Chemistry: Post your doubts here!

[Holmes]

http://papers.gceguide.com/A Levels/Chemistry (9701)/9701_s16_qp_13.pdf
Q30, ???
Q 33 What does statement 2 mean?
Q24 How can D be correct? Doesnt hot kmno4 oxidise to aldehydes and cooh?
Q23 Hiw do v know what radicals form?
q 21 plz show diagram..while explaining
Q14 ??

http://papers.gceguide.com/A Levels/Chemistry (9701)/9701_s16_qp_13.pdf

Respected amina1300 ,
the link you have posted is of variant 13 while when you click on the link variant "12" opens.
Kindly look to the problem.

 

[Holmes]

no the answer is a (br2).. i also chose d

Oh a bit tricky but an easy one:
the correct answer is A.
If you look at the oxidation state of Br2 .
Before the reaction it is 0 but t after the reaction is oxidation state decreases to -1.
Br2 = 0
CH3CHBrCH2Br : here oxidation state of Br is -1.

I hope it make sense.

 

[Holmes]

no the answer is a (br2).. i also chose d

 

[Holmes]

http://papers.gceguide.com/A Levels/Chemistry (9701)/9701_s16_qp_13.pdf
Q30, ???
Q 33 What does statement 2 mean?
Q24 How can D be correct? Doesnt hot kmno4 oxidise to aldehydes and cooh?
Q23 Hiw do v know what radicals form?
q 21 plz show diagram..while explaining
Q14 ??

 

[Holmes]

Q24 How can D be correct? Doesnt hot kmno4 oxidise to aldehydes and cooh?

It purely depends on the position of C=C and the number of groups attached to it.
A compound like this
CH3CH2CH2OH
will be oxidised to form :
CH3CH2COOH (forming Carboxylic Acid)

While a compound like this :
CH3CH(OH)CH2CH3
will be oxidised to :
CH3(C=O)CH2CH3 (forming a Ketone)

so watch out whether the alcohol is PRIMARY or SECONDARY.

(I cant actually display the skeletal formula so ....)

I hope I made some success.

 

[Holmes]

no the answer is a (br2).. i also chose d

 

[Holmes]

http://papers.gceguide.com/A Levels/Chemistry (9701)/9701_s16_qp_13.pdf
Q30, ???
Q 33 What does statement 2 mean?
Q24 How can D be correct? Doesnt hot kmno4 oxidise to aldehydes and cooh?
Q23 Hiw do v know what radicals form?
q 21 plz show diagram..while explaining
Q14 ??

 

[Holmes]

Q24 How can D be correct? Doesnt hot kmno4 oxidise to aldehydes and cooh?

It purely depends on the position of C=C and the number of groups attached to it.
A compound like this
CH3CH2CH2OH
will be oxidised to form :
CH3CH2COOH (forming Carboxylic Acid)

While a compound like this :
CH3CH(OH)CH2CH3
will be oxidised to :
CH3(C=O)CH2CH3 (forming a Ketone)

so watch out whether the alcohol is PRIMARY or SECONDARY.

(I cant actually display the skeletal formula so ....)

I hope I made some success.

 

[amina1300]

http://papers.gceguide.com/A Levels/Chemistry (9701)/9701_s16_qp_13.pdf

Respected amina1300 ,
the link you have posted is of variant 13 while when you click on the link variant "12" opens.
Kindly look to the problem.

Thanks ....but yeah I saw your explanations and realized that... I meant variant 13 though.

 

[amina1300]

Q 27)
5 possible oxidation products will contain groups this way..
acid & alcohol
acid & acid
acid and aldehyde
alcohol and aldehyde
aldehyde and aldehyde
This equals to acid and aldehyde both being used 4 times each.

Q10) As the question states Mn2+ (product) Catalyses the reaction, so rate gets higher as reaction proceeds. So faster decrease in MnO4-(reactant) conc. with time. So ans B. At the end, the graph is less steep as the reactant conc. very low so less collisions.
Sorry for brief explanations.. all the rest i can explain tomorrow.. i have bio p1 tomorrow.

I hope you Bio exam went well. Can you please explain Q27 in detail .

 

[darks]

I hope you Bio exam went well. Can you please explain Q27 in detail .

Went well
so for q27. All are 2 carbon structures. q. asks for all possible "oxidation products" without telling any reagent. So the products possible considering secondary alcohol,
can contain either acid group or/and aldehyde group. So consider all the possible combinations i have stated in previous reply. And draw the "5" possible products.. Then simply count the times, each group appears.

 

[amina1300]

http://papers.gceguide.com/A Levels/Chemistry (9701)/9701_s16_qp_11.pdf
Q4 I dont understand what Np Pu mean??
Q6 ??
Q17 ??
Q30??

http://papers.gceguide.com/A Levels/Chemistry (9701)/9701_s16_qp_13.pdf
Q9 ???
Q21 ??
Q33 Statement 2 ; No particles have zero energy at either temperature. ?? What does this mean in context?

 

[amina1300]

Went well
so for q27. All are 2 carbon structures. q. asks for all possible "oxidation products" without telling any reagent. So the products possible considering secondary alcohol,
can contain either acid group or/and aldehyde group. So consider all the possible combinations i have stated in previous reply. And draw the "5" possible products.. Then simply count the times, each group appears.

Thankyooouu!!!

 

[amina1300]

A student mixed 25.0cm3 of 4.00 moldm–3 hydrochloric acid with an equal volume of 4.00moldm–3 sodium hydroxide. The initial temperature of both solutions was 15.0°C. The maximum temperature recorded was 30.0°C.
Using these results, what is the enthalpy change of neutralisation of hydrochloric acid?
A –62.7kJ mol–1 B –31.4kJ mol–1 C –15.7kJ mol–1 D –3.14kJ mol–1

How do I solve this????
Im using Q = mc T
= (18*0.1)(4.2)(15)
the Q/(1000*0.1)
What am I doing wrong answer is B.

 

[darks]

A student mixed 25.0cm3 of 4.00 moldm–3 hydrochloric acid with an equal volume of 4.00moldm–3 sodium hydroxide. The initial temperature of both solutions was 15.0°C. The maximum temperature recorded was 30.0°C.
Using these results, what is the enthalpy change of neutralisation of hydrochloric acid?
A –62.7kJ mol–1 B –31.4kJ mol–1 C –15.7kJ mol–1 D –3.14kJ mol–1

How do I solve this????
Im using Q = mc T
= (18*0.1)(4.2)(15)
the Q/(1000*0.1)
What am I doing wrong answer is B.

I made the mistake of using wrong mass in p34 cuz it was tough and my mind stopped working
the mass in this in 25cm3 of each.. so 50cm3 total. Put in formula and you get the correct answer...Remember that the mass used is always of the liquid..

 

[amina1300]

I made the mistake of using wrong mass in p34 cuz it was tough and my mind stopped working
the mass in this in 25cm3 of each.. so 50cm3 total. Put in formula and you get the correct answer...Remember that the mass used is always of the liquid..

Oh i got it 1 cm3 of water has a mass of 0.001 kg or 1 g

 

[darks]

why do we use the volume ...?!! I could have never have thought of this.

That's what we always use! I take it as a rule.. don't know the reason behind it.. But i think it's that the temperature change that occurs, is of the "solution" so we consider the mass of the solution.

 

[amina1300]

That's what we always use! I take it as a rule.. don't know the reason behind it.. But i think it's that the temperature change that occurs, is of the "solution" so we consider the mass of the solution.

dummb me Im at my last Chem exam and I learn this now!!!!!!!
Any tips for tomorrows examm???

 

[SohaibButt]

Anyone?

 

[darks]

dummb me Im at my last Chem exam and I learn this now!!!!!!!
Any tips for tomorrows examm???

Metallic9896 tips!!! Especially for timing! i seem to take extra 10-15 minutes for chem!