Chemistry: Post your doubts here!

[ahmed abdulla]

Cr2O7 2– + 14H+ + 6e– → 2Cr3+ + 7H2O----Eo = 1.33 V
Cl2 + 2e– → 2 Cl– ---------------------------- Eo = 1.36 V
overall ionic equation:
Cr2O7 2– + 6Cl– + 14H+ → 2Cr3+ + 3Cl2 + 7H2O

But shouldn't one with more negative E0 value be reversed?
This is from w07

 

[Haya Ahmed]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_21.pdf


Q5 b(ii) and (iii) explain why we multiplied by 2 in (i) arent we supposed to divide by 2 ?

 

[hope4thebest]

Does CH3COOH give positive test in iodoform test? And also CH3CH2OH? there is some confusion because marking scheme gives positive with ethanol but not ethanoic acid

 

[AbbbbY]

Yes in a sense you can, however the better reason will be that C does not have empty D orbitals. just remember this one line statement it....

No! You can't!! In any sense whatsoever!
The second part. Always. Only.

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s04_qp_4.pdf Q2c(i) i get the answer but cant we state the size of carbon atom being smaller than silicon as a valid reason

You can't. Size is immaterial when Carbon has no d orbital so smaller or not, water just can't attack. It's not a matter of steric hindrance only. Thing is, you just can't. You're very right saying the carbon atom is significantly smaller, but even if it's crowded by H2O, there won't be a reaction because there are no d-orbitals present. I really hope you get what I'm trying to say.

i gave the answer .

Vaooooowwwww yaaar. Kya baat hay. Yeh lo bhai. Yeh trophy aapki hui. You're the best chemist around. Admitted. Now can we go back to 'the help thread' from the 'I know more than you' thread? Seriously guys. It's not a race here!

 

[AbbbbY]

Does CH3COOH give positive test in iodoform test? And also CH3CH2OH? there is some confusion because marking scheme gives positive with ethanol but not ethanoic acid

Ethanol yes Ethanoic Acid no.

Ethanol has an alcohol group besides a CH3- link so it'll show you a positive test with alkaline iodine.
See ethanol and think 3D. If it still doesn't make sense quote me and tell me I'll draw it out.

 

[periyasamy]

hi guys.Breaking head for this question.Just cant get it.Anyone can lend me a hand ...Thanks a lot in advance........I dont get the answer given .....
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w12_ms_43.pdf
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w12_qp_43.pdf
question 7 part 3.I posted the question in the picture below..Thank u ..

 

[Haya Ahmed]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_23.pdf

Q2e how to calculate the number of electrons ?!

 

[BeBeskii108]

Does anyone have A2 frequently asked question material ?

 

[AbbbbY]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_23.pdf

Q2e how to calculate the number of electrons ?!

Seriously?
Carbon has 6 electrons. Hydrogen has 1. So total = 18.

 

[danial 234]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_21.pdf


Q5 b(ii) and (iii) explain why we multiplied by 2 in (i) arent we supposed to divide by 2 ?

we will multiply by two cz the ques asks to write the number of atoms of hydrogen produced , and in one molecule of hydrogen, there are two atoms of H .. so we will multiply by 2 ... and then calculate the moles of X.. number of moles of X = 0.0067 moles.... H atoms= 0.0133 ..
if there is one OH then one H will be produced
and in X.. for 1 mole of X.. two moles of H ztoms are produced
so there are two OH in each molecule of X

 

[omaaaar]

How to calculate enthalpies using bond energies
And also can someone explain me the Hess ' s cycle

 

[Princess Raven]

can someone show how to draw the skeletal formula of both cis trans isomers of but-2-ene

 

[sitooon]

How to draw this :
PS : As students take care , this might be the question for you this session !!!

 

[AbbbbY]

can someone show how to draw the skeletal formula of both cis trans isomers of but-2-ene

 

[AbbbbY]

How to draw this :
PS : As students take care , this might be the question for you this session !!!
View attachment 41393

I'd go witth something like this

Though, I'm not sure exactly what the full question is. I guess it's asking for NO3- ion

 

[hope4thebest]

Ethanol yes Ethanoic Acid no.

Ethanol has an alcohol group besides a CH3- link so it'll show you a positive test with alkaline iodine.
See ethanol and think 3D. If it still doesn't make sense quote me and tell me I'll draw it out.

Doesn't CH3-CO group give positive test in iodoform test. Ethanoic acid involves CH3-CO group.

 

[AbbbbY]

Doesn't CH3-CO group give positive test in iodoform test. Ethanoic acid involves CH3-CO group.

You're very right that ethanoic acid has a terminal methyl with CO, but the C=O is delocalized here over the entire group. Remember how 2,4 DNPH reacts with carbonyl groups but not carboxylic groups even though all three have at least one C=O? Precisely that principle is applied here.

 

[hope4thebest]

You're very right that ethanoic acid has a terminal methyl with CO, but the C=O is delocalized here over the entire group. Remember how 2,4 DNPH reacts with carbonyl groups but not carboxylic groups even though all three have at least one C=O? Precisely that principle is applied here.

does I2 and NaOH also behaves as oxidising agent?

 

[papajohn]

Best of luck for all those appearing for Chemistry P2..

 

[robinhoodmustafa]

does I2 and NaOH also behaves as oxidising agent?

Iodine is a strong reducing agent because of that extra electron which is less attracted to the nucleus
and Na0H is a weak oxidizing agent since only H atom is reduce.

Correct me if I am wrong!