HSC Chemistry Question Thread

[RuiAce]

What are your thoughts so far?
I would be using the Henderson-Hasselbalch equation to solve this problem.

I don't see that anywhere in the new syllabus

[Jakeybaby]

I don't see that anywhere in the new syllabus

My apologies, not familiar with the syllabus - just assumed that it would be included.

[emiq]

HSC 2011. Question 26 (b).

I found solutions but I don't understand where the equation: H₃X_(aq) + 3NaOH_(aq) -> Na₃X_(aq) + 3H₂O_(l)

I understand the balancing of the equation, but more specifically, where did they get H₃X_(aq) ?

[Jakeybaby]

HSC 2011. Question 26 (b).

I found solutions but I don't understand where the equation: H₃X_(aq) + 3NaOH_(aq) -> Na₃X_(aq) + 3H₂O_(l)

I understand the balancing of the equation, but more specifically, where did they get H₃X_(aq) ?

H₃X_(aq) represents the triprotic acid (citric acid, in this case) - 3 acidic hydrogens

[emiq]

H₃X_(aq) represents the triprotic acid (citric acid, in this case) - 3 acidic hydrogens

Not sure if I'll need it for this year's exam, but I'm just curious, which 3 hydrogens did you mean? (Circle it or something please)

[Jakeybaby]

Not sure if I'll need it for this year's exam, but I'm just curious, which 3 hydrogens did you mean? (Circle it or something please)

Not something that I think you'd be required to know; but it's the 3 hydrogens which are within the carboxylic acid functional groups.

[belle12345]

Hi Everyone,

I'm not sure if this is the right place to ask this question but I shall ask anyway:

With a couple days until the 2018 Chemistry HSC, would you recommend to NOT study the questions/topics in last years (2017) paper?

For example, in Industrial Chemistry, the last question was about Sodium Hydroxide (the Mercury, Diaphragm, Membrane Process etc) so is there any chance it will show up in this years paper? (not as the last question obviously, but maybe a short answer)

In previous years have they ever had a topic (or parts of a topic) tested 2 years in a row?

[emily_wuuuuu]

hi everyone, can someone explain to me why it is Cr2O7 that is involved in the reaction with SO2 and not K?

[michelle_mcl]

Can anyone suggest easy ways to remember the anion and cation tests flow chart + results? Currently still struggling (((( Thanks in advance!

[Jakeybaby]

hi everyone, can someone explain to me why it is Cr2O7 that is involved in the reaction with SO2 and not K?

This is just due to the fact that K⁺ is a common spectator ion and does not take any active part in reactions.

[Bells_123]

Hi everyone, I'm doing the 'Shipwrecks and Salvage' option topic for chemistry and have been trying to have a clearer understanding of electrolytic cells and anaerobic bacteria in particular:

- Why can the electrodes in electrolytic cells be in the same electrolyte (unlike most galvanic cells)?
- What are the main reduction equation(s) for anaerobic bacteria reducing sulfate to sulfide (I've seen quite a few variations of similar equations but wasn't sure which ones were correct)?

Thanks!

[jazcstuart]

Hi Everyone,

I'm not sure if this is the right place to ask this question but I shall ask anyway:

With a couple days until the 2018 Chemistry HSC, would you recommend to NOT study the questions/topics in last years (2017) paper?

For example, in Industrial Chemistry, the last question was about Sodium Hydroxide (the Mercury, Diaphragm, Membrane Process etc) so is there any chance it will show up in this years paper? (not as the last question obviously, but maybe a short answer)

In previous years have they ever had a topic (or parts of a topic) tested 2 years in a row?

Yep this is a good place to ask  I think it could be asked again, as you said maybe as a shorter answer rather than a longer response or vice versa. I doubt you would get a question exactly the same as last year, but you could get one using similar principles. I would revise it to be safe, but I guess it's up to you, if you don't feel like you have enough time to study everything, that could be one of the things you leave until last because it would be less likiely to come up. I don't really know about previous years though.

Can anyone suggest easy ways to remember the anion and cation tests flow chart + results? Currently still struggling (((( Thanks in advance!

I struggle with this as well, I think everyone does    I have 2 strategies, one is using flashcards (I find flashcards good for chemistry for things like polyatomic ions and solubility rules, as well as this). My other strategy is writing it out as a process/flowchart, because I find it is easyier to remember one longer process rather than the individual results. I think you need to remember this anyway so you know in which order the tests need to be conducted. So I have just written it out a few times, trying to do as much of it from memory as I can each time (I find just copying it doesn't help me remember as much). Hope this helps!

Hi everyone, I'm doing the 'Shipwrecks and Salvage' option topic for chemistry and have been trying to have a clearer understanding of electrolytic cells and anaerobic bacteria in particular:

- Why can the electrodes in electrolytic cells be in the same electrolyte (unlike most galvanic cells)?
- What are the main reduction equation(s) for anaerobic bacteria reducing sulfate to sulfide (I've seen quite a few variations of similar equations but wasn't sure which ones were correct)?

Thanks!

For your first question I thought they can be in the same electrolyte, for example if you are using intert electrodes to electrolyse a salt solution. Where did you hear that they can't be in the same electrolyte?

For sulfate reducing bacteria there are 2 different equations depending on if it is occurring in an acidic or non-acidic microclimate, so this might have caused your confusion? I think you only need to remember 1 though. This is the one I am using for an acidic microclimate:
oxidation: Fe (s) ---> Fe²⁺ (aq) + 2e^-
reduction: SO₄^2- (aq) +10H⁺ (aq) + 8e^- ---> H₂S (aq) + 4H₂O
overall: 4Fe (s) + SO₄^2- (aq) +10H⁺ (aq) ---> 4Fe²⁺ (aq) + H₂S (aq) + 4H₂O

Hope this helps 

[horse9996]

Can anyone suggest easy ways to remember the anion and cation tests flow chart + results? Currently still struggling (((( Thanks in advance!

Just remember to solubility rules! (+ general knowledge about acid carbonate reactions to detect carbonate)

Always soluble: NAGSAG
nitrates, acetates, group 1, sulfates, ammonium, group 7

EXCEPTIONS: PMS, CaStroBar
PMS (sulfates and group 7): lead, mercury, silver
CaStroBar (sulfates only): calcium, strontium, barium

Make sure you know about flame colours as well, and distinguishing between Fe2/3+

[varun.amin]

Hi,

What are the main chemical you need to know equations  for the Shipwrecks and Salvage option topic? If anyone has a list that would be much appreciated. Thank you in advance

[sunshine32323123123123q3]

A 2001 HSC INDUSTRIAL CHEM QUESTION:
"Evaluate how environmental issues are addressed in the Solvay Process"
How would u go about answering this quesiton?