Q&A - PSLE Science

[Sun_2010]

CoffeeCat:

For 34c, your answer is problematic, because from where do you get the evidence to draw that comparison statement? You statement might be a fact but is unfortunately irrelevant to this question because no comparison is being made anywhere.


For 37b i think its an issue of interpreting.
Students might think that the question is asking literally for a possible answer which in your case is steel. But the teachers might be looking for the general term to cover all the possible materials, which is magnetic material in this case.

Better to learn to answer the syllabus way than risking having debatable answers, IMHO.

I am confused. My 2 cents...
Since the Flask2, (the first limewater flask) remained clear, how can we conclude that the air initially had carbon dioxide? is this not based on our \"prior knowledge\", not mentioned in the experiment.

If for b) we say that The flask4(second lime water flask) turnrd chalky, surely contained more carbon dioxide in it.
So i feel the worksheet answere is inaccurate, P5G's ans is the correct one. In fact this is what the experiment is about - to show carbon dioxide is given out during respiration.

[P5G]

CoffeeCat:

For 34c, your answer is problematic, because from where do you get the evidence to draw that comparison statement? You statement might be a fact but is unfortunately irrelevant to this question because no comparison is being made anywhere.


The first limewater did not turn chalky while the second limewater turned chalky, so more carbon dioxide from air breathed out by the snails.

How could I know that surrounding air contains carbon dioxide?
Flask A was supposed to remove carbon dioxide, but it did not show that there was carbon dioxide.
Flask B did not turn chalky, so air going into Flask C did not contain carbon dioxide.

For 37b i think its an issue of interpreting.
Students might think that the question is asking literally for a possible answer which in your case is steel. But the teachers might be looking for the general term to cover all the possible materials, which is magnetic material in this case.

So is my answer acceptable?


Better to learn to answer the syllabus way than risking having debatable answers, IMHO.

I thought my answers are all within syllabus.

Mr Coffeecat,

Please see my clarifications in blue. Thanks.

[CoffeeCat]

Lol P5G no i do not meant that your answers are not within syllabus. I was referring particularly for part B because its a matter of interpretation, and its the teachers who will interpret behind the scenes. I am merely suggesting trying to be on the safe side by learning the interpretation, because you never know the markers you get might just disagree with you or that the marking scheme omitted your interpretation (if it is valid).

hmm sorry i can’t answer your part b), you have to ask your teacher who should be more familiar with the psle marking scheme

ok for part c)
It is prior knowledge (in the syllabus) that surrounding air contains carbon dioxide.
So the job of of flask A is to remove carbon dioxide so that the limewater in flask B will remain clear (lack of carbon dioxide).
At this point, the air entering flask B and C is not "surrounding air" but "carbon dioxide-less surrounding air".
So the snails breathe out carbon dioxide that turns the limewater chalky.
I see no comparison being made in this logic about the amount & comparison of carbon dioxide in surrounding air and air breathed out,

[tianzhu]

Hi P5G


For Q34,the experiment sought to show that carbon dioxide is given off when the snails respire. To ensure a fair test the air passing through flask C must not contain carbon dioxide. Therefore, surrounding air is first passed through liquid X in flask A to remove carbon dioxide.

From prior knowledge, one knows that surrounding air contains carbon dioxide. However, the limewater in flash B remains clear; this shows that carbon dioxide has been removed from the surrounding air by liquid X.

Snails respire all the time to get energy for daily activities. During respiration, carbon dioxide is given off. This explains why the limewater in flash D turns chalky.

From the experiment set up, we can only say that exhaled air and surrounding air contain carbon dioxide. There is no information showing the concentration of carbon dioxide.

As for the second question, if the question is crafted like this, Give one example of materials that could have been used for Object C, your answer of steel is more appropriate.

From the context of the question, Object C is a magnetic material, however we are unable to confirm that it’s steel from the information given in the question.

Perhaps, a more kiasu way to answer this question would be

Object C could be made from magnetic material, such as steel.

Best wishes

[P5G]

tianzhu:

For Q34,the experiment sought to show that carbon dioxide is given off when the snails respire. To ensure a fair test the air passing through flask C must not contain carbon dioxide. Therefore, surrounding air is first passed through liquid X in flask A to remove carbon dioxide.


From prior knowledge, one knows that surrounding air contains carbon dioxide. However, the limewater in flash B remains clear; this shows that carbon dioxide has been removed from the surrounding air by liquid X.

Snails respire all the time to get energy for daily activities. During respiration, carbon dioxide is given off. This explains why the limewater in flash D turns chalky.

From the experiment set up, we can only say that exhaled air and surrounding air contain carbon dioxide. There is no information showing the concentration of carbon dioxide.

Hi Uncle Tianzhu,

Please see highlight in blue.

Since it is prior knowledge and not from the experiment, how can we conclude that surrounding air contains carbon dioxide?

Would appreciate your further clarification please.

TIA.

[tianzhu]

Hi P5G

You are very inquisitive, which is good for learning science.

Let me make another attempt to make it clearer.

First thing first, let’s us recap what‘s been covered in primary science which we can apply to Q34.
1)Air is made up of a mixture of gases including water vapour. The gases are oxygen, nitrogen, carbon dioxide and other gases.
2)Living things respire to produce energy for life processes. During respiration, oxygen and food are changed into energy, carbon dioxide and water.
3)The presence of carbon dioxide turns limewater chalky.

For Q34, the experiment sought to show that carbon dioxide is given off when the snails respire. To ensure a fair test the air passing through flask C must not contain carbon dioxide. Therefore, surrounding air is first passed through liquid X in flask A to remove carbon dioxide.

Snails respire all the time to get energy for daily activities. During respiration, carbon dioxide is given off. This explains why the limewater in flash D turns chalky.

From the experiment set up, we can only say that exhaled air and surrounding air contain carbon dioxide. There is no information showing the concentration of carbon dioxide.

Hope this helps.

Best wishes

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[CoffeeCat]

In my opinion, in psle you are meant to utilise your prior knowledge and answer to the question with evidence.

Were you taught that air contains carbondioxide? If yes then this questions expects to apply this fact to infer that the liquid x remove carbon dioxide(or perhaps the question states so) but either way this means that air contains carbon dioxide.
This qns is the case where you draws a conclusion by linking an experimental result with prior knowledge.

[starlight1968sg]

Hi,

I need some help.
We know many living things reproduce sexually ie a male and a female are needed for fertilisation. What are the animals reproduce asexually?
Thanks.

[atutor2001]

[quote]..... in psle you are meant to utilise your prior knowledge and answer .....[/quote]
Above statement is true only if there are no such clauses in the questions :

\"based/referring on the diagram given\"
\"based/referring on the picture\"
\"based/referring on the experimental setup\"
\"based/referring on the observation\"

In Q34, those 2 \"magic words\" are not in the question. Therefore, we can use our prior knowledge.

So all dear students, we need to analyse the question very carefully, lookout for \"keywords\" - e.g. base/refer; all the; only; ....

[Tang]

atutor2001:

[quote]..... in psle you are meant to utilise your prior knowledge and answer .....

Above statement is true only if there are no such clauses in the questions :

\"based/referring on the diagram given\"
\"based/referring on the picture\"
\"based/referring on the experimental setup\"
\"based/referring on the observation\"

In Q34, those 2 \"magic words\" are not in the question. Therefore, we can use our prior knowledge.

So all dear students, we need to analyse the question very carefully, lookout for \"keywords\" - e.g. base/refer; all the; only; ....[/quote]
Hi Auntie atutor2001,


This question may not have the 2 'magic words', but it has 4 'magic words'.


Q34c) From the experiment above, what can you conclude


So I believe no prior knowledge should be used.


Although Flask A is supposed to remove carbon dioxide based on our knowledge, the experiment does not show us that carbon dioxide indeed exists.
[But since Flask A is to remove carbon dioxide found in the surrounding air, it may infer that the surounding air contains carbon dioxide rather than based on prior knowledge.]

In the TOPIC 'Air', we learned that air contains hydrogen, oxygen, carbon dioxide and other gases.


In the TOPIC 'Respiratory systems', we learned that air inhaled is poor in carbon dioxide (0.03%) and air exhaled is rich in carbon dioxide (4%).


So can the experiment actually shows the second TOPIC rather than the first TOPIC.


By stating that 'air breathed out contains more carbon dioxide than the surrounding air' based on the second TOPIC is actually correct. It also does not contradict the experiment as Flask D shows that there was carbon dioxide in the air breathed out and the statement also does not imply that carbon dioxide exists in the surrounding air because

the experiment shows
carbon dioxide in air breathed in = 0, carbon dioxide in air breathed out > 0.


By extrapolation, if carbon dioxide in air breathed in = 0.03%, carbon dioxide in air breathed out > 0.03%.


So both answers should be accepted.


For further discussion please.