VCE Chemistry Question Thread

[Freddie Hg]

Hi, in 2016 students were asked to give the systematic name of ethnic anhydride. Is this still applicable to the current study design (if so, how would we know how to name it?)

i dont think so.

[Azim.m]

Hi, in 2016 students were asked to give the systematic name of ethnic anhydride. Is this still applicable to the current study design (if so, how would we know how to name it?)

That specific question (7.b) deals with the synthesis of aspirin which is no longer in the study design, therefore you would not need to know how to name that compound

[passbleh24]

In my TSFX notes I just read something that doesn't seem right to me.
" You cannot increase the reaction rate by adding an inert gas at constant temperature and volume, as reactant/product concentrations will have not changed"

Could someone confirm this for me ? I thought that since pressure has increased due to the addition of inert gas the reaction rate would increase. I know for a fact that the equilibrium position does not change but not so much about reaction rate.

Thanks

[Freddie Hg]

In my TSFX notes I just read something that doesn't seem right to me.
" You cannot increase the reaction rate by adding an inert gas at constant temperature and volume, as reactant/product concentrations will have not changed"

Could someone confirm this for me ? I thought that since pressure has increased due to the addition of inert gas the reaction rate would increase. I know for a fact that the equilibrium position does not change but not so much about reaction rate.
Thanks

adding an inert gas does not change the rate if reaction as the partial pressures of the reactants and products remain the same. there is an overall net increase in pressure of the container but not the system. the system refers to the species in involved in the chemical reaction.
the tsfx notes are correct. but you shouldnt worry about that fact too much since its not assessed by vcaa

[passbleh24]

adding an inert gas does not change the rate if reaction as the partial pressures of the reactants and products remain the same. there is an overall net increase in pressure of the container but not the system. the system refers to the species in involved in the chemical reaction.
the tsfx notes are correct. but you shouldnt worry about that fact too much since its not assessed by vcaa

Thank you !!

[Maya24]

Can someone please help me the 2017 chemistry exam question 8b? Shouldn't F2 go under reduction as it is the strongest oxidant? Thanks in advance

[Freddie Hg]

Can someone please help me the 2017 chemistry exam question 8b? Shouldn't F2 go under reduction as it is the strongest oxidant? Thanks in advance

hey there maya!
it says an equation at the anode  anode is always an oxidation reaction irreagrdless of it being an electrolytic cell or galvanic cell.
so you might want to look for the strongest reductant to go under oxidation.
next time provide a image of the question, as it helps others in the forum refer to your question. tho i have no problem with looking up the exam
good luck on tuesday!!

[zenith101]

can someone explain why q30 MC from VCAA sample exam is a systematic rather than random error? (i tried attaching  photo but it was too big )

[hums_student]

can someone explain why q30 MC from VCAA sample exam is a systematic rather than random error? (i tried attaching  photo but it was too big )

It's systematic because all the NaOH solution have absorbed the same amount of CO2 from the air. Therefore results would be skewed in the same direction during every single trial.
A random error would be something that results in data being skewed in different directions.

Also this is totally unrelated but @Freddie Hg, it took me way to long to realise what your username meant

[Freddie Hg]

can someone explain why q30 MC from VCAA sample exam is a systematic rather than random error? (i tried attaching  photo but it was too big )

regardless of how many times ruby repeats the experiment co2 will be absorbed by naoh. therefore the error is not random as it cannot be accounted for with repetition. its systematic. another way of deducing it being systematic, is thinking about why the error occurs? it does so because the procedure fails to account for naohs ability to absorb co2. its not ruby's fault that co2 is absorbed by naoh, its the fault of the procedure itsself. its an error that inherent within the system itself and not the experimenter. 
im interested to know what was your reasoning behind it being a random error?

It's systematic because all the NaOH solution have absorbed the same amount of CO2 from the air. Therefore results would be skewed in the same direction during every single trial.
A random error would be something that results in data being skewed in different directions.

Also this is totally unrelated but @Freddie Hg, it took me way to long to realise what your username meant

you beat me to it!
ahahhahah yeah a lot of people miss it 

mod edit: merged posts

[zenith101]

regardless of how many times ruby repeats the experiment co2 will be absorbed by naoh. therefore the error is not random as it cannot be accounted for with repetition. its systematic. another way of deducing it being systematic, is thinking about why the error occurs? it does so because the procedure fails to account for naohs ability to absorb co2. its not ruby's fault that co2 is absorbed by naoh, its the fault of the procedure itsself. its an error that inherent within the system itself and not the experimenter. 
im interested to know what was your reasoning behind it being a random error?
you beat me to it!
ahahhahah yeah a lot of people miss it 

mod edit: merged posts

I kind of thought wouldn't there be a different amount of CO2 absorbed from the air in every experiment Ruby does but yeah i think i understand a fair bit better now.

Also is molar heat of combustion expressed as an absolute value? I always thought enthalpy of combustion depended on released or absorbed, but i saw some solutions have molar heat of comb as positive.

[hums_student]

Also is molar heat of combustion expressed as an absolute value? I always thought enthalpy of combustion depended on released or absorbed, but i saw some solutions have molar heat of comb as positive.

I'm pretty sure that molar heat of combustion and enthalpy are not the same thing. The value of the enthalpy change can be positive or negative depending on whether it's an endo or exothermic reaction, however the molar heat of combustion will always be positive.

Enthalpy = delta H
Molar heat of combustion = delta Hc

-----ADD-----
Just read through VCAA's 2017 NHT examiners' report - they've got negative delta Hc values in there, even though I was taught that they're always positive. Now I'm confused lol.
If you refer to the data book you'll see that all molar heat of combustion values are positive. Possible mistake on VCAA's part?

[MAGGOT]

For electrolysis in molten ionic compounds, what are the states of all the reactants and products? Are they all liquid or does only aq stuff become liquid?

[Freddie Hg]

For electrolysis in molten ionic compounds, what are the states of all the reactants and products? Are they all liquid or does only aq stuff become liquid?

too my knowledge only (aq) becomes liquid. everything should stay the same

[Azim.m]

For electrolysis in molten ionic compounds, what are the states of all the reactants and products? Are they all liquid or does only aq stuff become liquid?

Most times (I think) the solid reagents also become liquid, because molten compounds are usually maintained at extremely high temperature