Physics, Chemistry and Biology: Post your doubts here!

[thats_me]

WHY THE ANSWER TO QUESTION 36 IS A ????? PLZ TELL

unsaturated so it should have double bonds
So, Its's neither B nor D
It forms a neutral solution so it's not C as C is acid (it has -CO2H)
So it's A

 

[Student of the year]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s08_qp_1.pdf
#12 - why is it not B?
#19 - final answer is D. Why does the oxidation state stay the same?

#12 -its not B bcz the terminals are arranged the wrong way,
the electrons always move from the anode(+) to the cathode (-), so the metal must be at the +ve terminal
got it??

 

[thats_me]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s08_qp_1.pdf
#12 - why is it not B?
#19 - final answer is D. Why does the oxidation state stay the same?

12 : NAil should be placed on cathode because reduction(reduction is gain) happens on cathode
19 :the oxidation will not be effected wen it's added in excess the pH increases because KOH is alkaline ..

 

[FATIMAH]

unsaturated so it should have double bonds
So, Its's neither B nor D
It forms a neutral solution so it's not C as C is acid (it has -CO2H)
So it's A

SO IT MEANS ALCHOL FORMS NEUTRAL SOL IN WATER NOT ACID ??? WHAT PH DO ACID FORMS IN WATER ??

 

[Student of the year]

#12 -its not B bcz the terminals are arranged the wrong way,
the electrons always move from the anode(+) to the cathode (-), so the metal must be at the +ve terminal
got it??

#19 - volume does not affect oxidation state & hope u know about the PH .

 

[FATIMAH]

12 : NAil should be placed on cathode because reduction(reduction is gain) happens on cathode
19 :the oxidation will not be effected wen it's added in excess the pH increases because KOH is alkaline ..

BUT POTASSIUM DICHROMATE IS NOT ADDED IN EXCESS

 

[thats_me]

SO IT MEANS ALCHOL FORMS NEUTRAL SOL IN WATER NOT ACID ??? WHAT PH DO ACID FORMS IN WATER ??

Yeaa Acid will obviously form acidic pH and it will be low as it is a weak acid

 

[FATIMAH]

#19 - volume does not affect oxidation state & hope u know about the PH .

CAN U EXPLAIN A BIT MORE FOR OXIDATION STATE ???

 

[Student of the year]

View attachment 12833

mass no of 1 H is 1 & the other is 2
soH2O= 16+ (2H= 1+1) = 18
also H2O= 16+ (2H= 2+2) =20
also H2O= 16+ (2H= 1+2)=19 ____here both the H are of diff mass

 

[gelato]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s08_qp_1.pdf
#13, anyone?

 

[thats_me]

BUT POTASSIUM DICHROMATE IS NOT ADDED IN EXCESS

Ok basically change in oxidation states takes place in redox reaction and this is not a redox reaction so there is no change in oxidation state
and wat i meant was by adding anything in excess the oxidation state is not effected

 

[always-smile :)]

plz need explanation for q. 19 june 2011

 

[Student of the year]

CAN U EXPLAIN A BIT MORE FOR OXIDATION STATE ???

oxidation state is the no of e that can be lost,& does not change with the volume .
take for eg Fe(ii) it has a oxidation state of 2 & even if it reacts with excess O2 its oxidation state will still remain 2.
hope u understood , if not plz tell.

 

[thats_me]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s08_qp_1.pdf
#13, anyone?

It cannot be bromine and oxygen as they form at anode (Br- & O2- are negative ions so attracted towards the positve electrode i.e anode)
So it's not A B or C
It's D the metals X and Y will form at cathode (as they form positive ions they are attracted towards the negative electrode i.e cathode)

 

[sultan ahmed]

has anyody finished with his chemistry mcq?

 

[Rahma Abdelrahman]

has anyody finished with his chemistry mcq?

U mean the exam itself?

 

[sultan ahmed]

U mean the exam itself?

yess

 

[FATIMAH]

 

[Rahma Abdelrahman]

yess

I don't think someone did it yet! And I heard that this year the 3 variants have different Q's!!!!

 

[always-smile :)]

plz need explanation for q. 19 june 2011