HSC Chemistry Question Thread

[Yasminpotts1105]

Yes

[RuiAce]

Subject to some minor inaccuracies but 75% of the question is done. Last bit I included the relevant formula

[kiwiberry]

why is polystyrene insulative to heat? and why is pvc weather resistant?

[jakesilove]

why is polystyrene insulative to heat? and why is pvc weather resistant?

Thankfully, not part of the curriculum! We don't really care WHY, we just care that it is

[kiwiberry]

Thankfully, not part of the curriculum! We don't really care WHY, we just care that it is

Oh really? so for a question like "Describe the uses of three named addition polymers in terms of their structure and properties", would you have to relate structure to properties?

[jakesilove]

Oh really? so for a question like "Describe the uses of three named addition polymers in terms of their structure and properties", would you have to relate structure to properties?

Sorry, I sort of understand where you're coming from now; properties are different from 'WHY' the properties are apparent. So, the PROPERTY is that it is a good insulator, and the use is thermal cups etc. Why is it a good insulator? You don't need to know that. You just need to be able to list the properties themselves (eg. insulator, hard, brittle, strong) and then relate that to a use. Does that make sense?

[Happy Physics Land]

Oh really? so for a question like "Describe the uses of three named addition polymers in terms of their structure and properties", would you have to relate structure to properties?

These are really all you need to know:

1. linear, crystalline structure = high tensile strength, high hardness, high impact resistance
2. non-linear, amorphous structure = low tensile strength, low hardness, low impact resistance
3. Bulky side groups/side chains = high stiffness because carbon chains cannot bend easily
4. Having a N, O or F in the structure (e.g. cellulose) = high tensile strength because hydrogen bonding between chains
5. Having double or triple bonds in the structure = higher boiling point, because more energy input required to overcome double or triple bonds

[RuiAce]

These are really all you need to know:

1. linear, crystalline structure = high tensile strength, high hardness, high impact resistance
2. non-linear, amorphous structure = low tensile strength, low hardness, low impact resistance
3. Bulky side groups/side chains = high stiffness because carbon chains cannot bend easily
4. Having a N, O or F in the structure (e.g. cellulose) = high tensile strength because hydrogen bonding between chains
5. Having double or triple bonds in the structure = higher boiling point, because more energy input required to overcome double or triple bonds

Fortunately even then those aren't that big of a deal, except for maybe thy double bond one. It doesn't hurt to know these though I reckon

[kiwiberry]

Fortunately even then those aren't that big of a deal, except for maybe thy double bond one. It doesn't hurt to know these though I reckon

These are really all you need to know:

1. linear, crystalline structure = high tensile strength, high hardness, high impact resistance
2. non-linear, amorphous structure = low tensile strength, low hardness, low impact resistance
3. Bulky side groups/side chains = high stiffness because carbon chains cannot bend easily
4. Having a N, O or F in the structure (e.g. cellulose) = high tensile strength because hydrogen bonding between chains
5. Having double or triple bonds in the structure = higher boiling point, because more energy input required to overcome double or triple bonds

Sorry, I sort of understand where you're coming from now; properties are different from 'WHY' the properties are apparent. So, the PROPERTY is that it is a good insulator, and the use is thermal cups etc. Why is it a good insulator? You don't need to know that. You just need to be able to list the properties themselves (eg. insulator, hard, brittle, strong) and then relate that to a use. Does that make sense?

yes, that makes sense!! thanks so much guys

[anotherworld2b]

Hi i was wondering if i could please get help with these 2 questions.
I am not sure how to write the equation needed for q5. For q7 iam not sure what to do 

[jakesilove]

Hi i was wondering if i could please get help with these 2 questions.
I am not sure how to write the equation needed for q5. For q7 iam not sure what to do 

For question 7, find the number of moles you have of each gas (using the weight), multiply that by the molar volume, and see which one equals 3.85L

For question 5, find the number of moles of the acid that have been added. If you multiply this by 6 (as there are 6 moles of flourine for every one mole of acid) you will get the moles of flourine released. Then, find the concentration in the solution, and you should be done.

[anotherworld2b]

I'm still a bit confused about q7. Could you please give me an example?
I tried q5. Would this be correct? I was wondering how would you write the chemical reaction?

For question 7, find the number of moles you have of each gas (using the weight), multiply that by the molar volume, and see which one equals 3.85L

For question 5, find the number of moles of the acid that have been added. If you multiply this by 6 (as there are 6 moles of flourine for every one mole of acid) you will get the moles of flourine released. Then, find the concentration in the solution, and you should be done.

[f_tan]

I've got a chem research task and one of the things I have to do is research the history of batteries. I'm a little confused - can anyone clarify the difference between the voltaic, galvani, and daniell cell, and who invented them? Thank you!

[jakesilove]

I'm still a bit confused about q7. Could you please give me an example?
I tried q5. Would this be correct? I was wondering how would you write the chemical reaction?

Looks correct. If the molar mass of a gas was 3g, then you find the moles of the gas by 5.78/3. Then, multiply this by 24.71L to get the molar volume. Clearly, that isn't equal to the required moles, so that isn't the correct gas.

[jakesilove]

I've got a chem research task and one of the things I have to do is research the history of batteries. I'm a little confused - can anyone clarify the difference between the voltaic, galvani, and daniell cell, and who invented them? Thank you!

My understanding was that the cells were actually the same, just different names! You need to know the development of battery technologies, but I believe that the names of the batteries aren't very important.