Chemistry: Post your doubts here!

[The Sarcastic Retard]

Q = mCT
m = grams
C = J/kg/K
T = celcius
Then how is Q is Joules?
Shouldn't the temperature be in Kelvin so that the K's cancel from T and C? :S

The formula is Q = mC(delta)T. Where deltaT is read as change in temperature.
So let us take 2 of the random temperatures, let it be 23(degree)C and 45(degree)C
Now change in to kelvin by adding 273, hence 23 becomes 296K and 45 becomes 318.
Now change in temperature in both kelvin and celsius is 22. So you see no change.
To save the time people let it be in celcius.

 

[The Sarcastic Retard]

Someone please help (M/J 2011 paper 22 question 5)
In part b, how come the answer is dilute H2SO4 not concentrated H2SO4??

Also part e(i) , the aldehyde products of the partial oxidation of CH3(CH2)7CH--CH(CH2)7X (where X represents the rest of the molecule)
the mark scheme wrote two products, one of them being OHC(CH2)7CX .. I dont understand why is there an additional C beside the X???

Thank you :3

b)Dilute H2sO4, Concentrated would cause other reaction.

e)i)CH3(CH2)7CHO
OHC(CH2)7CX
Split the double bond and partially oxidise it; that is keep the end point as the Aldehyde.

 

[The Sarcastic Retard]

Salam I need examiner reports of all past papers ... plz send me the link where i can get

At last you will get specimenpapers and examiner report

 

[The Sarcastic Retard]

I want specimen papers for 2015

 

[Metanoia]

View attachment 52918

question 7, answer is C, but how do you know that?

25 Use of the Data Booklet is relevant to this question. 2.30 g of ethanol were mixed with aqueous acidified potassium dichromate(VI) and the desired organic product was collected by immediate distillation under gentle warming. The yield of product was 70.0%. What mass of product was collected?
A 1.54g
B 1.61g
C 2.10g
D 2.20g
answer is A, and I'm not getting that answer, I'm getting C...!

product is ethanal C2H4O. (not ethanoic acid), as product is obtained by "immediate distillation under gentle warming"

mass of ethanol converted = 0.7 (2.3) = 1.61 g
moles of ethanol converted = 1.61/46 = 0.035 mol
moles of ethanal produced = 0.035 mol
mass of ethanal produced = 0.035 x 44 = 1.54 g

 

[The Sarcastic Retard]

product is ethanal C2H4O. (not ethanoic acid), as product is obtained by "immediate distillation under gentle warming"

mass of ethanol converted = 0.7 (2.3) = 1.61 g
moles of ethanol converted = 1.61/46 = 0.035 mol
moles of ethanal produced = 0.035 mol
mass of ethanal produced = 0.035 x 44 = 1.54 g

That's ethanal ryt?

 

[Tasneem_m98]

Since there has to be 8 carbon in total

But OHC(CH2)7CX has 9 carbon ..where did that final C beside the X come from?! It wasnt there in the original reactant.

 

[Tasneem_m98]

B

b)Dilute H2sO4, Concentrated would cause other reaction.

e)i)CH3(CH2)7CHO
OHC(CH2)7CX
Split the double bond and partially oxidise it; that is keep the end point as the Aldehyde.

But why is there an extra C beside the X? It wasnt even there in the original reactant.

 

[asadalam]

B


But why is there an extra C beside the X? It wasnt even there in the original reactant.

I think that may have been a typo in the ms,it shouldnt be there

 

[Metanoia]

That's ethanal ryt?

Yes, aldehyde.

 

[Tasneem_m98]

I think that may have been a typo in the ms,it shouldnt be there

Oh alright then, thank you so much!

 

[bubbles1997]

Please share the guess paper for biology practical 33
https://www.xtremepapers.com/community/threads/as-biology-33-2015-m-j.41027/

 

[nehaoscar]

The formula is Q = mC(delta)T. Where deltaT is read as change in temperature.
So let us take 2 of the random temperatures, let it be 23(degree)C and 45(degree)C
Now change in to kelvin by adding 273, hence 23 becomes 296K and 45 becomes 318.
Now change in temperature in both kelvin and celsius is 22. So you see no change.
To save the time people let it be in celcius.

Oh ok! I was converting the change itself to Kelvin Thanks!

 

[Midnight dream]

Well, i need an urgent help.
If we add H2 with platinium catalyst, wiil the aldehyde and ketone be reduced back to their alcohol forms?
Lola_sweet Metanoia
or anyone ?

 

[The Sarcastic Retard]

Well, i need an urgent help.
If we add H2 with platinium catalyst, wiil the aldehyde and ketone be reduced back to their alcohol forms?
Lola_sweet Metanoia
or anyone ?

The reduction of an aldehyde:
You get exactly the same organic product whether you use lithium tetrahydridoaluminate or sodium tetrahydridoborate.

For example, with ethanal you get ethanol:
Image attached.
[H] means "hydrogen from a reducing agent".

In general terms, reduction of an aldehyde leads to a primary alcohol.


The reduction of a ketone:

Again the product is the same whichever of the two reducing agents you use.

For example, with propanone you get propan-2-ol:
Image attached.

Reduction of a ketone leads to a secondary alcohol.

Look at the reaction below:¬

 

[Midnight dream]

The reduction of an aldehyde:
You get exactly the same organic product whether you use lithium tetrahydridoaluminate or sodium tetrahydridoborate.

For example, with ethanal you get ethanol:
Image attached.
[H] means "hydrogen from a reducing agent".

In general terms, reduction of an aldehyde leads to a primary alcohol.


The reduction of a ketone:

Again the product is the same whichever of the two reducing agents you use.

For example, with propanone you get propan-2-ol:
Image attached.

Reduction of a ketone leads to a secondary alcohol.

Look at the reaction below:¬

thnkss.. but i was actually asking whether H2 with platinium catalyst reduce the aldehyde or not?
i know NaBH4 will do it..

 

[nehaoscar]

Ok so i know the fehling's and tollens tests and what results you get and all
but i need what the actual reaction takes place
like sometimes it asks you to write the product that is formed with the reaction with fehlings and tollens
So can someone give me a example please and state what the product would be?

 

[qwertypoiu]

thnkss.. but i was actually asking whether H2 with platinium catalyst reduce the aldehyde or not?
i know NaBH4 will do it..

There are various reducing agents for carbonyl compounds:

• NaBH4(aq)
• LiAlH4/ether
• Na/ethanol
• H2/(Pt or Ni catalyst)

So yes, it would.

 

[Midnight dream]

There are various reducing agents for carbonyl compounds:

• NaBH4(aq)
• LiAlH4/ether
• Na/ethanol
• H2/(Pt or Ni catalyst)

So yes, it would.

*sobbing* then why does the m.s says it doesn't..
well thnkss..

 

[The Sarcastic Retard]

*sobbing* then why does the m.s says it doesn't..
well thnkss..

Paper?