VCE Chemistry Question Thread

[IndefatigableLover]

When writing a combustion reaction of a hydrocarbon, in which CO2 and H2O are produced, would the H2O  be written in the liquid or gaseous state?

Or would the question specify which of the two states it is?

Thanks

I've always written it in gaseous form when it's in a combustion reaction (even for incomplete as well) mainly because whenever writing reactions in general, you're writing for it when they spontaneously react (since H₂O would condense into a liquid over time) but I'm pretty sure reactions are written spontaneously hence why it's in gaseous form ).

Titre refers to the nitric acid which came out of the burette, in this instance 23.47mL.
Aliquot refers to the sodium carbonate which was pip-petted into the beaker, so 20mL.
Draw a diagram, it'll help you see it more clearly.

Very underrated skill in Chemistry. Always draw it out if you're unsure especially for the more ambiguous questions!

[Sense]

In a titration question, it gave 5 titres: 21.65, 21.58, 21.48,21.52 and 21.5.

Do I take all of them, except 21.65 and get an average titre, Because they're all within 0.1mL. Or do I just use the three closest to each other?

Tl;dr: Can you have more than three concordant titres?

[cosine]

In a titration question, it gave 5 titres: 21.65, 21.58, 21.48,21.52 and 21.5.

Do I take all of them, except 21.65 and get an average titre, Because they're all within 0.1mL. Or do I just use the three closest to each other?

Tl;dr: Can you have more than three concordant titres?

Im not 100% sure, but if they are +-0.1mL off, then you take as many as you can, because the more you do take that are in this range, the more accurate the titre actually is. It's usually three, but im guessing in this one it's four.

[RazzMeTazz]

Thanks IndefatigableLover for the help!

During addition/subtraction I know that you have to give your answer to the least number of decimal places, but just say  your calculator gives you two values that you need to subtract

e.g. 3.1234567 - 2.1234567, except  both of these values should actually be to 3 sf, so technically they are 3.12 and 2.12.
Does this mean in your subtraction of these values you would give it to 7 d.p or 2? (Since the calculator gave both the values to 7 d.p but technically they both should be written to 3 sf, thus giving 2dp as your lowest number of decimal places! )

Thanks

[wunderkind52]

Thanks IndefatigableLover for the help!

During addition/subtraction I know that you have to give your answer to the least number of decimal places, but just say  your calculator gives you two values that you need to subtract

e.g. 3.1234567 - 2.1234567, except  both of these values should actually be to 3 sf, so technically they are 3.12 and 2.12.
Does this mean in your subtraction of these values you would give it to 7 d.p or 2? (Since the calculator gave both the values to 7 d.p but technically they both should be written to 3 sf, thus giving 2dp as your lowest number of decimal places! )

Thanks

It should be 2 decimal places! Because technically the numbers you are concerned with are 3.12 and 2.12! That way you arent changing the accuracy of your result (becoming over accurate) Think of it like if i asked you to multiply both numbers together! You would go with 3 significant figures, not 7!

[RazzMeTazz]

Ohh okay thanks Wunderkind52! That makes a lot of sense!

Does anyone know what the oxidation state of Nitrogen would be in NH4NO2?

Thanks

[wunderkind52]

Ohh okay thanks Wunderkind52! That makes a lot of sense!

Does anyone know what the oxidation state of Nitrogen would be in NH4NO2?

Thanks

I would think that you would find them separately, so nh4+ would mean n is -3, abd n is +3! Not sure though!

[RazzMeTazz]

Thanks wunderkind52!

Is there a difference between the terms 'ionic equation' and 'net ionic equation' I thought that the difference between the two was that in an ionic equation you do not cancel out spectator ions, but in a net ionic equation you do?

However in some practice questions (TSFX, Lisachem etc) when they write an ionic equation, the spectator ions have been cancelled out, so I was a bit confused!

In an exam or SAC if it asked you to write an 'ionic' equation rather than a 'net' ionic equation, would you cancel out the spectator ions?

Thanks

[wunderkind52]

Thanks wunderkind52!

Is there a difference between the terms 'ionic equation' and 'net ionic equation' I thought that the difference between the two was that in an ionic equation you do not cancel out spectator ions, but in a net ionic equation you do?

However in some practice questions (TSFX, Lisachem etc) when they write an ionic equation, the spectator ions have been cancelled out, so I was a bit confused!

In an exam or SAC if it asked you to write an 'ionic' equation rather than a 'net' ionic equation, would you cancel out the spectator ions?

Thanks

generally when I see "ionic equation" i would write the net ionic. If it says full equation, or equation then I would go with the normal one! Then again, havent sat the exam so don't knowfor sure

[RazzMeTazz]

The molecule (attached in the photo below) is called 2-chloro-3-methylbutane.
I was wondering if it could also be called   3-chloro-2-methylbutane? Since I thought different functional groups don't get precedence over one another when labeling the carbon backbone?

Also when you have different functional groups branching off from the carbon backbone,  I know you have to state them in alphabetical order but are prefixes such as 'di' included into this?
So would dipentyl be listed before methyl? Because of the 'd' in dipentyl coming before the 'm' in methyl? Or is it only the 'p' of pentyl and the 'm' of methyl that count?

Thanks

[knightrider]

Does 0.20 have two or three sig figs?

[Alter]

Does 0.20 have two or three sig figs?

Two significant figures. Zeroes placed after other digits but behind a decimal point are significant.

To avoid confusion, something like 0.0225 would only be 3 sig figs instead of 4 (the zero isn't counted as it comes before the first non-zero number).

[alchemy]

The molecule (attached in the photo below) is called 2-chloro-3-methylbutane.
I was wondering if it could also be called   3-chloro-2-methylbutane? Since I thought different functional groups don't get precedence over one another when labeling the carbon backbone?

Also when you have different functional groups branching off from the carbon backbone,  I know you have to state them in alphabetical order but are prefixes such as 'di' included into this?
So would dipentyl be listed before methyl? Because of the 'd' in dipentyl coming before the 'm' in methyl? Or is it only the 'p' of pentyl and the 'm' of methyl that count?

Thanks

I think it's cause you start with the lowest number first (i.e 2 comes before 3)

[paper-back]

How prominent are Low resolution NMR questions in VCAA exams?

[keltingmeith]

How prominent are Low resolution NMR questions in VCAA exams?

Pretty sure they just generate NMRs based on theoretical knowledge = bloody high resolution, as opposed to running a sample themselves.

Basically, it should always be high enough that you can interpret them properly. The resolution of an NMR should not be a concern for you atm, wait until second year university.