Chemistry: Post your doubts here!

[PhyZac]

Assalamu Alikum.. XPFMember elbeyon

Why? the answer is C??

 

[XPFMember]

Assalamu Alikum.. XPFMember elbeyon

Why? the answer is C??
View attachment 16468

WaAlaikumAsSalam Wr Wb...

Product will be ethanoic acid...since it's left for a long time..!!

gotta go....work it out...if not will tell u later

 

[PhyZac]

WaAlaikumAsSalam Wr Wb...

Product will be ethanoic acid...since it's left for a long time..!!

gotta go....work it out...if not will tell u later

Jazak Allah so much....

Yes got is ...it is C......

Because like ethanol mole should be found and then find mass of ehanoic acid...and then take 75% ....i got it....Jazak Allah

Another Doubt WHy is the marked answer is right while others not ? :S

 

[zenyatales]

This is a simple dilution question.
First there's some acid - FA1.
We take 38 cm^3 of FA1 and dilute it in a 250 cm^3 flask by adding distilled water uptil the 250 mark. And call it FA3.
We take some of FA3 and titrate it and figure out that the conc of the acid in the burette = 0.732 mol/dm^3

Now, the question is to find the no. of moles of the acid in the 250 cm^3 flask.

Using n=v * c
= (?) * 0.732

Which volume to use here ? 38 cm^3 or 250 cm^3 ??

 

[XPFMember]

This is a simple dilution question.
First there's some acid - FA1.
We take 38 cm^3 of FA1 and dilute it in a 250 cm^3 flask by adding distilled water uptil the 250 mark. And call it FA3.
We take some of FA3 and titrate it and figure out that the conc of the acid in the burette = 0.732 mol/dm^3

Now, the question is to find the no. of moles of the acid in the 250 cm^3 flask.

Using n=v * c
= (?) * 0.732

Which volume to use here ? 38 cm^3 or 250 cm^3 ??

AOA!
see, it's 250cm^3....bcoz u find the conc. of FA3 right? if it's conc. of FA1 then you'll use 38

 

[zenyatales]

^thank you,for clearing my confusion.

AOA!
see, it's 250cm^3....bcoz u find the conc. of FA3 right? if it's conc. of FA1 then you'll use 38

 

[VicBoss]

S07 p31 colourless gas is released (effervescent observed ) by the addition of acid. So it can be CO2 or SO2 (its co2) ,how am i suppose to know which one it is without carrying out a test or using least time possible?

 

[Minato112]

S07 p31 colourless gas is released (effervescent observed ) by the addition of acid. So it can be CO2 or SO2 (its co2) ,how am i suppose to know which one it is without carrying out a test or using least time possible?

SO2 carries with it an smelly fume whereas CO2 doesnt. Hope it helps

 

[champ-student]

2 A student does some tests on hydrochloric acid to investigate its properties.
(a) A few drops of litmus solution are added to hydrochloric acid. An excess of aqueous
sodium hydroxide is added.
What colour change is seen?
The colour changes from ................................. to .................................

 

[champ-student]

2 A student does some tests on hydrochloric acid to investigate its properties.
(a) A few drops of litmus solution are added to hydrochloric acid. An excess of aqueous
sodium hydroxide is added.
What colour change is seen?
The colour changes from ................................. to .................................

 

[champ-student]

http://www.xtremepapers.com/community/threads/any-sort-of-o-level-doubts-solve-them-here.20512/

 

[Minato112]

2 A student does some tests on hydrochloric acid to investigate its properties.
(a) A few drops of litmus solution are added to hydrochloric acid. An excess of aqueous
sodium hydroxide is added.
What colour change is seen?
The colour changes from ................................. to .................................

From red to blue.
It turns red in acid. When NaOH is added, the acid in neutralised and the alkali NaOH remains. It thus turns blue.

 

[pranav014]

worksheet explaining enthalpy changes ny1...
tks very much!!

 

[allysaleemally]

Hii, could anyone explain me question 4 a, 4b from chemistry paper 2, may june 2009 v1.
here are the links: http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_s09_qp_2.pdf
marksheet: http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_s09_qp_2.pdf


Thank you very much

 

[Student12]

Hii, could anyone explain me question 4 a, 4b from chemistry paper 2, may june 2009 v1.
here are the links: http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s09_qp_2.pdf
marksheet: http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s09_qp_2.pdf


Thank you very much

In place of the MS its the question paper.. direct a link to the MS so someone could help you.

 

[Student12]

Hii, could anyone explain me question 4 a, 4b from chemistry paper 2, may june 2009 v1.
here are the links: http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s09_qp_2.pdf
marksheet: http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s09_qp_2.pdf


Thank you very much

Edit and place the MS.
i'm going to give a try..
For the part a :
Firstly you need to learn all the reactions of organic chemistry to solve this question:

• B- CH3CHO ---> CH3CH(OH)CN [When aldehyde reacts with HCN+NaCN at a temp of 10-20 degree C gives that product, Showing an increaase in the no.of carbon atoms and its a Nucleopilic addition rxn]
• When product B reacts with dilute H2SO4or HCl when heated it gives a -COOH in place of -CN and -OH remains the same. So its going to be like.. CH3CH(OH)CN ---> CH3CH(OH)COOH
• E- CH3CHO ---> CH3COO- [An aldehyde CH3CHO ----->CH3COO- + Ag when reacted with Tollens reagent [Ag(NH3)2]+ ]

• C- CH3=CHCOOH ----> OHCH2CH(OH)COOH [When alkene reacts with Cold KMnO4 when the double bond is broken two -OH are added, eg: CH2=CH2 ---> CH2(OH)CH2(OH) and its an electrophilic addition reaction. The -COOH remains the same.
• When C reacts with Cr2O7 2-/H+ the COOH at the right remains as it is.. the secondary alcohol changes to a Ketone and Primary alcohol to -COOH, so it has two reactions happening at the same time.. that is the rxn of Primary and secondary alcohol.
• D- aldehyde changes to primary alcohol on reduction. The -CHO changes to -OH.
  
  For part B i don't really know well but..
  (i) The carboxilic acid when reacted with a CH3CH2OH with concentrated H2SO4 (heat) gives an ester.
  (ii) Probably someone else could help u out cuz i'm not sure.
  
  Hope this will help you in someway and if i've made any mistake please correct me cuz even i'm still a learner. ​

 

[inquisitiveness]

Hi everyone,
my question is about the extraction of iron ore,limestone is used to neutralise sand,giving calcium silicate which is used for road building when solidifies....does that mean sand is an acid?and why is calcium silicate especially used for road building?
thank you

 

[snowbrood]

can a tertiary alcohol react with carboxyllic acid forming an ester??

 

[Miss_Z]

Hi everyone,
my question is about the extraction of iron ore,limestone is used to neutralise sand,giving calcium silicate which is used for road building when solidifies....does that mean sand is an acid?and why is calcium silicate especially used for road building?
thank you

Limestone, i.e Calcium carbonate, is actually first decomposed to give Calcium oxide and carbon dioxide. It is this Calcium oxide, which is a basic oxide, that then reacts with silicon dioxide (sand) which is an acidic oxide (since it is a non-metal oxide), to form calcium silicate.

 

[aiskw1]

Edit and place the MS.
i'm going to give a try..
For the part a :
Firstly you need to learn all the reactions of organic chemistry to solve this question:

• B- CH3CHO ---> CH3CH(OH)CN [When aldehyde reacts with HCN+NaCN at a temp of 10-20 degree C gives that product, Showing an increaase in the no.of carbon atoms and its a Nucleopilic addition rxn]
• When product B reacts with dilute H2SO4or HCl when heated it gives a -COOH in place of -CN and -OH remains the same. So its going to be like.. CH3CH(OH)CN ---> CH3CH(OH)COOH
• E- CH3CHO ---> CH3COO- [An aldehyde CH3CHO ----->CH3COO- + Ag when reacted with Tollens reagent [Ag(NH3)2]+ ]

• C- CH3=CHCOOH ----> OHCH2CH(OH)COOH [When alkene reacts with Cold KMnO4 when the double bond is broken two -OH are added, eg: CH2=CH2 ---> CH2(OH)CH2(OH) and its an electrophilic addition reaction. The -COOH remains the same.
• When C reacts with Cr2O7 2-/H+ the COOH at the right remains as it is.. the secondary alcohol changes to a Ketone and Primary alcohol to -COOH, so it has two reactions happening at the same time.. that is the rxn of Primary and secondary alcohol.
• D- aldehyde changes to primary alcohol on reduction. The -CHO changes to -OH.
  
  For part B i don't really know well but..
  (i) The carboxilic acid when reacted with a CH3CH2OH with concentrated H2SO4 (heat) gives an ester.
  (ii) Probably someone else could help u out cuz i'm not sure.
  
  Hope this will help you in someway and if i've made any mistake please correct me cuz even i'm still a learner. ​

For Part B (ii) I think the answer would still be an ester formation

Heres what I thought for B(ii) :

the compound cam be drawn for C as

CH2OH
|
CHOH
|
COOH

therefore only the top and second chain will react with CH3COOH to form an ester

CH2OOCCH3
|
CHOOCCH3
|
COOH

I don't know why it is written as this though as they both essentially mean the same thing, as if the 2nd carbon on the top chain was an ether, and joined by single bond to O then it would not have a full octet shell (8 electrons)

CH2OCOCH3
|
CHOCOCH3
|
CO2H

I hope someone could explain why it's written as it is like that