Chemistry: Post your doubts here!

[awesomaholic101]

Paper 5 is the biggest trouble which will not let me end with nice grades. Help me. I usually end to get 80 in paper 4 and 15 in paper 5

Paper 5 is the easy one. You don't even have to study that much. I guess you just need practice and basic logic.

 

[The Sarcastic Retard]

Paper 5 is the easy one. You don't even have to study that much. I guess you just need practice and basic logic.

What is the minimum and maximum score u got in it?

 

[shahzaib9291]

part 3 and 4

 

[The Sarcastic Retard]

part 3 and 4View attachment 60077

 

[awesomaholic101]

What is the minimum and maximum score u got in it?

I had only two tests in p5 ... both of which were my mocks.
Scored 24 in one and 19 in the other.
But it's true that sometimes we mess up easily in p5 ... that problem is there.

 

[The Sarcastic Retard]

I had only two tests in p5 ... both of which were my mocks.
Scored 24 in one and 19 in the other.
But it's true that sometimes we mess up easily in p5 ... that problem is there.

Can u link that papers here.
True.

 

[princess Anu]

Can u link that papers here.
True.

I haven't even started P5
Can someone guide me on what I should do
what are the specific p5 topics that I must cover?
pls help
Guide me for physics & bio p5 too

qwertypoiu

 

[awesomaholic101]

Can u link that papers here.
True.

I am not sure I have them. But I'll search and let you know.

 

[qwertypoiu]

I haven't even started P5
Can someone guide me on what I should do
what are the specific p5 topics that I must cover?
pls help
Guide me for physics & bio p5 too

qwertypoiu

You should attempt a few paper 5s and compare your answers with the mark schemes. Most of the questions are logical and only require basic chemistry concepts.
In question 1 you'll be asked a few questions then asked to devise an experiment. You just need to be careful t mention the independent, dependent, and control variables. You must make clear how you'll change the independent variable. You must specify all the apparatus to be used. You must explain how the control variables will be controlled. They'll guide you on these points. Then they'll ask you a few more questions like precautions. You just have to think logically.
In question 2, you'll be given data. You just have to draw graphs and analyse. Even simpler.

For physics it's mainly same. In question 2 there is uncertainties involved and you'll need to learn to draw "line of worst Fit". Again a few mark schemes and examiner reports will make it very clear what they want.

Bio is also same.

 

[The Sarcastic Retard]

You should attempt a few paper 5s and compare your answers with the mark schemes. Most of the questions are logical and only require basic chemistry concepts.
In question 1 you'll be asked a few questions then asked to devise an experiment. You just need to be careful t mention the independent, dependent, and control variables. You must make clear how you'll change the independent variable. You must specify all the apparatus to be used. You must explain how the control variables will be controlled. They'll guide you on these points. Then they'll ask you a few more questions like precautions. You just have to think logically.
In question 2, you'll be given data. You just have to draw graphs and analyse. Even simpler.

For physics it's mainly same. In question 2 there is uncertainties involved and you'll need to learn to draw "line of worst Fit". Again a few mark schemes and examiner reports will make it very clear what they want.

Bio is also same.

Hats off man! ^_^

 

[pundadesh]

Hi guys can I ask if

CH3CHClCHClCH3 is the same as CH3CH(Cl)CH(Cl)CH3, cause the mark scheme specifies CH3CH(OH)CH(OH)CH3 for the -OH functional group

 

[The Sarcastic Retard]

Hi guys can I ask if

CH3CHClCHClCH3 is the same as CH3CH(Cl)CH(Cl)CH3, cause the mark scheme specifies CH3CH(OH)CH(OH)CH3 for the -OH functional group

You can write without brackets as well in this case, no problem.

 

[pundadesh]

You can write without brackets as well in this case, no problem.

Would CIE accept though?

 

[The Sarcastic Retard]

Would CIE accept though?

To be at safer side include brackets. In my As level I did without brackets. ^_^

 

[Eugene99]

So precipitate with aquous silver nitrate means that could be any of the halogens but what does solubility with aquous ammonia tell about?

 

[qwertypoiu]

View attachment 60111


So precipitate with aquous silver nitrate means that could be any of the halogens but what does solubility with aquous ammonia tell about?

The silver ions will form the following precipitates:
AgCl - white ppt
AgBr - creamy ppt
AgI - yellow ppt

These ppt will dissolve as follows:
If dilute ammonia is added to AgCl, it dissolves.
If concentrated ammonia is added to AgBr, it dissolves.
Even conc. NH3 is not able to dissolve AgI.

Therefore, in your question, since they said dilute ammonia cannot dissolve the ppt, we know that X cannot be a chloro-compound.

 

[Eugene99]

The silver ions will form the following precipitates:
AgCl - white ppt
AgBr - creamy ppt
AgI - yellow ppt

These ppt will dissolve as follows:
If dilute ammonia is added to AgCl, it dissolves.
If concentrated ammonia is added to AgBr, it dissolves.
Even conc. NH3 is not able to dissolve AgI.

Therefore, in your question, since they said dilute ammonia cannot dissolve the ppt, we know that X cannot be a chloro-compound.

thank u so much I get that...here is another
Question is :
Compound A is a liquid which does not react with 2,4-DNPH reagent or with aqueous bromine. Suggest two structural formula of A.
(We found the molecular formula in previous part which was C2H4O2) Here is what the markscheme says

It's (d)
I know ethanoic acid is formed but isn't HCO2CH3 just another way of writing CH3CO2H?

 

[qwertypoiu]

thank u so much I get that...here is another
Question is :
Compound A is a liquid which does not react with 2,4-DNPH reagent or with aqueous bromine. Suggest two structural formula of A.
(We found the molecular formula in previous part which was C2H4O2) Here is what the markscheme says
View attachment 60113
It's (d)
I know ethanoic acid is formed but isn't HCO2CH3 just another way of writing CH3CO2H?

No!
HCO2CH3 is in fact an ester!
The name is methylmethanoate.
It can be formed by esterification of methanoic acid (HCOOH) and methanol (CH2OH).
If we wanted to write ethanoic acid with the acid group on the left, we'd write:
HO2CCH3.

Because otherwise an R1-CO2-R2 is interpreted as an ester.

 

[Eugene99]

No!
HCO2CH3 is in fact an ester!
The name is methylmethanoate.
It can be formed by esterification of methanoic acid (HCOOH) and methanol (CH2OH).
If we wanted to write ethanoic acid with the acid group on the left, we'd write:
HO2CCH3.

Because otherwise an R1-CO2-R2 is interpreted as an ester.

wow, you just cleared my concept. thank you! Okay, just one more please


We have to draw the Hess's law here. In b(iii), we found enthalpy change of K2CO3, it was -32.6 kJ/mol and in c(iii), we found enthalpy change of KHCO3, it was +23.19 kJ/mol , can you please draw the Hess's cycle for me??

 

[Iris Dylan Lane]

Solids W, X, Y and Z are compounds of two different Group II metals. Some of their applications are described below. Compound W is used as a refractory lining material in kilns. Compound X is used as a building material. It can also be heated in a kiln to form compound Y. When Y is hydrated, it forms compound Z which is used agriculturally to treat soils.
Which statements about these compounds are correct?

1 Adding W to water has less effect on pH than adding Y.
2 Adding Z to soil increases the pH of the soil.
3 The metallic element in Y reacts with cold water more quickly than the metallic element in W.

Answer A.
My Name? How please?