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Chemistry: Post your doubts here!

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Muhammad Asif

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nerdybookworm said:
ok sorry i posted the wrong link..now here help........paper 1 m/j 03 Q 2,4,8,10,16,20,27,28,30 & 39......


http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s03_qp_1.pdf
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Q2: see that one chain in residue has 2 double bonds while and 2 chains have single double bonds thus 4 doubl bonds in all....thus only 5 are hydrogenated.....1 double bond needs 1mol H2 so 5 needs 5mol H2

Q4:the highest difference in ionisation energies is 6 and 7th thus the element contain 6 electrons in outer shell thus group 6 that is C

Q8:the only change is in A....

Q10:the molar ratio of HI:I2:H2= 2:1:1 the change in HI is .26 so change in rest would be .26/2=.13......moles at equillibrium would be for H2=.07 and I2=.02 thus the only ans is C

Q16:chlorine disproportionate in conc hot NaOH forming NaClO3 where chlorine is +5(fact)

Q20:there are seven possible structures.....try to draw them

Q27=only chlorine----carbon bond can be broken to form a redical Cl....thus C is d answer as in the other options no Cl bond is broken

Q28=sorry:p

Q30=the answer is D as an additional C is added to Chain and an OH + acid group are made from the product hydrolysis....


q39=fehling test is positive thus the product is an aldehyde which can only be form from a primary alcohol which are shown in only 2 and 3
 
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smartangel

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Casablanca said:
Hmm, that sounds strange. Are you sure they all have a double bond though? Because it asks for ones with a double bond.
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yeah all of them have a double bond..cis trans, but 1 ene and but 2 ene...
anyone else who understands why the answer is 3?
 
Ashique

Ashique

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nerdybookworm said:
ok sorry i posted the wrong link..now here help........paper 1 m/j 03 Q 2,4,8,10,16,20,27,28,30 & 39......


http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s03_qp_1.pdf
Click to expand...

For question 2, 2 double bonds in he compound were removed, thus 4 mole of hydrogen was required (since 2 hydrogens are added to the chain once you break a double bond). If you notice, CH2 was changed to CH3 thus one more mole os Hydrogen was required. So in total, 5 mole of hydrogen was required.

Question 4, look for a major change in the ionisation energy. The first 6 value lie close to each other, (or say, one value ot numerically close to the previous value), but the 7th value 13200. Which is BIG increase in ionisation energy. But the first six values lie close to one another. What does this tell about the atom and the ionisation energy? This indicates that 6 electrons were easily removed. And a lot of energy was required to remove the 7th electron. This indicates that the 7th electron lies in a different shell than the first 6. And we can also figure out than the quantum shell (or the outer most shell) has 6 electrons in it. Hence it's in group six. Te is the only element in group VI, hence answe is C.

Question 8- you have to know how to calculate the oxidation number, of a compound in a chemical equations. Go through your book, and I' m sure you'll find out how to do it, (if you don't know that is). The greatets oxidation number change happened in A, which is 20. In B, C and D the oxidation number changes are 6, 4 and 2 respectively.

Question 10- (Since no volume was given, we assume the volume to be 1 dm3, hence the concentrations will have the same numerical value as their mol.)
Now, First calculate the total number of moles at the begining- 0.20+0.15= 0.35 mol.
At equilibrium the number of moles of the products(ie HI) was 0.26. So what is the TOTAL volume of the reactant? 0.35-0.26= 0.09.
Now 0.09 was the TOTAL volume of the reactant. Now look at the denominator, addition of which two concentrations willl give us 0.09? Hence answer is C.

Question 16- Addition of hot alkali will make chlorine go through a disproportionation reaction. Which will give chlorine of two oxidation states -1 and +5, hence answer is D.

Question 20- you simply have to draw out all possible isomers of the compund. It should be 7.

Question 27- You have to find the carbon which has lost the chlorine, since homolytic fission using ultraviolet light, will only give chlorine and the corresponding compound as free radicals. Since C is the only one which lost the chlorine, answer should be C.

Question 28- Reaction of the first three compounds with sodium would give- sodium ethoxide for A and B, with the loss of producing moles of hydrogen, when you balance the equation). Reaction of C with sodium would give sodium ethanote again giving off two moles of hydrogen. It is only compound D which gives of only 1 mole of H2.

Question 30- nucleophilic addiotn of HCN to propanone would give you CH3CH(OH)(CN)CH3. When you reflux this this H2SO4, You'll lose the nitrile and get a carboxylic group , CH3CH(OH)(CO2H)CH3. This compound is represented by D, so thats your answer.
 
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Muhammad Asif

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smartangel said:
yeah all of them have a double bond..cis trans, but 1 ene and but 2 ene...
anyone else who understands why the answer is 3?
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but-1-ene will only have cis no trans........becuse in both cases H will face H.....but-2-ene will have cis and trans thus the answer is C
 
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smartangel

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Muhammad Asif said:
but-1-ene will only have cis no trans........becuse in both cases H will face H.....but-2-ene will have cis and trans thus the answer is C
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no..what i meant was that the compound they"ve shown has cis trans isomers. other STRUCURAL isomers are but 1 ene and but 2 ene due to the different position of double bond.
 
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TheMan123

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muneexa said:
Which organic molecules are planar other than ethene????
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There are many, to name all of them would be difficult. Just remember planar= either 2 bonding pairs(180) or 3 bonding pairs(120) or 2bonding pair with 1 lone pair(120)
 
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Muhammad Asif

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smartangel said:
no..what i meant was that the compound they"ve shown has cis trans isomers. other STRUCURAL isomers are but 1 ene and but 2 ene due to the different position of double bond.
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what?????????????????????????????no way?????how does the compound shown have cis-trans?????the methyl group are on same carbon atom not on different carbon atoms..........
 
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TheMan123

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when an alcohol is oxidised to a carbonyl, it is not considered a condensation reaction even though H2O is formed, can someone explain?
 
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Muhammad Asif

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TheMan123 said:
when an alcohol is oxidised to a carbonyl, it is not considered a condensation reaction even though H2O is formed, can someone explain?
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in condensaton reaction two monomers or groups are joined by eliminating water here alcohol is oxidised and water is the oxidation product
 
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smartangel

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Muhammad Asif said:
what?????????????????????????????no way?????how does the compound shown have cis-trans?????the methyl group are on same carbon atom not on different carbon atoms..........
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oh God. plz see the question. it says additional isomers. if you switch the positions of CH3 and H it will form a cis trans isomer!!
 
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Muhammad Asif

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