Q&A - P4 Science

[charsen]

Jamesbond:

Hi Have another doubt...


If salt is added to ice, how will it affect the melting point and freezing point...Can somebody give me the answer...

If I am correct...the melting point is lowered...

Also...when salt is added to ice, will the ice melt faster or slower?

Pl help...

Hi
You are correct.The melting point and the freezing point is lowered.It is a good thing as this concept may be tested on a application question.For example,in winter,many countries would sprinkle salt on almost everywhere if the environment is covered mostly in snow.Then,they would ask why the people in those countries do that.Now,that invovles this concept of lowering down the freezing point and the melting point of ice when salt is sprinkled on it.
Charsen

[Jamesbond]

Thank you atutor2001 and charsen for ur explanations....

[verykiasumummy]

atutor2001:

Jamesbond:

Hi Have another doubt...


If salt is added to ice, how will it affect the melting point and freezing point...Can somebody give me the answer...

If I am correct...the melting point is lowered...

Also...when salt is added to ice, will the ice melt faster or slower?

Pl help...

These are the effects when salt is added to water :

1. Melting point / Freezing point will be lowered.
2. Ice will melt faster.
3. Water will take a longer time than usual to freeze.
4. Boiling point will be raised.
5. Water will take a longer time than usual to boil.

Best not to explain why ice melt faster. It is too complex.

regarding pt 2, allow me to share my 2 cents worth..

melting and freezing point will be lowered when salt is added to ice, so lets say the melting/freezing point is lowered to -3 C. which means that while pure ice melts at 0 C, ice with salt melts at -3 C, and that explains why ice with salt will melt earlier and faster than pure ice.

[PiscesLeo]

http://i48.tinypic.com/2hrkgo7.jpg\">

SCGS 2010 SA1 Q9
Question 9) Mrs Gin asked her pupils to observe an insect with a 3 stage life cycle at home and record their observations daily. It will take approximately 10 days for the insect to complete one cycle from the egg stage. Which of the following pupil did not record her observations correctly?

For no 3. - Chui Imm / It ate and moulted / It was active and eating

Answer key is 3. Is that correct?

Thank you.

[PiscesLeo]

http://i47.tinypic.com/w83ott.png\">


SCGS 2010 SA1
Answer key for (d) -True. Is it correct?

Thank you.

[verykiasumummy]

PiscesLeo:

http://i48.tinypic.com/2hrkgo7.jpg\">

SCGS 2010 SA1 Q9
Question 9) Mrs Gin asked her pupils to observe an insect with a 3 stage life cycle at home and record their observations daily. It will take approximately 10 days for the insect to complete one cycle from the egg stage. Which of the following pupil did not record her observations correctly?

For no 3. - Chui Imm / It ate and moulted / It was active and eating

Answer key is 3. Is that correct?

Thank you.

hi PiscesLeo, i suppose answer is 4. it says 10 days to complete the whole cycle, so 2 weeks which is 14 days, they should have already completed 1 cycle and in the nymph stage of the next cycle. for nymph stage, it will be active and will be eating, since options 1 to 3 mention \"eating\", \"moulting\" and \"active\" and only option 4 mention \"not eating\", it should be incorrect. so ans should be 4.

[verykiasumummy]

PiscesLeo:

http://i47.tinypic.com/w83ott.png\">


SCGS 2010 SA1
Answer key for (d) -True. Is it correct?

Thank you.

yes D is true, because B is in the lower part of the cup, since air can be compressed, some water can enter the cup so the part B will be wet.

[PiscesLeo]

:thankyou: verykiasumummy for the explanation. :thankyou:

[Jamesbond]

http://i48.tinypic.com/35lrdj9.jpg\">


what could be the answer for this.....Answer in the paper says just in one line...They are made up of diff materials.

But my son says should explain as follows:

For container R, It is a good conductor of heat and hence lost heat quickly. And for container S, It is a poor conductor of heat and hence lost heat slowly...

I feel this way of answering is correct...

Pl let me know which is better and why?

Thx..

[verykiasumummy]

Jamesbond:

http://i48.tinypic.com/35lrdj9.jpg\">


what could be the answer for this.....Answer in the paper says just in one line...They are made up of diff materials.

But my son says should explain as follows:

For container R, It is a good conductor of heat and hence lost heat quickly. And for container S, It is a poor conductor of heat and hence lost heat slowly...

I feel this way of answering is correct...

Pl let me know which is better and why?

Thx..

offering my answer :

the 2 containers are made of different material, hence they have different conductivity of heat, which cause them to cool down at different timing.