HSC Chemistry Question Thread

[RuiAce]

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.

Though gonna add on, pretty sure that the Daniell cell is a specific type of galvanic cell because it has to be between copper and zinc. (Going off memory here; my teacher did give us a worksheet.)

[f_tan]

Though gonna add on, pretty sure that the Daniell cell is a specific type of galvanic cell because it has to be between copper and zinc. (Going off memory here; my teacher did give us a worksheet.)

Hi, sorry I'm back with this question again
I'm still confused with which one the Daniell cell is, because different websites have different descriptions and diagrams?
Which one is the Daniell cell?
OR
Thanks!

[RuiAce]

Hi, sorry I'm back with this question again
I'm still confused with which one the Daniell cell is, because different websites have different descriptions and diagrams?
Which one is the Daniell cell?
(Image removed from quote.) OR (Image removed from quote.)
Thanks!

They are the same cell. The only difference in that diagram is that one of them has the electrolytes in two seperate compartments, whereas the other has them in the same.

That doesn't change the cell. The cell is the same because all the chemicals (copper etc.) are the same

[J.B]

I was just wondering in calculation questions, how do you know how many decimal places your answer should be to?

[RuiAce]

I was just wondering in calculation questions, how do you know how many decimal places your answer should be to?

Always round to the LEAST number of SIGNIFICANT FIGURES given in the question. Never rely solely on decimal points without good reason.

[J.B]

Always round to the LEAST number of SIGNIFICANT FIGURES given in the question. Never rely solely on decimal points without good reason.

Thank you

[FallonXay]

Hello~

[Prelim Question] I'm looking at examples of triatomic molecules in the textbook and one example is water (H₂O). Why is water a molecule, I thought it was just a compound? Also what does 'Molecules are particles that can move independently of one another' mean?

Thanks.

[RuiAce]

Hello~

[Prelim Question] I'm looking at examples of triatomic molecules in the textbook and one example is water (H₂O). Why is water a molecule, I thought it was just a compound? Also what does 'Molecules are particles that can move independently of one another' mean?

Thanks.

Compounds are a subclass of molecules.

Molecules just mean there's more than one atom in your substance. Note that a molecule can be a compound (H₂O) or an element (O₂)

All compounds are molecules. However elements are either molecules (O₂) or single atoms (Al)


Not too sure what they really mean by move independently. I thought that was just a given; one molecule moving doesn't have to affect the other molecule moving.

[FallonXay]

All compounds are molecules. However elements are either molecules (O₂) or single atoms (Al)

And can all single atoms also be called monatomic molecules?

(It says helium atoms He and argon atoms Ar are examples monatomic molecules)

[RuiAce]

And can all single atoms also be called monatomic molecules?

(It says helium atoms He and argon atoms Ar are examples monatomic molecules)

I don't think 'monatomic molecules' is a part of the chemistry glossary. It's a contradiction.

Molecule implies two or more atoms. Monatomic implies just one atom.

[Yasminpotts1105]

Why do we specifically use cold water in the prac to determine and compare the heat of combustion of alcohols?

[Yasminpotts1105]

How do we produce large amounts of butanol?

[RuiAce]

Why do we specifically use cold water in the prac to determine and compare the heat of combustion of alcohols?

I think this is to do with how heating works, but considering heat losses as well.

In a way, it is 'easier' to heat cold water, as opposed to hot water. This mainly has to do with how we have heat losses everywhere; heat gets absorbed by the calorimeter, lost to surroundings and all sorts of problems that damage the accuracy of the practical.

If we could heat the water, so that literally all of the heat went into the water and not any surroundings, I believe using cold water or hot water will not matter. But because there's all these other things to consider, cold water can potentially make our measurements more realistic and accurate.

That and it may also have to do with the thermometer as well. I feel like I rambled in helping you though.

Jake!!!

How do we produce large amounts of butanol?

This is not in the syllabus. You may be able to just fugde it though and compare it to how ethanol is produced.

[jakesilove]

Why do we specifically use cold water in the prac to determine and compare the heat of combustion of alcohols?

The short answer is that we don't. The formula only cares about the change in temperature, so based on that the same amount of energy is required to raise water's temperature from 25 to 26 degrees as it takes to raise water's temperature from 89 to 90 degrees. So, we generally start with cold water and heat it up because that's just the easiest thing to do. What's the alternative? Heat some water up using a hot plate, then do the experiment? Then, you'll encounter problems with determining the initial temperature accurately (as it continues to drop before more heat is applied), consistent heating of the liquid, heating of glassware and metal etc.

However, Rui also has a point. A heated system (in comparison to the environment around it) is more likely to cool, because the 'aim' of a system is to reach a single temperature. So, if we start with room temperature water, it will be very hard for it to cool down. However, water at 80 degrees can cool down much more easily, as the environment REALLY wants to suck up some of that heat. To be honest, I think this affect has very, very little impact on the experiment as a whole. I think my first answer is more pertinent to your question.

[jakesilove]

Why do we actually need to know the molar heat of combustion of alcohols?

Do you mean, like, why is it important for chemists to understand the molar heat of combustion? Essentially, it allows us to understand and predict how much energy we can release, by burning a set quantity of a liquid. From that, we can determine which fuels are most efficient, and thus which we should use to power cars etc. For instance, the molar heat of combustion of Ethanol is 2/3 that of Octane, making it a worse fuel. Does that answer your question?