HSC Chemistry Question Thread

[ringring]

Hey!
Would appreciate any help/explanation for the following question..

An electrolytic cell contained platinum electrodes and 100.0 mL of an aqueous solution containing magnesium, nickel(II), silver, and sodium ions. The concentration of each of the ions in the solution was 0.200 M. A current of 0.800 A was passed through the cell for 2.50 hours. After this time the mass of the cathode would have increased by...
 (answer is 3.33g btw)

[kiwiberry]

Can i please have help with this question??

You can also do part ii) by comparing the K value at different temperatures
At 25^oC, 0.04 moles of N₂O₄ forms. Thus, 0.08 moles of NO₂ were reacted (2:1 ratio) and 0.132-0.08=0.052 moles are left. Concentration of both are the same as the moles as v=1L. So K at 25^oC is \(\frac{0.04}{(0.052)^2} = 14.79...\)
This tells us that when the temperature decreases from 100 --> 25^oC, K increases. So to oppose the decrease in temperature, the concentration of products has increased, ie. equilibrium has shifted to the right to produce more heat (by Le Chatelier). Because the forward reaction is the one which produces more heat, it is exothermic.

[jakesilove]

what is a solid procedure for carrying out the decarbonation practical - im finding it hard to discern between just letting the can sit on the bench and coool - or using a warm bath - in which case how do i warm the water (school doesnt exactly have a good lab facility so a hot plate is very unlikely - pretty much why we havent done any computer based pracs or even physics cathode ray ones)

Already answered this here. As for prac techniques, I'm afraid there are just too many. Like, correct washing technique, meniscus, stuff like that is all specific to the prac. So, the best study you can do for yourself is write up complete practical reports for you to learn from

[jakesilove]

Hey!
Would appreciate any help/explanation for the following question..

An electrolytic cell contained platinum electrodes and 100.0 mL of an aqueous solution containing magnesium, nickel(II), silver, and sodium ions. The concentration of each of the ions in the solution was 0.200 M. A current of 0.800 A was passed through the cell for 2.50 hours. After this time the mass of the cathode would have increased by...
 (answer is 3.33g btw)

I have literally never seen any question like this. Is it part of an HSC elective topic? I could maybe sort of think about it, if I had resistance or voltage, but with Current? Genuinely no idea.

[ringring]

I have literally never seen any question like this. Is it part of an HSC elective topic? I could maybe sort of think about it, if I had resistance or voltage, but with Current? Genuinely no idea.

sorry, I didn't realise this was the HSC thread, the question is part of the VCE study design.

[jakesilove]

sorry, I didn't realise this was the HSC thread, the question is part of the VCE study design.

Aha no worries! You can find the VCE Chemistry question thread here

[beau77bro]

Already answered this here. As for prac techniques, I'm afraid there are just too many. Like, correct washing technique, meniscus, stuff like that is all specific to the prac. So, the best study you can do for yourself is write up complete practical reports for you to learn from

hey jake, i already took notes on this the control idea was really helpful - essential to my prac. but im just confused on how to deal with condensation - and whether or not to use a water bath - is simplest always best or will the heated water provide a better source for removing carbon dioxide?  i will post 2 example methods below - any input appreciated.

thankssss

[chelseam]

Hi! Can someone please explain what the range of an indicator is? How you can tell what the range is if they give you a bunch of pHs and the colours they show when reacting with an indicator? Sorry if this is a silly question but I've just had a complete mind blank Thank you!

[jakesilove]

hey jake, i already took notes on this the control idea was really helpful - essential to my prac. but im just confused on how to deal with condensation - and whether or not to use a water bath - is simplest always best or will the heated water provide a better source for removing carbon dioxide?  i will post 2 example methods below - any input appreciated.

thankssss

Either experiment is fine, totally up to you which you prefer. I did the first one, which is definitely easier.

[jakesilove]

Hi! Can someone please explain what the range of an indicator is? How you can tell what the range is if they give you a bunch of pHs and the colours they show when reacting with an indicator? Sorry if this is a silly question but I've just had a complete mind blank Thank you!

The 'range' of an indicator just asks where the indicator is useful. For instance, Bromothymol Blue changes colour around a pH of 7. So, it wouldn't be useful at all to tell the difference between two acidic substances. However, it would be very useful to determine the difference between an acidic and a basic substance! So, range just discusses in what region of the pH scale the indicator is useful to us as scientists

[beau77bro]

hey jake could you check this prac? - im bad at titrations - gonna make a standard solution one independent of this.

[chelseam]

So, range just discusses in what region of the pH scale the indicator is useful to us as scientists

Thanks so much Jake!

Also, what would be the main points that we need to know about AAS? Is knowing how to draw a diagram of it important? My notes include stuff on hollow-cathode lamp selection and preparing the standard solution - are things like this necessary? Thank you 

[parthie]

Hey does anyone know if titrations have dependent, independent and controlled variables if ur just titrating one thing

[beau77bro]

wait for glavanic cells, if it is the case that a the voltage is independent of the concentration in the cells - that is the molar ratio doesnt matter as it will simply use one faster than the other - then should we use 1 molar solutions? - may eat up prac time.

[beau77bro]

Hey does anyone know if titrations have dependent, independent and controlled variables if ur just titrating one thing

OK so to me - the independant is the colour of the solution/the neutralisation of the acid or base being tested
the dependant is what you measure - so it's the volume used to titrate it
the controlled will be the indicator and the primary standard used (pH constant, as well as how much is tested (if it is in the flask))