Chemistry: Post your doubts here!

[Scafalon40]

Are the questions I posted two hard
Or two easy?

 

[Nikesh]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and 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 ?

1---> D because use the formula to calculate the mole ratio
to do this follow these steps
i) change % composition to no. of moles i.e. % composition / molar mass
ii) divide number of moles by lowest no. of moles
iii) if mole ratio is in fraction then multiply it by suitable no. to make it whole number
4-----> D because from 13 to 15 electrons start to be filled up in p orbital, and when it reaches 16 it starts to be paired up
8---> B simply use Hess law by forming the intermediate

 

[JD REBORN]

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_s06_qp_1.pdf
Q33 why is statement 2 incorrect?
http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w06_qp_1.pdf
In Q5 why isnt answer D?
In Q32 why is statement 1 correct and 2 and 3 wrong?
http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w07_qp_1.pdf
Q9,32
Plz anyone just explain them properly.Surely that cant be too hard??

 

[J_Line]

Could anyone explain what standard cell potential is?

 

[pratikdahal]

Can anyone please help me out with this?? November 2008, Paper 4, Question 2(b).

 

[ousamah112]

Can anyone please help me out with this?? November 2008, Paper 4, Question 2(b).
View attachment 7680

only those reactants will take part in the slowest step if their order of reaction is other thn zero order. For step 1 slowest, no H+ takes part in reaction so its zero order and other two are first order. For step 2 to be slowest, all will be 1st order because HOI is proportional to the conc of H+ and IO- and IO- is proportional to H2O2 and I-. For third ans will be 1 2 2,for this look at all three equations.

 

[JD REBORN]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s06_qp_1.pdf
Q33 why is statement 2 incorrect?
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w06_qp_1.pdf
In Q5 why isnt answer D?
In Q32 why is statement 1 correct and 2 and 3 wrong?
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w07_qp_1.pdf
Q9,32
Plz anyone just explain them properly.Surely that cant be too hard??

 

[Zishi]

Could anyone explain what standard cell potential is?

Read any good textbook. . .

 

[étudiante]

Could anyone explain what standard cell potential is?

It is the potential difference measured when a metal in a solution of its ions is connected to a standard hydrogen cell.

 

[JD REBORN]

Q33 the statement IS correct but is not applicable to the situation as it has no bearing on the fact that hydrazine does not undergo spontaneous coombustion.

Q5 it should have only two lobes and not four

Q32
1) is correct because a substance will readily change to its more stable state (and this is implied in the question so this is the information you can dduce from the question)
2) The reactivity of carbon monoxide has nothing to do with enthalpy change of formation of the two substances, if it were combustion, then it would be relevant.
3) This is no doubt true, but the statement is reffering to a complete conversion and not equillibrium so you can ignore this.

The statements can be true but you need to choose the one RELEVANT to the question.

U have mixed up the questions.And judging by your response obviously are trying to prove the statements are wrong but they are correct 2 and 3.

 

[étudiante]

U have mixed up the questions.And judging by your response obviously are trying to prove the statements are wrong but they are correct 2 and 3.

can u rewrite dem again pls so dat i get which questions ur talking abt den?
i never said any of the statements are wrong... just irrelevant

 

[hm12]

Calculate the pH of the buffer formed when 10.0 cm3 of 0.100 mol dm–3 NaOH is added to 10.0 cm3 of 0.250 mol dm–3 CH3CO2H, whose pKa = 4.76.

please explain how the answer is 4.58?

 

[hassam]

well.....there are 0.001 moles of naoh and .0025 moles of acid.
now naoh will react with acid and the resulting solution contains .001 mole salt and .0015 mole unreacted acid.now finnd their conc with the total volume now being 20cm^3 and now simply apply the henderson-hasselbalch equation

 

[hassam]

http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_w09_qp_41.pdf
q 3 b (ii)
i cnt undrstnd ms.....smbody explain please

 

[Scafalon40]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s06_qp_1.pdf
Q33 why is statement 2 incorrect?
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w06_qp_1.pdf
In Q5 why isnt answer D?
In Q32 why is statement 1 correct and 2 and 3 wrong?
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w07_qp_1.pdf
Q9,32
Plz anyone just explain them properly.Surely that cant be too hard??

Fellows need help with these paper 1 questions​

others have explained some of them but im not entirely satisfied.​

​

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

http://www.xtremepapers.com/papers/...and AS Level/Chemistry (9701)/9701_w08_er.pdf​

Q3 how do we work out the answer of this question?(which is D)​

Q31 Why is the answer not A?​

Q38 Why is the answer not B?(someone in a previous post said that flourine has to be present in order for a hydrocarbon to be a flame retardant. Can someone confirm that and tell me why?)​

​

http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_s11_qp_11.pdf​

Q9 Why is the answer not A?​

Q31 Why cant the answer be B? The second statement seems correct.​

Lets make a deal...
I'll try to help you in your problems if YOU JUST ANSWER MY QUESTIONS!

 

[étudiante]

Lets make a deal...
I'll try to help you in your problems if YOU JUST ANSWER MY QUESTIONS!

what questions? i can try to help u...

 

[Scafalon40]

what questions? i can try to help u...

In my signature below

 

[gary221]

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

it cant be D bcoz they r tlkng abt solidification of butane, in which van der waals' forces dnt hv 2 b ovrcum

 

[gary221]

Fellows need help with these paper 1 questions​

others have explained some of them but im not entirely satisfied.​

​

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

http://www.xtremepapers.com/papers/...and AS Level/Chemistry (9701)/9701_w08_er.pdf​

Q3 how do we work out the answer of this question?(which is D)​

Q31 Why is the answer not A?​

Q38 Why is the answer not B?(someone in a previous post said that flourine has to be present in order for a hydrocarbon to be a flame retardant. Can someone confirm that and tell me why?)​

​

http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_s11_qp_11.pdf​

Q9 Why is the answer not A?​

Q31 Why cant the answer be B? The second statement seems correct.​

For 3, v hv 2 see which pair of atoms hv 1 electron in thr s orbital...
In A, the electronic configuration of Ca is [Ar], 4S2...ie 2 electrons in s orbital thus A is wrong
In B, the e.c. of Cu is [Ar], 3d10, 4S1...bt Be is 1S2, 2S2.....thus B is wrong.
In C, the e.c. of H is 1S1...bt He is 1S2...thus C is wrong.
In D, Li = 1S2, 2S1...n Cr = [Ar], 3d5, 4S1....so D is correct

 

[étudiante]

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

it says OVERCOME.... in solidifiction, they will be made stronger... dats y its not the answer...
only in C will they be broken, for the others threr are H-bonds as well...