Chemistry: Post your doubts here!

[h4rriet]

An organic compound J reacts with sodium to produce an organic ion with a charge of –3.
J reacts with NaOH(aq) to produce an organic ion with a charge of –1.
What could be the structural formula of J?
A HO2CCH(OH)CH2CO2H
B HO2CCH(OH)CH2CHO
C HOCH2CH(OH)CH2CO2H
D HOCH2COCH2CHO

The functional groups that react with Na are CO2H and OH, so three of any of these should be present in the compound. B and D are ruled out. NaOH will react with CO2H, so there should be 1 CO2H and 2 OH groups.

 

[h4rriet]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w12_qp_11.pdf
Q23, Q17

17. Find the number of moles of O2 and construct equations for the combustion of Ca and Mg. Find the moles of the metal and check mole ratios.
23.

 

[Dr.MMM]

C

The functional groups that react with Na are CO2H and OH, so three of any of these should be present in the compound. B and D are ruled out. NaOH will react with CO2H, so there should be 1 CO2H and 2 OH groups.

Can you please further explain the process. Also, solve the following
A sample of ethyl propanoate is hydrolysed by heating under reflux with aqueous sodium
hydroxide. The two organic products of the hydrolysis are separated, purified and weighed.
Out of the total mass of products obtained, what is the percentage by mass of each product?
A 32.4% and 67.6%
B 38.3% and 61.7%
C 42.3% and 57.7%
D 50.0% and 50.0%

 

[LeoMessi]

Q 11 of this paper
Please help. I don't get a single thing. Please somebody explain without using the actual answer i mean do the working for all the options. It would be very kind of you.
Please its very urgent . I don't understand equilibrium AT ALL!!!!!

 

[h4rriet]

C
Can you please further explain the process. Also, solve the following
A sample of ethyl propanoate is hydrolysed by heating under reflux with aqueous sodium
hydroxide. The two organic products of the hydrolysis are separated, purified and weighed.
Out of the total mass of products obtained, what is the percentage by mass of each product?
A 32.4% and 67.6%
B 38.3% and 61.7%
C 42.3% and 57.7%
D 50.0% and 50.0%

I don't know how to explain it further. What part don't you understand? I'll explain from there.
Ethyl propanoate is an ester and will get hydrolysed by NaOH. It'll give the sodium salt of the carboxylic acid and the alcohol. Find the molecular masses of those and then calculate the % by mass.

 

[h4rriet]

Q 11 of this paper
Please help. I don't get a single thing. Please somebody explain without using the actual answer i mean do the working for all the options. It would be very kind of you.
Please its very urgent . I don't understand equilibrium AT ALL!!!!!

Q. 11 isn't an equilibrium question; it's the activation energy question.

 

[LeoMessi]

Q. 11 isn't an equilibrium question; it's the activation energy question.

Sorry , Q 11 for this paper please

 

[Aries_95]

Sorry , Q 11 for this paper please

Answer by h4rriet

 

[cute97]

21. The functional groups that react with Na are CO2H and OH, so three of any of these should be present in the compound. B and D are ruled out. NaOH will react with CO2H, so there should be 1 CO2H and 2 OH groups.
22. Find the molecular mass of the products of the hydrolysis of ethyl propanoate. Then find the % by mass.
23. The compound is an ester and will get hydrolysed by the acid.

Thank you but for q21 WHAT ABT the -1 and -3 charges and how did you knw that there should be 1 CO2H and 2 OH grps
Q22 yhh but how sry but am a little bad in chem
Q23 yhh all four answers have COOH grp ?? plz ans

 

[Dr.MMM]

"NaOH will react with CO2H, so there should be 1 CO2H and 2 OH groups." This part please
As for the second question the products will be ethanol and propanoic acid in the ratio 1:1 right?

 

[h4rriet]

Sorry , Q 11 for this paper please

Q. 11: Draw ICE charts for A, B, C and D. That is, initial moles, change in moles and equilibrium moles.
For B, it'll be like this:

 

[Student12]

how does NF3 have 6 bonding pair ?

 

[h4rriet]

Thank you but for q21 WHAT ABT the -1 and -3 charges and how did you knw that there should be 1 CO2H and 2 OH grps

"NaOH will react with CO2H, so there should be 1 CO2H and 2 OH groups." This part please
As for the second question the products will be ethanol and propanoic acid in the ratio 1:1 right?

They're saying that the compound reacts with Na to give a 3+ charged ion. Only OH and CO2H react with Na to give a 1+ charged ion, so there must be 3 functional groups, either CO2H or OH. When NaOH reacts, a compound with a 1+ charge is produced by CO2H only, not OH. That means there is only ONE CO2H in the compound we're talking about. So there is ONE CO2H and TWO OH groups, that makes it 3 overall. So they can react with Na to give a 3+ charged ion and with CO2H to give a 1+ charged ion.

 

[h4rriet]

how does NF3 have 6 bonding pair ?

It doesn't.

 

[LeoMessi]

Answer by h4rriet

Thanks alot.
Could you please answer Q9 of this paper as well. And could you please work out the answer for all the options if its not a problem.
Thanks once again for ur time and effort.

 

[h4rriet]

Q22 yhh but how sry but am a little bad in chem
Q23 yhh all four answers have COOH grp ?? plz ans

22. Ethyl propanoate will give ethanol and sodium propanoate when hydrolysed with NaOH. Find the molecular masses of both, and then find the % by mass. For example, to find the % by mass of ethanol, do (mass by ethanol)/(mass of ethanol + sodium propanoate).
23. Yes, but you have to take into account the number of C atoms as well.

 

[darkxangel]

Propanone has the molecular formula C3H6O.
The enthalpy change of combustion of hydrogen is –286kJmol–1
.
The enthalpy change of combustion of carbon is –394kJmol–1
.
The enthalpy change of combustion of propanone is –1786kJmol–1
.
Using this information, what is the enthalpy change of formation of propanone?
A –1106kJmol–1
B –540kJmol–1
C –254kJmol–1
D +1106kJmol–1

I need help in this question.!

 

[LeoMessi]

Q. 11: Draw ICE charts for A, B, C and D. That is, initial moles, change in moles and equilibrium moles.
For B, it'll be like this:

Thanks alottttt!!!!!!!!!!

 

[Dr.MMM]

They're saying that the compound reacts with Na to give a 3+ charged ion. Only OH and CO2H react with Na to give a 1+ charged ion, so there must be 3 functional groups, either CO2H or OH. When NaOH reacts, a compound with a 1+ charge is produced by CO2H only, not OH. That means there is only ONE CO2H in the compound we're talking about. So there is ONE CO2H and TWO OH groups, that makes it 3 overall. So they can react with Na to give a 3+ charged ion and with CO2H to give a 1+ charged ion.

Thanks

A number of alcohols with the formula C4
H10O are separately oxidised. Using 70g of the alcohols
a 62% yield of organic product is achieved.
What mass of product could be obtained?
1 42.2g of butanone
2 51.6g of butanoic acid
3 51.6g of 2-methyl propanoic acid

 

[h4rriet]

Propanone has the molecular formula C3H6O.
The enthalpy change of combustion of hydrogen is –286kJmol–1
.
The enthalpy change of combustion of carbon is –394kJmol–1
.
The enthalpy change of combustion of propanone is –1786kJmol–1
.
Using this information, what is the enthalpy change of formation of propanone?
A –1106kJmol–1
B –540kJmol–1
C –254kJmol–1
D +1106kJmol–1

I need help in this question.!

Draw a Hess cycle.