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Question

post-21542

Please help, how to answer this question? Thanks. 

Answer

Without searching online and goggling as a student, I will no doubt do process of elimination first

Firstly, we can rule 1) and 4) out immediately

Option 1 is out because we all know that the melting process like boiling will mean temperature will be stable for a while due to the change of state (Secondary School Physics knowledge) 

Option 4 is definitely out due to prior knowledge that salt will affect the temperature (Given in the hint)

I’ll choose 3 simply because of the hint that clearly suggest that melting point is lowered due to addition of the salt, but yes it is a very strange question,

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I am not sure it will lower the temperature of the ice. It will lower the freezing point of water but not cause temperature to fall.

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Edited 21-Nov-2016

Actually, the question is not very clear.  It should clearly state when the salt is added.  If the ice is at 0 C at the point when the salt is added, temperature will drop below 0 C, and the ice will melt even the temperature is below 0 C.  This is because adding impurities will lower the melting point of ice.

If we assume that the ice was already below 0 C and the freezing point of saline before the addition of the salt, then (3) will be the answer, since the salt will no lower be able to lower temperature any further.

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Thanks ShockedParent & CKS,

however the answer sheet is (3). Looking at the link below, it does seems that adding salt lowers the melting point of ice, thus (3) is the answer. Do you agree?

http://science.howstuffworks.com/nature/climate-weather/atmospheric/road-salt.htm

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