Chemistry: Post your doubts here!

[omarjaved619]

Because it has a positive charge on top!

Doesnt "2+" mean losing two electrons? Isnt it just +? Wont it lose only 1 e? :S

 

[AbbbbY]

Doesnt "2+" mean losing two electrons? Isnt it just +?

[CH3]- has the complete octet
[CH3] has lost one electron/not gained one electron
[CH3]+ has lost one further electron

Thus, a total of two electrons.

 

[omarjaved619]

[CH3]- has the complete octet
[CH3] has lost one electron/not gained one electron
[CH3]+ has lost one further electron

Thus, a total of two electrons.

Ohhhh I get it nowww. Thanks a ton

 

[saadgujjar]

how GT is calculated for as level.in the GT it is wriiten that total marks for as level is 130 for chemistry but actually it is 140.plz explain

 

[shaista]

*Not allowed*

 

[hela]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s09_qp_1.pdf Q9 A Q20 C

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf Q7 D

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s10_qp_12.pdf Q9 D Q25 C

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w12_qp_13.pdf Q22 B Q25 A

 

[AbbbbY]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s09_qp_1.pdf Q9 A Q20 C

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_12.pdf Q7 D

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s10_qp_12.pdf Q9 D Q25 C

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w12_qp_13.pdf Q22 B Q25 A

You need explanations for these or are you answering them for someone?

 

[hela]

You need explanations for these or are you answering them for someone?

YES I NEED EXPLANATION PLEASE

 

[hela]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s09_qp_1.pdf Q9 A Q20 C

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_12.pdf Q7 D

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s10_qp_12.pdf Q9 D Q25 C

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w12_qp_13.pdf Q22 B Q25 A

can anyone explain thanks

 

[rawaaaan]

hello
plz help this this question looks easy but i cant solve
here u go ...Which mass of gas would occupy a volume of 3dm3 at 25°C and 1 atmosphere pressure? [1mol of gas occupies 24dm3 at 25°C and 1 atmosphere pressure.]
a)3.2g O2 gas
b)5.6g N2 gas
c)8.0g SO2 gas
d)8.0g SO2 gas

 

[omarjaved619]

W11_qp11 Q27

A reaction between chlorine and propane in ultraviolet light produces two isomeric
monochloropropanes, C3H7Cl, as products. Which information about this reaction is correct?

Help?

 

[AbbbbY]

hello
plz help this this question looks easy but i cant solve
here u go ...Which mass of gas would occupy a volume of 3dm3 at 25°C and 1 atmosphere pressure? [1mol of gas occupies 24dm3 at 25°C and 1 atmosphere pressure.]
a)3.2g O2 gas
b)5.6g N2 gas
c)8.0g SO2 gas
d)8.0g SO2 gas

Simple!
1 mol : 24 dm3
x mol : 3 dm3
x= 0.125 mol
Next, you simply see which gas has 0.125 moles.
So the answer is C/D [8g of SO2] whichever isn't the incorrectly written 8g of SO2.

 

[AbbbbY]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s09_qp_1.pdf Q9 A Q20 C

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_12.pdf Q7 D

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s10_qp_12.pdf Q9 D Q25 C

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w12_qp_13.pdf Q22 B Q25 A

ON09
Q9 - Sorry I suck at Electo. Maybe someone else can answer this for you and invariably for me.

MJ12 P12
Q7
P -> <- Q + R
Start: 2 mol : 0 mol : 0 mol
Eq: 2-x : x/2 : x mol

Total moles, 2+x/2
Moles of P and R = (2-x)+x = 2
Moles of Q: 2+(x/2)-2 = x/2

Having done such questions enough times, I can simply deduce the ratio is 2: 1 : 2

However, if you can't, use any value of X under 2 and over 0.

1.5 will work too, but to simplify things, lets take x=1
1 : 1/2 : 1
= 2 : 1 : 2
So 2P -> <- Q + 2R

MJ10 P12
Q9

pH 6 is a very weak acid, so Student P HAS to be wrong
pH 9 is a weak base, but relative to a neutral of 7, it's stronger than the acid.

Change of 1 under neutral pH for the Acid, but change of 2 over the neutral pH for the base. Since concentrations are the same, the base will dissociate more than the acid, thus Student Q is corrent.

Since student Q only is correct, it's D



Sorry, I can't answer the Organic chem questions. I've only done Physical and Inorganic. Maybe someone else here can help you with that

 

[hela]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s10_qp_12.pdf Q9 D Q25 C
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w12_qp_13.pdf Q22 B Q25 A
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_11.pdf Q14 B Q27 D Q36 A
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_11.pdf Q9 B Q13 C Q18 C Q22A Q38 A

 

[rawaaaan]

hey help in this please
in leaded petrol there i an additive composed of lead,carbn and hydrogen only.this compound contains 29.7% and 6.19% hydrogen by mass.
what is the value of x in the empiricl formula pbc8hx
a)5
b)6
c)16
d) 20

 

[rawaaaan]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w09_qp_11.pdf
question 11,19,20,21,23,28,2,30,36,35,31 i know its too much :/ but plz help

 

[bogus]

mj 2010 question paper 11 question 40. Help!

 

[rawaaaan]

Simple!
1 mol : 24 dm3
x mol : 3 dm3
x= 0.125 mol
Next, you simply see which gas has 0.125 moles.
So the answer is C/D [8g of SO2] whichever isn't the incorrectly written 8g of SO2.

thnx a lot

 

[AbbbbY]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_qp_11.pdf
question 11,19,20,21,23,28,2,30,36,35,31 i know its too much :/ but plz help

2- D!
Two methods. I'll tell you the quicker one.

CxHy -> xCO2 + y/2H2O
35.2/44 = 0.8 mol
14.4/18 = 0.8 mol
0.2 mol -> 0.8 mol + 0.8 mol
= 1 -> 4 : 4

Next, you write up the combustion equations and balance them to see which one falls under the molar ratio.
simply by looking at the ratio I can tell that it has to be CnH2n so it's A or D.

Next, since xCO2 = 4 mol, so C4 has to be the answer. You're left with C4H8.

If this is too hard or confusing, you can write the combustion equations for each and cross check. Will waste a lot of time though.

11 A!

A-> Cu+ is changing to Cu2+ in Reaction two which in turn reacts in 3 to form Cu+ again in the final step, so it's technically unused. Hence it is acting as a catalyst.

B-> Cu+ ions are oxidised so act as reducing agents

C-> Changes w.r.t light are due to Silver atom concentration. It can become dark and light so reaction is reversible, hence A is the reaction absorbing light. Besides, Reaction 2 has no Ag so it's out automatically

D-> Ag+ is reduced to Ag


19, 20, 21, 23, 28, 30, 31
All Organic. I only know Physical and Inorganic. Someone else will answer these for you


35 C
Easy method:

Simple neutralization reaction so Sulfuric acid can never form! 1 is out so Option C is left.

Time breaking method:
CaO + (NH4)2SO4 -> CaSO4 + NH3 + H2O


36: D

Just by reading, eliminate 3 because Only I- is reduced to I2 in such reaction.

NaBr + H2SO4 -> HBr + Na2SO4

2 and 3 are incorrect.

Left with D
[Please check marking scheme if I'm correct].

 

[AbbbbY]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s10_qp_12.pdf Q9 D Q25 C
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w12_qp_13.pdf Q22 B Q25 A
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_11.pdf Q14 B Q27 D Q36 A
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_11.pdf Q9 B Q13 C Q18 C Q22A Q38 A

Sorry just saw your questions.

ON11 P11
Q14 B

CaCO3 -> CaO + CO2

Mass of Limestone: 1000+200 = 1200m ton
Mol = 1200/100 = 12 mol
1 mol = 44m ton
12 mol = 44*12 mton = 528m tonnes.

I must've rounded off something in the Ar but the closest answer gets it hence B. Do it properly and you'll get it to 527. [Didn't have data booklet]



Q36 A

Nitrogen is the element (Not metallic so not lead)

Oxide = NO
Oxidation = NO2
Verification: NO + 0.5O2 -> NO2

1- Yes. NH3 is formed.
2- N2 exists, so yes.
3- N is the third most polar so defo yes. (NOF)

Hence A
The rest I'll answer later. Too tired.