Biology; Chemistry; Physics: Post your doubts here!

[SalmanPakRocks]

no problem.

 

[snowbrood]

http://www.xtremepapers.com/CIE/Cambridge O Levels/5070 - Chemistry/5070_w10_qp_11.pdf can anyone answer q12 please and with explanation

 

[Silent Hunter]

whats the correct answer in MS?

 

[SalmanPakRocks]

I guess the answer is C.

 

[Silent Hunter]

yes ........ seems C to me too

 

[SalmanPakRocks]

let's check the marking scheme!

 

[Silent Hunter]

Hydrogen goes to negative electrode while sulphate and hydroxide goes to positive....... sulfate ones are never reduced........ so hydroxide releases oxygen.........

 

[legion]

http://www.xtremepapers.com/CIE/Cambridge O Levels/5070 - Chemistry/5070_w10_qp_11.pdf can anyone answer q12 please and with explanation

its C i thnk. cz copper sulphate has copper deposition on cathode. conc. sodium chloride ll have hydrogen gas and chlorine gas as products but their proportion will be same cz 2 chloride ions loose 2 electrons used by 2 hydrogen ions. H2SO4 'll give oxygen gas and hydrogen gas. the proportion of hydrogen gas ll be double to oxygen cz liberation of one oxygen gas gives 4 electrons and each H2 molecule uses 2 electrons. i dunno about the reason of ethanol but i thnk its cz its a weak acid n electrolysis is difficult

 

[awaisbuttrocksCIE]

http://www.xtremepapers.com/CIE/Cambridge O Levels/5070 - Chemistry/5070_w10_qp_11.pdf can anyone answer q12 please and with explanation

the answer is C) Dilute H2SO4.... If you see clearly on the diagram the volume towards cathode is half the volume at anode....this is because oxygen is deposited at the anode and hydrogen at the cathode.

Reaction at cathode: 2h+2e=H2
Reaction at anode: 4oh= O2+H2O+ 4e


now if you mulitply the whole equation of the cathode with 2 to make both equations having 4e then you will get cathode equation like this:

4h+4e=2H2
... now look at the volume of both hydrogen and oxygen...oxygen has one volume and hydrogen has two volume....this is the way i was taught...If this is incorrect do point out and let me know...

 

[legion]

the answer is C) Dilute H2SO4.... If you see clearly on the diagram the volume towards cathode is half the volume at anode

umm isnt cathode the negative electrode? tht makes volume at anode half the volume of gas at cathode. isnt it????

 

[SalmanPakRocks]

cathode = -ve
anode = +ve

 

[snowbrood]

the answer is C) Dilute H2SO4.... If you see clearly on the diagram the volume towards cathode is half the volume at anode....this is because oxygen is deposited at the anode and hydrogen at the cathode.

Reaction at cathode: 2h+2e=H2
Reaction at anode: 4oh= O2+H2O+ 4e


now if you mulitply the whole equation of the cathode with 2 to make both equations having 4e then you will get cathode equation like this:

4h+4e=2H2
... now look at the volume of both hydrogen and oxygen...oxygen has one volume and hydrogen has two volume....this is the way i was taught...If this is incorrect do point out and let me know...

hey in case if aqueous copper sulphate is used i gues copper will deposit on cathode and thus water level will rise right in cathode

 

[scouserlfc]

hey in case if aqueous copper sulphate is used i gues copper will deposit on cathode and thus water level will rise right in cathode

I dont think we really know all that its out of our syllabus,except for H2SO4 thing !
Anyways for Cu electrolysis no one will use this setup ! this is a typical gas collection electrolytic cell used for H2SO4 !

 

[scouserlfc]

Okay ill make a flow chart thing later when i get time ill just tell u how this works !

For choosing how to make the salts by different methods we do the following !
1.First u check whether the metal in the salt to be made is reactive enuf to replace the hydrogen in the acid or not,if it can replace it then u check if its way too reactive and therefore dangerous a reaction, if not then u proceed and react with the acid excess metal and then filter and crystallize !
2.But if the metal is not reactive enuf or it is way too reactive then u use Plan B.
3.Plan B involves reacting base or carbonate with acid but it involves two parts !
i.First u check whether the base or carbonate of the metal in the salt to be made is soluble of not then u make the salt by reacting with acids solid metal carbonates or solid base !
ii.But if the base or carbonate is soluble then u take the titration method and u react the metal base or carbonate with acid by using titration method

and thats it,u have to go point by point if any metal in the salt to be made agrees to the points u use the method !
I hope u all get it !

 

[scouserlfc]

those having problems in salt prep read this i think this is from Harwood book and it was in the notes @SalmanPakRocks gave !

 

[legion]

thankuuu scouserlfc and salmanpakrocks

 

[SalmanPakRocks]

np

 

[scouserlfc]

 

[snowbrood]

I dont think we really know all that its out of our syllabus,except for H2SO4 thing !
Anyways for Cu electrolysis no one will use this setup ! this is a typical gas collection electrolytic cell used for H2SO4 !

but i wanted to say is that in case of cuso4 copper will deposit on cathode and thus water level will rise thats what i wanted to say u are right about the test tube thing

 

[scouserlfc]

but i wanted to say is that in case of cuso4 copper will deposit on cathode and thus water level will rise thats what i wanted to say u are right about the test tube thing

yeah it shud !