HSC Chemistry Question Thread

[Bubbly_bluey]

This is a question from shipwrecks: Steel rusts more rapidly than pure iron. Give one reason for this in terms of the structure of steel.
Thanks

[seventeenboi]

Hi
Why is the first step of the ionisation of polyprotic acid the one that occurs to the greatest extent ??

[MisterNeo]

Hi
Why is the first step of the ionisation of polyprotic acid the one that occurs to the greatest extent ??

Hi!
Polyprotic acids ionisation becomes weaker with after each proton.
Let's look at sulfuric acid:


Sulfuric acid is a strong acid that will fully ionise into its conjugate base, hydrogen sulfate, which is amphiprotic. So it becomes less of an acid because of it becoming a conjugate base.
Hence, hydrogen sulfate will only partially ionise in a equilibrium into its conjugate base, sulfate ion.

They basically (lol) get more basic as they donate hydrogen ions and become less of an acid, thus less extent of ionisation.

Also, it's worth noting that weak acids have stronger conjugate bases than strong acids. So, polyprotic weak acids like citric acid become more basic than sulfuric acid after each proton donation.

[seventeenboi]

Hi!
Polyprotic acids ionisation becomes weaker with after each proton.
Let's look at sulfuric acid:


Sulfuric acid is a strong acid that will fully ionise into its conjugate base, hydrogen sulfate, which is amphiprotic. So it becomes less of an acid because of it becoming a conjugate base.
Hence, hydrogen sulfate will only partially ionise in a equilibrium into its conjugate base, sulfate ion.

They basically (lol) get more basic as they donate hydrogen ions and become less of an acid, thus less extent of ionisation.

Also, it's worth noting that weak acids have stronger conjugate bases than strong acids. So, polyprotic weak acids like citric acid become more basic than sulfuric acid after each proton donation.

OHHH mm that makes a lot of sense!! thank youu nice pun HAHA

[RuiAce]

Remind Jake to look at it when he has time. He still has some more lectures to go. But he did shipwrecks.

[winstondarmawan]

This is a question from shipwrecks: Steel rusts more rapidly than pure iron. Give one reason for this in terms of the structure of steel.
Thanks

Hey! I do shipwrecks.
Okay so basically, rusting is a special type of corrosion (that occurs with iron), which is a redox reaction.
So, we know that in pure iron, this occurs:
Anode: Fe(s) > Fe2+(aq) + 2e
Cathode: H2O (l) + 1/2 O2 (g) + 2e > 2 OH- (aq)
However, in steel (which is composed of iron and carbon), not only this reaction occurs, but another galvanic cell is set up with iron as the anodic site and carbon as the cathodic site. Pretty sure you do not need to know the half reactions for this, it should be in your theory that impurities (with less ease of oxidation, which carbon is) act as cathodic sites whilst iron acts as the anodic site. Hence, this accelerates the corrosion oxidation-reduction process and thus rusting occurs more rapidly in steel.
Hope this helps!

[anotherworld2b]

I was wondering for electro refining of copper and electroplating
Are there constant key differences that would help to differentiate between the two when given a diagram?

[anotherworld2b]

Ah I see
thank you for your help

The only difference I see between them is that the anode/cathode are different metals in electroplating, whereas they are the same metal in electrorefining.
They both work off the same concept of electrolysis, so it's not that big of a deal if you can't distinguish between them. They usually tell you what's happening in the question like "Student A performed this electroplating experiment, and here are his results." 

[Bubbly_bluey]

hi! Is it necessary to memorise the chemical equations at the cathode and anode of lead acid cells and button cells. (They're just long  )

[Bubbly_bluey]

Hey! I do shipwrecks.
Okay so basically, rusting is a special type of corrosion (that occurs with iron), which is a redox reaction.
So, we know that in pure iron, this occurs:
Anode: Fe(s) > Fe2+(aq) + 2e
Cathode: H2O (l) + 1/2 O2 (g) + 2e > 2 OH- (aq)
However, in steel (which is composed of iron and carbon), not only this reaction occurs, but another galvanic cell is set up with iron as the anodic site and carbon as the cathodic site. Pretty sure you do not need to know the half reactions for this, it should be in your theory that impurities (with less ease of oxidation, which carbon is) act as cathodic sites whilst iron acts as the anodic site. Hence, this accelerates the corrosion oxidation-reduction process and thus rusting occurs more rapidly in steel.
Hope this helps!

Yes it makes sense! Thanks so much!

[seventeenboi]

hello
what are some problems associated with high levels of TDS in an aquatic body

[MisterNeo]

hello
what are some problems associated with high levels of TDS in an aquatic body

Total dissolved solids is everything except gases that is dissolved in water. This includes cations/anions (salts) and faeces.

-Metals like copper and zinc are very common dissolved metals, which cause health problem because they are a trace element, which is naturally present in very small concentrations in the human body and should not be high.
-Lead can also be present in the water, which is a neurotoxin that can be transferred to humans through seafood.
-pH can be affected.
-An increase in metal ions such as magnesium and calcium result in water hardness, which stops soap from lathering.
-Dissolved poo causes eutrophication, which leads to excessive plant.algae growth. It also causes the BOD to increase and kill the fish in the water.
-Polluted water usually has less oxygen dissolved in it for aquatic life.
-Water with high TDS also has high turbidity, which indicates contaminated water and is unsuitable for aquatic life.

These are the main concerns with high TDS that affect not only the fish, but also has impacts on humans.

[Bubbly_bluey]

Hi again!
Just a little confused between the Vienna Convention 1985 and the Montreal Protocol 1987. I know they were both associated with world leaders coming together to stop release of CFCs and introducing alternatives. But what is the difference between them.
Thanks 

[winstondarmawan]

Hello! Just wanted to ask if anyone had any clever ways (e.g. mnemonics) to remember the anion/cation testing, as well as ion flame test colours. They always slip out of my mind.
TIA

[MisterNeo]

Hello! Just wanted to ask if anyone had any clever ways (e.g. mnemonics) to remember the anion/cation testing, as well as ion flame test colours. They always slip out of my mind.
TIA

This is Jake's older post on mnemonics for the cation/anions and flame tests.
I use these for my solubility rules and flame memorising. 
(Just click the "image removed from quote".)

Hey! Basically, you just need to remember your solubility rules/flame tests. Then, you'll likely be given a solution containing a number of ions. Use the solubility rules/flame test colours to figure out a way of determining each ion. There isn't much to this one in terms of prep, except you really do need to memorise the rules (Assuming they don't give them to you!). I've put the way I remember each rule below.

(Image removed from quote.)
(Image removed from quote.)

Let me know if I can add anything else!