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AS Chemistry Doubts

R

raamish

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thunderingthunder said:
In May June 2011 Q.20 it says what statement about acrylic acid is not correct?
A.Both bond angles are 120.
B.It decolourises Bromine.
C.It gives an orange ppt with 2-4 dinitrophenyl hydrazine.
D.Ir reacts with an alcohol to form an ester.
According to the mark scheme,the answer is C.Why is that?Acrylic acid consists of a carbonyl carbon so it should give an orange ppt with 2-4 dinitrophenyl hydrazine.shouldn't it?
Click to expand...

That is b/c there are no aldehydes nor ketones present. Look closely there is a carboxylic acid (COOH) group. carboxylic acids do not give orange ppt with DNPH :))
 
thunderingthunder

thunderingthunder

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raamish said:
That is b/c there are no aldehydes nor ketones present. Look closely there is a carboxylic acid (COOH) group. carboxylic acids do not give orange ppt with DNPH :))
Click to expand...
DNPH is a test used to detect the presence of carbonyl carbon.Carboxylic acids do contain a carbonyl carbon.then why dont they give a positive result with DNPH?:confused:
 
G

geek101

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TSZ said:
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_12.pdf
Q.11, Q.23, Q.37, Q.40
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_11.pdf
Q.9
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w07_qp_1.pdf
Q.33
Can any body please help me wid dese questions....i'll be very grateful
Click to expand...

Q23) here first write down the products. its gonna be X > CH4 + C2H4 + C3H6
in this equation the mole fraction of ethene is 1/4 = 0.25
but it is supposed to be 2/4 = 0.5 so multiply ethene by two
and add all the products to get the alkane. you will get C8H18.

Q37) 1 - is hydrogenation to form ethane > 1 step
2 - polymerisation > 1 step
3 - this is reaction with cold acidified potassium permanganate (however you spell that :p), which produces a diol > 1 step
so the answer is A

Q40) this is the formula of the salt > Ca2+(CH3CO2–)2

Q9 june 11 11) the energy (q) = m x c x (change in) T
this asks for the ''molar'' enthalpy change. so whatever q you get divide it by the no of moles.
mass = 50 + 50 (the total mass of the liquids should be taken assuming that 1 cm3 = 1 g)
c = 4.2 (given)
change in T = 17 (do not convert to kelvin since the change will not change regardless of the units)

moles = (50/1000) x 2.5

so now do q/moles = option C

Q33 w07) 1 is wrong because inside the syringe the PCl5 is dissociating so the products are increasing ans so is the volume, when the volume increases the pressure decreases. so inside the syringe the pressure is lesser than the atmospheric pressure, hence 1 is wrong >>so the answer is C.
 
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geek101

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1

1357913579

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fasih58 said:
Why are you doing paper 11 ? Paper 12 is our..
btw leme try the question you've asked!
2. Find moles of CO2 and H2O Both would be 0.8

so CxHy + O2 ------> xCO2 + y/2 H2O

By mole - mole relation...
we have moles corresponding to 0.2 moles of Hydrocarbon... find for 1 Mole ... i.e 4 moles in each case..
so X = 4
and Y/2 = 4
y = 8

C4H8 ANSWER!

5. A all are C to Cl... will cancel
B ... It has dipoles.... C to O , H to C , H to C
C ... C to O , C to Cl , C to Cl *last 2 will cacnel each other
D Both are C to O and will cancel..
B ANSWER

7 Oxidition = GOLEH ( Gain of Oxygen, Loss of Electrons & Hydrogen)
Reduction = LOGEH ( Loss of Oxygen, Gain of Electrons & Hydrogen)
Easy way to remember = GOLI LAGI :p

11 A is correct, Cu+ and Cu2+ are obtained at end of reactions... so they are catalyst
B is straight away wrong, as Cu is oxidized so its Reducing agent
C in Reaction I Ag ppt is formed which darkens it ,,, wo light is absorbed in it...
D Ag is reduced*

13 C. its a fact... SiCl4 + H2O ---> SiCl2 + 4H+ (ion) + 4 Cl- (ion) 9.1 (i) of syllabus.. look at that

19. A its a FACT!

20 In such structures.. all junction points are chiral centres... except ones with double bonds! :)

21. If you can draw it you'll find that out... other wise cram it! ;) Draw it and you'll be left with some additional Hydrogen atoms needs to be justified with double bonds.... and its a Cis retinal... be careful with that.........
A cyclohexane ring alters the C:H ...

24 C-C double bonds = 2 ..
Hydrogen atoms required 4....
and moles of H2 required would be 2... 2 x 2 = 4

Same with bromine.... 2 Br2 = 4 atoms of bromine to dissolve double bond

28 29 30 PM me the answers when you get em!
Click to expand...

i didnt get your explanation for number-5 thats the only problem i got wrong and saw your explanation and coudnt understand from it,
because you said C-CL and another C-CL will cancel each other so why not C-H bond and another C-H bond cancel each other.
by the way as for as remeber the concept of cancelling was like when each bond is polar in the molecule but the molecule is non-polar . so there are no lone pairs and each bonded pair same angel with the other so they cancel each other out
 
iFuz

iFuz

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1357913579 said:
i didnt get your explanation for number-5 thats the only problem i got wrong and saw your explanation and coudnt understand from it,
because you said C-CL and another C-CL will cancel each other so why not C-H bond and another C-H bond cancel each other.
by the way as for as remeber the concept of cancelling was like when each bond is polar in the molecule but the molecule is non-polar . so there are no lone pairs and each bonded pair same angel with the other so they cancel each other out
Click to expand...


That arrows would be from H to C..!
 
D

donorsolutions

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fasih58 said:
No, Chiral centre is different!
If I'm right stereocentre is in CisTrans Isomerism and that means AB-C=C-AB
In this C=C is stereocentre as It has 2 different groups on each side...

Correct me if i'm wrong! I think i am wrong ! :(
Click to expand...
Stereo Centre refers both to an optical isomer and cis-trans isomer
 
E

Emziar

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Do you have some revision handouts, Ive my paper1 in two days! Please help me out!
 
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