Hey hey,
-Do we need to know about Normal Phase HPLC vs Reverse Phase HPLC??
-What exactly is an analyte? Is it, like, synonymous with molecule?
-I do not understand Q 5 C i on the 2018 exam. Could somebody please talk me through it? (I don't really understand the formulas used in the examiner's report)
-Q 8. Woah. I have NO IDEA what is going on there. That's a fuel cell right?? Could somebody please direct me to like a super basic youtube video or something cos my knowledge is SERIOUSLY lacking here
I have no idea what the polarity is at Electrode W or Y, what happens in an alkaline environment (and for that matter an acidic environ) and ahh I am so sorry for probably annoying everybody on here with my incessant questions.
1) You don't need to know about the normal/reverse phase HPLC
2) An analyte is a substance which is being analysed. If you are analysing a particular molecule, then you can call it the analyte since you are analysing it.
3) sorry, I can't help with the 2018 chem exam questions as I am saving that exam to do a bit later and don't want to read through it yet haha.
However, I can say that when a question asks for the polarity of an electrode, it is asking if it is of positive or negative polarity.
To determine this, you first want to identify if it's discharging/producing voltage or recharging/receiving voltage.
- If it's discharging, the negative electrode will be where the oxidation reaction occurs (loss of electrons) and is the anode, and the positive electrode will be where the reduction reaction occurs (gain of electrons) and is the cathode.
- If its recharging/consuming voltage, the negative electrode will be where the reduction reaction occurs and will the cathode, and the positive electrode will be where the oxidation reaction occurs and will the anode
To summarise:
Discharge(producing voltage):
- Anode=Oxidation=Negative
- Cathode=Reduction=Positive
Recharge(consuming voltage):
- Anode=Oxidation=Positive
- Cathode=Reduction=Negative
In terms of Balancing in acidic and alkaline environments:
- In acidic environments, when balancing the hydrogens in a half cell reaction, you add H+ ions to the relevant side
- In alkaline environments, when balancing the hydrogens in a half cell reaction, you would add OH- ions to the relevant side. In order to work this out, you would first balance by adding H+ ions to the relevant side, but would then add a necessary amount of OH- ions to
both sides such to neutralise the H+. After this, your balanced half cell equation should involve water on one side and OH- on the other.
This is probably a confusing explanation, so I will put an example here:
Write the half-equation for the oxidation of MnO2 to MnO4- in an Acidic environment1. Balance main/key atoms
- here this is Mn, and is already balanced so:
2. Balance Oxygen by adding H2O
3.Balance Hydrogen by adding H+
4. Add electrons (in order to balance out the oxidation numbers of both sides of the reaction)
5. Add states
Write the half-equation for the oxidation of MnO2 to MnO4- in an alkaline environmentdo the above 5 steps, but add an aditional 6th step:
6. Add OH- to both sides to neutralise the H+
and then combine the H+ and OH- to get:
and finally, cancel out any water on both sides
I didn't really use any videos for chem, so I can't really recommend any. I can recommend looking at the chemistry 3/4 lecture slides here:
https://atarnotes.com/note/lecture-slides-september-2019-42/ as they do a good job at summarising the course, but are perhaps not the best if you are lost on a topic.
And as a side note, don't be sorry about asking so many questions. People here are happy to answer questions especially since you have a go at them and explain what you're thought processes are.