Chemistry paper & Option (1 Viewer)

Menomaths

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But to produce NaOH, electrolysis of brine occurs, not water? Cl- is oxidised and water is reduced.



OH- seems okay to me as well, but who knows what's up with the marking criteria.

Was there a question asking for the uses of NaOH? Great. Lol.
No, I wrote for the evidence part 'if the electrode is clean then naoh was there' because i couldn't think of anything at that time...
 

hamstar

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I'm thinking the exact opposite haha. I wrote OH- and I'm scared that they wanted NaOH.
I think it doesn't matter that much because NaOH is still basic and can be shown through a red litmus paper turning blue or any other indicator test.
Hopefully this should be correct as it is asking how to identify the products.
I hope using OH- is correct as i did this aswell
 

bedpotato

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Wouldn't it depend on whether it was dilute or concentrated?
To produce NaOH, it's always brine - which is concentrated.

The electrolysis of dilute NaCl solution is basically the electrolysis of water - which produces only 2 products, O2 and H2. The question asked for 3 products.

So for this question, it was concentrated.
 

hamstar

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For q32 d (i) the safety precaution question. I said, use of a fume cupboard as chlorine gas is released which is toxic and causes damage to the human health as it effects the respiratory system. IS THIS CORRECT???
 

pHyRe

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but O2 can be produced from electrolysis of brine, as can H2. so would mine be right? even if they arent simulataneous they are both products
 

pHyRe

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also in my notes i have for dilute brine:

Cathode: 2H2O(l) + 2e- H2 (g) + 2OH-(aq)
Anode: 2H2O(l) O2 (g) + 4H+(aq) + 4e-

and for conc. i have the chlorine. and since they didnt specify and i said all 3 that should be 3 marks right? (assuming the tests are correct)
 

pHyRe

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i only had Na forming for molten nacl, which wasnt asked.

and most of my notes were from the jacaranda text book, school notes (reliable) or tutoring notes. so they should be alright
 

hamstar

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Also, NaOH is used as a cleaning agent so do you think my answer would be good?
That might be acceptable if you say initially the beaker or the electrode was stained or rusted, but tbh the answer they were looking for was the indicator test.

But marking guidelines are unpredictable. Atleast your answer is not wrong like wat one person that i know did, test for NaOH by putting your hand in the solution and if you get burns then sodium hydroxide is present. I cracked up so hard after hearing that.

Im not sure if he was srs that he wrote that in the exam. He probably was trolling.
 
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Menomaths

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That might be acceptable if you say initially the beaker or the electrode was stained or rusted, but tbh the answer they were looking for was the indicator test.

But marking guidelines are unpredictable. Atleast your answer is not wrong like wat one person that i know did, test for NaOH by putting your hand in the solution and if you get burns then sodium hydroxide is present. I cracked up so hard after hearing that.

Im not sure if he was srs that he wrote that in the exam. He probably was trolling.
Aahahhaa shit, and I thought my answer was retarded
 

ocatal

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also in my notes i have for dilute brine:

Cathode: 2H2O(l) + 2e- H2 (g) + 2OH-(aq)
Anode: 2H2O(l) O2 (g) + 4H+(aq) + 4e-

and for conc. i have the chlorine. and since they didnt specify and i said all 3 that should be 3 marks right? (assuming the tests are correct)
But it said 'an' aqueous solution. So it has to be either concentrated or dilute solutions of NaCl meaning you can't write the products of two different solutions.
 

martin96

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hey guys, enjoying the feedback. I wrote indicator for OH/NaOH. I was going to write pop test for hydrogen, but how could you do a pop test from a solution? I just wrote bubbles of gas are formed (which I think is wrong) . I'm also not sure what I wrote for choline is right. I wrote precipitate out with chloride ions. Is that right or?
 

hamstar

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hey guys, enjoying the feedback. I wrote indicator for OH/NaOH. I was going to write pop test for hydrogen, but how could you do a pop test from a solution? I just wrote bubbles of gas are formed (which I think is wrong) . I'm also not sure what I wrote for choline is right. I wrote precipitate out with lead ions. Is that right or?
Sorry bro, i don't think that will be right. because chlorine ions is not the product, chlorine gas is.
I'm not sure about the bubbles.
just be hopeful that you can achieve 2 marks for that question, which is still a good mark for that question.
 

martin96

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Hmm i see. How many marks was it worth? I wrote the equation write and I definetley got the OH ions right. What would be the hydrogen test then?
 

Menomaths

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Hmm i see. How many marks was it worth? I wrote the equation write and I definetley got the OH ions right. What would be the hydrogen test then?
It'd be hydrogen gas so the test would be the pop test
 

bedpotato

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hey guys, enjoying the feedback. I wrote indicator for OH/NaOH. I was going to write pop test for hydrogen, but how could you do a pop test from a solution? I just wrote bubbles of gas are formed (which I think is wrong) . I'm also not sure what I wrote for choline is right. I wrote precipitate out with chloride ions. Is that right or?
H2 gas is produced. The gas is just floating around near the cathode I guess ? So the pop test would be right.

Same with chlorine, the gas. Not ions.
 

JohnMaximus

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That might be acceptable if you say initially the beaker or the electrode was stained or rusted, but tbh the answer they were looking for was the indicator test.

But marking guidelines are unpredictable. Atleast your answer is not wrong like wat one person that i know did, test for NaOH by putting your hand in the solution and if you get burns then sodium hydroxide is present. I cracked up so hard after hearing that.

Im not sure if he was srs that he wrote that in the exam. He probably was trolling.
In my trial I had to describe chemical tests for eutrophication.

Couldn't think of HOW to test for phosphate ions, or low DO etc. so I said:

Put fish in water. Did they die? Eutrophication.


I think I ticked off my teacher.
 

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