Chemistry M/J 2002 Paper 1

[Ismail Breiwish]

Questions 3 & 4, explain please.

 

[Adham-amr]

in question 3, it assumes here that the process of crystallization ( heating till crystallization point ) is already done, so what we have to do is leave the solution to cool, then filter off the crystals so the answer is B
in question 4 im not sure but i think it's A

 

[Abdullatif Dablouk]

Dear ismail breiwish,

What Adham-amr said about question 3 is right. About question 4, liquid X is placed in a cooling mixture (in fact it is a mixture of water and melting ice) and the temperature of the liquid is being measured. The graph plotted on the right indicates that the temperature of liquid X is decreasing and it then remains at a constant for a while, even though the temperature of the cooling mixture is still decreasing, this is because energy is being taken in to form bonds so that the liquid turns to a solid and this (as shown by the graph) is at 0 degrees celcius, which is the freezing point of water. So you know that liquid X could be H2O(l) (note: the (l) indicates that it is in the liquid form), so the answer is either A or B. NaCl (aq) is an aqueous solution, which means that it contains water, BUT since it has an impurity dissolved in it (NaCl), it's freezing point wikk change. The graph is a similar thing to the latent heat to fusion, in physics, but is just an inverse. I hope this post will help further your understanding and i'm happy to be of an assistance to you

Ismail you jew bastard :lol:

 

[Ismail Breiwish]

Thank you very much, ya aboo teez. You could have just called me to explain it, LOL.