HSC Chemistry Question Thread

[jakesilove]

Thanks! Just wondering, acid has to have H+ right? So are acidic oxide and acid different things?

An acid is a substance that donates protons (ie. H+)

An acidic oxide is a substance that, when combined with water, forms an acid.

So yeah, they are totally different things! Can get a bit confusing, but just keep those definitions in mind

[limtou]

An acid is a substance that donates protons (ie. H+)

An acidic oxide is a substance that, when combined with water, forms an acid.

So yeah, they are totally different things! Can get a bit confusing, but just keep those definitions in mind

Ah I see. Since the syllabus states that non-metal oxides act as acid, I was confused. Thanks for the clarification Jake

[Jenny_trn]

What is the monomer of polystyrene? I'm going through the HSC chemistry topic tests and the answer is ethenylbenzene, but i thought that was the systematic name for polystyrene, so styrene would be the monomer name? I'm honestly not sure.

[beau77bro]

What is the monomer of polystyrene? I'm going through the HSC chemistry topic tests and the answer is ethenylbenzene, but i thought that was the systematic name for polystyrene, so styrene would be the monomer name? I'm honestly not sure.

YES OMG THIS GOT ME TOO, but yea generally the systematic name of the monomer is very similar to the polymer minus 'poly' so the systematic of the monomer name is ethenylbenzene, and for the polymer it is polyethenylbenzene. just like 1-chloroethane has a polymer of poly(1-chloroethane). i hope i smelt this all right ahhaha, and hope it helps

[limtou]

What is the monomer of polystyrene? I'm going through the HSC chemistry topic tests and the answer is ethenylbenzene, but i thought that was the systematic name for polystyrene, so styrene would be the monomer name? I'm honestly not sure.

ethenylbenzene is the systematic name for styrene, not polystyrene  

I also have a question~
I read somewhere that: Anionic detergents are alkyl benzene sulfonates with a negatively charged end. The negative end on the ion allows it to strip oil from negative surfaces.
Can someone explain the negative surface bit? Does it matter that the surface is negative :O
Overall, I don't think I understand how the charge of the anionic/cationic heads have anything to do with their cleaning action.
Please explain! Thanks

[winstondarmawan]

Hello! Would appreciate help for the following qs:
13. https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/20314573_1278708645587989_1998027790_o.png?oh=38e3a434d7181b6baec60d24e42d5f18&oe=5975528E
20. https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/20217105_1278709285587925_1449257879_n.png?oh=47b49a7b666c0b83837f22bedf9b96e1&oe=5975AB3B
27. https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/20289766_1278717925587061_773511986_n.png?oh=9985c24d14c7c4b1ace4f78626b04414&oe=597550CE
TIA

[kiwiberry]

ethenylbenzene is the systematic name for styrene, not polystyrene  

I also have a question~
I read somewhere that: Anionic detergents are alkyl benzene sulfonates with a negatively charged end. The negative end on the ion allows it to strip oil from negative surfaces.
Can someone explain the negative surface bit? Does it matter that the surface is negative :O
Overall, I don't think I understand how the charge of the anionic/cationic heads have anything to do with their cleaning action.
Please explain! Thanks

Not sure about anionic detergents, but cationic detergents are used in hair conditioners as the surface of hair is negatively charged

[kiwiberry]

Hello! Would appreciate help for the following qs:
13. https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/20314573_1278708645587989_1998027790_o.png?oh=38e3a434d7181b6baec60d24e42d5f18&oe=5975528E
20. https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/20217105_1278709285587925_1449257879_n.png?oh=47b49a7b666c0b83837f22bedf9b96e1&oe=5975AB3B
27. https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/20289766_1278717925587061_773511986_n.png?oh=9985c24d14c7c4b1ace4f78626b04414&oe=597550CE
TIA

13) has been addressed here
20) Bromine has a higher ozone depleting potential than chlorine, so B is the answer. (However CFCs have contributed more to ozone depletion in the atmosphere because they are more abundant and have longer lifetimes)
27) Reading off the graph, concentration of a sample with absorbance 0.45 will have a concentration of about 0.45 micrograms/25mL

[winstondarmawan]

13) has been addressed here
20) Bromine has a higher ozone depleting potential than chlorine, so B is the answer. (However CFCs have contributed more to ozone depletion in the atmosphere because they are more abundant and have longer lifetimes)
27) Reading off the graph, concentration of a sample with absorbance 0.45 will have a concentration of about 0.45 micrograms/25mL

Thank you! How about 27.b)?

[Shadowxo]

Thank you! How about 27.b)?

Ppm is by weight, and like it says it's parts per million, eg mg per kg, micrograms per gram, etc. Easiest way to convert the answer to ppm is by making it micrograms / mL ie micrograms / g (as 1mL water = 1g).

Answering the question:
There are 0.45micrograms in the 25mL solution, so 0.45 micrograms of lead from the precipitate from the 100mL sample. This means there was 0.45 micrograms of lead in 100 mL of original water. Changing this to micrograms per mL (or ppm) just divide it by 100 for 0.0045 micrograms per mL or ppm
Hope this helps

[phoebegresham]

Hey Jake!
In Example 2.1 in the Chemistry ATAR notes (Acidic Environment), the question 'is NaOH a good substance to use as a standard solution?' is asked, which i recently also saw in one of our topic tests, but I had no idea what the answer was! I don't think its answered in the book however, it just calculates the concentrations (also asked), but i don't think is says why or why not it is a good substance as a standard solution. I was just wondering what the answer is to that question?
Thanks heaps 

[kiwiberry]

Hey Jake!
In Example 2.1 in the Chemistry ATAR notes (Acidic Environment), the question 'is NaOH a good substance to use as a standard solution?' is asked, which i recently also saw in one of our topic tests, but I had no idea what the answer was! I don't think its answered in the book however, it just calculates the concentrations (also asked), but i don't think is says why or why not it is a good substance as a standard solution. I was just wondering what the answer is to that question?
Thanks heaps 

NaOH is not a good standard solution - it is hygroscopic, which means that it absorbs water from the atmosphere, so it's very hard to accurate measure the mass of solid NaOH. It can also react with CO2 in the air, changing its concentration. Standard solutions need to have a known concentration, so NaOH is not appropriate as its concentration is always changing.

[phoebegresham]

NaOH is not a good standard solution - it is hygroscopic, which means that it absorbs water from the atmosphere, so it's very hard to accurate measure the mass of solid NaOH. It can also react with CO2 in the air, changing its concentration. Standard solutions need to have a known concentration, so NaOH is not appropriate as its concentration is always changing.

thank you!

[winstondarmawan]

Would appreciate help with the following Qs:
14. https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/20270053_1279294878862699_251626619_n.png?oh=0833834537ad91acfa67f1eec4e6a948&oe=59763A9F
The answer is D and I understand, but can someone explain why it is not C?
Shipwrecks Q:
https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/20270053_1279294878862699_251626619_n.png?oh=0833834537ad91acfa67f1eec4e6a948&oe=59763A9F
The sample answer in the booklet was literally 2 pages and far too detailed for 6 marks. What would this Q require for the 6?

[VanillaRice]

Would appreciate help with the following Qs:
14. https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/20270053_1279294878862699_251626619_n.png?oh=0833834537ad91acfa67f1eec4e6a948&oe=59763A9F
The answer is D and I understand, but can someone explain why it is not C?

AAS is typically used to measure concentrations of metal ions in solutions. The light source is a hollow cathode lamp made of the metal being analysed, and emits light of a certain frequency. Hence, C is incorrect, as white light is not used.