Chemistry: Post your doubts here!

[darks]

THANKYOUU n SRRY ABOUT Q 26 THIS IS WHEN I SOLVE A Q.P AT 3:00 AM.
CAN U PLZZ EXplain Q27??
if u hv time 19 n 10 too?

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.

 

[Metanoia]

What paper is this??
Variant???

You can check my youtube playlist, there are a few years available.

 

[shahzaib ihsan]

hello guys can anyone help me with this question it is urgent!
http://imgur.com/FB1n0m4

 

[shahzaib ihsan]

The last one .Ethyl methanoate + H2SO4 ( ester hydrolysis)

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

 

[Holmes]

A- Inital: 2 : 0 : 0
Final : 2-x: 2x : x
Total moles: 2-2+2x+x = 3x so A is incorrect.

B-
Initial: 2 : 0 : 0
Final: 2-2x : 2x : x
Total moles: 2-2x+2x+x = 2+x so B is incorrect

C-
Initial: 2 : 0 : 0
Final 2-2x:x:x
Total = 2-2x+x+x = 2 incorrect

D-
Initial: 2 : 0 : 0
Final: 2-x : x/2 : x [x = 2R]
Total moles = 2-x+x/2+x =2+x/2 mols!

I am speechless. You are great. Thanks for TEACHING me this question.
Thanks again and again.

 

[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 ??

Q 30. X has a Ph=3 so this shows that this is an acid.
so it would be :
CH3CH2CH2COOH

Compound Y is a secondary alcohol which would be like:
CH3CH(OH)CH3

When X and Y are heated together with Concentrated H2SO4 an ESTER and water is obtained. following steps are occur.
H from acid and OH from Alcohol is removed to form a product WATER.

CH3CH2CH2COO......H + OH....CH(CH3)2
AND this is formed:
CH3CH2CH2COOCH(CH3)2
or it can be written as :
CH3(CH2)2CO2CH(CH3)2

Hope it helped.

 

[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.