain? thanks!

7. shivaanand commented in tuition class

2011
Nov
14
Mon
10:38am
8. Goh Rui Yi commented in tuition class

2011
Nov
14
Mon
10:44am
9. Anonymous commented in tuition class

2011
Nov
14
Mon
10:57am

9

Can someone please explain qn 22 35 and 37? Shouldn't 37 be D?

10. 2 commented in tuition class

2011
Nov
14
Mon
11:01am

10

Hi can you explain q3,5,12,22? For q3 why is it not ammonium nitrate since ammonia is given off? For q5 shouldn't the electrons become lesser cuz electrons are used to carry charges? For q12 why is it a and not c? They intersect at a point for volume of gas doesn't mean they are same rate isnt it? Doesnt rate refer to the gradient of volume time graph? For q22 I chose d as I thought recycling would not produce less co2 as the co2 produced is due to the reaction of coke with oxygen and not the purity of iron. Thank you!

11. Anonymous commented in tuition class

2011
Nov
14
Mon
11:05am
12. LM commented in tuition class

2011
Nov
14
Mon
11:06am

12

can u estimate the belll curve tis time for a1?

13. X. commented in tuition class

2011
Nov
14
Mon
11:11am

13

yea can someone pls explain Qn 22,
I put my ans as 1,2,3 (option A) I know 1 and 3 is correct cos it's in the TB , but im not sure about 2!

um can someone explain qn 35 too? i put option a too :O

i know for qn 37, the ans is B cos since the number of carbon atoms increases, its harder to burn THUS less flamable. it becomes more viscous as number of carbon atoms increase! so D is wrong.

14. unknown commented in tuition class

2011
Nov
14
Mon
11:12am

14

why qn4 ans is not B? and qn19, why is th ans not B?

15. X. commented in tuition class

2011
Nov
14
Mon
11:13am

15

i hope i can get a1, had 38/40 for this mcq but im not rly confident for paper 2. found this years papers harder than last years ones 🙁 quite a few weird qns i never see before! the qn 22 esp.
depending on chem + bio . my physics cmi one hahahah

16. 2 commented in tuition class

2011
Nov
14
Mon
11:15am

16

Hi can you explain q5,12,22? For q5 shouldn't the electrons become lesser cuz electrons are used to carry charges? For q12 why is it a and not c? They intersect at a point for volume of gas doesn't mean they are same rate isnt it? Doesnt rate refer to the gradient of volume time graph? For q22 I chose d as I thought recycling would not produce less co2 as the co2 produced is due to the reaction of coke with oxygen and not the purity of iron. Thank you ^^

• X. replied to 2’s comment

2011
Nov
14
Mon
12:19pm

16.1

@2: according to my friend,
for qn 5, ans is A cos number of electrons must match the protons! and it doesnt become lesser over time. im not sure if this is the right explanation but i also put my ans as A.
for qn 12 i know its A definitely becos i did that qn so many times in exam papers.... they are at different rates cos exp 1 has a steeper gradient than exp 2! different rates of reaction but same vol of gas produced. so exp 1 takes less time for the reaction to end.

• SQhi replied to 2’s comment

2011
Nov
14
Mon
1:22pm

16.2

@2: Q5

The incoming electrons from one end of the metal displaces electrons at the other end of the metal, period.

Q12 excellent explanation by X. above

Q 22 my opinion is A(deviation from miss loi)

1. The blast furnace process produces a lot of CO2 as CO is used to reduce hematite, and a lot of heat is needed, fuel burnt = more CO2. Iron products already have a high percentage of iron, such as steel, see no. 2

2. Scrap steel does contain a higher percentage of iron than iron ore, iron ore is mostly earth!

3 is always right.

17. unknown commented in tuition class

2011
Nov
14
Mon
11:33am
18. 린젠레  commented in tuition class

2011
Nov
14
Mon
11:33am

18

Hi! May i ask whether for question 39, can the answer be A?

19. Daniel commented in tuition class

2011
Nov
14
Mon
11:33am

19

Hey can i ask out of curiosity why is qs 22 the part about scrap steel having a higher percentage of iron is not a reason?

20. commented in tuition class

2011
Nov
14
Mon
11:36am

20

Can you explain why the ans. for 22 and 35 isn't A?

21. 린젠레  commented in tuition class

2011
Nov
14
Mon
11:43am

21

@Daniel & W: For Qn 22, if you go and calculate the mass percentage of iron in Fe2O3, you'll realise that the % is higher than the 40% that is contained in scrap metal.

22. NY commented in tuition class

2011
Nov
14
Mon
12:08pm
23. Alissya commented in tuition class

2011
Nov
14
Mon
12:11pm

23

Hi may i ask why question 28 is D? can it be A since they asked for fossil fuels? CO(carbon monoxide) is from incomplete combustion of fuels that contain carbon i thought? and the SO2 was from incomplete combustion of fossil fuels/ volcanic eruptions?

24. Joseph commented in tuition class

2011
Nov
14
Mon
12:18pm

24

Hi, isnt question 22 answer be A instead of C? Because Steel contains 98% iron and 2% carbon?

25. XOXO commented in tuition class

2011
Nov
14
Mon
12:34pm

25

hello:)
can someone pls explain Q28
cause i thought that C8H18 (octane) is a liquid and not a GAS resulting in incomplete combustion?
so why is the answer D?
and can it be B? lols
pls and thankyou:)

26. Elaine commented in tuition class

2011
Nov
14
Mon
12:44pm

26

Can someone upload the question paper? Cos our school haven return our question paper ...

27. crapper commented in tuition class

2011
Nov
14
Mon
1:57pm

27

shouldn't question 9 be option D?
Shouldn't question 19 be option A? (how could the last element in the period -noble gas have an increase in valency electron?)

28. Dannie commented in tuition class

2011
Nov
14
Mon
2:51pm

28

i think i ald lost 1-2 marks: qn 5,35
paper 2 was ok but im afraid i might lose marks esp becos i did the organic chem qn, the calculations part
hopefully can get A1/A2:)

29. marc commented in tuition class

2011
Nov
14
Mon
3:46pm

29

can miss loi post the full soln ans, + qn pp just like physics, thanks very much.

30. hk commented in tuition class

2011
Nov
14
Mon
5:26pm

30

31. commented in tuition class

2011
Nov
15
Tue
4:14pm
32. skylar commented in tuition class

2011
Nov
15
Tue
11:02pm

32

Qns 5 , very disputed. Some say A some say D. Can someone explain to me with a solid answer ? thanks in advance.

• 2011
Nov
17
Thu
8:48pm

32.1

@skylar: I believe those who chose D are looking only at the positive ions and electrons on the original diagram that have subsequently flowed to one side of the metal.

While the number of electrons in the metal remains constant due to the conservation of mass, the metal being part of a closed circuit will have more electrons coming from the circuit to take the place of those who have flowed on from one side to another, so the electrons cannot be permanently held at one end only.

Furthermore with the current switched off, the arrangement of the electronics should return to what it was like before the current was switched on i.e. the original diagram!

33. Little Miss Loi commented in tuition class

2011
Nov
17
Thu
9:41pm

33

Folks, after staring long and hard at the ang moh anomaly that is Q22, I’ve decided to change its answer to A. Reason being that scrap steel, containing a higher percentage (98%) of iron, will lead to a better yield and reduce mining wastes when iron is produced from it via recycling.

The highlighted portion would definitely confirm chop stamp qualify as a correct reason if only it had been included in the original statement – instead of sparking intense debates all over SIngapore 🙁

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