Paper 5 Tips !! :)

[xhizors]

AsSalamalaikum wr wb

I would like to share some keyPoints i discovered, Learned while doing papers ( a wide variety)

here you go!

Generally there are 4 or more types of Questions
a) Stoichiometry(Mole Ratio Ones), titrations too
b) Enthalpy Changes Questions
c) Common Ion Effects guys
d) and last electrodes types also molality, Solubility etc will tell more in a while

 

[xhizors]

When you are required to measure enthalpy changes of:
a) Neutralization
b) Solution
c) Combustion
use Calorimeter:

To setup a Calorimetery type Apparatus:
-Take a polystyrene Cup(usually 150cm^3) or Metal Can (any like Copper) and Vacuum flask
(if you are taking polystyrene cup it is a good practice to place the cup in a beaker as reaction is exothermic might cause injury to your hand)
-Reactants amount should be known(like 50cm^3 of acid and 50^cm3 of alkali (specific case in neutralisation))
-offcourse in enthalpy change their is a Temperature change so u need a thermometer too with a graduations of either 0.1*C or 0.2*C with a minimum and maximum range marked of either 0*C to 100*C or -10*C to 110*C
if stirring is needed, stir it with Thermometer
In Calorimeter we assume
a) volume of solution is equal to the mass of it
b) for any solution in calorimeter energy required to change the temperature of 1g by 1*C is 4.18 or 4.2 J

In the end
for Energy Changes use formula
q=mc4T*
*"4=delta"

Their are some heat losses to air so cover the container with LID it will minimises the effect
heat losses can also happen to container
Thats why energy changes are different from the booklet values

Hope it helps
Procedures to Measure enthalpy changes of:
a) Neutralization
b) Solution
c) Combustion
are coming

 

[xhizors]

Measuring Enthalpy Change of Neutralisation!(remember we have to use calorimeter)
For this You have to have an equal amounts of both Reactants to make a solution
1) Take 150cm3 Polystyrene/Plastic cup(it is a good insulator)
2) use burette to measure 50cm3 of acid
3) Transfer 50cm3 of acid in a polystyrene cup stir it a little with thermometer and measure its acid(initial temp)
4) use another burette to measure 50 cm3 of alkali
5) Transfer it into polystyrene cup and stirr it with thermometer and measure the highest temperature
(note: cup could get hot)
now dummy Data
mass: 50cm3 + 50 cm3 = 100g
specific heat capacity=4.2
temp rise(final - initial) = (45-25) = 20*C

for heat change Q=mc4T=(100x4.2x20) = 8400J
now suppose we have acid of 1moldm-3 and alkali 1 moldm-3
then mols = ( conc/vol) = 0.05mol
0.05 mol ---> 8400J
1mol --> x
x= -168kJ (as we know reaction is exo we place a -ve sign)..

 

[xhizors]

Ce(SO4)2 solubility decreases in sulfuric acid as concentration increases due to common ion effect!!

 

[xhizors]

Feel free to give feedback or any comment!! waiting

 

[xhizors]

Enthalpy Change of Solution(Use Calorimeter)

-Pour Water 50cm3 in Plastic cup
-stir a little and measure its temperature (remem 0.2 graduations) its initial temp
-cautiously take NaOH as it is corrosive (use hand gloves as it can react with a moisture in your hand) measure 30cm3 of Naoh using measuring cylinder
-pour alkali in plastic cup stir it with thermometer and record the highest temperature

Thats it no more Rocket science
use equation Q=mc4T => 80gx4.2x(65-30)
here u get the Enthalpy change of Solution

Pray for me that i get able to make my way toward a World Distinction Inshallah!!

 

[xhizors]

Zn + I2 --> ZnI2
so reacting I2 gives I2 means no. of moles of I2 used divided by its Ar,

(any comment on this one specifically)

JazakAllah

 

[Silent Hunter]

xhizors


JazakAllah tell something about the concentrations numericals...... the place where we have to make a range of concentrations ? how to do them? For example the following paper:

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_51.pdf

its question 1 (c)

 

[xhizors]

xhizors


JazakAllah tell something about the concentrations numericals...... the place where we have to make a range of concentrations ? how to do them? For example the following paper:

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_51.pdf

its question 1 (c)

They are v.easy

assume u have 2mol/dm3 HCl and u have to prepare 5 solutions of HCL of different concentrations
sol A) u take 50cm3 of 2 mol/dm3 --> conc= 2mol each dm3
sol B) u add 10cm3 of Distilled water and 40cm3 of HCl in any container
50cm3-->2mol/dm3
40cm3--> x
by unitry method x = 1.6mol/dm3

so conclusion u add water and drop the concentration !!
for C) add 20cm3 of distilled water and 30 cm3 of hcl, further conc dropped !!

hope it helps

 

[Silent Hunter]

and how do we know from what concen to what concen do we have to take them. the ranges ?

 

[xhizors]

and how do we know from what concen to what concen do we have to take them. the ranges ?

it really depends and it is mostly not suitable to have concentrated solutions having concentration above 2mol/dm3

 

[Silent Hunter]

so conclusion u add water and drop the concentration !!
for C) add 20cm3 of distilled water and 30 cm3 of hcl, further conc dropped !!

hope it helps

in (c) it asks about the range of concentrations of copper (II) sulphate ..... hw to do this ? :\ we are just given solid cooper sulphate ..... with no concentrations

 

[xhizors]

in (c) it asks about the range of concentrations of copper (II) sulphate ..... hw to do this ? :\ we are just given solid cooper sulphate ..... with no concentrations

in this question u r making a solution of NaOH and CuSO4
use c1v1=c2v2
push a little harder and bingo u'll get it!!

tell me if prob resist

 

[xhizors]

Measuring enthalpy change of combustion!!
Take an empty spindle weigh it and then pour any alcohol and re weigh it
setup a dry wrick and cap the spindle to avoid evaporation ofuel
take 150 cm3 metal can pour 50 cm3 water and place it over spindle on a table alike
measure the initial temp of water
light the spindle and keep measuring temperature until their is a rise of 10*C
recap spindle allow it to cool remove cap and wrick and reweigh it
substract mass after heating and before heating u'll get the mass which is burnt in excess oxygen
use q=mc4T and u'll get enthalpy change of combustion

 

[xhizors]

Most of the time q's are asked to calculate no of moles of reactant which gives of any gas say oxygen.
Measure mass of the reagants
just calculate the volume of gas collected in a gas syringe(U GETits mass) apply unitry method with a known stoichmetric number u'll get other mol number

 

[xhizors]

To find the solubility of any solid dissolved in any solution
Take 250 cm3 conical flask pour 50 cm3 of water
weigh a sample of solid and add it into water and stirr it until no more solid dissolves
then leave it for sometime to cool down to give crystals
filter the solution transfer the residue and discard the saturated solution
wash the residue with distilled water thoroughly and discard water then add propanone to absorb any water droplet left
warm a little or place the container under oven or sun (not bunsen burner else it will decompse solid) to evaporate any propanone left
now weigh the residue
repeat until constant mass is acheived
substract mass if residue with the initial mass so u'll get mass of solid dissolved to make a saturated solution,
now to find solubility use ( mass of solid use x 100)/mass of water

 

[xhizors]

Molality = (no.of Moles x 1000) / mass of water

 

[xhizors]

To determine the moles of H2O in washing soda
Weigh the sample first
heat it
reweigh the sample
substract masses
voila u get the water evaporated
divide the mass of h2o by 18 and u get its mols

 

[xhizors]

To Get the mols of Cu(CO3)2 by decomposing it
heat the sample
let all of the CO2 evaporated
so now u only get the CuO
measure mass, Calculate its mols
apply mol ratio
1:1
mols of CuO = mols of Cu(CO3)

 

[Wanderer]

xhizors

Please can you tell me how we are supposed to draw the diagram for JUNE12/52 q1 c
It's a decomposition reaction of Ammonium Nitrate in which both water vapour has to be condensed and collected and Nitrogen(I)oxide has to be collected too...I cant understand how both water vapour and gas collection has to be done?