Chemistry: Post your doubts here!

[angelgirl:)]

AoA,
1 is redox
Br goes from -1 to 0 [oxidation]
S goes from +6 to +4 [reduction]

2 is not redox
P is same at 5
Br is same at -1

As 2 is wrong, you dont need to see 3
Definitely D is the answer but i will solve to clear any doubts!

3 is not redox
N is same at 5
Br is same at -1
thanks...so for solving the redox questions u can jtake any example u want...and then carry out the calculation? isnt it?
and soory for not posting the link coziam soling in the paper...

 

[angelgirl:)]

35 In a car engine, non-metallic element X forms a pollutant oxide Y.
Further oxidation of Y to Z occurs in the atmosphere. In this further oxidation, 1 mol of Y reacts
with ½ mol of gaseous oxygen.
What can X be?
1 carbon
2 nitrogen
3 sulfur
why cant it be carbon?

ohhh even i have doubt in this question...

 

[smzimran]

ohhh even i have doubt in this question...

35 In a car engine, non-metallic element X forms a pollutant oxide Y.
Further oxidation of Y to Z occurs in the atmosphere. In this further oxidation, 1 mol of Y reacts
with ½ mol of gaseous oxygen.
What can X be?
1 carbon
2 nitrogen
3 sulfur
why cant it be carbon?

It is because Carbon is not there in the car engine!
Yes, carbon and CO maybe produced by incomplete combustion of hydrocarbon fuels but they are produced outside (not in the engine itself)

 

[angelgirl:)]

ohhh even i have doubt in this question...

plz some1 give an explaining for this question...

 

[saudha]

It is because Carbon is not there in the car engine!
Yes, carbon and CO maybe produced by incomplete combustion of hydrocarbon fuels but they are produced outside (not in the engine itself)

here it is angelgirl

 

[smartangel]

It is because Carbon is not there in the car engine!
Yes, carbon and CO maybe produced by incomplete combustion of hydrocarbon fuels but they are produced outside (not in the engine itself)

oh ok so instead of carbon if they give hydrocarbon as an option it'll be included in the answer?

 

[angelgirl:)]

It is because Carbon is not there in the car engine!
Yes, carbon and CO maybe produced by incomplete combustion of hydrocarbon fuels but they are produced outside (not in the engine itself)

ok...thanks

 

[smzimran]

oh ok so instead of carbon if they give hydrocarbon as an option it'll be included in the answer?

No,
Read the question it says a NON-METALLIC element!
Hydrocarbon is a compound

 

[smartangel]

No,
Read the question it says a NON-METALLIC element!
Hydrocarbon is a compound

oops. my bad oh and btw they give this question again n again with some variation. in one of them they said it is a polar molecule. CO is a polar molecule right? sorry i knw its like basic stuff but im kinda freaking out right now!

 

[smartangel]

4 Sulfur dioxide, SO2, is added to wines to prevent oxidation of ethanol by air. To determine the
amount of SO2, a sample of wine is titrated with iodine, I2. In this reaction, one mole of SO2 is
oxidised by one mole of I2.
What is the change in oxidation number of sulfur in this reaction?
A +2 to +4 B +2 to +6 C +4 to +5 D +4 to +6
ans D. whats the equation for this rxn?

 

[TheMan123]

Yea i understood that part.. but i'm still confused. Why did you take 4 for NO2? & the 2 for XO.
We don't take the values of the balancing part for the Molar mass isn't it ?

Sorry I was gone for awhile, where was I...
Normally we don't but you have to understand the maths going on here...
OK, alternative method. Assuming we have 2 moles of the nitrate

2X(NO3)2 --> 2XO + 4NO2 + O2
Masses will be:
(248+2x)g-->(32+2x)g +(216 )g
x is 1 mole
Real masses are:
5g ............ --> 1.71g +[ 3.29g ]

the ratios of the reactants and products are the same but the amounts are different
therefore:
ratio of nitrate mass to oxide mass will be the same in both situations
(248+2x)/ (32+2x)=5/1.71
cross multiply
424.08 + 3.42x =160 + 10x
264.08 = 6.58x
x= 40.1 grams per mole
x=calcium

 

[smartangel]

http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_w10_qp_11.pdf
Q7

 

[nerdybookworm]

ok sorry i posted the wrong link..now here help........paper 1 m/j 03 Q 2,4,8,10,16,20,27,28,30 & 39......


http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_s03_qp_1.pdf

 

[Student12]

Sorry I was gone for awhile, where was I...
Normally we don't but you have to understand the maths going on here...
OK, alternative method. Assuming we have 2 moles of the nitrate

2X(NO3)2 --> 2XO + 4NO2 + O2
Masses will be:
(248+2x)g-->(32+2x)g +(216 )g
x is 1 mole
Real masses are:
5g ............ --> 1.71g +[ 3.29g ]

the ratios of the reactants and products are the same but the amounts are different
therefore:
ratio of nitrate mass to oxide mass will be the same in both situations
(248+2x)/ (32+2x)=5/1.71
cross multiply
424.08 + 3.42x =160 + 10x
264.08 = 6.58x
x= 40.1 grams per mole
x=calcium

Thanks

 

[user]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_11.pdf
Q7

Aoa wr wb!

1 has no lone pairs and 4 atome attached, so angle is 109.5

2 has no lone pairs and 3 atoms attached, so angle is 120

3 has 2 lone pairs and 2 atoms attached..so angle is 107

so ans. is 3 => 1 => 2

therefore C

 

[smartangel]

Aoa wr wb!

1 has no lone pairs and 4 atome attached, so angle is 109.5

2 has no lone pairs and 3 atoms attached, so angle is 120

3 has 2 lone pairs and 2 atoms attached..so angle is 107

so ans. is 3 => 1 => 2

therefore C

thanks..what abt 4 Sulfur dioxide, SO2, is added to wines to prevent oxidation of ethanol by air. To determine the
amount of SO2, a sample of wine is titrated with iodine, I2. In this reaction, one mole of SO2 is
oxidised by one mole of I2.
What is the change in oxidation number of sulfur in this reaction?
A +2 to +4 B +2 to +6 C +4 to +5 D +4 to +6
ans D. whats the equation for this rxn?

 

[Muhammad Asif]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_11.pdf
Q7

the answer woud be C.....in 1 there are four electron cloud regions around central atom C here with no lone pair thus the angle is 109.5°....in 2 there are three electron clouds(bonds)with no lone pair thus the angle is 120.....in 3 there are 2 electron clouds on central atom O with two lone pairs thus angle is reduced to 104.5 thus answer is 3-----1-----2

 

[user]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_13.pdf

QUESTION - ANSWER
15 - B
23 - A
25 - C
36 - A

Someone plz explain ?

Aoa wr wb!

Q:15
Mr of CaCO3 = 100.1
Mr of CO2 = 44
CaCO3 àCaO + CO2
So 1 mol of CaCO3 will give 1 mol CO2
We have a total of 1200 million tonnes (=1200 x 10^6 x 10^3 g) of CaCO3
No of moles of CaCO3 = 1200 x 10^6 x 10^3 /100.1
This is equal to no of moles of CO2 = mass of CO2/44
Mass of CO2 = no. of moles x 44 = 527 x 10^6 x 10^3 g = 527 million tonnes
so the ans. is B

 

[nerdybookworm]

15-

Question 23
You need to know the general formulas of the organic compounds listeed-
A- alcohols- CnH2n+1OH, hydrogen to carbon ratio- 4:1
B- Aldehydes- CnH2n+1CHO. hydrogen to carbon ratio- 2:1
C carboxylic acid, CnH2n+2COOH. hydrogen to carbon ratio- 2:1
D- Halogenoalkanes, CnH2n+1X, hydrogen to carbon ratio- 3:1

Greatest ratio shown by alcohols. Hence answer is A.

Question 25-
When ethanol refluxed with potassium dichormate, you'll get a carboxylic acid. Molar ratio remails 1:1. So moles of ethanol react was 2.76/46= 0.06 mol,
Since molar ratio is 1:1, 0.06 mol of ethanoic acid will also form, so mass of ethanoic acid formed= 0.01*61=3.66g
The yeild of product was 75%, so 75% of 3.66= 2.75, almost equal to 2,70, hence answer is C.

can yu help me too..i posted my link a bit up..scroll up n chk n ans..plzz

 

[user]

Assalamoalaikum wr wb!

need help, plz... ...

P.S. I'm reposting them