VCE Chemistry Question Thread

[taylorjj57]

Acid + Base --> Salt and Water
Acid + Metal oxide --> Salt and Water
Acid + Metal Hydroxide --> Salt and Water
Acid + Metal Carbonate --> Salt and Water and Carbon Dioxide
Acid + Metal Sulfide --> Salt and H2S
Acid + Metal --> Salt and Hydrogen gas

Thanks heaps for that one, exactly what I was looking for

[anotherworld2b]

hi could I please get help with these questions please

[Individu]

Can someone pls help me out with this:

The concentration of sodium ions in a solution can be determined by atomic absorption spectroscopy.
Consider the following tasks.
I Detection of the presence of sodium fluoride in a town water supply
II Determination of the potassium chloride concentration in mineral water
III Determination of the sodium nitrate concentration in sausage meat
Which analysis tasks could be performed successfully?
A. III only
B. I only
C. I and III only
D. I, II and III


The answer is C; I and III are possible. But how can sodium concentration in meat be analysed through UV-Vis, isn't it the case that a) the analyte needs to be in solution for UV-Vis to work and b) you can't really determine concentration of something in a solid (meat)?

[larissaaa_]

How much do we need to know about fossil fuels and nuclear energy for the current vce 3/4 study design? Does vcaa expect us to know everything about it? I remember my teacher going through it briefly in class but I was on excursion that day, now I don't know whether I should spend a lot of time studying all its concepts or focus on other stuff within the course!

[sweetiepi]

How much do we need to know about fossil fuels and nuclear energy for the current vce 3/4 study design? Does vcaa expect us to know everything about it? I remember my teacher going through it briefly in class but I was on excursion that day, now I don't know whether I should spend a lot of time studying all its concepts or focus on other stuff within the course!

Hey Larissa!
According to VCAA's study design (pg 26), it essential to know the comparisons between the renewability of

• Coal
• Nuclear Power
• Petrol
• Natural gas
• Biochemical fuels

Going by past VCE questions I've looked at, you can be assessed on which fuels are renewable or non-renewable, production of electricity through coal-fired power stations, as well as the odd combustion of fuel equations (such as combustion of octane or ethane).
From what I've experienced- there's not been detailed questions about any of the energy sources on their own. 

All in all, getting an understanding of which forms of energy are renewable or not is the most important thing to understand, I recommend brushing over it, however you should focus on other topics, such as the unit 3 areas of study and the galvanic/electrolytic cells.

(Hope this helps a little! )

[larissaaa_]

Hey Larissa!
According to VCAA's study design (pg 26), it essential to know the comparisons between the renewability of

• Coal
• Nuclear Power
• Petrol
• Natural gas
• Biochemical fuels

Going by past VCE questions I've looked at, you can be assessed on which fuels are renewable or non-renewable, production of electricity through coal-fired power stations, as well as the odd combustion of fuel equations (such as combustion of octane or ethane).
From what I've experienced- there's not been detailed questions about any of the energy sources on their own. 

All in all, getting an understanding of which forms of energy are renewable or not is the most important thing to understand, I recommend brushing over it, however you should focus on other topics, such as the unit 3 areas of study and the galvanic/electrolytic cells.

(Hope this helps a little! )

Okay thank you so much! Because my teacher had said there may be the odd one or two multiple choice questions on it but it's not a major part of the exam, but my textbook has two whole chapters on it and goes into so much detail about each energy source! Thank you

[Biology24123]

Can someone pls help me out with this:

The concentration of sodium ions in a solution can be determined by atomic absorption spectroscopy.
Consider the following tasks.
I Detection of the presence of sodium fluoride in a town water supply
II Determination of the potassium chloride concentration in mineral water
III Determination of the sodium nitrate concentration in sausage meat
Which analysis tasks could be performed successfully?
A. III only
B. I only
C. I and III only
D. I, II and III


The answer is C; I and III are possible. But how can sodium concentration in meat be analysed through UV-Vis, isn't it the case that a) the analyte needs to be in solution for UV-Vis to work and b) you can't really determine concentration of something in a solid (meat)?

You dissolve it I guess?

[Sine]

if we are using delta H in energy calculations but are only using the positive value (i.e delta H is negative  - producing energy ) how would we convey this without suggesting that delta H is positive when it isn't.

[sweetcheeks]

if we are using delta H in energy calculations but are only using the positive value (i.e delta H is negative  - producing energy ) how would we convey this without suggesting that delta H is positive when it isn't.

Do you have a specific question where this would be an issue? If you are doing a calculation where you are working out how much energy is obtained, you could write something like 'x joules is released to the enviroment'

[Sine]

Do you have a specific question where this would be an issue? If you are doing a calculation where you are working out how much energy is obtained, you could write something like 'x joules is released to the enviroment'

no specific question just weird writing deltaH then not replacing it with it's equivalent - what should i write in it's place to ensure each line of working is equivalent.

[Gogo14]

For 1/2 chem,
In titrations, why is the standard solution rinsed with deionised water and the buret and pipette rinsed with the acid used? I know it is something to do with maintaining concentration and moles, but still can't get my head around it

[Sine]

when marking VCAA chem exams if our answer is correct but the examiners report uses different sig figs would we still get a mark if the examiners report doesn't state something along the lines of "The fourth mark was awarded for the correct number of significant figures. " ? - sometimes the reports have wrong sig figs too.

[Elizawei]

when marking VCAA chem exams if our answer is correct but the examiners report uses different sig figs would we still get a mark if the examiners report doesn't state something along the lines of "The fourth mark was awarded for the correct number of significant figures. " ? - sometimes the reports have wrong sig figs too.

I reckon you can give yourself that mark. My teacher (who's an assessor) says that there's one question where they specifically look for sig figs (usually at a question where it's very obvious), and don't worry about the rest of the exam. The examiner's report isn't perfect, sometimes they even round off their numbers to use in the next step of the calculation.

[ml125]

For 1/2 chem,
In titrations, why is the standard solution rinsed with deionised water and the buret and pipette rinsed with the acid used? I know it is something to do with maintaining concentration and moles, but still can't get my head around it

The conical (erlenmeyer) flask is rinsed with deionised water to remove any outstanding impurities that may be present on the glassware. You could also think of it like this: if you were to rinse with solution from the pipette, it would increase the amount of this solution used in reaction - resulting in a greater titre value. Rinsing with solution from the burette would result in excess titrant being introduced into the reaction - thus you would have a lower titre value.
In terms of the burette and pipette, if rinsed with deionised water, the solution would be diluted. The known concentration would then become inaccurate. Rinsing with the solution to be used eg. acid also removes moisture present on glassware which can contribute to dilution.

[zsteve]

I reckon you can give yourself that mark. My teacher (who's an assessor) says that there's one question where they specifically look for sig figs (usually at a question where it's very obvious), and don't worry about the rest of the exam. The examiner's report isn't perfect, sometimes they even round off their numbers to use in the next step of the calculation.

Thought I'd add on this topic:
- There is a common method of doing your calculations to an arbitrary degree of precision and then rounding down to the lowest number of sig figs in the input data. Strictly speaking, this is WRONG and only works for questions involving multiplication only.
- In general, the best approach is to write intermediate steps down to the correct number of sig figs, storing values in your calculator for later use.