VCE Chemistry Question Thread

[redpanda83]

Sounds great! Take confidence in the work you have done, don't burn out, and don't forget to pay at least some attention on your English subject  (Top 4, am I right!)
Remember you are free regardless of whether you have exam responsibilities or not!

I don't like English.   I will definitely pay a lot of attention to it. As I know it's not my strong point.  I will be spending most of my time on English throughout the year and I will definitely will try not to burn out.
But it won't really happen xD as i like to keep learning.
Ik VCE isn't all about studying, so I will keep my social life balanced as well!
If I have any difficulties while doing exam style questions or anything else, I will ask you guys!
I can't rely that much on my teacher next year (sadly I heard I will be having a teacher with no year 12 chem and physics exp, so I will be on my own for most of the time. Old one went on long service leave) can't really do much about this

[Scribe]

Would it be useful to write notes for chemistry? I have purchased Thushan's notes and a couple other commercial resources so I was wondering whether I should just answer questions to revise instead. Realistically, Chemistry will probably be in my bottom 2 and will receive the least of my efforts this year but I still want to do well in it (who knows?).

Thanks 

[redpanda83]

Would it be useful to write notes for chemistry? I have purchased Thushan's notes and a couple other commercial resources so I was wondering whether I should just answer questions to revise instead. Realistically, Chemistry will probably be in my bottom 2 and will receive the least of my efforts this year but I still want to do well in it (who knows?).

Thanks 

Honestly, using study design to write notes is a good idea. It would be good if you just write rough notes of a chapter as you do the course and when you are done use study design to summarise things. It would be a good revision as well. Then comes exam style questions.
Thats what i do anyway.

[Lear]

I definitely agree with above. If you’re aiming high it is super useful to make your own notes. Personally I compiled several resources to make a doc of about 80 pages worth of notes. This was very useful.

However you did mention that this will likely be in your bottom two. Firstly I’d encourage it to give it your best anyway. You may be surprised!
But I do understand if you feel like it would take away from your other subjects that perhaps you are more passionate about.

In that case I think it is definitely viable to simply use someone else’s notes. This will save you time and also allow you to practice more with exam style questions. It’s pretty much what I did with legal this year!

[addict]

Would it be useful to write notes for chemistry? I have purchased Thushan's notes and a couple other commercial resources so I was wondering whether I should just answer questions to revise instead. Realistically, Chemistry will probably be in my bottom 2 and will receive the least of my efforts this year but I still want to do well in it (who knows?).

Thanks 

I'm one of the weird people out there who would actually caution against making notes for everything. If you think about it, your textbook is just a comprehensive collection of notes based on the study design. Isn't that awesome? If you like compressed versions and have bought more notes, great (not that it's something I'd recommend since it takes out some necessary details). I'm not saying 'don't take any notes', but certainly consider only making notes that will help you. For example, I would select small, specific topics I don't feel confident with, jot down everything (so messily that other people wouldn't understand it) I think I know about it that I might forget before the exam, then use the textbook/study design/chemguides to complete the sections I have qualms about. That way I can easily glance through my (very brief. but targeted) notes before assessments.

[lzxnl]

Would it be useful to write notes for chemistry? I have purchased Thushan's notes and a couple other commercial resources so I was wondering whether I should just answer questions to revise instead. Realistically, Chemistry will probably be in my bottom 2 and will receive the least of my efforts this year but I still want to do well in it (who knows?).

Thanks 

For what it's worth, I found writing notes at university to be very useful (high school not so much, because question bashing was usually enough to get the point of the course material). To me, writing notes a month or so after learning the content would act as revision. Then, I would have the opportunity to write any steps or reasoning in words that made sense to me, and the act of thinking of my own words helped with the understanding of said material.

To give a chemistry example, if you're looking at what a fat is, you might just remember that fats are composed of triglycerides, and that looking at the name suggests that there is glycerol and three of something. Then you would remember that triglycerides are made from fatty acids, and that glycerol contains OH (says so in data book), so triglycerides must have three ester groups in them. If you write your notes and think about them when you write them, the knowledge sticks better.

[Monkeymafia]

Having trouble answering:

c) iii) Name the alkane

[VanillaRice]

Having trouble answering:

c) iii) Name the alkane

Hey there,

Have you answered part (ii)? If you have, consider that (as per the question stem) alkanes only have two types of atoms - carbon and hydrogen. How can we use the mass of one mole of a molecule to determine how many carbon and hydrogen atoms are within the molecule (i.e. what are the values x and y)?

Hope that helps. Post if you're still stuck

[Quinapalus]

Hey there,

Have you answered part (ii)? If you have, consider that (as per the question stem) alkanes only have two types of atoms - carbon and hydrogen. How can we use the mass of one mole of a molecule to determine how many carbon and hydrogen atoms are within the molecule (i.e. what are the values x and y)?

Hope that helps. Post if you're still stuck

Hint: Alkenes conform to a general formula of C_nH_2n

[Monkeymafia]

Hey there,

Have you answered part (ii)? If you have, consider that (as per the question stem) alkanes only have two types of atoms - carbon and hydrogen. How can we use the mass of one mole of a molecule to determine how many carbon and hydrogen atoms are within the molecule (i.e. what are the values x and y)?

Hope that helps. Post if you're still stuck

So I got 29.9 for ii)

Alkanes have general formula CnH2n+2,

so 3n+2=30

n =(approximately) 9

so C9H21, but don't think thats right.

[VanillaRice]

So I got 29.9 for ii)

Alkanes have general formula CnH2n+2,

so 3n+2=30

n =(approximately) 9

so C9H21, but don't think thats right.

Your answer for part (ii) means that one mole of that compound weights 29.9 g. In other words, its mass is 29.9 g/mol, which is precisely the units we usually have for molar/molecular mass.

The way you have gone about part (iii) is to find the value of n (which is a fair attempt). However, you have tried to solve 3n+2=30. This equation assumes that your molecule has 30 atoms. We actually don't have any information about the number of atoms in our molecule. But, we do have the molar mass of our molecule. Think about what molar mass represents, and how we can use this information to solve the problem. Hopefully this helps you with your question - feel free to post if you're still stuck

[studyingg]

Using 29.9 g and 1 mol means that the molar mass is also equal to 29.9

which means

12*n + (2n+ 2) *1  = 29.9
giving n = 1.99 which is aproximately 2, therefore n= 2

meaning the alkane is C2H6 which means the name is ethane

[Monkeymafia]

Using 29.9 g and 1 mol means that the molar mass is also equal to 29.9

which means

12*n + (2n+ 2) *1  = 29.9
giving n = 1.99 which is aproximately 2, therefore n= 2

meaning the alkane is C2H6 which means the name is ethane

Where does the 12n come from in this step: 12*n + (2n+ 2) *1  = 29.9

[studyingg]

Using 29.9 g and 1 mol means that the molar mass is also equal to 29.9

which means

12*n + (2n+ 2) *1  = 29.9
giving n = 1.99 which is aproximately 2, therefore n= 2

meaning the alkane is C2H6 which means the name is ethane

Where does the 12n come from in this step: 12*n + (2n+ 2) *1  = 29.9

Because M= 29.9g/mol (which is your molar mass), this value can be obtained by looking at the molar masses in the periodic table, what 29.9g/mol means is that  every mole of CxHy weighs 29.9 grams. Therefore we can find n as we know the molar masses of Carbon and Hygrogen, and we know that this substance is comprised of Carbon and Hydrogen atoms, what we don't know however is how many carbon and hydrogen atoms make up the alkane. We can find this by using the general formula of an Alkane.
so
12 (which is the molar mass of carbon) * n (which is the number of carbon atoms -unknown-) + 1 (molar mass of hydrogen) * (2n+2) (no. of hydrogen atoms) = 29.9

from this, n roughly = 2, and so you have C2H6.

If you are still unsure, go to chapter 5 of unit 1 chem to refresh your memory, or watch a video about n= m/M

[Scribe]

What is the oxidation number for H in NaH?
According to my book, the oxidation of H in NaH is -1. However, this online calculator (https://www.periodni.com/oxidation_numbers_calculator.php) suggests two different solutions. With regards to the VCE course, is one answer more correct than the other or are they both perfectly acceptable?

Thanks