HSC Chemistry Question Thread

[roygbivmagic]

So this would have increased the number of moles of sodium carbonate, and therefore the number of moles of HCl. So HCl would end up having a calculated concentration higher than its actual concentration.

Thanks!! I don't quite get the last part though - so the sodium carbonate actually used has a higher concentration. So wouldn't more HCl be needed to titrate it and reach the end point? Meaning HCl calculated concentration is lower than its actual concentration?

[ACCC]

Thank you so much Jess1113!

[toasted]

Thanks!! I don't quite get the last part though - so the sodium carbonate actually used has a higher concentration. So wouldn't more HCl be needed to titrate it and reach the end point? Meaning HCl calculated concentration is lower than its actual concentration?

If more moles of HCl are needed to titrate it. The concentration will increase as C=n/V where V will stay constant and the number of moles calculated would increase. Hence, the concentration will be higher than its actual concentration. Hope that made sense! 


Hey guys!

For those titration questions where they give the titres in a table format, do you eliminate the first titre (assuming its a test run), and also what defines an outlier in those types of questions?

Thanks!

Mod edit: Merged posts

[kauac]

Hey guys!

For those titration questions where they give the titres in a table format, do you eliminate the first titre (assuming its a test run), and also what defines an outlier in those types of questions?

Thanks!

An outlier is a result that is largely different to the others. If there is an outlier in a titration, it will generally be the first one. However, if the volume used for the first titration does not differ much from the rest of the titres, then I would still count it, even though it is the first one... That's just my opinion though...

[MisterNeo]

Hey guys!

For those titration questions where they give the titres in a table format, do you eliminate the first titre (assuming its a test run), and also what defines an outlier in those types of questions?

Thanks!

Mod edit: Merged posts

Don't include rough titres, and exclude anything doesn't match with the other titres, then find the average.

[Noorijaz]

gday

i have a quick question

can someone plz explain the difference between polar and non-polar substances in the most easiest way possible.

thanks

[kauac]

Hi...
Do we need to write the states of ions when writing equations in the exam?

[RuiAce]

gday

i have a quick question

can someone plz explain the difference between polar and non-polar substances in the most easiest way possible.

thanks

Depends on what you're aiming for.

Oversimplified explanation of what actually happens: A pair of electrons have a greater tendency to just hang around a corner/side of the atom. In water, there is an electron pair that just hangs on the opposite side of O, which makes it \(\delta- \).

Oversimplified explanation of what the outcome is: As a rough example, a polar molecule is basically behaves like a charged molecule, but the charge is something like +0.01 instead of +1 (if not less).

Hi...
Do we need to write the states of ions when writing equations in the exam?

With ions, I've skipped writing states and never got penalised for them, so that may be food for thought. I also do vaguely recall my teacher saying it doesn't matter.

Simple reason - if it's charged, it's assumed to be (aq).

(Of course, everything else - obviously yes.)

[MisterNeo]

gday

i have a quick question

can someone plz explain the difference between polar and non-polar substances in the most easiest way possible.

thanks

Basically, polar substances usually have hydrogen bonded to a highly electronegative element, which pull the hydrogen's electron towards itself and makes the hydrogen slightly positive.
C-H are non-polar because carbon isn't very electronegative.
O-H or N-H are polar (in alkanols and carboxylic acids, ammonia, etc).
(Halogen)-H are also polar.
Ozone is also polar.

Hi...
Do we need to write the states of ions when writing equations in the exam?

I always write them just to be safe even though they really only exist in aqueous form. I did lose a mark in Prelims for not writing aqueous. 

[Noorijaz]

hi

how do i cram all of chem most effectively in two days??

plz provide advice

thanks

[ACCC]

Hey guys can someone please help me with this question??
Thank you!!

[angelahchan]

hi

how do i cram all of chem most effectively in two days??

plz provide advice

thanks

Go through the syllabus and highlight everything you don't know( e.g. red = know nothing, yellow = need to revise more, green = good)- next go through everything in red and try to memorize it (e.g. look, cover, write, use mnemonics etc.). Then do past papers, skipping the questions which you know how to do (do most of the multichoice since it won't take as long as short answer) , and mark, look at exemplar responses.  It really depends on how much content you have left which you have to go over again, though

[RuiAce]

Hey guys can someone please help me with this question??
Thank you!!

which best rounds to 55g.

[MisterNeo]

Hey guys can someone please help me with this question??
Thank you!!

hi
how do i cram all of chem most effectively in two days??
plz provide advice
thanks

I usually go through past HSC papers to see what I know and don't know. The notes section is what I recommend if you wanted to cram the entire syllabus, and go through them with a highlighter or something to memorise the key points of each core topic.

[J.B]

Hi,
I was told that  50000 is considered 5 significant figures in chemistry. Is this true?

Also can someone explain to me avogrado's number and how we use it?

Thanks