VCE Chemistry Question Thread

[juicethelemon]

1. When adding an inert gas, does the concentration/time graph show an immediate incline or no because the partial pressures of the gases are not affected?
2. Also with adding a catalyst will the rate/time graph will the graph be a complete straight line for both the net forward and back reaction?

[passbleh24]

Argon won't react with O2 as it is a noble gas. The question was just stating that the formation of Ti was done under inert conditions (absence of oxygen). It is worded poorly imo but the answer didn't mean that argon literally excluded oxygen but rather that the reaction was done in the presence of argon instead of oxygen so it wouldn't form pure TIO2. Hope this helps.

Thanks for correcting me, I was just assuming.

[hums_student]

Hey my fellow chemists, I asked my teacher regarding the sig figs question on the previous page from the 2018 NHT exam - so apparently VCAA would NEVER let you leave the answer to ONE sig fig as it is horribly inaccurate, so if the question include numbers to one sig fig it's a sign that the examiners are not marking for sig figs in that question.

Hope this helped

[smamsmo22]

1. When adding an inert gas, does the concentration/time graph show an immediate incline or no because the partial pressures of the gases are not affected?
2. Also with adding a catalyst will the rate/time graph will the graph be a complete straight line for both the net forward and back reaction?

Inert gas: yes; no change to rate or time as the partial pressures of each gas are the same
Catalyst: rate of both forwards and backwards reaction will increase vertically to the same extent and will remain equal.

That's my understanding at least, hopefully it's right (:

[MAGGOT]

For 2017 nht q3a, couldn't the wave number at 300cm^-1 be a O-H bond as well as a C-H bond

[zenith101]

How to generally improve the accuracy, validity and precision of an experiment?

[Freddie Hg]

For 2017 nht q3a, couldn't the wave number at 300cm^-1 be a O-H bond as well as a C-H bond

no OH bonds are considered to be characterised by broad bands.

[Lear]

https://sdbs.db.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi

Highly recommend Chem students to do some searches here for common molecules such as alcohols, esters, carboxylic acids, amines, amides etc and view their corresponding IR spectrum. You’d be surprised how similar spectrums can look despite changing chain lengths. I personally think just looking at a few of these had allowed me to get the general idea of what an alcohol or anime or Ester looks like on IR.

Peaks around 3000-3600 can be hard to differentiate otherwise.

[crawlingvines]

For question 8b) ii. of the 2017 VCAA sample exam, why are there only straight lines on the graph?

[Lear]

For question 8b) ii. of the 2017 VCAA sample exam, why are there only straight lines on the graph?

Which direction, if any, do you think the reaction will shift to when the volume is halved?

[crawlingvines]

Which direction, if any, do you think the reaction will shift to when the volume is halved?

Equal moles on both sides of reaction so none I had a genuine brain fart over that

[Lear]

Equal moles on both sides of reaction so none I had a genuine brain fart over that

This is completely fine! Good thing you’ve made that mistake now instead of tomorrow

[zenith101]

for question 10d) on VCAA sample, couldn't the results also be skewed by the fact that exothermic nature can impact the rate of reaction as well as concentration? Therefore its not only a change in concentration that affects reaction rate?

[Freddie Hg]

for question 10d) on VCAA sample, couldn't the results also be skewed by the fact that exothermic nature can impact the rate of reaction as well as concentration? Therefore its not only a change in concentration that affects reaction rate?

ik what your saying here but i think this is overthinking the question and rates of reaction. remember keep it basic. your observation is unlikely to be tested (if its true)

i saw this answer regarding exothermic reactions:
Temperature change: The flasks becoming hot indicates an
exothermic reaction. Chris's observation that the 2.0 M HCl
caused the flask to become the hottest suggests a faster rate
of reaction, which resulted in more energy released in the
given time. More reliable observations could have been
obtained by measuring temperature changes in the flask.

[muji_MA31]

Could someone explain the possible safety concerns regarding the following substances used in an experiment?
H2SO4
NaOH
Bromide
Iodine
Alkanes in general