HSC Chemistry Question Thread

[Bubbly_bluey]

Hey! A half cell just refers to a beaker where either oxidation or reduction occurs. Remember that a galvanic cell is made up of 2 separate cells.
So the electrolyte will be platinum iodide because the platinum electrode will undergo reduction at the cathode.
For the second question, B isn't correct because a new sample was used each time a reagent was added, so it doesn't really matter which order they added them. The correct answer would be that many precipitates are white. Lead iodide is a yellow precipitate and the particular test doesn't account for the presence of the iodide ion or any other anions that also make white precipitates.
Hope this helps

Thanks I understand the second question (didn't read how there was a fresh sample was used for each). For the first question I got C as well but the answer said that it was A which is HCl. Not sure if I'm misunderstanding something or a typo.

[Britany24]

Hey, can someone help identify the difference between anode and cathode in cells as I'm having trouble doing that, Thanks

[kiwiberry]

Thanks I understand the second question (didn't read how there was a fresh sample was used for each). For the first question I got C as well but the answer said that it was A which is HCl. Not sure if I'm misunderstanding something or a typo.

Platinum is inert - so it wouldn't be able to be reduced, it's used in galvanic cells when gases are involved. From the table of standard potentials, the oxidation potential of Mg is 2.36 V. Because the cell's potential is 3.8 V, the substance that gets reduced in the cathode half cell needs to have a reduction potential of around 1.44 V - the closest one on the data sheet is chlorine gas with 1.40 V! So HCl is the answer

[jakesilove]

Hey, can someone help identify the difference between anode and cathode in cells as I'm having trouble doing that, Thanks

Hey Britany! Welcome to the forums In any Chemical cell, there is an Anode and a Cathode. The Anode is where oxidation occurs (oxidation state goes up, ie. the substances LOSES an election). The Cathode is where reduction occurs (oxidation state goes down, ie the substances GAINS electrons). So, when you've got a chemical cell, all you have to do is identify which side oxidises, and which side reduces! Then, use REDCAT (Reduction @ Cathode) and ANOX (Anode is Oxidation) to identify which is which!

Hope that made sense

Edit: Also, as the Cathode gain electrons, and the anode loses electrons, current runs from Anode to Cathode

[winstondarmawan]

Shipwrecks Q:
https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/20270053_1279294878862699_251626619_n.png?oh=0833834537ad91acfa67f1eec4e6a948&oe=59763A9F
The sample answer in the booklet was literally 2 pages and far too detailed for 6 marks. What would this Q require for the 6?

I think my Q got missed
EDIT: Sorry, wrong link! This is the right link.
https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/20317181_1279305045528349_178776397_o.png?oh=762a343efa70030204d6bfa7bf0ccdbf&oe=59780E00

[jakesilove]

I think my Q got missed
EDIT: Sorry, wrong link! This is the right link.
https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/20317181_1279305045528349_178776397_o.png?oh=762a343efa70030204d6bfa7bf0ccdbf&oe=59780E00

Hey! I don't remember too much from Shipwrecks, but basically I would be going through:

Initially, Wood was used to build ships. Look at positives (easy to find resource) and negatives (decays very quickly).

Then, ships started being covered in various metals. Honestly, I just don't remember this part of the curriculum very well, so you may have to look this up yourself. Basically, you want to discuss the importance of having some sort of sacrificial hull, that doesn't cause the nails on the ship to corrode (by setting up a galvanic cell). Um. Yeah. Hopefully someone else can help me out here!

[Bubbly_bluey]

Hey! I'm confused for part (e) in this question which is about electrolytic cells. So there is two possible choices for reduction: water or Zinc. I chose Zn because it requires less energy for it to reduce. However the answer chose water to reduce instead? Is it something to do with them being close together?
Thanks

[kiwiberry]

Hey! I'm confused for part (e) in this question which is about electrolytic cells. So there is two possible choices for reduction: water or Zinc. I chose Zn because it requires less energy for it to reduce. However the answer chose water to reduce instead? Is it something to do with them being close together?
Thanks

In electrolytic cells, energy is inputted to drive a non-spontaneous redox reaction, so you would pick the reactions that would not occur by themselves. With Zn and water, Zn would be reduced spontaneously because it requires less energy than water, so in an electrolytic cell it would be oxidised - vice versa for water

[Bubbly_bluey]

In electrolytic cells, energy is inputted to drive a non-spontaneous redox reaction, so you would pick the reactions that would not occur by themselves. With Zn and water, Zn would be reduced spontaneously because it requires less energy than water, so in an electrolytic cell it would be oxidised - vice versa for water

I'm so sorry but still confused. In a spontaneous reaction (with is a galvanic?) water is more reactive because its above Zn on the standard potentials so it will oxidise readily than Zn. But in a eletrolytic cell shouldn't Zinc be reducing because it has -0.76V compared to water -0.83V because it requires less energy?

[anotherworld2b]

I was wondering if anyone had any tips on how to remember the order in which to name organics?

[MisterNeo]

I'm so sorry but still confused. In a spontaneous reaction (with is a galvanic?) water is more reactive because its above Zn on the standard potentials so it will oxidise readily than Zn. But in a eletrolytic cell shouldn't Zinc be reducing because it has -0.76V compared to water -0.83V because it requires less energy?

This is for electrolytic cells.
Galvanic cells preference those on the very top and bottom (most energy), whereas electrolytic cells prefer those closest to 0V because they require less energy.

I was wondering if anyone had any tips on how to remember the order in which to name organics?

Are you referring to those fluoro-chloro naming rules, or prefix and suffix when naming things like aldehydes, ketones, etc?
I recommend this for naming different compounds.

[ellipse]

http://imgur.com/a/7aEdG

Could someone please explain why the answer is C?

[Bubbly_bluey]

Hi again! When cobalt-60 is used for medicinal treatment of cancer, the gamma radiation emitted kills these cancer cells. But when cobalt-60 decays it also releases beta radiation, so is this useful in anyway for the treatment as well?
Thanks

[jakesilove]

Hi again! When cobalt-60 is used for medicinal treatment of cancer, the gamma radiation emitted kills these cancer cells. But when cobalt-60 decays it also releases beta radiation, so is this useful in anyway for the treatment as well?
Thanks

Hey! Honestly, I can't find anything about Beta radiation and cancer therapy. I would just stick to the Gamma radiation, and the point you've probably already got in your notes

[vanessa mbogo]

what is the typical cell voltage and cell temperature of
a) mercury cell
a) diaphragm cell
c) membrane cell

please help !

Mod Edit: Moved to Q&A