HSC Chemistry Question Thread

[jakesilove]

Thanks Jake. And also I've seen another chart where barium is added. Is there any difference?

Barium is way more common; most students/tests/assessments use Barium. Either will work!

[Wren]

Barium is way more common; most students/tests/assessments use Barium. Either will work!

Thank you

[Kekemato_BAP]

Hey guys..
What prac would this be? What should I know beforehand?
I have this prac exam this Thursday

Thanks so much 

[jakesilove]

Hey guys..
What prac would this be? What should I know beforehand?
I have this prac exam this Thursday
(Image removed from quote.)
Thanks so much 

Hey! I suspect this would be about finding the concentration of common ions in a solution? Check the top post on this page for ways to memorise solubility rules! Honestly, though, it's impossible to predict; I would just be brushing up on the whole of Chemical Monitoring and Management (maybe a bit of the Acidic Environment) as well as ways to write practical tasks up, use reliability/validity/accuracy etc.

[Kekemato_BAP]

Hey! I suspect this would be about finding the concentration of common ions in a solution? Check the top post on this page for ways to memorise solubility rules! Honestly, though, it's impossible to predict; I would just be brushing up on the whole of Chemical Monitoring and Management (maybe a bit of the Acidic Environment) as well as ways to write practical tasks up, use reliability/validity/accuracy etc.

If it were a finding ion experiment, what could I write about validity/reliability/accuracy? I usually struggle with those areas.

[parthie]

Does anyone know the validity/accuracy of titration experiment, esters, and identifying anion and cation experiments?

Thanks

[jakesilove]

If it were a finding ion experiment, what could I write about validity/reliability/accuracy? I usually struggle with those areas.

So validity will go to whether you are testing what you've been trying to test; did you use the right materials? Did you perform the right steps? etc. Reliability asks whether you repeated the experiment, and accuracy would be whether you a 'right'. ie. How close to the real answer were you?

[jakesilove]

Does anyone know the validity/accuracy of titration experiment, esters, and identifying anion and cation experiments?

Thanks

Hey! See above re anion and cation.

For titration, Validity will also be about whether you washed every piece of glassware with the right substance. If you didn't you're not 'testing' what you're trying to test, as the concentrations of the liquids will change. Validity would also be called into question if you used the wrong indicator. Accuracy just asks how 'close' you are to the real result. You use equipment that is fairly accurate, as Burettes can read to 0.05 of a mL etc. Reliability is increased by repeating the titration multiple times.

For esters, you're not really testing anything quantitative (so no accuracy), you're not repeating the experiment (no reliability), and you don't really check if there is in fact an ester in the final solution (no validity). It's more of a demonstrative experiment than a 'proper' experiment

[Aussie1Italia2]

I have a question asking me to describe the characteristics and uses of esters. Do I just talk about the chemical properties and how they allow esters to be used in industries

[Aussie1Italia2]

Hi, sorry, also

Drawing a chemical model in this case of an ester formation, can I please have an example? How to do it has slipped my mind.

Thank you for all the help!

[parthie]

Hey! See above re anion and cation.

For titration, Validity will also be about whether you washed every piece of glassware with the right substance. If you didn't you're not 'testing' what you're trying to test, as the concentrations of the liquids will change. Validity would also be called into question if you used the wrong indicator. Accuracy just asks how 'close' you are to the real result. You use equipment that is fairly accurate, as Burettes can read to 0.05 of a mL etc. Reliability is increased by repeating the titration multiple times.

For esters, you're not really testing anything quantitative (so no accuracy), you're not repeating the experiment (no reliability), and you don't really check if there is in fact an ester in the final solution (no validity). It's more of a demonstrative experiment than a 'proper' experiment

Thanks so much! but how exactly would you word the validity/accuracy of anions/cations bc I'm still confused about that??

sorry one last thing...what are improvements that can be made for all those experiments?

[jakesilove]

Thanks so much! but how exactly would you word the validity/accuracy of anions/cations bc I'm still confused about that??

sorry one last thing...what are improvements that can be made for all those experiments?

Hey! With regards to anion/cation, I would literally just say that if the steps carried out were legit, then the experiment is valid (ie. testing what you are trying to test). If the results you gain are close to the 'true' results, and the equipment you use is accurate (ie. high number of decimal places etc) then the experiment is accurate. The important part is identifying issues in validity, accuracy and reliability, which is entirely dependant on the experiment you perform (therefore cannot be predicted).

Improvements, again, come down to the experiment. You need to have a good idea of the theory behind each prac, and be ready to improve the experiment yourself. I can't tell you how to improve an experiment that you haven't planned yet! Again, know the theory, know your experimental design, and you'll be fine. In terms of identifying improvements, I would 1) Find issues in accuracy/reliability/validity and 2) Solve them by improving experimental design.

Jake

[hansolo9]

Hello!
How do I draw a line of best fit?
I always have trouble knowing how to draw them and where to stop the line.
Especially for calibration curves in AAS.
Thank you

[RuiAce]

Hello!
How do I draw a line of best fit?
I always have trouble knowing how to draw them and where to stop the line.
Especially for calibration curves in AAS.
Thank you

Whilst in the real world it's possible to determine the equation of the actual line of best fit, as far as HSC science goes your toolbox is quite limited. Given a set of (plotted) data, to draw your line of best fit simply draw in the line that best represents the slope of the curve itself. The following are some tips you may choose to employ

- If almost all of your data can be represented on a smooth line, and by almost all I mean only a few weird ones (maybe 2), you should ignore the weird ones and treat them as outliers or mistakes in the experiment and just draw the line through the other points.
- If your data is very scattered (unlikely to appear in the HSC) and you insist on drawing a line of best fit, focus on the slope of the line of best fit.
- Stop at least the largest value on the x-axis given. We draw lines of best fit for the sake of an 'interpolation' - determining a trend within the extreme values given. Alternatively, stop until you go over the grid that you're given (because in the HSC they usually give grids), because you may need it later for an 'extrapolation'.
- If your data doesn't look linear go for a curve of best fit. Never happens with AAS in particular though.

[beau77bro]

hey so in the atarnotes by you guys it says this about preparing for titration:
" First test small quantities of each solution to find their pH. This tells you which indicator to use; if they are a strong acid and a strong base, you want an indicator with an equivalence point around 7(bromothymol blue )"
 or close too, and i don't really get. Testing their pH how? As well as how will you know if it’s a strong acid or strong base? What if it’s just a really concentrated weak acid, and how does this affect the equivalence point, because it will be an acidic salt formed? Or basic salt, what if both are weak? Then use 7? But how do we know? Confused ahahah.
like what do you treat as the equivalence point, can't you just make it 7, and then just add acid to force the equilibrium of the weak base across enough so that its completely neutralised - i am very confused. sorry if it doesnt make sense, im not great at this part.