HSC Chemistry Question Thread

[bsdfjnlkasn]

What would the substitution reaction equation between an alkane (like hexane) and bromine water be when exposed to UV light ?

[RuiAce]

What would the substitution reaction equation between an alkane (like hexane) and bromine water be when exposed to UV light ?

The product is the same product as in the addition reaction involving alkenes. But hydrogen gas is also produced (you should be able to see why)

[bsdfjnlkasn]

Saying we used cyclohexane, would this be correct:

C6H12 + Br2 –UV light -> C6H11Br + HBr?

I'm not sure what you mean there being hydrogen produced because by drawing out the molecules this is what I got. Is there a better/quicker method to use?

[RuiAce]

Saying we used cyclohexane, would this be correct:

C6H12 + Br2 –UV light -> C6H11Br + HBr?

I'm not sure what you mean there being hydrogen produced because by drawing out the molecules this is what I got. Is there a better/quicker method to use?

That reaction is wrong.

Cyclohexene addition reaction:
C6H10 + Br2 -> C6H10Br2

Cyclohexane substitution reaction:
C6H12 + Br2 -> C6H10Br2 + H2


Edit: Strikethrough - Or maybe it's correct. It makes sense, but was definitely not what I was taught for addition/substitution reactions. Time to call in Jake

[Yasminpotts1105]

What is an overall reduction-oxidation equation?

Because for a dry cell, I have the anode and cathode half equations but I don't understand how I condense it into one?

[RuiAce]

What is an overall reduction-oxidation equation?

Because for a dry cell, I have the anode and cathode half equations but I don't understand how I condense it into one?

Give an example of two half equations and I'll remake the complete equation

[jakesilove]

That reaction is wrong.

Cyclohexene addition reaction:
C6H10 + Br2 -> C6H10Br2

Cyclohexane substitution reaction:
C6H12 + Br2 -> C6H10Br2 + H2


Edit: Strikethrough - Or maybe it's correct. It makes sense, but was definitely not what I was taught for addition/substitution reactions. Time to call in Jake

Definitely stick with Rui's reactions above. Whilst yours are possible, his are the 'likely' reaction products, and the most useful ones for your purpose

[Yasminpotts1105]

Zn (s) = Zn^2+ + 2e^-
2MnO2 + 2NH4 = Mn2O3 + H2O + 2NH3

[RuiAce]

Zn (s) = Zn^2+ + 2e^-
2MnO2 + 2NH4 = Mn2O3 + H2O + 2NH3

That second one is incorrect. There should be two more electrons on the left.

2MnO2 + 2NH4 + 2 e^- = Mn2O3 + H2O + 2NH3

Now it should be clearer as to how they can be combined.

[Aaron12038488]

for prelim chem, the first topic, it looks really boring. Is this the case for the rest of the topics. Also for chem and other sciences, should i memorise everything

[jakesilove]

for prelim chem, the first topic, it looks really boring. Is this the case for the rest of the topics. Also for chem and other sciences, should i memorise everything

Whether a topic is 'boring' will be entirely dependent on what you're interested in! Try to find something that you care about, and focus on that in your studies.

I think that most of Science is about understanding the content, and then there is some memorisation involved. You'll learn to strike the right balance over time

[bluecookie]

For the HSC, do we need to memorise the colour range of common indicators, and also the pH that they change? Or will those values be provided for us in the question?

[RuiAce]

For the HSC, do we need to memorise the colour range of common indicators, and also the pH that they change? Or will those values be provided for us in the question?

You will need to remember what colour they are in generic ranges (e.g. strongly acidic, weakly basic). And you do need to know where abouts it changes colour (e.g. phenolphthalein changes colour over the basic range). That's for the four common indicators in the course; there are tons of indicators out there but only the four common ones matter.

However, the specific values are usually stated. A band 6 student will probably memorise them anyway because writing it down impresses the examiner, but I've found that usually they tell you them if you need to refer to it.

[bluecookie]

Thanks On a similar note, is it expected we memorise the carbon dioxide water equilibrium equations?

[RuiAce]

Thanks On a similar note, is it expected we memorise the carbon dioxide water equilibrium equations?

Yes that's crucial.


As a rule of thumb, memorise as many equations as you can. However Jake made a list a while back.