Chemistry: Post your doubts here!

[mamoon123]

Q. 2.80g of a group II metal carbonate, XCO3, is added to 50cm^3 of 2.00 moldm^-3 HCl (excess) in a plastic cup. the temperature rose by 9.7K. Calculatre the Mr of the carbonate.

for this question, can we assume that q= sum of all the bond energies of bonds involved in the formula q=mcdT? I cant think of any other technique..

XCO3 + 2HCl ---> XCl2 + H2O + CO2
2.80g of XCO3 (ignore it for now)
x mol of XCO3 react with 2x mol of HCl
Moles of HCl = Volume(cm^3) multiplied by concentration(mol dm-3) DIVIDED by 1000
--> (50*2.00) / 1000
--> 0.1 mol

Compare the mole ratio.
If 2x = o.1 mol
then x = 0.05 mol

Now that you have the moles and the mass, find the Mr by using this:
Mr = mass/mol
--> 2.8/0.05
--> 56
Is this the correct answer?

Do forgive me if I wrote anything incorrect. Allah knows best.

 

[mamoon123]

View attachment 21026
In this question, I'm unsure of the products of each reaction as in the book it only details about when you have only one halogen attached to an alkene/alkane... What kind of reaction will happen with each answer? THis confused me because for example with NaOH, I'm not sure which of the carbon atoms the OH- ion attaches to. Do you classify this as an alkene or a halogenoalkene? And the syllabus doesn't say anything about halogenoalkenes... So how would you know how it would react with each one?

Asalam alaikum brother.
Is the answer A?
In questions like these you have to keep in mind ALL the products that would be produced if the reactant is mixed separately with the substance in the options and all the required conditions are met.
I'll start with the incorrect one's first.
B) HCl; keeping our knowledge of organic chemistry in mind, this will be an addition reaction, in which the double bond will be changed into a single bond, giving room for the H and Cl to attach to DIFFERENT carbon atoms.
The products will be:
-> CH2CCl3
-> CHCl2CHCl2
Neither are chiral, lets move on to C.
C) NaCN; this would again lead to an addition reaction (nucleophilic), but if memory serves me, it only happens when there is a carbonyl group attached to a carbon atom. Incorrect.
D) NaOH; again, a nucleophilic substitution will occur BUT the C-C double bond will still remain, and for a carbon atom to be chiral it MUST have 4 different alkyl groups/atoms attached to it. Incorrect.

Now for the correct option, A.
Br2.
This will be an electrophilic addition reaction which involves the forming of a carbon cation thus resulting in the breaking to the double bond.
The only product will be:
-> CHClBrCCl2Br
Which is indeed chiral.

Do forgive me if I wrote anything incorrect. Allah knows best.

 

[aalmuhannadi]

Asalam alaikum brother.
Is the answer A?
In questions like these you have to keep in mind ALL the products that would be produced if the reactant is mixed separately with the substance in the options and all the required conditions are met.
I'll start with the incorrect one's first.
B) HCl; keeping our knowledge of organic chemistry in mind, this will be an addition reaction, in which the double bond will be changed into a single bond, giving room for the H and Cl to attach to DIFFERENT carbon atoms.
The products will be:
-> CH2CCl3
-> CHCl2CHCl2
Neither are chiral, lets move on to C.
C) NaCN; this would again lead to an addition reaction (nucleophilic), but if memory serves me, it only happens when there is a carbonyl group attached to a carbon atom. Incorrect.
D) NaOH; again, a nucleophilic substitution will occur BUT the C-C double bond will still remain, and for a carbon atom to be chiral it MUST have 4 different alkyl groups/atoms attached to it. Incorrect.

Now for the correct option, A.
Br2.
This will be an electrophilic addition reaction which involves the forming of a carbon cation thus resulting in the breaking to the double bond.
The only product will be:
-> CHClBrCCl2Br
Which is indeed chiral.

Do forgive me if I wrote anything incorrect. Allah knows best.

Thanks for the explanation, the answer was actually A after I did it again, I misread the mark scheme! Thank you so much for explaining it though, really helped.

 

[mamoon123]

Thanks for the explanation, the answer was actually A after I did it again, I misread the mark scheme! Thank you so much for explaining it though, really helped.

Cheers
Glad I could be of help.

 

[Kelly Li]

Need help with this

Which of the following exerts the highest pressure?
A 1 mol of N2 at 0°C in 11.2 dm3
B 1 mol of N2 at 27 0°C in 22.4 dm3
C 1 mol of H2O at 27 0°C in 1 dm3
D 1 mol of C4H10 at its normal boiling point

 

[mamoon123]

Need help with this

Which of the following exerts the highest pressure?
A 1 mol of N2 at 0°C in 11.2 dm3
B 1 mol of N2 at 27 0°C in 22.4 dm3
C 1 mol of H2O at 270°C in 1 dm3
D 1 mol of C4H10 at its normal boiling point

Is the answer C?

 

[Kelly Li]

Is the answer C?

No. The answer is A. I can't figure out why though

 

[mamoon123]

No. The answer is A. I can't figure out why though

Can you specify the year you got this question from? The paper variant as well.

 

[Kelly Li]

Can you specify the year you got this question from? The paper variant as well.

J94/IV/4

 

[aleezay]

XCO3 + 2HCl ---> XCl2 + H2O + CO2
2.80g of XCO3 (ignore it for now)
x mol of XCO3 react with 2x mol of HCl
Moles of HCl = Volume(cm^3) multiplied by concentration(mol dm-3) DIVIDED by 1000
--> (50*2.00) / 1000
--> 0.1 mol

Compare the mole ratio.
If 2x = o.1 mol
then x = 0.05 mol

Now that you have the moles and the mass, find the Mr by using this:
Mr = mass/mol
--> 2.8/0.05
--> 56
Is this the correct answer?

Do forgive me if I wrote anything incorrect. Allah knows best.

But it says that the acid is in excess.. by what amount,we dont know.. shouldnt there be some other technique? Thank you for trying btw

 

[mamoon123]

But it says that the acid is in excess.. by what amount,we dont know.. shouldnt there be some other technique? Thank you for trying btw

Ah, didn't see that it was excess.
A thousand pardons.

 

[darknessinme]

Need help with this

Which of the following exerts the highest pressure?
A 1 mol of N2 at 0°C in 11.2 dm3
B 1 mol of N2 at 27 0°C in 22.4 dm3
C 1 mol of H2O at 27 0°C in 1 dm3
D 1 mol of C4H10 at its normal boiling point

For A and B you can figure out pressure using the ideal gas equation. C can be eliminated by asking what state is water in at 27 Celsius? For D, at boiling point , vapor pressure=atmospheric pressure=100kPa.
You can then conclude A must be the answer.

 

[Kelly Li]

For A and B you can figure out pressure using the ideal gas equation. C can be eliminated by asking what state is water in at 27 Celsius? For D, at boiling point , vapor pressure=atmospheric pressure=100kPa.
You can then conclude A must be the answer.

Ty

 

[!>@/^~^\@<!]

When hydrogen halide reacts with alkene, the conditions of the reaction r conc. aq solution of hydrogen halide in "cold" at "room temperature"..
Isn't it contradictory cold and room temperature...???
Plz ans asap..

 

[!>@/^~^\@<!]

Hi everyone, AsSalamoAlaikum Wr Wb..

To get things organized in a better way, I am making this thread. As othewise, some queries remain unanswered!

So post your CHEMISTRY doubts in this thread. InshaAllah members around will help you.

Any Chemistry related notes and links will be added here in this post. Feel free to provide the links to your notes around the forum, or any other websites!

Chemistry Notes:


http://www.chemguide.co.uk This is the website, which contains almost everything classified according to the syllabus.

Tips for solving chemistry MCQs 9701/01

Chemistry P5 Tips and Notes

Some links & Notes - by 'destined007'

Chemistry worksheets Link shared by hassam

Chemistry Application Booklet: Mistakes and Corrections!

Calculations for A level Chemistry, author E.N. Ramsden third edition ebook download.


Regards,
XPC Staff.

Can u plz ans this ques..
When hydrogen halide reacts with alkene, the conditions of the reaction r conc. aq solution of hydrogen halide in "cold" at "room temperature"..
Isn't it contradictory cold and room temperature...???

 

[Warrior66]

When hydrogen halide reacts with alkene, the conditions of the reaction r conc. aq solution of hydrogen halide in "cold" at "room temperature"..
Isn't it contradictory cold and room temperature...???
Plz ans asap..

basically over here, room temperature is taken to be "cold conditions" {cold dilute acidified manganate (VII) solution} and under harsher conditions "Hot conditions" is taken to be higher temperatures {hot, concentrated manganate (VII) solution}.

 

[scouserlfc]

Salaam. Plz help me with this simple calculation.View attachment 21135

Wallaikumassalam !
Well as u see that oxygen is in excess and only 30cm^3 is used in the reaction so 20 of it remains plus the volume of CO2 is 10 and SO2 is 20 this i came to know using that Avogadro gas law which states in a reaction involving gases the volume are in ratio with the moles(remember only use this when u have all gases ) so since 1 mole corresponds to 10cm^3 (from looking at CS2) then u can calculate all volumes plus O2 !
Now when NaOH reacts with the gases remaining it actually first reacts with CO2 (just like limewater does with CO2 and forms the CaCO3 which is insoluble ) here it forms Na2CO3 which is soluble also since it is in excess you should remember that SO2 is an acid so it actually reacts with NaOH and forms Na2SO3 leaving that 20 of O2 only !

 

[TERMINATOR]

Wallaikumassalam !
Well as u see that oxygen is in excess and only 30cm^3 is used in the reaction so 20 of it remains plus the volume of CO2 is 10 and SO2 is 20 this i came to know using that Avogadro gas law which states in a reaction involving gases the volume are in ratio with the moles(remember only use this when u have all gases ) so since 1 mole corresponds to 10cm^3 (from looking at CS2) then u can calculate all volumes plus O2 !
Now when NaOH reacts with the gases remaining it actually first reacts with CO2 (just like limewater does with CO2 and forms the CaCO3 which is insoluble ) here it forms Na2CO3 which is soluble also since it is in excess you should remember that SO2 is an acid so it actually reacts with NaOH and forms Na2SO3 leaving that 20 of O2 only !

JazaakAllahu khairan.

 

[Student12]

i neeed help ! AS questions..

How many isomers with the formula C5H10 have structures that involves pi bonding?
A 3 B 4 C 5 D6

The ans is D !

 

[aalmuhannadi]

In this question, I know the answer is D but why is C wrong? It does have a chiral centre as well as a carboxylic acid group, so it's both chiral and acidic...