Chemistry: Post your doubts here!

[Jaf]

what do they call the compound i mentioned above?

2-hydroxy-2-methylpropanol

 

[USMAN Sheikh]

Jaf can u pls reply my ques bond angles one that is on previous pafge

 

[USMAN Sheikh]

Ooops, sorry. I misread the question.

NDH3Cl would produce NH3 or NH2D at best. It can_not produce ND3.

can u also pls elaborate each option aswell

 

[Nikesh]

any one pls q 2 aand 5 pls be quick

for 2 its B) Carbon as it has total of 2 electron pairs and and 2 unpaired electrons in 2 principle quantum orbital (Draw box electronic configuration to see that)
for 5) its C because double bond acts as a single bond pair...

 

[USMAN Sheikh]

for 2 its B) Carbon as it has total of 2 electron pairs and and 2 unpaired electrons in 2 principle quantum orbital (Draw box electronic configuration to see that)
for 5) its C because double bond acts as a single bond pair...

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??/?

 

[JD REBORN]

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w08_qp_1.pdf
Q6 and Q17

 

[USMAN Sheikh]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w08_qp_1.pdf
Q6 and Q17

For 6 only paper and poly etherne are combustible hence option A and D gets cancel both B and C are eectrical insulator and but only polmers melt over range of temp !! its C

 

[namraahmad]

Aslamaliakum.....
Can you help me out in calculating retention time i mean is there any way to calculate it or its just read off from the graph??

 

[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 ?

 

[Student12]

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/...d AS Level/Chemistry (9701)/9701_s04_qp_1.pdf
Q- 9,18
http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w04_qp_1.pdf
Q-3,10,19,23,31

Help would be appreciated =D

 

[Nibz]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s04_qp_1.pdf
Q- 9,18

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.

 

[UltimateHustla]

Thats not true if you do it well, you will be fine
I wasnt screwed, got a good grade

well i hope you are right cause i worked my ass off

 

[tom ed]

Yeah, I did get the answer. If you want, I'll put up a picture of how I did it (if you're THAT fond of getting shocks )

how is "wanting to know... how to get to a conclusion?" related to "being fond of getting shocks"....btw i also got the answer,thanks anyway!

 

[DPratik]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w08_qp_1.pdf
Q6 and Q17

in question number 6) as the question has mentioned as insulator which means the answer is either polyethene or silicon oxide....but the question has also said that the compound melts over a wide range of temperature which means the answer is obviously polyethene because silicon oxide has a high temperature and doesn't has variable melting temperature !!!

i question 17) there are few things which must be remembered,first chlorine is stronger oxidizing agent than sulphuric acid and H3PO4 is less oxdizing agent than iodine because when H3PO4 is treated with sodium iodide,acidic gas which shows that H3PO4 is a weak oxidizing agent,so after all this you have only one option left and i.e sulphuric acid is stronger oxidizing agent than iodine !!!

 

[panda222]

Question 5 on that page:

http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_w09_qp_11.pdf

Why isnt the answer C or A?

 

[imanmalik]

There are 4 chlorines in A. The resultant dipole is 0 because all 4 chlorines have the same electronegativities and cancel each other out. It's not C because the dipole formed by O and Cl cancel each other out due to their similar electronegativities. It's B because of the difference between the electronegativites of the O and H are different (the electronegativity of O is much greater than the electronegativity of H) So the O end is negative and the C-H2 end being positive

 

[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