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Chemistry: Post your doubts here!

Charlotte20102013

Charlotte20102013

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Hi guys. Can you help me on a few past year questions? (ON 2013 P13)
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w13_qp_13.pdf
3. A 10cm3 sample of 0.30moldm–3 Tl+NO3– required 20cm3 of 0.10moldm–3 acidified NH4VO3 to oxidise it to Tl3+ in solution. Vanadium is the only element reduced in this reaction.
What is the oxidation number of the vanadium in the reduced form?
A +1 B +2 C +3 D +4
Ans: B
15. Ammonia exists as simple covalent molecules, NH3. Ammonia can react with suitable reagents to form products containing ammonium ions, NH4+. Ammonia can also react with suitable reagents to form products containing amide ions, NH2–.
Which of these nitrogen-containing species are present in an aqueous solution of ammonia?
A ammonia molecules, ammonium ions and amide ions
B ammonia molecules and ammonium ions only
C ammonia molecules only
D ammonium ions only
Ans: B
23. Pent-2-ene, CH3CH2CH=CHCH3, reacts in a similar way to ethene.
Pent-2-ene is reacted with cold, dilute, acidified manganate(VII) ions.
What will be produced in the greatest amount?
A CH3CH2CH(OH)CH(OH)CH3
B CH3CH2COCOCH3
C a mixture of CH3CH2CH(OH)CH2CH3 and CH3CH2CH2CH(OH)CH3
D CH3CH2COOH and CH3COOH
Ans: A
27. An alcohol with molecular formula CnH2n+1OH has a chiral carbon atom but does not react with
hot, acidified K2Cr2O7.
What is the smallest possible value for n?
A 5 B 6 C 7 D 8
Ans: C
38 The reaction of ethanal, CH3CHO, with HCN to form a cyanohydrin is catalysed by NaCN.
What are features of the intermediate of this reaction?
1 It is chiral.
2 It has a single negative charge on one of its atoms.
3 It is a nucleophile.
Ans: A (1,2,3)
39 The ester C2H5CO2CH2CH2CH3 can be made in a school or college laboratory by a sequence of
reactions using compound X as the only organic material.
What might be the identity of compound X?
1 CH3CH2CH2OH
2 CH3CH2CHO
3 CH3COCH3
Ans: B(1,2)

Hope you could provide me steps/explanations to these questions(Whichever you could help with)ASAP. Thanks! :)

 
Metanoia

Metanoia

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Charlotte20102013 said:
Hi guys. Can you help me on a few past year questions? (ON 2013 P13)
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w13_qp_13.pdf
Hope you could provide me steps/explanations to these questions(Whichever you could help with)ASAP. Thanks! :)
Click to expand...

Q3.
Ti+ --> Ti3+ + 2e-

moles of Ti+ : moles of e- : moles of VO3-
0.003 moles : ? : 0.002 moles
3 moles : ? moles : 2 moles

Using the half equation, we can see that 3 moles of Ti+ will transfer 6 moles of electrons to 2 moles of VO3-.

In other words, 1 mole of VO3- gains 3 moles of electrons (its oxidation number would decrease by 3 units).

Original oxidation number of vanadium in VO3- is +5, final oxidation number would then be +2 (since it decreases by 3 units).

Q15.
NH3 is a stronger base than H2O, so we have NH3 accepting protons from H2O

NH3 + H2O <--> NH4+ + OH-

Q23.
Using cold dilute KMnO4, we will add OH to each of the carbons across the C=C double bonds.

Q27.
It should be a tertiary alcohol as it is not oxidized. The carbon holding the OH is expected to be joined to 3 other branches containing different number of carbons.

......C
C2-C-C3
.....OH

Q38. Which option are you unsure of? See if you can google for the mechanism of the reaction.

Q39.
Option 1 is correct
CH3CH2CH2OH (alcohol) can be oxidized to CH3CH2CO2H (acid)
CH3CH2CH2OH (alcohol) and CH3CH2CO2H (acid) can undergo esterifcation to form the desired product.

Option 2 is correct
CH3CH2CHO (aldehyde) can be oxidized to CH3CH2CO2H (acid)
CH3CH2CHO (aldehyde) can be reduced to CH3CH2CH2OH (alcohol)
CH3CH2CH2OH (alcohol) and CH3CH2CO2H (acid) can undergo esterifcation to form the desired product.
 
loveyuan

loveyuan

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RoOkaYya G said:
ull get CO2. u can also have it in a carbonate compound. depending on the reagent added like KOH or NaOH (any basic). since here NaOH was used so it can be NaCO3

Ans: NaCO3 /CO2
since there is an amine group due to hydrolysis(breaking bonds) it'll break apart n be in ion state or can be in amine compound which r stable enough.
so it may be CH3NH3+ Cl- or CH3NH2 (amine)

moreover, theres the aryl group there. so due to hydrolysis...the R group is seperated leaving the aryl group. i wont call it phenol exactly coz theres 2 rings joined there. so generalising it ...it becomes an aryl


in short answer : CH3NH3+Cl- and CO2 and the aryl with a phenol nxt to it (means one ring will have OH group on carbon 1)
Click to expand...
Thanks :) appreciated :)
 
loveyuan

loveyuan

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savera said:
Sure why not..... can you please be specific. For which chapter are you talking about.
Click to expand...

hi ,
for an example
http://www.cie.org.uk/images/157296-november-2012-question-paper-43.pdf
question number 7 iii

I can solve the 7 i and ii
and from the question i know there will have 2 -CH3 group and 2-CH2 group
and one of the element beside C and H is O

and according to chemical shift ,
there is some group in ~around 1 and 2.5
but everytime i cant find something fit to information

here is the data booklet :
http://fmcapechemistry.weebly.com/uploads/5/6/3/3/5633072/chem_data_booklet.pdf
 
♣♠ Magnanimous ♣♠

♣♠ Magnanimous ♣♠

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Pink Flower said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s08_qp_1.pdf
Can someone please explain me Question 2???????????
Click to expand...
We have to find concentration of Nitrogen in that solid

Answer ---> First of all we need to know how we can fine concentration
Conc = moles/volume
Units : Mol/dm3
Moles --> moles
Volume --> dm3

According to the ratio given of that solid material we have 15 gram of N per 100 g of fertiliser which means 15% and the usage of fertiliser in 14 g so :
14(15/100) ===> 2.1 grams.

Converting Grams to Moles we get ---> 0.15 moles

We have volume 5 dm3

Now put the values in equation :
Conc : 0.15/ 5 --> 0.03 mol/dm3

I hope you got it :)
 
Pink Flower

Pink Flower

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♣♠ Magnanimous ♣♠ said:
We have to find concentration of Nitrogen in that solid

Answer ---> First of all we need to know how we can fine concentration
Conc = moles/volume
Units : Mol/dm3
Moles --> moles
Volume --> dm3

According to the ratio given of that solid material we have 15 gram of N per 100 g of fertiliser which means 15% and the usage of fertiliser in 14 g so :
14(15/100) ===> 2.1 grams.

Converting Grams to Moles we get ---> 0.15 moles

We have volume 5 dm3

Now put the values in equation :
Conc : 0.15/ 5 --> 0.03 mol/dm3

I hope you got it :)
Click to expand...
How did u convert grams to moles?
 
Pink Flower

Pink Flower

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RoOkaYya G said:
conc in g per dm^3 = conc in mol * Mr
so conc in mol= conc in g per dm^3 / Mr
Click to expand...
♣♠ Magnanimous ♣♠ said:
We have to find concentration of Nitrogen in that solid

Answer ---> First of all we need to know how we can fine concentration
Conc = moles/volume
Units : Mol/dm3
Moles --> moles
Volume --> dm3

According to the ratio given of that solid material we have 15 gram of N per 100 g of fertiliser which means 15% and the usage of fertiliser in 14 g so :
14(15/100) ===> 2.1 grams.

Converting Grams to Moles we get ---> 0.15 moles

We have volume 5 dm3

Now put the values in equation :
Conc : 0.15/ 5 --> 0.03 mol/dm3

I hope you got it :)
Click to expand...
Thank you!
 
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