VCE Chemistry Question Thread

[s3r3ndipity8]

Sup! Is this statement true or false: "Fats have lower melting points than oils but they are both classified as triglycerides." (Justify your answer)

[Syndicate]

Sup! Is this statement true or false: "Fats have lower melting points than oils but they are both classified as triglycerides." (Justify your answer)

false. Fats are solid at room temperature, whilst oils are liquid at room temperature (generally). This implies that fats have a higher melting point than oils.

[Phenomenol]

Thanks Phenomenal. So for Q9aii when you say things get "exotic" are you saying that the answer's equation is correct or my logic correct?

Your answer can actually be ruled out by the simple fact that it is not a half-equation - there are no unbalanced electrons on either side of the equation.

I am saying that you need to consider the possibility of unusual half-equations when nothing else is applicable.

Your thought process should be: "I need this to be a reduction half-equation therefore I need electrons on the LHS. The electrolyte is solid therefore I cannot have typical aqueous ions like H⁺ or OH^-, but I can just balance the equation using the species present".

For the new study design, heat of combustion/reaction is now a scalar quantity right? So you only needa negative since if it asks for delta H or enthalpy change?

Heat of combustion, according to the data book, is positive because it refers to the heat released in a combustion reaction.

Enthalpy of combustion is the difference in enthalpy between reactants and products, and would be a negative value. So you are correct

[QueenSmarty]

Is q8 (short answer) from the 2014 VCAA exam still part of the course?

[crackleking]

Do we have to know what addition polymerisation is?

[usernameincorrect]

Can someone please explain what happens if we use thymol blue which has a pH range of 1.2-2.8, for a acid-base reaction that has an equivalence point of anything from pH 3 and above? Will it just change from red to yellow when pH in volumetric flask is around 1.2-2.8, and then just remain yellow from there? Thanks!

[Willba99]

Can someone please explain what happens if we use thymol blue which has a pH range of 1.2-2.8, for a acid-base reaction that has an equivalence point of anything from pH 3 and above? Will it just change from red to yellow when pH in volumetric flask is around 1.2-2.8, and then just remain yellow from there? Thanks!

Assuming the original solution had a pH<1.2, yeah

[wij0020]

Hi there, I just wanted to ask if anyone could explain to me why ( in Phenomenol's exam for Question18 MCQ) the answer is D not A

[Somedudelmaoy]

In question 9biii of the 2016 exam, why do they put the answer to 2 sig figs. Should it not be 3?

[Phenomenol]

Is q8 (short answer) from the 2014 VCAA exam still part of the course?

2014 Section B Q8: Part a) and b) are not relevant as they involve a precipitation reaction which was taken out, but c) is relevant.

Do we have to know what addition polymerisation is?

Technically, I'm not sure, but it really doesn't hurt to remember what you learnt in year 11 about this.

Can someone please explain what happens if we use thymol blue which has a pH range of 1.2-2.8, for a acid-base reaction that has an equivalence point of anything from pH 3 and above? Will it just change from red to yellow when pH in volumetric flask is around 1.2-2.8, and then just remain yellow from there? Thanks!

If the indicator is not suitable, the colour change will not occur at the right stoichiometry and it will not happen rapidly (which is desired). So, yes.

Hi there, I just wanted to ask if anyone could explain to me why ( in Phenomenol's exam for Question18 MCQ) the answer is D not A

In question 9biii of the 2016 exam, why do they put the answer to 2 sig figs. Should it not be 3?

See my responses in their appropriate threads.

[s3r3ndipity8]

Pls help: 

"For the titration, a 20.00 ml sample of pure lemon juice was made up to 250.00 ml with de-ionised h20 in a 250 ml volumetric flask. The average titre was found to be 15.65 ml....etc..."
--How many sig figs should i for use my answers?
--In particular, does vcaa accept 250 ml as 2 sigfigs or 3 sigfigs?

"The battery discharged for 60 minutes, produced a current of 1.15A"
--Is this a 1 or 3 SF answer?

VCAA 2017 sample short answer
--Q8c) I wrote 2C4H10 + 9O2 --> 8CO + 10H2O but my teacher's answer has the coefficients halved. Is my solution correct?
--Q9ai) "predicted maximum temperature rise of the water" is this qs asking to find the delta T value at 49.7 or the final temperature at 71 degrees? #comprehension-help

Cheerz.

[plsbegentle]

difference between titrant, titre and aliquot? getting these terms confused

[sweetiepi]

difference between titrant, titre and aliquot? getting these terms confused

Titrant: usually the chemical you titrate with- the one with the known concentration that goes in the burette
Titre- the volume of known solution used to get to the endpoint- usually used afterwards to find the unknown's concentration
Aliquot- the sample, or unknown

(This is based off a semester of doing titrations, I may be slightly inaccurate haha)

[Crowley99]

the answer of a question in 2017 insight exam is confusing. Multiple choice q 24:
A mixture of propan-1-ol and butan-1-ol is injected into an HPLC column that is using a polar solvent. The print out below is obtained.
peak(min)               Area
7.6                                    4200
9.4                                    3600
A second sample is passed through the same column and produces only one peak with a retention time of 9.4 minutes and an area of 1200 units. the second sample contains:
A. propan-1-ol and butan-1-ol at lower concentrations than the original solution.
B. propan-1-ol only, with a concentration that is one third of the original solution.
C. butna-1-ol only, with a concentration that is one third of the original solution.
D. butan-1-ol only, with a concentration that is three times that of the original solution.

[keltingmeith]

the answer of a question in 2017 insight exam is confusing. Multiple choice q 24:
A mixture of propan-1-ol and butan-1-ol is injected into an HPLC column that is using a polar solvent. The print out below is obtained.
peak(min)               Area
7.6                                    4200
9.4                                    3600
A second sample is passed through the same column and produces only one peak with a retention time of 9.4 minutes and an area of 1200 units. the second sample contains:
A. propan-1-ol and butan-1-ol at lower concentrations than the original solution.
B. propan-1-ol only, with a concentration that is one third of the original solution.
C. butna-1-ol only, with a concentration that is one third of the original solution.
D. butan-1-ol only, with a concentration that is three times that of the original solution.

Polar solvent: so the more polar molecule will move faster (elute first)

And peak area is proportional to concentration, so the larger the peak area, the more compound, and vice versa.

Does that help?