VCE Chemistry Question Thread

[anoushka_iyer]

grease adds impurities to the electrode and hence makes reactions less efficient due to interference with the grease.

I think it's good to mention that it can cause 'irreversible side reactions'
Also, grease makes it harder for the plated metal to adhere to the cathode, so the deposited metal is more likely to fall off, leading the an underestimated mass of metal deposited/ reduced quality of plating

[sk2000]

When rounding to a number of significant figures and there is a 5, do you round up or down?
For example, when rounding 46.65 to 3 significant figures, would you round down to make it 46.6?
I heard that when rounding 5s, you round to the number that will make the last decimal even? Is this true?

Also, question about electrolytic cells (from TSFX 2018 exam Q2)
Say an electrolytic cell is set up with a negative iron cathode and positive copper anode, and Nickel Nitrate in solution, what reaction would occur at the iron cathode? I know that Nickel ions in solution are a stronger oxidant than water, but wouldn't the oxidation of the Copper electrode produce Cu2+ ions that are stronger oxidants, thus Copper metal is produced at the cathode? The answer says that the Nickel ions in solution are reduced.

Thanks

[osbus]

hey! just wondering if we need to include states when we're writing the catalysts for organic reactions (e.g. during esterification, is it fine to just write H₂SO₄ or should i include its state?)

[KiNSKi01]

For calibration curves do we take max temp and time which it occurred or final temp/final time

[turtlebanana]

Can anyone PLEASE explain how to do question 2c) i) from the VCAA 2015 exam, please???

I do not understand how to do that.

In the previous questions for that, you calculate the mols of HCl two times in a row, then in question c) i) it asks you to calculate it a third time. My head is going crazy.

P.S. It is a question on titration/stoichiometry (average mark was: 1.7/4)

[KiNSKi01]

Can anyone PLEASE explain how to do question 2c) i) from the VCAA 2015 exam, please???

I do not understand how to do that.

In the previous questions for that, you calculate the mols of HCl two times in a row, then in question c) i) it asks you to calculate it a third time. My head is going crazy.

P.S. It is a question on titration/stoichiometry (average mark was: 1.7/4)

Hey I wouldn't worry about this- the question is from the old study design where you had to know about back titrations (something involving a back titration shouldn't come up tomorrow)

[KiNSKi01]

Yo do we need to know what the units are for (m/v, w/w,m/w and all of that stuff  ) or will the question tell us to provide our answer in a percentage in terms of e.g grams per litre

[Little Miss Cocopops]

Hi,
When finding the heat capacity of water, do you always use the density of water 0.997gL to find mass, even if the reaction doesn't take place at 25 degrees?

Thank-you 

[sk2000]

Yo do we need to know what the units are for (m/v, w/w,m/w and all of that stuff  ) or will the question tell us to provide our answer in a percentage in terms of e.g grams per litre

They could ask you to express like that I'm pretty sure, but it's all just per 100g
m/v = grams per 100ml
v/v = ml per 100ml
m/m = grams per 100g

Then there's ppm which is grams per million grams, milligrams per Litre or milligrams per kilogram

[angrybiscuit]

hey! just wondering if we need to include states when we're writing the catalysts for organic reactions (e.g. during esterification, is it fine to just write H₂SO₄ or should i include its state?)

You need to indicate that it's concentrated. This by either writing "concentrated H₂SO₄" or H₂SO₄ (l)

[angrybiscuit]

Can anyone PLEASE explain how to do question 2c) i) from the VCAA 2015 exam, please???

I do not understand how to do that.

In the previous questions for that, you calculate the mols of HCl two times in a row, then in question c) i) it asks you to calculate it a third time. My head is going crazy.

P.S. It is a question on titration/stoichiometry (average mark was: 1.7/4)

Hi!
This question is back titration which is not in the recent study design. You DO NOT need to know about back titrations (I'm pretty sure it has a different method and stuff though I could be wrong because I've never done them!)

[anoushka_iyer]

Does using concordant titres increase accuracy or reliability?

[angrybiscuit]

Hi,
When finding the heat capacity of water, do you always use the density of water 0.997gL to find mass, even if the reaction doesn't take place at 25 degrees?

Thank-you 

I've heard differing opinions on this. My teacher says to just use a 1:1 ratio unless it's 25 degrees Celcius but I've heard from others to use 0.997g L regardless of the temperature (which I don't find correct as the density of water varies for every temperature).

Does using concordant titres increase accuracy or reliability?

It increases reliability because you have values within a close range.

[sk2000]

Does using concordant titres increase accuracy or reliability?

What angrybiscuit says, also by averaging concordant titres you minimise the effect of random error.

[sk2000]

For calibration curves do we take max temp and time which it occurred or final temp/final time

You have to draw a line back from the max temp to when the current was turned on to account for heat loss. This is the absolute maximum temperature change.
This diagram explains it