Edexcel CHEMISTRY DOUBTS!!!!

[Ibiza279]

i want to noe the procedure that we have to write when they ask us for :-

1. How to form crystals from a solution ?

2. how to form a saturated solution ?

Thanks all !

[Darth Austrakast]

Since 1g of Mg powder is added in excess its mass is likely to be <1g and hence can be ignored
density of aq solⁿ=density of water so mass of solⁿ=50cm^3*1gcm^-3=50g
so energy change= m*c*del-theta =50*4.2*(43-22)=4410 J

[Ibiza279]

                  Mg(s) + Cu(NO3)2(aq)        Mg(NO3)2(aq) + Cu(s)
In the self-heating cans, the bottom has a compartment containing copper(II) nitrate
solution. When a button on the bottom of the can is pressed, the magnesium powder is
released into the compartment where it reacts with the copper(II) nitrate solution.
(a) A student investigated the enthalpy change for this reaction by measuring
     50.0 cm3 of 0.300 mol dm–3 copper(II) nitrate solution into a 100 cm3 beaker and
     adding 1g (an excess) of magnesium powder.
     The results are shown below.
         Temperature of copper(II) nitrate solution at start       = 22 C
         Temperature of mixture after reaction                     = 43 C

(i) Calculate the energy change which took place. The specific heat capacity of the
    solution is 4.20 J g–1K–1.
    Which is the correct value for the energy change in joules?

[6CH01, Specimen Paper]

How to solve this? Answer in mark scheme is 4410 Joules

dude thats simple, as 50 cm^3 of solution is used, jus do the simple math, 50 X (43 - 22) X 4.2 = 4410

[Darth Austrakast]

i want to noe the procedure that we have to write when they ask us for :-

1. How to form crystals from a solution ?

2. how to form a saturated solution ?

Thanks all !

i don't think these are required for unit 1 xams

[Ibiza279]

dude thats simple, as 50 cm^3 of solution is used, jus do the simple math, 50 X (43 - 22) X 4.2 = 4410

oh yh and as the density of water 1g/cm^3, the density is 1 so the mass = volume, so 50 cm^3 = 50g

[Ibiza279]

i don't think these are required for unit 1 xams

dude these small experiments are, if u check the latest papers, i mean jan 09 till jan 10, ull find such questions :|

[Darth Austrakast]

Oh OK i didn't solve the papers yet

for saturated solution they will ask for a particular volume of solution so what u need to do is measure the required mass of salt/substance using electronic mass balance and accurately transfer the solid to a volumetric flask.Then add 50cm^3 of distilled water and shake the mixture well to dissolve the solid.Then add distilled water and make the solution up to the mark.

[Ibiza279]

Oh OK i didn't solve the papers yet

for saturated solution they will ask for a particular volume of solution so what u need to do is measure the required mass of salt/substance using electronic mass balance and accurately transfer the solid to a volumetric flask.Then add 50cm^3 of distilled water and shake the mixture well to dissolve the solid.Then add distilled water and make the solution up to the mark.

uh no, wrong, with saturated, they mean that the solution should have the max amount of salt content in it so that no more salt can further b dissolved. for that, in 100 cm3 distill water which is in a beaker, add salt and dissolve it with a glass rod. while dissolving, keep adding excess of salt until no more salt can b dissolved. filter the solution to remove any excess salt, and u hav a saturated salt solution

[Kim]

hey u guys
i was wondering if u guys have any mcq to study from??
how are you studing for em??
where can i get sum mcq like those in the papers?

[annie_angel]

HII  KIM!!!!

[Darth Austrakast]

well you can study from the cie mcq questions 

[Kim]

HII  KIM!!!!

hey how r ur exams goin???
i have an exam tomorrow
not in the mood

@austrakast--lol i mean is there any where else?

[Darth Austrakast]

@kim:lol.......nah dunno other sources 

[Ibiza279]

well MCQs are like normal question, the trick with um is, read um carefully and answer with the right (X) on the options, u cant actually "study" for um. but a point is that do all the HSW from the textbook cause they come as 10% of the paper hope that helps

[raimunts]

4 The first five ionization energies of an element, Z, are:
  790, 1600, 3200, 4400, 16100 kJ mol–1
  In which group of the Periodic Table is Z found?
           A 2
           B 3
           C 4
           D 5


Answer is C 4.
How can you tell?