angel:

can water which is freezed in the fridge falls below 0 degrees?


A graph shows water (A) at 30 degrees, took 15 mins to turn to 0 degrees (B), stayed at 0 degrees for 15 mins (C) and dropped to -10 degrees after 10 mins (D) and stayed -10 degrees for next 15 mins (E).
(x-axis is TIME and y-axis is TEMP)
(A) 0/30, (B) 15/0, (C) 30/0, (D) 40/-10 & (E) 60/-10

Qn asked :
1)What was the temperature of the freezer compartment?

2) Explain what happened to the beaker of water from B to C.

3) Which part of graph shows cooling of water to freezing point of water?


Is the ans
(1) -10 degrees
(2) The water freezed at 0 degrees at (B) and stayed for 15 mins at 0 degrees.
(3) Part A to B.

Anyone can help?

Assuming that the water is pure, water in the liquid state can never fall below 0 degrees, as that is the freezing point of water. Once the water has frozen, its temperature can continue to decrease, till it reaches the temperature of its surroundings.

And the answers you have given are all correct.

Hope this helps!

iamastudent:

Hi,

May I know what is the oxidation state of ions? Example like the equation:
(S2O3)2- + 4Cl2 + 5H2O --> 2(SO4)2- + 8Cl- + 10H+

What is the oxidation state of H in H+? Is it +1 or is it 0?
O in (SO4)2-? Is it -2? S in (SO4)2-? Is it +6? Thank you

The oxidation state of simple ions is always the charge of the ion. For example, in the case of H+, its oxidation state would be +1. In the case of Cl-, its oxidation state would be -1.

In the case of polyatomic ions, such as the sulfate ion, the sum of all the individual oxidation states of the atoms present in an ion must add up to the charge of the ion. In the case of (SO4)2-, the oxidation state of the 1 sulfur atom and 4 oxygen atoms must add up to -2. Oxygen generally has an oxidation state of -2. So the total oxidation state of the 4O atoms would be -8. So in order for the sulfate ion to have a charge of 2-, the S atom must have an oxidation state of +6.

Note that oxygen can have other oxidation states. For example, it will have an oxidation state of -1 in peroxide ions (O2)2-. It can also have an oxidation state of -0.5 in the case of superoxides (O2)-

Hope this helps!

HFPMAT:

Laurel111:

[quote=\"jwxh\"]In reply to Laurel111, my understanding is that water vapour cannot be seen so when they said that person observed some white mist, it rules out water vapour and the answer should be clouds. Hope this helps!

:thankyou: Need to go back to Textbook for basics...

Gaseous state ...water vapour
liquid state....mist, cloud, fog, steam[/quote]Sorry that this is coming a bit late. A point to note here is that steam is in the gaseous state, not the liquid state. The white mist seen coming from boiling water is steam that has already condensed, and isn't steam at that point.

Hope this helps!

mel2sg:

Hello my daughter is teaching Science and she would like to post this question about P4 Matter - Mass and Weight.


Mass is the amount of substance in an object, while weight is dependent on the pull of gravity. From information online and textbooks she read, weight is 1/6 of mass on the moon, but from another book, a person was said to be weightless on the moon too. Which of the two information is more scientifically correct? Would really appreciate your help and input. Thanks in advance.

You are not weightless on the moon as the moon has a gravitational field. You can only be weightless when present at a location where there is no gravitational field.

Hope this helps!

guchengyouzi:

Hi Dioprem,

What substances do you have in mind?

Do you mean the exceptions where the substances actually have freezing and melting points?

One substance that I know of is agar. Its melts at 85 degrees and solidifies from 31 degrees to 40 degrees. (All temperatures in Celsius.)

Mary Joy:

Can someone help me with this physics question.... :thankyou:


http://i57.tinypic.com/a4t0y0.jpg\">

Not too much information given here, so I'm going to make the assumption that the M113 has to be afloat in pure water. In order for a body to float in a liquid, it needs to have a lower density as compared to the liquid. In the case of pure water, its density is 1000 kg/m3.

Since density = mass / volume,

1000 = 1.115 X 10^4 / volume

Hence volume = 11.15 m3

So the M113 would need a volume greater than that to stay afloat.

Hope this helps!

P.S The print is a little small so the value I used for the mass of the M113 could be wrong, but the principle is still the same.

pensiveowl:

Could someone pls help with this question.. thanks


http://i58.tinypic.com/2hs2893.jpg\">

From the diagram, we can see that object Z causes the magnet to be attracted to it. However we cannot say that Z is a magnet as it could also just be an object made from a magnetic material. So statement A isn't true. The only way to make sure an object is a magnet is if it repels another magnet.

Objects W and Y have no effect on the magnets as they have remained in their original positions. So W and Y must have been made from non-magnetic materials. So statement B is true.

Object X has repelled the magnet, as can be seen since the magnet is the highest up. This would been that the poles facing each other would have been like poles. Hence statement C is wrong.

So the answer would be (2). Hope this helps

angel:

How do prawns, tadpoles and frogs breathe?

Which of these animals have similar breathing parts?

Prawns and tadpoles breathe through their gills. A frog is able to breathe through its lungs and skin. When on land, the frog uses its lungs. It uses its skin to breathe when in water.

Hope this helps.

S-H:

Hi, can someone help to the following question, thanks!


Does elastic spring force act on any object that is stretched?

An elastic spring force will only act on elastic objects that are stretched or compressed.

Hope this helps.

Jamesbond:

http://i57.tinypic.com/119seu8.jpg\">

Shouldn't the answer be 1 for this. Ans in answer key is 2. Pl help.

For seeds that are dispersed by wind, an important adaptation they have is that they are generally light. Being light allows them to travel greater distances when carried by the wind. So if a seed is lighter, it would travel a greater distance than one that is heavier.

From the question, seed Z is the lightest as it has no plasticine attached to it. Thus it should travel the furthest. Conversely seed Y has the greatest mass, and so should travel the shortest distance.

Hence the answer is (2).

Hope this helps.