VCE Chemistry Question Thread

[Lear]

I think when your calculations involve a number like "4" not "4.0" then you ignore the sig figs in calculations?

I had that understanding too but according to VCAA
‘For the purpose of the VCE Chemistry Study Design, whole numbers will have the same significant figures as number of digits, for example 400 has three significant figures while 400.0 has four’

Maybe, then, we should have our answer to 2 sig figs? Considering the graph shows a maximum of two.

Scientifically it seems odd that we should give a result in more sig figs than that of which we can be certain of. In my opinion the graph is also a sort of ‘data’ from which we extract information so perhaps our answer can only be as accurate as the graph. Quite ambiguous

[Bri MT]

I think when your calculations involve a number like "4" not "4.0" then you ignore the sig figs in calculations?

Pretty sure this is for if it's a "mathematical 4"  so 4 m would be 1 sig fig, but  if you multiplied something by 4 you wouldn't then go "oh but there's only 1 digit in four so the answer only has 1 sig fig"

Not sure how VCAA feels about that, but yeah
Hope this helps

[vceme]

hey guys,
has anyone who has done multiple chem exams (ive only done a few whoops ) have noticed any patterns? in particular, are questions that majority of the state could not answer get repeated? thanks!!! 

[Lear]

Perhaps someone should start a ‘common tricky Chemistry questions’ thread?

[vceme]

Perhaps someone should start a ‘common tricky Chemistry questions’ thread?

I'm all for this, and common mistakes?

[Bri MT]

]

Perhaps someone should start a ‘common tricky Chemistry questions’ thread?

I'm all for this, and common mistakes?

There's no reason why that someone couldn't be either of you - even if you don't know what to contribute you could start it off with a couple of questions you've gotten wrong a few times & invite others to contribute


My advice would be to just start it and work out the details along the way

[Lear]

]
There's no reason why that someone couldn't be either of you - even if you don't know what to contribute you could start it off with a couple of questions you've gotten wrong a few times & invite others to contribute


My advice would be to just start it and work out the details along the way

Can't argue with that
I'll have on up in a bit.

[smamsmo22]

So I wasn't aware of the sig fig rule about temperatures. So we use the number of sig figs used in the value EXCLUDING TEMPERATURES with the lowest sig figs. And when giving temp we give the same decimal points as the lowest value given.

Thanks!

[Freddie Hg]

So I wasn't aware of the sig fig rule about temperatures. So we use the number of sig figs used in the value EXCLUDING TEMPERATURES with the lowest sig figs. And when giving temp we give the same decimal points as the lowest value given.

Thanks!

i didnt know this either but the sig fig rule also doesnt work when adding and subtracting, in that case you have to use lowest decimal places.
can someone confirm?

[smamsmo22]

Also this is in regards to a question I posted a few days ago  but didn't get a clear response, in the 2017 sample theres an MC about the purpose of argon in a reaction and the answer is;
C. exclude oxygen and hence prevent Ti from forming oxides.
How does argon "exclude oxygen"?

Thank you!

[passbleh24]

Also this is in regards to a question I posted a few days ago  but didn't get a clear response, in the 2017 sample theres an MC about the purpose of argon in a reaction and the answer is;
C. exclude oxygen and hence prevent Ti from forming oxides.
How does argon "exclude oxygen"?

Thank you!

Maybe argon binds to oxygen preventing reaction with Ti

[passbleh24]

Hey everyone, I've made a list of advantages and disadvantages, If you guys can think of any more could you please add on ? This always comes up on the exam and for some reason I tend to go blank. Thanks !!

Biofuels better than fossil fuels:
- biofuels are renewable where as fossil fuels are not
- Less effect on environment through greenhouse emissions. CO2 consumed in photosynthesis is released in combustion

Fossil fuels better than Biofuels:
- Higher energy content and fuel efficiency

General disadvantages for both:
- Using resources and crops
- Degradation of land through oil spills and drilling
- Emissions of CO2 or other particulate
- Incomplete combustion chances

Petrodiesel is better than biodiesel
- biodiesel is hygroscopic, higher viscosity.
- Biodiesel has a higher melting point so solidifies and requires additives where as petrodiesel has a lower melting point.
- Cloud point is higher in Biodiesel ^
- More efficient, produces more energy

Biodiesel is better than Petrodiesel:
- Renewable uses triglycerides to form
- Less emissions

Bonds:
- Petrodiesel - dispersions forces ( lower melting and boiling point )
- Biodiesel - polar bonds ( higher melting and boiling point )
- Plant - double bonds are formed which weaken dispersion forces. So lower melting point.
- Animal - saturated.

Comparing both biogas and natural gas:
- CH4 captured from biogas is better for the environment because CH4 is a stronger greenhouse gas
- CH4 obtained from natural gas is introducing more greenhouse gases into the atmosphere
- Both release CO2 when combusted.
- One is renewables whilst the other is non renewable
- Natural gas has a higher energy content than biogas which is a mixture of gases

Primary Cells vs Secondary Cells
- Recharging opportunity
- Products do not stay in tact in primary cells and are consumed by side reactions where as for secondary cells they must stay in tact.

Fuel Cells Advantages:
- Continuous supply of reactants means that continuous supply of electricity can be produced and no need for recharging or discarding.
- Very efficient due to direct conversion of chemical energy to electricity.
- Possibility of less green house gases depending on which one. 

Fuel Cells Disadvantages:
- Constant need of fuel supply
- Expensive

[joshgoundar]

can we use pencil for calculations for tomorrow's exam?

[nicholas9027]

Hey all,
Can someone please confirm this definition for equivalence point?
Equivalence Point: a point where the mole ratio of reactants are stoichiometrically equal.

Thanks

[joshgoundar]

Hey all,
Can someone please confirm this definition for equivalence point?
Equivalence Point: a point where the mole ratio of reactants are stoichiometrically equal.
Thanks

yup youre definiton is accurate, keep in mind that should know that it differs from an endpoint which is when an indicator changes colour, suggesting the end of a tritation