questions about industrial chemistry. (1 Viewer)

[BadMeetsEvil]

What was your mass of cacl2 from a tonne of nacl?
What were your explanations of the anode and cathode... Like what was the bubbles, why was the litmus red at positive and blue at negative?

 

[zhuang281]

Anode was the oxidation of Chlorine ions producing chlorine gas bubbles as observed
Cathode was the reduction of water producing hydrogen gas bubbles as observed.
I was a bit confused at first about the red/blue thing, then assumed that the litmus paper was red in neutral/acidic solutions.
So the paper stayed red at the anode where it was neutral and turned blue at the cathode where hydroxide ions were produced, making it basic.

 

[_deloso]

Anode was the oxidation of Chlorine ions producing chlorine gas bubbles as observed
Cathode was the reduction of water producing hydrogen gas bubbles as observed.
I was a bit confused at first about the red/blue thing, then assumed that the litmus paper was red in neutral/acidic solutions.
So the paper stayed red at the anode where it was neutral and turned blue at the cathode where hydroxide ions were produced, making it basic.

I did this too but my mate said it was O2 instead of Cl2 because it was diluted NaCl solution.
but I wrote blue where H2 was produced because of OH (basic) and I wrote Red at Cl2 because Cl2 reacts with H2O to form hcl thus acidic.

 

[zhuang281]

It didnt state diluted but in the prac we did in class, we use concentrated. Also, if you assume it is dilute the bit where they tell you it is electrolysis of Sodium Chloride would be rather pointless wouldnt it?

 

[_deloso]

It didnt state diluted but in the prac we did in class, we use concentrated. Also, if you assume it is dilute the bit where they tell you it is electrolysis of Sodium Chloride would be rather pointless wouldnt it?

it says 0.05 mol/L so that would make it diluted right?

 

[jayy100]

I did:
Anode: 2H20 --> O2 (g) + 4H+ (aq) + 4e- [Used standard potential tables]
Cathode: 2H20 + 2e- --> H2 (g) + 2OH- [Also on standard potential sheet]

Looking at the products, this explains for the change of the litmus paper. Btw, Cl2 (g) bleaches litmus paper WHITE
Since, NaCl is very dilute, its basically the electrolysis of water.

_Deloso i think your friend is right? Is he smart/reliable?

 

[zhuang281]

Hmm you have a point there, i am no longer sure However, i havent ever heard of a set threshold defining what is conc/dilute when we talk about NaCl Solution so its all rather subjective.

On second thought you guys are probably correct. Ahh well

 

[_deloso]

I did:
Anode: 2H20 --> O2 (g) + 4H+ (aq) + 4e- [Used standard potential tables]
Cathode: 2H20 + 2e- --> H2 (g) + 2OH- [Also on standard potential sheet]

Looking at the products, this explains for the change of the litmus paper. Btw, Cl2 (g) bleaches litmus paper WHITE
Since, NaCl is very dilute, its basically the electrolysis of water.

_Deloso i think your friend is right? Is he smart/reliable?

but why is litmus red?? because of O2?
and nah he's not that smart.. just got that question right by fluke. he's coming last in my class so yeah raw mark of around 12/100 for him. hahaha
I'm sorry to my friend who is reading this...

 

[jayy100]

Yeahh my school didnt go through pracs. properly aswell. But i read about it somewhere. 0.1 mol/L was considered dilute, hence 0.05 mol/L is def. dilute.


This prac. was meant to STRESS the importance of using BRINE (This is just CONC. NaCl) in Electrolytic cells; not just dilute NaCl

 

[jayy100]

LOL @ _deloso, anode half-equation produces H+ (Hydrogen ions)..... Hence, why the solution becomes acidic and litmus papers turns red.
(Cathode also produces OH-)

Farrout, your friend is F'd btw Scaling can't help him, with a raw mark that low!!

 

[khorne]

but why is litmus red?? because of O2?
and nah he's not that smart.. just got that question right by fluke. he's coming last in my class so yeah raw mark of around 12/100 for him. hahaha
I'm sorry to my friend who is reading this...

Because of H+ and blue because of OH-. Chlorine isn't oxidised because the concentration is not enough to overcome the -0.1 extra Vredox.

 

[BadMeetsEvil]

Because of H+ and blue because of OH-. Chlorine isn't oxidised because the concentration is not enough to overcome the -0.1 extra Vredox.

better listen to khorne! He is the master of chemistry. What's your raw mark estimate khorne?

 

[_deloso]

LOL @ _deloso, anode half-equation produces H+ (Hydrogen ions)..... Hence, why the solution becomes acidic and litmus papers turns red.
(Cathode also produces OH-)

Farrout, your friend is F'd btw Scaling can't help him, with a raw mark that low!!

yeah he is pretty stupid!!

Because of H+ and blue because of OH-. Chlorine isn't oxidised because the concentration is not enough to overcome the -0.1 extra Vredox.

aahhh okay, got it now!!!

 

[CalSandercock]

Guys i think its the other way around

Anode: 1/2H2(g) + OH- -> H2O + e-

Cathode: 1/2O2(g) + H20 + 2e- -> 2OH-


Because although the charge of the electrodes change, Oxidation still happens at the anode and Reduction still happens at the cathode

I think.......

Any what was the answer to the 2nd part of this question ? - What happens to the enrgy required if this is a galvanic cell? Does this just mean the cell provides the energy rather than the energy required for the chemical change in the electrolytic cell?

 

[Nympha]

Hmm you have a point there, i am no longer sure However, i havent ever heard of a set threshold defining what is conc/dilute when we talk about NaCl Solution so its all rather subjective.

Concentrated NaCl = brine = approx 30% solution of NaCl. So yes 0.05mol/L was definitely dilute.

 

[khorne]

Guys i think its the other way around

Anode: 1/2H2(g) + OH- -> H2O + e-

Cathode: 1/2O2(g) + H20 + 2e- -> 2OH-


Because although the charge of the electrodes change, Oxidation still happens at the anode and Reduction still happens at the cathode

I think.......

Any what was the answer to the 2nd part of this question ? - What happens to the enrgy required if this is a galvanic cell? Does this just mean the cell provides the energy rather than the energy required for the chemical change in the electrolytic cell?

dude, you picked the wrong equations...there's not hydrogen in the water lol

 

[umz93]

Well at least I had the cathode correct....

 

[Nympha]

Guys i think its the other way around

Anode: 1/2H2(g) + OH- -> H2O + e-

Cathode: 1/2O2(g) + H20 + 2e- -> 2OH-


Because although the charge of the electrodes change, Oxidation still happens at the anode and Reduction still happens at the cathode

I think.......

Any what was the answer to the 2nd part of this question ? - What happens to the enrgy required if this is a galvanic cell? Does this just mean the cell provides the energy rather than the energy required for the chemical change in the electrolytic cell?

uh? You have the order of the equations around the wrong way.

At anode, H2O + e --> 1/2H2 + OH
At cathode, H2O --> 1/2O2 + 2H + 2e. (this equation was lower down - the 1.23V one)

Re: second part, yeah. Electrolytic require energy input, galvanic are spontaneous and produce energy.

 

[umz93]

How many marks if we identified the correct cathode?

 

[_deloso]

What was your mass of cacl2 from a tonne of nacl?
What were your explanations of the anode and cathode... Like what was the bubbles, why was the litmus red at positive and blue at negative?

what about op's first question guys... I got around 900 kg
what did you guys get?