HSC Chemistry Question Thread

[bsdfjnlkasn]

Hey there!

Can I get some help with this question?

[winstondarmawan]

Hi!

The answer would be D (HCl and H₂O):
- The addition of HCl, as Savas_P pointed out, would make the conditions acidic. According to LCP, the reaction would shift to the right to favour the forward reaction (and the formation of HOCl) as the OH^- will neutralise the HCl
- The addition of H₂O (one of the reactants) will also favour the formation of HOCl: The equilibrium will shift to minimise the change, which in this case, will favour the forward reaction ('uses up' the additional water)

Hope this helps

The answer provided was B. My friend's explanation was that the solution is already in a swimming pool so adding water would have basically no effect. How relevant is this explanation?

[MisterNeo]

The answer provided was B. My friend's explanation was that the solution is already in a swimming pool so adding water would have basically no effect. How relevant is this explanation?

From my understanding, equilibriums will only shift if the concentration of any of the species changes. Adding water doesn't shift the equilibrium because water is in liquid state, which is pure and cannot change concentration (1L of water is the same conc. as 1000L of water). However, by adding water, the other aqueous species will decrease in concentration. But since both sides have aqueous species, the concentrations of both sides will decrease in concentration, maintaining that special ratio of products over reactants.

Hey there!
Can I get some help with this question?
(Image removed from quote.)

None of them would be correct, unless there was a typo where pH 2 was supposed to be pH 3. In that case, the answer would be B since a weak acid would need much higher concentration to obtain the same pH as a strong acid.

[winstondarmawan]

From my understanding, equilibriums will only shift if the concentration of any of the species changes. Adding water doesn't shift the equilibrium because water is in liquid state, which is pure and cannot change concentration (1L of water is the same conc. as 1000L of water). However, by adding water, the other aqueous species will decrease in concentration. But since both sides have aqueous species, the concentrations of both sides will decrease in concentration, maintaining that special ratio of products over reactants.

So just confirming, the answer is indeed B?

[itssona]

heyy so I'm kinda lost rn, isn't steam and thermal cracking the same thing? we learnt that they are different and that we need to know ALL 3??? :/ wjat should i know

[Savas_P]

heyy so I'm kinda lost rn, isn't steam and thermal cracking the same thing? we learnt that they are different and that we need to know ALL 3??? :/ wjat should i know

yeah thermal cracking is also called steam cracking

[itssona]

a

yeah thermal cracking is also called steam cracking

Ah okay thank you!!

[limtou]

Can someone please explain this? Thanks!

[MisterNeo]

Can someone please explain this? Thanks!

Hey
So the answer is A, citric acid. This is because weak acids form a buffer solution that minimises the changes in pH when sodium hydroxide is added. Out of the two weak acids, citric acid is triprotic and would require more base than acetic acid to use up all the H⁺.

[limtou]

Hey
So the answer is A, citric acid. This is because weak acids form a buffer solution that minimises the changes in pH when sodium hydroxide is added. Out of the two weak acids, citric acid is triprotic and would require more base than acetic acid to use up all the H⁺.

Thanks! Though can you clarify what you meant by buffer solution?

[Savas_P]

Can someone please explain this? Thanks!

this question is easy because the acids are the same concentration and volume. also it doesn't matter if they are weak or strong, the NaOH will completely ionise all the solutions regardless. this means we just have to look at how many Hydrogen ions there is in the acid solutions. the HCl and acetic acid requires equal amount of NaOH, the sulphuric acid because diprotic requires twice as much and the citric acid will require three times as much NaOH.

[anotherworld2b]

Hi I was wondering if I could have some help filling out the table and answering this question about a copper recovery lab

[clarence.harre]

I've attached an extract from the 2009 past paper. I honestly had no idea what to do when I encountered this question.
Could someone please explain how to do this?

[MisterNeo]

I've attached an extract from the 2009 past paper. I honestly had no idea what to do when I encountered this question.
Could someone please explain how to do this?

You’d start by finding the amount of oxygen dissolved in 1L at 25’C (8mg), then multiply it by 10 to get amount in 10L (80mg). Divide this by 1000 to get the mass of dissolved oxygen in grams (0.08g). Divide 0.08g by 32g/mol to get the moles of oxygen dissolved (0.0025mol). Multiply this by 24.79L/mol to get the volume of the oxygen that can dissolve (0.062L), which is A (62mL).

[J.B]

HI,
In industrial Chemistry for the head of an anionic detergent, is it sulfate or sulfanoate? and how do these look structurally?

Also for esterification my school used a bunsen burner, which I understand we should not use for safety reasons. I was just wondering when drawing a diagram for this prac, how do we draw the heating mantle? Like does it also need a water bath, and boiling chips, and a retort stand etc?
Thanks.