VCE Chemistry Question Thread

[HopefulLawStudent]

So basically, the flame supplies its own activation energy? Where does that energy come from? Is it the thermal energy from the flame?

(PS: Thank you for answering my Q! )

[kimmie]

Hey can anyone explain what oxidising strength is because I'm confused. Is it the ability to take electrons from other substances? I don't get it. Help meeee

[jyce]

Hey can anyone explain what oxidising strength is because I'm confused. Is it the ability to take electrons from other substances? I don't get it. Help meeee

Hi, kimmie

Your definition of oxidising strength is spot-on 

[solution]

Hi, kimmie

Your definition of oxidising strength is spot-on 

This is a 1/2 question, but I'd appreciate an answer. When am I supposed to use scientific notation? In my assessments, I haven't been marked down for not using scientific notation but I'm not sure whether this is due to my teacher being lenient or not. For example, when I calculate empirical formulas and molecular formulas from percentage compositions, I don't use scientific notation. Am I supposed to? If so, how/when?

[jyce]

This is a 1/2 question, but I'd appreciate an answer. When am I supposed to use scientific notation? In my assessments, I haven't been marked down for not using scientific notation but I'm not sure whether this is due to my teacher being lenient or not. For example, when I calculate empirical formulas and molecular formulas from percentage compositions, I don't use scientific notation. Am I supposed to? If so, how/when?

The only time you absolutely must give your final answers in scientific notation is in the situation where otherwise your answer would be to an incorrect number of significant figures. For example, let's say your final answer to a calculation is 1300 mol, but you're supposed to give your answer to three significant figures only. 1300 mol is to four significant figures and rounding the number won't do any good, so you'd need to instead express the answer as 1.30 x 10³ mol. Other than such a scenario, it's also a good idea to give an answer in scientific notation when it's a really small value (e.g. 0.00004 mol = 4 x 10^-5 mol)

As for calculating empirical and molecular formulas, you never have to use scientific notation. Why? Because your final answer won't be numerical; it'll be a formula. You can't express an empirical or molecular formula using scientific notation.

[solution]

The only time you absolutely must give your final answers in scientific notation is in the situation where otherwise your answer would be to an incorrect number of significant figures. For example, let's say your final answer to a calculation is 1300 mol, but you're supposed to give your answer to three significant figures only. 1300 mol is to four significant figures and rounding the number won't do any good, so you'd need to instead express the answer as 1.30 x 10³ mol. Other than such a scenario, it's also a good idea to give an answer in scientific notation when it's a really small value (e.g. 0.00004 mol = 4 x 10^-5 mol)

As for calculating empirical and molecular formulas, you never have to use scientific notation. Why? Because your final answer won't be numerical; it'll be a formula. You can't express an empirical or molecular formula using scientific notation.

Okay, that makes sense. What about method marks? Will you be marked down for not using scientific notation in your working out? (In general)

[jyce]

Okay, that makes sense. What about method marks? Will you be marked down for not using scientific notation in your working out? (In general)

Nope. Only your actual answer for each question needs to be to the correct number of significant figures.

[HasibA]

what would be the absolute maximum amount of marks lost over sig figs on the exam? i heard they dock 1 , but unsure

[HopefulLawStudent]

I was told 1 mark but to quote my teacher, that one mark could be very important.

[HasibA]

I was told 1 mark but to quote my teacher, that one mark could be very important.

thank you, and i agree- every mark counts!

[Jakeybaby]

thank you, and i agree- every mark counts!

Here in SA, I've been told that it could be potentially 2 or even 3 depending on the number of times that significant figures have not been used correctly. I know that in my physics exam, if you make a mistake with significant figures in one question, but use them correctly in following questions, no marks will be lost unless it states: Marks will be allocated for correct use of significant figures in the question.

[jyce]

Here in SA, I've been told that it could be potentially 2 or even 3 depending on the number of times that significant figures have not been used correctly. I know that in my physics exam, if you make a mistake with significant figures in one question, but use them correctly in following questions, no marks will be lost unless it states: Marks will be allocated for correct use of significant figures in the question.

Yeah, it's a bit different here in Victoria. In fact, you're not penalised at all for significant figures in VCE Physics.

[knightrider]

Yeah, it's a bit different here in Victoria. In fact, you're not penalised at all for significant figures in VCE Physics.

Wow is that true ? 

my teachers always say you will lose marks in the exam for not showing sig figs (physics)

[Swagadaktal]

Yeah, it's a bit different here in Victoria. In fact, you're not penalised at all for significant figures in VCE Physics.

oh I actually did not know that - but there's guidelines right? If the answer is 4.65650 can you write 4.7? Where do you draw the line?

Does anyone have any tough equilibrium questions they wanna throw at me(within reason of the study design)? Keen for a tough question rn

[keltingmeith]

Does anyone have any tough equilibrium questions they wanna throw at me(within reason of the study design)? Keen for a tough question rn

Here's a few:

The "fizzing" is a result of a dynamic equilibrium between carbon dioxide and the water in the bottle, described as follows:
CO2 + H2O <-----> H2CO3
Explain why soft drinks can go flat.

A particular reaction has the following equilibrium:

A+2B <------> C, K=7
2 mole of A and 1 mole of B are allowed to equilibriate. How much mole of C are present at the end of this reaction? If 3 mole of A is added to the solution, how much mole of B and C are left after the solution is allowed to equilibriate?