Chemistry: Post your doubts here!

[Student12]

Q9. Enthalpy Change = T.Enthalpy Change of formation of products - T.Enthalpy of formation of reactants
= -1676 - 3(-266)
= -878
Answer is B.


Q.18
Reaction for electrolysis of Brine 2NaCl + 2H2O --> 2NaOH + H2 + Cl2
Moles of NaCl used = 58500/ 58.5 = 1000 mol

NaCl and Cl2 are in the ration 2:1
So mass of Cl2 = 1000/2 x 71 = 35500 g = 35.5 kg

NaCl and H2 are also in the ration 2:1
Mass of H2 = 1000/2 x 2 = 1000g = 1 kg

NaCl and NaOH are in the ration 1:1
Mass of NaOH = 1000 x 40 = 40000g = 40kg

So Answer is A.

Thank you But.. i had asked for Q9 not Q8 ?
& can you please answer the questions from the other paper too ?

 

[Thampi4]

hey
is there any practical notes anyone has that helps?

 

[abcde]

Thank you But.. i had asked for Q9 not Q8 ?
& can you please answer the questions from the other paper too ?

AoA!
9: It's B, nitric acid. Ethanoic acid is a weak acid i.e it undergoes only partial dissociation, giving lesser H+ ions in solution. NaOH does not dissociate to give H+ ions. H2SO4 gives 2 moles of H+ ions per mole (it's a dibasic acid) and thus would not give the same H+ ion concentration.

 

[Scafalon40]

11 In which change would only van der Waals’ forces have to be overcome?
A evaporation of ethanol C2H5OH(l) → C2H5OH(g)
B melting of ice H2O(s) → H2O(l)
C melting of solid carbon dioxide CO2(s) → CO2(l)
D solidification of butane C4H10(l) → C4H10(s)
Ans C
Why is it not D?
Butane is also non polar, in addition to CO2

 

[DPratik]

hey can anyone help with question no 33) of may/june 2003 !!!

 

[Nikesh]

Cant it be B as trigonal planar(120) means 3 bonding pair hence there are 2 bonding and a lone pair which dec the anlgle a bit so it shld be around 109??/?

trigonal planor means obviously 3 pairs in central atom, here there are 2 bond pairs (1 single bond and next double bond) another one is lone pair.....the expected angle is 120 and there will certainly be effect of lone pair but it won't affect too much that its angle decreases to 109 there won't be such vast deflection....

 

[Most_UniQue]

Can anyone hep me how to find bond angles? I dont get it!

 

[histephenson007]

11 In which change would only van der Waals’ forces have to be overcome?
A evaporation of ethanol C2H5OH(l) → C2H5OH(g)
B melting of ice H2O(s) → H2O(l)
C melting of solid carbon dioxide CO2(s) → CO2(l)
D solidification of butane C4H10(l) → C4H10(s)
Ans C
Why is it not D?
Butane is also non polar, in addition to CO2

Read carefully, the D option says solidification! and in the equation it says from (l) to (s). In such case, intermolecular forces are formed, not broken. Since hydrogen bonding occurs in A & B, we may know the answer is C.

 

[Student12]

How many structural and cis-trans isomers are there for dichloropropene, C3H4Cl2 ?
A 3
B 5
C 6
D 7
The answer is D! Can anyone draw all the 7, please ?

How many alcohols (including both structural isomers and stereoisomers) can have the molecular
formula C4H10O?
A 3 B 4 C 5 D 6
The answer is C can anyone draw and show ?


http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w04_qp_1.pdf
Q-3,10,19,23,31

Help would be appreciated =D

Pleaseee answer these !! & can you specify the sub topic these mcq's are based on ?

 

[Scafalon40]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_11.pdf
Q8,19,27
M.Shttp://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_ms_11.pdf
11) 0.144 g of an aluminium compound X react with an excess of water, to produce a gas. This gas
burns completely in O2 to form H2O and 72 cm3 of CO2 only. The volume of CO2 was measured at
room temperature and pressure.
What could be the formula of X?
[C = 12.0, Al = 27.0; 1 mole of any gas occupies 24 dm3 at room temperature and pressure]
A) Al 2C3 B) Al 3C4 C) Al 4C3 D) Al 5C3
Ans C
17) Concentrated sulfuric acid can behave both as a strong acid and as an oxidising agent.
With which compound does concentrated sulfuric acid react in this way?
A ethanol
B magnesium carbonate
C propanenitrile
D sodium bromide
Ans D
Also,
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_12.pdf
Q6
M.Shttp://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_ms_12.pdf

 

[leosco1995]

June 2008, P1. Q34

How do we know if the reaction is endothermic or not?

 

[JD REBORN]

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w07_qp_1.pdf
Q32 how can statements 2 and 3 be correct.
Q9

 

[Student12]

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_s09_qp_1.pdf
Q1, 4, 8, 13 ,20,28
Q36 - Doesnt the bond length decrease ? and what does the 3rd point mean ?
Q38- doesnt KMnO4 react with secondary alcohol ?
Can you specify the sub topic these msqs are based on ?

 

[iKhaled]

guys guys guysssss...is Cambridge acting crazy or what??

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w05_qp_1.pdf

question 17 in nov/05 P1 is an A2 level..how come they ask us this and we r not even suppose to study it for an AS exam?

can somone explain plssss.. :/

 

[gary221]

Question 5 on that page:

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_qp_11.pdf

Why isnt the answer C or A?

Its B bcoz u hv 2 see the greatest dipole moment.
In A, thr r 4 Cl, so the dipole moment is cancelled out. Thus no dipole in A
In C, O n Cl both r electronegative, so d dipole moment wnt b very gr8..
Whereas in B, O is Electronegative n H is electropositive... hence Greatest dipole moment...
Hope i helped...

 

[hmlahori]

guys guys guysssss...is Cambridge acting crazy or what??

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w05_qp_1.pdf

question 17 in nov/05 P1 is an A2 level..how come they ask us this and we r not even suppose to study it for an AS exam?

can somone explain plssss.. :/

Dont worry. Cambridge would never give anything thats not in or related to our syllabus.
As you might know that the syllabus keeps changing regularly.
This is a very old paper. maybe at that time this topic might have been included in the AS syllabus but as you say it is not included in ours now.
So i guess you dont really need to know abt it.

 

[iKhaled]

Dont worry. Cambridge would never give anything thats not in or related to our syllabus.
As you might know that the syllabus keeps changing regularly.
This is a very old paper. maybe at that time this topic might have been included in the AS syllabus but as you say it is not included in ours now.
So i guess you dont really need to know abt it.

phewwww if u r sure of what u r saying then u really made me feel so much better

have a look at the question and correct me if i am wrong ( that it is not in the syllabus 12 )

thanks..

 

[hmlahori]

phewwww if u r sure of what u r saying then u really made me feel so much better

have a look at the question and correct me if i am wrong ( that it is not in the syllabus 12 )

thanks..

Yes it is not in our syllabus. Ligands is in the A2 course not AS.
And you'r welcome.

 

[Jaf]

Dont worry. Cambridge would never give anything thats not in or related to our syllabus.
As you might know that the syllabus keeps changing regularly.
This is a very old paper. maybe at that time this topic might have been included in the AS syllabus but as you say it is not included in ours now.
So i guess you dont really need to know abt it.

Dude don't mislead people.

We ARE supposed to know what ligands are [complex ion formation]. I've seen this term used in the book.

 

[histephenson007]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w07_qp_1.pdf
Q32 how can statements 2 and 3 be correct.
Q9

Q32

Statement 1 - Obviously disagrees with the sentence 'Carbon monoxide burns readily in oxygen to form Carbon dioxide'
Statement 2 - More negative means exothermic reaction (which is easy to occur), so it fits with the sentence
Statement 3 - Kc = [product] / [reactant], if this is high means there is high concentration of CO2 produced. Hence it fits.

Q9

Answer is A. In the equation they've given : SO3 --> SO4. The oxidation number of Sulphur increased from +4 to +6 (change is +2). So, for the metal, there should have been the same magnitude of change but in the negative direction. (Change = -2) So, because it is +3, it would become +1.