HSC Chemistry Question Thread

[RuiAce]

Why is ethanol a good source for alternative fuel in terms of boiling point and heat of combustion?

Note that it's only truly good relative to octane with B.P.

With heat of combustion, I'd argue ethanol is worse than octane because it releases a lower amount of energy.

[jakesilove]

Note that it's only truly good relative to octane with B.P.

With heat of combustion, I'd argue ethanol is worse than octane because it releases a lower amount of energy.

Yes, it's definitely worse! Just trying to answer the question of why it can be considered good.

[marynguyen18]

with the layers of the atmosphere what do each of them do? I'm really confused on which layer is ozone good and bad in? (if that questions makes any sense)

[marynguyen18]

by any chance can anyone give me a brief overview on the topic Shipwrecks its my weakest topic in Chemistry

[jakesilove]

with the layers of the atmosphere what do each of them do? I'm really confused on which layer is ozone good and bad in? (if that questions makes any sense)

Ozone is a pollutant in the Troposphere (as it is toxic) and great in the higher atmosphere (stratosphere) as it absorbs UV light! Definitely do some research and figure out what happens in each layer of the atmosphere, as that's really important. As for your next question, that's way too big a question to answer here. Try find some online notes

[bethjomay]

The answers for this question say that the change from 4-10 seconds is due to an increase in temperature. Could it also be a decrease in pressure as there are more moles of gas on the right hand side? Would this be accepted as an answer?

[RuiAce]

(Image removed from quote.)

The answers for this question say that the change from 4-10 seconds is due to an increase in temperature. Could it also be a decrease in pressure as there are more moles of gas on the right hand side? Would this be accepted as an answer?

Nope. Note that concentration is the y-axis. Not moles.

If those were moles then that would be fine. However concentration is different. Recall that C=n/V

Concentration depends on volume as well. If we change the pressure, we change the volume. Thus, for a pressure change, there would be a spike in the graph, similar to at 14 seconds.

[bethjomay]

I was wondering if anyone could help me with the dot point in Industrial Chem - "Perform a first-hand investigation to gather information and describe the properties of a named emulsion and relate these properties to its uses." We didn't cover it in class except for actually making the emulsion (butter) and my teacher isn't getting back to me.

[DaCoon]

What is the molecular formula for 2-butanol and the structural formula? I tried to search it up and it wasn't there on the internet. What is the systematic name for c5h11OH?

[RuiAce]

What is the molecular formula for 2-butanol and the structural formula? I tried to search it up and it wasn't there on the internet. What is the systematic name for c5h11OH?

The prefix but- states that we have FOUR carbons. Using the formula C_nH_2n+1OH we have

Butanol: C₄H₉OH

And similarly, C₅H₁₁OH is pentanol.


Observe that we do not know if this is 1-pentanol, 2-pentanol or 3-pentanol. This isn't given to us.
On the other hand, because we know that it's 2-butanol, we know what its structural formula is.

The 2 means that the -OH group (for alkanols) lies on carbon #2.

[DaCoon]

Thanks

When it says "Outline the procedure" are you supposed to retell the method word for word or what?

[RuiAce]

I was wondering if anyone could help me with the dot point in Industrial Chem - "Perform a first-hand investigation to gather information and describe the properties of a named emulsion and relate these properties to its uses." We didn't cover it in class except for actually making the emulsion (butter) and my teacher isn't getting back to me.

One example could be mayonnaise, which is an emulsion of oil and water. Egg is the emulsifying agent.

You would most likely know what mayonnaise is used for.

Thanks

When it says "Outline the procedure" are you supposed to retell the method word for word or what?

Yeah. A procedure is just another way of saying a method.

[DaCoon]

Can someone help me on question 18 in the 2014 paper

https://www.boardofstudies.nsw.edu.au/hsc_exams/2014/pdf_doc/2014-hsc-chemistry.pdf

[RuiAce]

Can someone help me on question 18 in the 2014 paper

https://www.boardofstudies.nsw.edu.au/hsc_exams/2014/pdf_doc/2014-hsc-chemistry.pdf

Closely inspect the polymer given. It repeats itself once. Note the alternating (CH2)4 and (CH2)6

Thus, ignore the repeat and only consider one of it.


Clearly, B is wrong as it has no (CH2)6

The (CH2)6 is connected to N, not O. Suddenly we just realised that C and A are also wrong due to this problem.

So the correct answer is D.



It's all about knowing what you're looking for. You have to break the molecule apart.

[nimasha.w]

hi! i don't know where to begin with this question, can someone please explain it to me :-)