HSC Chemistry Exam Solutions / Thoughts (1 Viewer)

[Arrowshaft]

would you say the exam was more maths than theory? if so how much roughly like was it basically all maths?

I’d say like roughly 65% of it was maths but tbh i remember nothing rn, my mind is blank

 

[akkjen]

I’d say like roughly 65% of it was maths but tbh i remember nothing rn, my mind is blank

hahah ok np, hopefully physics will be similar

 

[Jendeukie]

omg I'm so dumb, i completely forgot about sodium and pop test for alcohol, forming an alkoxide and hydrogen gas...
i just went with the oxidation to an acid and having it test positive so it's a primary alcohol omg but that's kinda two in one, i really hope they're nice about it but who knows
lucky for ester though, i guessed right with the fruity smell. didn't have any other idea what it could be

 

[worldno17]

for ester, i did fruity smell in addition to how you can add in dilute naoh, which hydrolyses the ester linkage --> forms sodium acetate which can hydrolyse in solution to form acetic acid (aka vinegar smell). that works too, right?

also, i don't recall the question explicitly asking to name the compounds. i think i did anyway but it wasn't as blatant (like compound 2 = ethanol) or whatever. rip.

 

[Idkwhattoput]

for ester, i did fruity smell in addition to how you can add in dilute naoh, which hydrolyses the ester linkage --> forms sodium acetate which can hydrolyse in solution to form acetic acid (aka vinegar smell). that works too, right?

also, i don't recall the question explicitly asking to name the compounds. i think i did anyway but it wasn't as blatant (like compound 2 = ethanol) or whatever. rip.

I remember specifically adjusting my answer to clearly outline each compound as it said something like 'identify the reagents in each reaction'.

 

[Jendeukie]

hey can i ask does anyone remember what they did for stormwater
i didn't understand what the question meant, initially i even calculated the concentrations PRIOR to the treatment of the water plant (because they gave us initial absorbances too????) but in the end i crossed that out and only calculated the final absorbances for both ions. i got one really low, and the other a bit higher than 1 mg/L. so like, one ion passed and the other didn't, provided the concentrations were meant to be below 1 mg/L or something. but i'm super confused (why'd they give us initial absorbances??) and i don't know if i got the right answers even if i did it the right way.


also said lead hydroxide is a kinda greyish precipitate for the first part i swear to GOD if i lose a mark for that ,,,,,,



if there are ever any MC answers, please link me too! thanks

 

[Arrowshaft]

I remember specifically adjusting my answer to clearly outline each compound as it said something like 'identify the reagents in each reaction'.

Yep

 

[Arrowshaft]

for ester, i did fruity smell in addition to how you can add in dilute naoh, which hydrolyses the ester linkage --> forms sodium acetate which can hydrolyse in solution to form acetic acid (aka vinegar smell). that works too, right?

also, i don't recall the question explicitly asking to name the compounds. i think i did anyway but it wasn't as blatant (like compound 2 = ethanol) or whatever. rip.

I don’t think you have to go that in depth to talk about the fruity smell, my school and my textbooks don’t even mention that, so I think you‘re advantaged by going into more detail. Rip, my chem teacher taught us barely anything for mod 8, had to self teach myself pree much everything

 

[Arrowshaft]

hey can i ask does anyone remember what they did for stormwater
i didn't understand what the question meant, initially i even calculated the concentrations PRIOR to the treatment of the water plant (because they gave us initial absorbances too????) but in the end i crossed that out and only calculated the final absorbances for both ions. i got one really low, and the other a bit higher than 1 mg/L. so like, one ion passed and the other didn't, provided the concentrations were meant to be below 1 mg/L or something. but i'm super confused (why'd they give us initial absorbances??) and i don't know if i got the right answers even if i did it the right way.


also said lead hydroxide is a kinda greyish precipitate for the first part i swear to GOD if i lose a mark for that ,,,,,,



if there are ever any MC answers, please link me too! thanks

I think you had to compare them. I said, initially both absorbances and hence conc. were higher than the limit, and after although it reduced the conc. it was not AS effective as it should have been. That’s the evaluation I made, since it was a “to what extent” question.

 

[Jendeukie]

I think you had to compare them. I said, initially both absorbances and hence conc. were higher than the limit, and after although it reduced the conc. it was not AS effective as it should have been. That’s the evaluation I made, since it was a “to what extent” question.

AHH damnit I hope they're nice to me because my working's still there. Wasn't thinking smart enough for this. The whole thing was like 7 marks!? Goodbye 1 or 2 marks then

 

[worldno17]

I remember specifically adjusting my answer to clearly outline each compound as it said something like 'identify the reagents in each reaction'.

OH REAGENTS my gosh, i think i may have misread that as reactants, woops, bc i remember dot-pointing out the reactants. uhhhh i think i definitely mentioned all of the reagents (incl. water as by-product for esterification) at least once throughout my answer (praying) considering how long my answer was. should be ok, right?

 

[Arrowshaft]

OH REAGENTS my gosh, i think i may have misread that as reactants, woops, bc i remember dot-pointing out the reactants. uhhhh i think i definitely mentioned all of the reagents (incl. water as by-product for esterification) at least once throughout my answer (praying) considering how long my answer was. should be ok, right?

I had the same issue lol, luckily i remembered just in time to mention by products. Also for the formation of alcohol from the halogen did you say nucleophillic substitution with NaOH or gently heating solution with water? Either way, both are right, just curious

 

[Arrowshaft]

I cannot believe I messed up the values for the AAS stormwater thingo though, uuuggggh Idk what I did wrong, it cant be the calibration curve cos i remember everything fitting well, but I got like 1.26 for Cu and 1.9 for Pb. Maybe interpolated on the wrong line for Cu but idk. How many marks do you reckon I’ll lose for that?

 

[worldno17]

I had the same issue lol, luckily i remembered just in time to mention by products. Also for the formation of alcohol from the halogen did you say nucleophillic substitution with NaOH or gently heating solution with water? Either way, both are right, just curious

reacted with water in presence of dilute h2so4, didn't do the substitution with oh- because there's no "reaction conditions" to describe. don't think i said heating tho.

wait is heating necessary though? h2so4 catalyst would alr speed up reaction rate.

 

[dumbfuck]

B5 cut off?

 

[Arrowshaft]

reacted with water in presence of dilute h2so4, didn't do the substitution with oh- because there's no "reaction conditions" to describe. don't think i said heating tho.

Do you reckon I’d lose marks for saying NaOH..? Damn it, shouldve gone with water, had way more conditions!

 

[Arrowshaft]

B5 cut off?

Looking at previous year info from rawmarks.info, b5 was usually 60-63 I’d say since new syllabus, maybe around 60-61

 

[worldno17]

Do you reckon I’d lose marks for saying NaOH..? Damn it, shouldve gone with water, had way more conditions!

umm did u describe any conditions for naoh? i personally rlly wanted to do naoh because frankly, couldn't quite remember conditions for water

(p.s. do you think i need heating? i didn't say it bc i alr used h2so4 as a catalyst. but hmm, in the grand scheme of the marking criteria, they probs won't mark that....harshly? touchwood)

 

[Arrowshaft]

reacted with water in presence of dilute h2so4, didn't do the substitution with oh- because there's no "reaction conditions" to describe. don't think i said heating tho.

wait is heating necessary though? h2so4 catalyst would alr speed up reaction rate.

Yeah, its usually better to say heating but as long as you mentioned sulfuric acid you should be all g, I dont think they have a wide opportunity to penalise

 

[Arrowshaft]

umm did u describe any conditions for naoh? i personally rlly wanted to do naoh because frankly, couldn't quite remember conditions for water

(p.s. do you think i need heating? i didn't say it bc i alr used h2so4 as a catalyst. but hmm, in the grand scheme of the marking criteria, they probs won't mark that....harshly? touchwood)

You dont need conditions for NaOH right? At least thats what I was taught