Chemistry: Post your doubts here!

[Metanoia]

Could someone explain this equation?

The commonest form of iron(II) sulfate is the heptahydrate, FeSO4.7H2O. On heating at 90 C this loses some of its water of crystallisation to form a different hydrated form of iron(II) sulfate, FeSO4.xH2O. 3.40g of FeSO4.xH2O was dissolved in water to form 250 cm3 of solution. A 25.0cm3 sample of this solution was acidifi ed and titrated with 0.0200 mol dm–3 potassium manganate(VII). In this titration 20.0cm3 of this potassium manganate(VII) solution was required to react fully with the Fe2+ ions present in the sample.

Complete and balance the ionic equation for the reaction between the manganate(VII) ions and the iron(II) ions.

MnO4 – (aq) + 5Fe2+(aq) + ........H+(aq)  ..... +....(aq) + 5Fe3+(aq) + .......H2O(l)

? what is the part you are having difficulty with? The balance equation or finding out x?

Also this question!

Another element, Z, in the same period of the Periodic Table as A, reacts with chlorine to form a compound with empirical formula ZCl 2. The percentage composition by mass of ZCl 2 is Z, 31.13; Cl, 68.87.

Calculate the relative atomic mass, Ar , of Z. Give your answer to three significant figures.

I've attached the mark scheme for reference! http://maxpapers.com/wp-content/uploads/2012/11/9701_s14_ms_21.pdf

 

[qwertypoiu]

Yes. Cis isomers would be very unlikely in small rings (less than 8 carbons) due to the strain on the bonds.

Thank you so much

 

[AlexMan]

Does anyone know about Partition Coefficient? How do we know which substance is at the top and which is at the bottom?

 

[Studydayandnight]

? what is the part you are having difficulty with? The balance equation or finding out x?



View attachment 52469

Balancing the equation!

 

[The Sarcastic Retard]

Could someone explain this equation?

The commonest form of iron(II) sulfate is the heptahydrate, FeSO4.7H2O. On heating at 90 C this loses some of its water of crystallisation to form a different hydrated form of iron(II) sulfate, FeSO4.xH2O. 3.40g of FeSO4.xH2O was dissolved in water to form 250 cm3 of solution. A 25.0cm3 sample of this solution was acidifi ed and titrated with 0.0200 mol dm–3 potassium manganate(VII). In this titration 20.0cm3 of this potassium manganate(VII) solution was required to react fully with the Fe2+ ions present in the sample.

Complete and balance the ionic equation for the reaction between the manganate(VII) ions and the iron(II) ions.

MnO4 – (aq) + 5Fe2+(aq) + ........H+(aq)  ..... +....(aq) + 5Fe3+(aq) + .......H2O(l)


Also this question!

Another element, Z, in the same period of the Periodic Table as A, reacts with chlorine to form a compound with empirical formula ZCl 2. The percentage composition by mass of ZCl 2 is Z, 31.13; Cl, 68.87.

Calculate the relative atomic mass, Ar , of Z. Give your answer to three significant figures.

I've attached the mark scheme for reference! http://maxpapers.com/wp-content/uploads/2012/11/9701_s14_ms_21.pdf

Just balance key element first then O and then H.

 

[Studydayandnight]

Just balance key element first then O and then H.

Thanks!!

 

[Metanoia]

Balancing the equation!

Just balance key element first then O and then H.

An alternative would be to realize that the half equations are in the data booklet

Fe2+ --> Fe3+ + e ---(1)

MnO4- + 8H+ + 5e --> Mn2+ + 8H2O ---- (2)

We simply need to multiply eqn (1) by 5 before adding to eqn (2)

 

[Metanoia]

Does anyone know about Partition Coefficient? How do we know which one substance is at the top and which is at the bottom?

Look at the density, the denser liquid would be at the bottom.

 

[Midnight dream]

Yes. Cis isomers would be very unlikely in small rings (less than 8 carbons) due to the strain on the bonds.

Thanks
But the question had 17 carbons in it...Shouldn't it then display cis trans....The answer said no..

 

[Metanoia]

Thanks
But the question had 17 carbons in it...Shouldn't it then display cis trans....The answer said no..

Its not about the total number of carbons. Its about the number of carbons within a ring.

For that question, if i remember correctly, the number of carbons in the rings are either five or six.

 

[Midnight dream]

Its not about the total number of carbons. Its about the number of carbons within a ring.

Thank you soo much..

 

[Studydayandnight]

Guys please help!!

I don't understand how to answer the questions (c) (iii), d(i), d(ii) .

How does the reaction show that it's a carboxylic acid? How do we identify it as ethanoic acid?

I've attached the mark scheme as well!

http://freeexampapers.com/A-Level/Chemistry/CIE/2013-Jun/9701_s13_ms_22.pdf

 

[My Name]

Guys please help!!

I don't understand how to answer the questions (c) (iii), d(i), d(ii) .

How does the reaction show that it's a carboxylic acid? How do we identify it as ethanoic acid?

I've attached the mark scheme as well!

http://freeexampapers.com/A-Level/Chemistry/CIE/2013-Jun/9701_s13_ms_22.pdf

For part c iii
in the question they mention
A third sample of R gave an effervescence with sodium carbonate
so it has to be carboxylic acid ! ( since no other functional group would give effervescence)

for the next part d i
refer to this post
https://www.xtremepapers.com/commun...st-your-doubts-here.9859/page-600#post-896183
Credits to Metanoia for that ^

 

[shaeer999]

w2014 qp 11. ans= A, how is it done??

 

[My Name]

View attachment 52496 w2014 qp 11. ans= A, how is it done??

Refer to this post:
https://www.xtremepapers.com/commun...st-your-doubts-here.9859/page-602#post-896283

 

[Studydayandnight]

I need more help! :/

For (a) (ii) I just wanted to confirm that we know it's carboxylic because CO2 is given out and there'll be effervescence?

Can someone please explain part (b) to me?

Here's the mark scheme.

http://freeexampapers.com/A-Level/Chemistry/CIE/2012-Jun/9701_s12_ms_23.pdf

 

[asadalam]

I need more help! :/

For (a) (ii) I just wanted to confirm that we know it's carboxylic because CO2 is given out and there'll be effervescence?

Can someone please explain part (b) to me?

Here's the mark scheme.

http://freeexampapers.com/A-Level/Chemistry/CIE/2012-Jun/9701_s12_ms_23.pdf

Ok,so just a little something to keep in mind if it says heat with conc H2so4 its most likely a dehydration reaction,or elimination.The formula of H can be deduced as dehydration takes out the OH and H bonded with one of the C the structural formula that i came up with was CH2(OH)CH2C02H you can draw that on paper to be sure.The h2so4 will take out the H and OH and cause to form a double bond with 2 C atoms in between( not the CO2H one),which will be oxidised by cold dilute kmno4 to make it colorless,and form a diol with both C=C getting a an OH bond.


Practice more and more organic and eventually you'll get a hang of this.

 

[Studydayandnight]

Ok,so just a little something to keep in mind if it says heat with conc H2so4 its most likely a dehydration reaction,or elimination.The formula of H can be deduced as dehydration takes out the OH and H bonded with one of the C the structural formula that i came up with was CH2(OH)CH2C02H you can draw that on paper to be sure.The h2so4 will take out the H and OH and cause to form a double bond with 2 C atoms in between( not the CO2H one),which will be oxidised by cold dilute kmno4 to make it colorless,and form a diol with both C=C getting a an OH bond.


Practice more and more organic and eventually you'll get a hang of this.

CH2=CHCO2H , this is the answer from the markscheme. It has no OH group present. :/

 

[ahmedish]

Which part in the syllabus does it have the bit where AgCl or AgBr react with NH3 to give Ag(NH3)2Br?? I have found it twice in the past papers (old though like 2004 and 2006)

 

[Studydayandnight]

5 (c) http://freeexampapers.com/A-Level/Chemistry/CIE/2012-Jun/9701_s12_ms_23.pdf

May/June/2012

Variant 23

I've attached the mark scheme! Please help guys, this question alone carries 4 marks :/