VCE Chemistry Question Thread

[jyce]

so i got a question on volumetric analysis, it first asked me to determine the amount(in moles) of HCl placed in a volumetric flask then the second question asked us to find the amount of moles of HCl once the volumetric flask has been filled to the calibration line. Isn't it the same amount since the actual amount of HCl doesn't change since were just adding de-ionised water, (which changes it's concentration?)

Is it okay to say Hydrocarbons contain ONLY Hydrogen and Carbon (and that it doesn't contain oxygen?)

Thanks

In response to your first question, you'd be correct - based on the information you've provided.

And yes, hydrocarbons contain only hydrogen and carbon, hence their name.

[Sine]

What are you guys thoughts on the heinemann textbook questions, do they prepare you well enough for prac exams?

Also some questions say stuff like "oxygen" and "nitrogen" when do we assume they are in gas form? when do we assume they are elemental?

[jyce]

What are you guys thoughts on the heinemann textbook questions, do they prepare you well enough for prac exams?

Also some questions say stuff like "oxygen" and "nitrogen" when do we assume they are in gas form? when do we assume they are elemental?

The textbook is pretty decent. However, it does not provide an accurate representation of all the different types of questions you will come across in exams. For example, the textbook questions tend to have little background information, whereas exam questions tend to be accompanied by more information that you need to sift through. Textbook questions should be used to develop a foundational grasp of concepts, and then you should move on to applying this knowledge to exam questions.

As for your second question, oxygen and nitrogen are generally in the form of gases so it's a safe assumption. 

[The Usual Student]

What are you guys thoughts on the heinemann textbook questions, do they prepare you well enough for prac exams?

Also some questions say stuff like "oxygen" and "nitrogen" when do we assume they are in gas form? when do we assume they are elemental?

The general consensus was that textbook questions assist greatly in clarifying and assuring you understand your concepts, however I am not going to depend on them for sac prep. Firstly, everyone would have been exposed to them already and the trickier questions used to differentiate the students require more complex practice questions. I have heard that Lisachem is good for this but I have never used it, also, NEAP is fairly recommended. Secondly, they are pretty generic from what I have heard.

[knightrider]

For the image attached.

Isnt the volume of   meant to be 100ml not 50 ml as the solution says?

[zsteve]

Yeh you're right. It's a mistake

[vanilla and sunflower]

Hello everyone

I've been doing some chemistry work over the holidays and have some questions!

I would really appreciate it if someone could answer them. I've filed them in a word document and attached them.

They are not a lot. 

Thanks

[vanilla and sunflower]

Hello everyone

I've been doing some chemistry work over the holidays and have some questions!

I would really appreciate it if someone could answer them. I've filed them in a word document and attached them.

They are not a lot. 

Thanks

bump!

[keltingmeith]

Hello everyone

I've been doing some chemistry work over the holidays and have some questions!

I would really appreciate it if someone could answer them. I've filed them in a word document and attached them.

They are not a lot. 

Thanks

Wooooow that's a lot of questions - I can only help you with what I have time for (i.e., everything except 24. Particularly when this is waaaaaay beyond anything they'd actually give you in VCE).

29. That's a bad spectra - I wouldn't call either of them a C-H or an O-H peak. However, it's important to know that the figures in your data book are a guideline. IR is not as easy as VCE makes it out to be, and there can be variation in the numbers. Particularly for chemical bonds where deprotonation can occur (in this case, the O-H peak).

My take - ignore this question. If VCAA were to give you something, it would go by the "rules" they've given you. If it comes from a textbook or worksheet, it can get a little weird.

33. Use the n+1 rule. For propane, note that the starred proton has an equivalent protons. Equivalent protons don't couple - so, it won't affect the splitting. This means that only the protons on the two CH3 groups will couple, giving 6H+1=7 peaks. The same goes for the Tartaric acid - the proton you think it's coupling with is in the same environment, note the symmetry of the molecule.

[vanilla and sunflower]

Wooooow that's a lot of questions - I can only help you with what I have time for (i.e., everything except 24. Particularly when this is waaaaaay beyond anything they'd actually give you in VCE).

29. That's a bad spectra - I wouldn't call either of them a C-H or an O-H peak. However, it's important to know that the figures in your data book are a guideline. IR is not as easy as VCE makes it out to be, and there can be variation in the numbers. Particularly for chemical bonds where deprotonation can occur (in this case, the O-H peak).

My take - ignore this question. If VCAA were to give you something, it would go by the "rules" they've given you. If it comes from a textbook or worksheet, it can get a little weird.

33. Use the n+1 rule. For propane, note that the starred proton has an equivalent protons. Equivalent protons don't couple - so, it won't affect the splitting. This means that only the protons on the two CH3 groups will couple, giving 6H+1=7 peaks. The same goes for the Tartaric acid - the proton you think it's coupling with is in the same environment, note the symmetry of the molecule.

It makes sense!  Thank you EulerFan101
Maybe it was a lot of questions  I tend to get carried away sometimes

[HasibA]

In order to standardise a solution of hydrochloric acid, a
student titrated the solution against 20.00 mL aliquots of
a standard solution of sodium carbonate. Methyl orange
indicator was used to identify the end point of the reaction:
2HCl(aq) + Na2CO3(aq) → 2NaCl(aq) + H2O(l) + CO2(g)
The sodium carbonate solution had been prepared by
dissolving 1.236 g of anhydrous Na2CO3 in water and making
the solution up to 250.0 mL in a volumetric fl ask. The titres
recorded were 21.56 mL, 20.98 mL, 20.96 mL
and 21.03 mL.

a What value for the titre of hydrochloric acid solution
should the student use in the calculation of the acid
concentration? Explain your answer.

b What is the molarity of the sodium carbonate solution?

c Calculate the concentration of the HC l, in mol L−1.


with part c, i calculated the amount, in mol, of na2co3 and then i used the molar ratios to get twice the amount of na2co3 mol. After, i used what i found and plugged it into c= n/v, and got an answer as 1.11 something molar, which was incorrect. The answers did this:

c Step 1 From the equation, 2 mol of HCl reacts with 1 mol of Na2CO3 in the

Step 2 Calculate the concentration of hcl

n(HCl) = 2 x 0.04666 M x 0.02000 L

= 0.00186636 mol

c(HCl) = 0.00186636 mol/0.02099 L

= 0.088918 M

= 0.08892 M

help please!!

[Sine]

In order to standardise a solution of hydrochloric acid, a
student titrated the solution against 20.00 mL aliquots of
a standard solution of sodium carbonate. Methyl orange
indicator was used to identify the end point of the reaction:
2HCl(aq) + Na2CO3(aq) → 2NaCl(aq) + H2O(l) + CO2(g)
The sodium carbonate solution had been prepared by
dissolving 1.236 g of anhydrous Na2CO3 in water and making
the solution up to 250.0 mL in a volumetric fl ask. The titres
recorded were 21.56 mL, 20.98 mL, 20.96 mL
and 21.03 mL.

a What value for the titre of hydrochloric acid solution
should the student use in the calculation of the acid
concentration? Explain your answer.

b What is the molarity of the sodium carbonate solution?

c Calculate the concentration of the HC l, in mol L−1.


with part c, i calculated the amount, in mol, of na2co3 and then i used the molar ratios to get twice the amount of na2co3 mol. After, i used what i found and plugged it into c= n/v, and got an answer as 1.11 something molar, which was incorrect. The answers did this:

c Step 1 From the equation, 2 mol of HCl reacts with 1 mol of Na2CO3 in the

Step 2 Calculate the concentration of hcl

n(HCl) = 2 x 0.04666 M x 0.02000 L

= 0.00186636 mol

c(HCl) = 0.00186636 mol/0.02099 L

= 0.088918 M

= 0.08892 M

help please!!

a) 20.99mL
b)0.0466M
c)n(HCl)=2 x n(Na2CO3) = 2 x 0.01166 x 20/250 = 0.00187mol

c(HCl)=n/v=0.00187/0.02099=0.0889M

I think the books correct.

The mistake you seem to have made is using the mole ratios between the 250mL of Na2CO3 and the 20.99mL of HCl where you should've found the mole of the aliquot before using mole ratios to calculate the mole of HCl to do this i've multiplied the original mole by 20/250 to find the mole of the 20mL aliquot from the 250mL solution. (I have highlighted this step in red)

Note i took a slightly different approach to the worked solution.




         

[Biology24123]

Is going through the review questions in the Heinemann text book the most effective thing to do?

[IndefatigableLover]

Is going through the review questions in the Heinemann text book the most effective thing to do?

For Unit 3 AOS1, I definitely believe that there is some merit in doing the review questions in the Heinemann textbook however afterwards, you'll want to be moving onto other resources such as Checkpoints, NEAP Smartstudy Questions and the Kevin Barry LisaChem Question Book since they'll have harder questions and more too (since questions relating to Spectroscopy were very minimal in the Heinemann textbook).

[Biology24123]

For Unit 3 AOS1, I definitely believe that there is some merit in doing the review questions in the Heinemann textbook however afterwards, you'll want to be moving onto other resources such as Checkpoints, NEAP Smartstudy Questions and the Kevin Barry LisaChem Question Book since they'll have harder questions and more too (since questions relating to Spectroscopy were very minimal in the Heinemann textbook).

Do you think it's worth trying to start unit 4 as well. The first 5 chapter of Heinemann are basically a review of 1/2 aren't they?