chemistry MCQs

[izzahzainab]

Number 12, 17 and 38 are very confusing, if any1 can help me it will be great

 

[intelnehalem]

Q12 : Copper electrodes
so at anode Cu --> Cu2+ + 2e (anode dissolves)
at cathode Cu2+ + 2e ---> Cu
Copper is deposited on cathode.
Overall concentration of Copper ions remain the same so electrolyte colour is blue!(no change)
Answer is B

 

[intelnehalem]

Q 17 Answer is A
When an alcohol is oxidised, a carboxylic acid is formed ! However,forming ethyl ethanoate during esterification and forming sodium ethanoate doesn't involve oxidation !

 

[intelnehalem]

Q38 Answer is Ethanoic acid which is B
ethanoic acid can react with ethanol to form ethyl ethanoate and it can react with Potassium hydroxide which is a base to form Potassium ethanote. It also reacts with sodium carbonate to form Sodium ethanoate, carbondioxide and water. here they are asking for a carboxylic acid

 

[izzahzainab]

Q12 : Copper electrodes
so at anode Cu --> Cu2+ + 2e (anode dissolves)
at cathode Cu2+ + 2e ---> Cu
Copper is deposited on cathode.
Overall concentration of Copper ions remain the same so electrolyte colour is blue!(no change)
Answer is B

but doesnt the copper in the electrolyte also move towards cathode and gets deposited?
i think sulfuric acid should remain in solution :unknown:

 

[izzahzainab]

Q 17 Answer is A
When an alcohol is oxidised, a carboxylic acid is formed ! However,forming ethyl ethanoate during esterification and forming sodium ethanoate doesn't involve oxidation !

hey, oxidation can also be called loss of hydrogen. when sodium ethanoate is formed, 1 hydrogen is removed....????

 

[abcde]

Answer 12: When copper electrodes are used, the copper atoms at the anode are oxidised to copper ions so the anode dissolves. These ions(positive) are attracted to the (negative)cathode, where they gain electrons and are reduced back to copper, a pink solid. The blue colour of the solution remains unchanged since the copper ions reduced are the ones which have come from the anode and not the electrolyte! Thus, B is correct.
17: A is correct. Alcohols are always OXIDISED to carboxylic acids. Neutralisation (Y) and Esterification (Z) do not involve oxidation!
38: Only acids react with both carbonates and bases so your choice is first narrowed to B and D. But then mineral acids such as hydrochloric acids don't react with ethanol! Ethanoic acid CAN react with ethanol to form ethyl ethanoate (recall esterification again).
Hope you understand now.
Good luck for your exams!

 

[izzahzainab]

Q38 Answer is Ethanoic acid which is B
ethanoic acid can react with ethanol to form ethyl ethanoate and it can react with Potassium hydroxide which is a base to form Potassium ethanote. It also reacts with sodium carbonate to form Sodium ethanoate, carbondioxide and water. here they are asking for a carboxylic acid

thanx, but can't the answer be hydrochloric acid??

 

[abcde]

Q 17 Answer is A
When an alcohol is oxidised, a carboxylic acid is formed ! However,forming ethyl ethanoate during esterification and forming sodium ethanoate doesn't involve oxidation !

hey, oxidation can also be called loss of hydrogen. when sodium ethanoate is formed, 1 hydrogen is removed....????

This is a neutralisation reaction, which are always non-redox!

 

[intelnehalem]

Answer 12: When copper electrodes are used, the copper atoms at the anode are oxidised to copper ions so the anode dissolves. These ions(positive) are attracted to the (negative)cathode, where they gain electrons and are reduced back to copper, a pink solid. The blue colour of the solution remains unchanged since the copper ions reduced are the ones which have come from the anode and not the electrolyte! Thus, A is correct.
17: Again A is correct. Alcohols are always OXIDISED to carboxylic acids. Neutralisation (Y) and Esterification (Z) do not involve oxidation!
38: Only acids react with both carbonates and bases so your choice is first narrowed to B and D. But then mineral acids such as hydrochloric acids don't react with ethanol! Ethanoic acid CAN react with ethanol to form ethyl ethanoate (recall esterification again).
Hope you understand now.
Good luck for your exams!

hey dude , isn't the answer for Q12 B? in A it says colour of electrolyte fades

 

[intelnehalem]

Q12 : Copper electrodes
so at anode Cu --> Cu2+ + 2e (anode dissolves)
at cathode Cu2+ + 2e ---> Cu
Copper is deposited on cathode.
Overall concentration of Copper ions remain the same so electrolyte colour is blue!(no change)
Answer is B

but doesnt the copper in the electrolyte also move towards cathode and gets deposited?
i think sulfuric acid should remain in solution :unknown:

No dude ! Here since Copper electrodes are used, Copper is oxidised at the anode and copper ions are discharged at the cathode. Overall concentration of copper ions in the electrolyte remains the same, they are not deposited on cathode since the electrodes are Copper ! Sulphuric acid is formed if carbon electrodes

 

[CaptainDanger]

Its B... Explained by abcde but she wrote the answer wrong...

 

[izzahzainab]

ok thankyou!

 

[intelnehalem]

Its B... Explained by abcde but she wrote the answer wrong...

abcde is a girl? :shock:

 

[CaptainDanger]

Yeah.... Why are you shocked ?

 

[intelnehalem]

Yeah.... Why are you shocked ?

I thought that abcde was a boy for all this time :shock: Damn, I'm so sorry abcde

 

[CaptainDanger]

She won't mind don't worry...

 

[abcde]

Lol.. Thank's okay! Yes, thanks for pointing that out Captain!

 

[CaptainDanger]

 

[izzahzainab]

http://www.xtremepapers.me/CIE/index.ph ... 8_qp_1.pdf

check question 12