Chemistry paper 1 doubts!!

[Sucker Bino]

Oh i c .Thanx! Btw, how can we calculate for oxidation state..It is asked for in number 19 of this paper.
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s08_qp_1.pdf

A compounds oxidation no is = to zero, thus u find the oxidation no of chromate ions in both compunds nd then compare them

 

[Shepard97]

Can some1 plz explain no 20,http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w08_qp_1.pdf,answer is B,y

pH increases due to formation of Nitric Acid ( HNO3) ...
and Barium Chloride is formed which is not a precipate.. but aqueous

 

[Sucker Bino]

some1 plz xplain quest 11,http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w07_qp_1.pdf

 

[To2a Bahaa]

Can some1 plz explain no 20,http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w08_qp_1.pdf,answer is B,y

Barium nitrate is a salt with ph 7 and when you add acid ph decrease since acid has low ph and the resulting salt is barium chloride which is soluble so no ppt appears

 

[To2a Bahaa]

It

Oh i c .Thanx! Btw, how can we calculate for oxidation state..It is asked for in number 19 of this paper.
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s08_qp_1.pdf

It's given in the question (VI) remains (VI)

 

[To2a Bahaa]

Guys question 15 is confusing , why can't the answer be A?
http://olevel.sourceforge.net/papers/0620/0620_s12_qp_13.pdf

 

[Sucker Bino]

Guys question 15 is confusing , why can't the answer be A?
http://olevel.sourceforge.net/papers/0620/0620_s12_qp_13.pdf

each compound has an oxidation number equal to zero, thus from this u can find the oxidation no,answer is D since V2O3... 2x +3(-2)=0,x=3, then V2O5... 2x+5(-2)=0,x=5.......thus there is an increase in oxidation no from 3 to 5, thus it has been oxidised

 

[Fatima18]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s10_qp_11.pdf
In number 4, isnt the particle gained supposed to be electron?

 

[Fatima18]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s10_qp_11.pdf
Heyzz.
-In number 4, isnt the particle gained supposed to be electron?

-In number 39 I got D...why is it B?

 

[To2a Bahaa]

-In number 39 I got D...why is it B?

Addition polymerisation requires double bond ie ethene and the product formed will just be poly added to the monomer ethene ie polyethene

 

[NKPyo]

Oh i c .Thanx! Btw, how can we calculate for oxidation state..It is asked for in number 19 of this paper.
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s08_qp_1.pdf

For e.g. Cr gives 6 electrons to oxygen in K2CrO4 so its oxidation state is Cr(-6)
While in K2CrO7 Cr gives 12 electrons so it state is (-12).
However in this question the products remain same that is why the oxidation state of the chromium ion remains same however due to the excess k2cro7 the ph increases

 

[NKPyo]

Can some1 plz explain no 20,http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w08_qp_1.pdf,answer is B,y

The answer is C in the mark scheme and should be C as only non-metallic oxides are acidic.

 

[Afzal1]

because acid is added to alkaline solution so pH decreases. and secondly the precipitate forms with sulphuric acid not with hydrochloric acid so it precipitation reaction fails

 

[Afzal1]

chlorination just purifies thw water from germs and bacteria. so only filtration would remove the excess fertilizers.
the 13th question is about electrolysis ,the ions in the solution are H+, Cl-, Na+and OH- so H+ discharges at the cathode
but Na+ is also present there so the colour of the indicator changes to purple. At the anode Cl- discharges so it bleaches damp
litmus paper (making it colourless) so D is rhe correct answer. Hope this helps

 

[Afzal1]

Can some1 plz explain no 20,http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w08_qp_1.pdf,answer is B,y

when an alkali is added to an acid the pH naturally decreases and secondly the sulphate test would fail

 

[Afzal1]

the

Guys question 15 is confusing , why can't the answer be A?
http://olevel.sourceforge.net/papers/0620/0620_s12_qp_13.pdf

answer is clearly D, it cannot be A because it is a redox reaction Vanadium is getting reduced and oxygen is getting oxidised

 

[To2a Bahaa]

the
answer is clearly D, it cannot be A because it is a redox reaction Vanadium is getting reduced and oxygen is getting oxidised

oops I didn't notice Vanadium getting reduced, thanks a ton

 

[Afzal1]

oops I didn't notice Vanadium getting reduced, thanks a ton

U are most welcome to ask any queries on Maths Physics Chemistry, Biology i will be most obliged to help you

 

[To2a Bahaa]

U are most welcome to ask any queries on Maths Physics Chemistry, Biology i will be most obliged to help you

Thanks again