Chemistry: Post your doubts here!

[smzimran]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s03_qp_1.pdf

This is CIE
not IGCSE section
dear bro

 

[TheMan123]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s03_qp_1.pdf

A level questions only!!!
Anyway the answers are
1. C, because cooling a material causes it to lose heat energy, so energy is lost in the cooling tube
2. B, because during change of state there is no temp change, so its B or D, but melting is at a lower temp than boiling, so B

 

[smzimran]

Use of the Data Booklet is relevant to this question.
Lead(IV) chloride will oxidise bromide ions to bromine. The Pb4+ ions are reduced to Pb2+ ions in
this reaction.
If 6.980 g of lead(IV) chloride is added to an excess of sodium bromide solution, what mass of
bromine would be produced?
A 0.799 g B 1.598 g C 3.196 g D 6.392 g

The answer is C ?? explain someone!

AoA,
The key to solving this question is forming the equation
PbCl4 + 2NaBr ------> PbCl2 + Br2 + 2NaCl

Mr(lead chloride) = 207 + 4(35.5) = 349
moles of lead chloride = 6.980 / 349 = 0.02 mol

Since molar ratio b/w lead chloride and Br2 is 1:1
moles of Br2 = 0.02
mass of Br2
= 0.02 * Mr
= 0.02 * (2 * 79.9)
= 3.196

C is the answer!

 

[Muhammad Asif]

Use of the Data Booklet is relevant to this question.
Lead(IV) chloride will oxidise bromide ions to bromine. The Pb4+ ions are reduced to Pb2+ ions in
this reaction.
If 6.980 g of lead(IV) chloride is added to an excess of sodium bromide solution, what mass of
bromine would be produced?
A 0.799 g B 1.598 g C 3.196 g D 6.392 g

The answer is C ?? explain someone!

equation:- PbCl4+2NaBr----->Br2+ other stuff
mol of PbCl4=mol of Br2
6.980 mass
------------------ = -----------------
(207+(35.5*4) 79.9 *2
furthur solve it you will get the answer 3.196

 

[Student12]

Use of the Data Booklet is relevant to this question.
A 5.00 g sample of an anhydrous Group II metal nitrate loses 3.29 g in mass when heated
strongly.
Which metal is present?
A magnesium
B calcium
C strontium
D barium

Ans is B ? There are many such Q's in the past papers. i dont know how to do it !?

 

[TheMan123]

Use of the Data Booklet is relevant to this question.
A 5.00 g sample of an anhydrous Group II metal nitrate loses 3.29 g in mass when heated
strongly.
Which metal is present?
A magnesium
B calcium
C strontium
D barium

Ans is B ? There are many such Q's in the past papers. i dont know how to do it !?

let metal be X

2X(NO3)2 --> 2XO + 4NO2 + O2
5g ............ --> 1.71g +[ 3.29g ]

Mass of 1 mole of (4no2+ o2)=216grams
There are 3.29/216 moles of (4no2+o2)present
Also 3.29/216 moles of 2XO present
Therefore there is (2*3.29)/216 moles of XO
molar mass of XO = g/mol= 1.71/[(2*3.29)/216]=56.1grams
X=56.1-16=40.1 grams permole
Therefore answer is:

B.Calcium

 

[Student12]

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 ?

 

[Student12]

let metal be X

2X(NO3)2 --> 2XO + 4NO2 + O2
5g ............ --> 1.71g +[ 3.29g ]

Mass of 1 mole of (4no2+ o2)=216grams
There are 3.29/216 moles of (4no2+o2)present
Also 3.29/216 moles of 2XO present
Therefore there is (2*3.29)/216 moles of XO
molar mass of XO = g/mol= 1.71/[(2*3.29)/216]=56.1grams
X=56.1-16=40.1 grams permole
Therefore answer is:

B.Calcium

How did you get the 216g from ?

 

[TheMan123]

How did you get the 216g from ?

216 grams is 4NO2 + O2
N=14grams per mol
O=16 grams per mol

 

[smartangel]

The Cl radical can bond to any CH3 or CH2 carbons by substituting a hydrogen. There are 5 such carbons here, however there are 3 CH3 groups bonded directly to the alpha central carbon. If the Cl radical bonds to any three of this, you get the same molecule. The 3 CH3 groups form only one type of molecule. There are another two carbons which Cl can bond to, which makes 3 Chloroalkanes in total.
Answer: C. 3 (I checked)
Sorry for the messy explanation, not very good at this, ask me to clarify if needed
EDIT: Fixed typo

no its a great explanation..i got it..thanks

 

[angelgirl:)]

question no32 m/j 2010 ppr 11...some 1 plz help me out ...withthese kind of questions ...coz i can never solve like this kind of question...

 

[Student12]

216 grams is 4NO2 + O2
N=14grams per mol
O=16 grams per mol

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 ?

 

[Oliveme]

help with question 11 please. http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w06_qp_1.pdf

 

[Student12]

question no32 m/j 2010 ppr 11...some 1 plz help me out ...withthese kind of questions ...coz i can never solve like this kind of question...

It would be easier for others if you give the link of the paper.

 

[saudha]

It would be easier for others if you give the link of the paper.

http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_s10_qp_11.pdf

 

[saudha]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s10_qp_11.pdf

Q32
sorry .... angelgirl ...im not getting th answer

 

[smzimran]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s10_qp_11.pdf

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

 

[Student12]

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 ?

HELPP !!

 

[smartangel]

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?

 

[saudha]

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

thxx a lott really