Chemistry: Post your doubts here!

[HorsePower]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w12_qp_11.pdf
plz help me in Q. 11, 21, 29

 

[Rahma Abdelrahman]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w12_qp_11.pdf
plz help me in Q. 11, 21, 29

For question 11, I also had a doubt...
Q21--> A compound will not have cis trans isomers in one case, which is when 2 identical groups are present on the same carbon atom, so instead of R here u shd have CH2CH3 which is the same as C2H5 in D
For question 29, I guess this comes from ur knowledge (I mean just memorisation of the reactions and their conditions)
h4rriet Can u please check out question number 11 ?

 

[KWIKIW]

for Q11
lone pairs make compounds polar more lone pairs means more polar so ammonia can not be more polar than water.
stronger base will pull those H+ protons with greater ease.
for Q16
for option A u get a complex ion where Cl has oxidation number of -1
for option B u get HCl again -1
for option C u get NaClO here u get +1
for option D u get NaClO3 here u get +5 so this is the correct answer.
for q32
right hand side of the molecule is polar as the oxygen atom has lone pairs any compound that has lone pair is considered polar.
like gets like which means polar molecule dissolves in polar and non polar dissolves in nonpolar. so polar cant dissolve in non polar oil u know oil does not dissolve in water.
for q33
refer to this diagram
when u break the bonds in graphite and diamond u get carbon gas carbon gas would be at the same energy that is the hess law.

View attachment 28218

Thanks.
Your explanations were very helpful.

 

[Mairaxo]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w04_ms_1.pdf
Help me with Q:38,39,40

You have been helped already..maybe next time

 

[Mairaxo]

sorry if i am annoying you !
y not a ketone .... how u knew it gonna be an acid

because when the double bond broke, the C was bonded to only one other C and one H and double bonded to an O which is a CHO group of aldehyde. Always just join an O atom whenever u break a double bond using KMnO4. then check if the C is bonded to 1 or 2 other C. If its bonded to 1 C then make an acid. If its with 2 other C then its a ketone

 

[Mairaxo]

For question 11, I also had a doubt...
Q21--> A compound will not have cis trans isomers in one case, which is when 2 identical groups are present on the same carbon atom, so instead of R here u shd have CH2CH3 which is the same as C2H5 in D
For question 29, I guess this comes from ur knowledge (I mean just memorisation of the reactions and their conditions)
h4rriet Can u please check out question number 11 ?

For Q11 - for A XYn-->X + nY
there are n X-Y bonds in the molecule. Enthalpy change is the energy needed to break these n bonds. They all break and form atoms of X and Y. So dividing the enthalpy by n we get the energy for one bond.

 

[Rahma Abdelrahman]

For Q11 - for A XYn-->X + nY
there are n X-Y bonds in the molecule. Enthalpy change is the energy needed to break these n bonds. They all break and form atoms of X and Y. So dividing the enthalpy by n we get the energy for one bond.

thanks

HorsePower

 

[Mairaxo]

thanks

HorsePower

no problem

 

[bravegirl123]

The answer is C. Why cant the it be D?

 

[Mairaxo]

The answer is C. Why cant the it be D?

there is no affect of the Cl-Cl bond or Br-Br bond here. The main bond here is H-Cl and H-Br. U should refer to there bonds to answer the question. Bond energies are diff according to the elements they are bonded to so we cant relate Cl-Cl and Br-Br to H-Cl and H-Br

 

[A star]

For Q11 - for A XYn-->X + nY
there are n X-Y bonds in the molecule. Enthalpy change is the energy needed to break these n bonds. They all break and form atoms of X and Y. So dividing the enthalpy by n we get the energy for one bond.

caan you explain again :/

 

[h4rriet]

For question 11, I also had a doubt...
Q21--> A compound will not have cis trans isomers in one case, which is when 2 identical groups are present on the same carbon atom, so instead of R here u shd have CH2CH3 which is the same as C2H5 in D
For question 29, I guess this comes from ur knowledge (I mean just memorisation of the reactions and their conditions)
h4rriet Can u please check out question number 11 ?

11 is A, if I'm not mistaken. If you take n to be 4, for example, you'll see there are 4 X-Y bonds, so the total energy can be divided by 4 to get the energy for one bond. Not so for the B, C and D.

 

[HorsePower]

11 is A, if I'm not mistaken. If you take n to be 4, for example, you'll see there are 4 X-Y bonds, so the total energy can be divided by 4 to get the energy for one bond. Not so for the B, C and D.

In A) it says XYn ..... but in D) it says nXY , so doesnt D) tell us that there are 'n' X-Y bonds.....

 

[h4rriet]

In A) it says XYn ..... but in D) it says nXY , so doesnt D) tell us that there are 'n' X-Y bonds.....

No, in D n is the number of moles of the compound XY.

 

[HorsePower]

No, in D n is the number of moles of the compound XY.

i just got it.... thnx alot

 

[A star]

No, in D n is the number of moles of the compound XY.

can you explain still dont get it

 

[h4rriet]

can you explain still dont get it

In D, the compound ix XY. n is the number of moles, not the number of bonds. There is only one bond in the compound X-Y.

 

[HorsePower]

can you explain still dont get it

think of XYn as CH4.... there are 4 C-H bond to be broken... so we divide the enthalpy change by 4 , to get bond enthalpy of 1 C-H bond

 

[A star]

aah i get it thankyou both

 

[Alice123]

Is dis d thread being used for chem p1???