Chemistry: Post your doubts here!

[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.

9 is to be done the same way. Draw an ICE chart and add up the equilibrium moles.

 

[darkxangel]

Draw a Hess cycle.

Can you do it for me ?

 

[magnesium]

="h4rriet

q10 same ppr

 

[magnesium]

15. In the equation for the decomposition of a Group II metal nitrate, the metal nitrate and the metal oxide have a mole ratio of 1:1. So (mass of nitrate)/(molecular mass of nitrate)=(mass of metal oxide)/(molecular mass of metal oxide). The mass of nitrate is given to be 2 grams. The mass of the metal oxide will 2 minus the mass of gas produced.
17. Find the moles of O2 from the information given. Write a balanced equation for the combustion of Ca and Mg. Then use mole ratios to determine whether the metal is Ca or Mg.

q10 same ppr

 

[kiran11]

how shall we come to know which molecule has largest overall dipole as in Q10http://papers.xtremepapers.com/CIE/...20Level/Chemistry%20(9701)/9701_s12_qp_12.pdf

 

[Dr.MMM]

Find the molecular mass of butanone, butanoic acid and 2-methyl propanoic acid. Then find the yield using actual mass/calculated mass x 100. Choose the options whose yield = 62 %.

CAn you please solve one option for me, as im getting 58.6 for all three of them

 

[h4rriet]

CAn you please solve one option for me, as im getting 58.6 for all three of them

Sorry, I didn't read the question properly. It's to be done this way:

 

[Raiyan3]

Question number 7 please help
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf And question number 11 and 23
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_12.pdf

 

[h4rriet]

how shall we come to know which molecule has largest overall dipole as in Q10http://papers.xtremepapers.com/CIE/...20Level/Chemistry%20(9701)/9701_s12_qp_12.pdf

In symmetrical molecules, dipoles cancel out.

 

[kiran11]

In symmetrical molecules, dipoles cancel out.

yes but how we will choose btwn C and B option of the same question?

 

[h4rriet]

Can you do it for me ?

Working on it.

 

[cute97]

16. This is something you have to memorise. Cl2 + cold, dilute NaOH will give a ClO- ion (oxidation state = +3) and Cl2 + hot, concentrated NaOH will give a ClO3- ion (oxidation state = +5).
20. Find the molecular masses of the products of propyl propanoate. The find the % by mass of each compound.
28. -NH2 from NH3 substitutes one Br atom. NH2 is a nucleophile too, and has to be close to the other C-Br bond so that it can attack it. 1,5 is closer than 1,4.

thank you here again Q20 same like the ques in previous paper plz explain one of them

 

[h4rriet]

yes but how we will choose btwn C and B option of the same question?

Can't see the question because your link doesn't work.

 

[h4rriet]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_12.pdf
Q4 h4rriet

Construct the balanced equation for the reaction between N2 and H2. 120-96 kg of H2 is used. Use mole ratios.

 

[h4rriet]

="h4rriet

q10 same ppr

Draw a Hess cycle.

 

[kiran11]

Can't see the question because your link doesn't work.

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf Q10, i have confusion btwn B and C

 

[h4rriet]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_12.pdf Q10, i have confusion btwn B and C

B's dipole is 6 multiplied by the dipole of C-H, whereas C's dipole is 2 multiplied by the dipole of C-Cl.

 

[cute97]

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.

okk got it thank you very much frnd

 

[cute97]

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.

ooohh okkk thankss

 

[Jiyad Ahsan]

yes but how we will choose btwn C and B option of the same question?

the Cl and the O cancel each others effects somewhat as they both are quite electronegative.. in option C,
while in option B the O side becomes electronegative quite easily, no resistance from the CH4 to become electro-positive whatsoever

the correct link..
papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_12.pdf