VCE Chemistry Question Thread

[redset8]

From my understanding, water is always a liquid as it is assumed that the experiment is performed in SLC (standard lab conditions).

Ah ok thanks heaps.

[LE-0130]

Hi!
Current stuck on this question, seems rlly basic, but for some reason I can't do it, bcuz I'm not quite sure what the chemical equation would look like. Anyways, any help or advice would be greatly appreciated! Thanks

Question:
"How many faradays of charge are required to produce:
(d) 1 mole of hydrogen molecules (H2) from sodium chloride solution?"

[Erutepa]

Hi!
Current stuck on this question, seems rlly basic, but for some reason I can't do it, bcuz I'm not quite sure what the chemical equation would look like. Anyways, any help or advice would be greatly appreciated! Thanks

Question:
"How many faradays of charge are required to produce:
(d) 1 mole of hydrogen molecules (H2) from sodium chloride solution?"

For this questions we are considering an electrolytic cell with solution of sodium chloride (meaning water will be present).
Knowing that the chemical species present consists of Na+, Cl- and H20, we can now consider the electrochemical series. At the anode, an oxidation reaction will occur - the two potential reactions listed in the series is the oxidation of chloride ions to chlorine gas, and the oxidation of water to hydrogen peroxide and H+. Remember that the reaction that requires the least electrode potential (volts) to proceed will occur first, since the oxidation of these chloride ions has a lower electrode potential requirement (needs input of 1.36v at slc) this is the reaction that will be occuring at the anode.
For the cathode, the two possible reduction reactions we see in the electrochemical series is the recuction of sodium ions to sodium metal, and the reduction of water to hydroxide ions and hydrogen gas. Applying the same rule that the reaction that requires the least electrode potential (volts) to proceed will occur first, we can see that the reduction of water requires the least electrode potential and thus will occur at the cathode.
to summarise, here we will have the oxidation of chloride ions at the anode, and the reduction of water at the cathode.
Hopefully this will help you get through the rest of the question, but feel free to ask for help or to point out anything i poorly explained.

[LE-0130]

For this questions we are considering an electrolytic cell with solution of sodium chloride (meaning water will be present).
Knowing that the chemical species present consists of Na+, Cl- and H20, we can now consider the electrochemical series. At the anode, an oxidation reaction will occur - the two potential reactions listed in the series is the oxidation of chloride ions to chlorine gas, and the oxidation of water to hydrogen peroxide and H+. Remember that the reaction that requires the least electrode potential (volts) to proceed will occur first, since the oxidation of these chloride ions has a lower electrode potential requirement (needs input of 1.36v at slc) this is the reaction that will be occuring at the anode.
For the cathode, the two possible reduction reactions we see in the electrochemical series is the recuction of sodium ions to sodium metal, and the reduction of water to hydroxide ions and hydrogen gas. Applying the same rule that the reaction that requires the least electrode potential (volts) to proceed will occur first, we can see that the reduction of water requires the least electrode potential and thus will occur at the cathode.
to summarise, here we will have the oxidation of chloride ions at the anode, and the reduction of water at the cathode.
Hopefully this will help you get through the rest of the question, but feel free to ask for help or to point out anything i poorly explained.

Thank you! It makes so much more sense now!

[Ruchir]

Hello I am in year 11. In the Heinmann textbook do we cover all chapters this year?
Or do we miss a few of them?

[Sine]

Hello I am in year 11. In the Heinmann textbook do we cover all chapters this year?
Or do we miss a few of them?

Really depends on the school. Some teachers solely rely on textbooks whilst others just use it as one of many resources.

Personally, we covered a lot of the content in the textbook but definitely not all. Textbooks are typically bloated with a lot of irrelevant content.

[Ruchir]

Really depends on the school. Some teachers solely rely on textbooks whilst others just use it as one of many resources.

Personally, we covered a lot of the content in the textbook but definitely not all. Textbooks are typically bloated with a lot of irrelevant content.

Thanks fo the answer
 if the textbook has 20 chapters how many (approx)do you think will be covered in school if my school only uses the textbook?

[Sine]

Thanks fo the answer
 if the textbook has 20 chapters how many (approx)do you think will be covered in school if my school only uses the textbook?

I'm not too sure about the current edition of the Heinemann textbook so wouldn't really be able to give you an accurate answer.

If your school has given you an outline of the topics you are covering this year you might be able to see where everything fits and what chapters will be relevant to you.

[miyukiaura]

Do we need to know specific numbers for the energy content of fuels? Also, do we need to worry about energy efficiency? It's not on the study design but I see some resources mention it.

 Edit: I was also wondering what the difference is between petrol and liquified petroleum gas? The Heinemann textbook treats them as if they are two separate things but which are we supposed to know about?

[Sine]

Do we need to know specific numbers for the energy content of fuels? Also, do we need to worry about energy efficiency? It's not on the study design but I see some resources mention it.

Have you had a look at the databook? They should be in there.

As for energy efficiency, I think you should be covering it.

[miyukiaura]

Have you had a look at the databook? They should be in there.

As for energy efficiency, I think you should be covering it.

Yeah, I've seen the databook but it doesn't have the figures for coal or crude oil. Thanks anyway

[hel256]

Do we need to know specific numbers for the energy content of fuels? Also, do we need to worry about energy efficiency? It's not on the study design but I see some resources mention it.

 Edit: I was also wondering what the difference is between petrol and liquified petroleum gas? The Heinemann textbook treats them as if they are two separate things but which are we supposed to know about?

I don't think you need to know specific numbers per se for coal or crude oil. You do need to know roughly the energy content of those fuels however in order to compare them; often you'll see questions asking you to compare the energy content of fossil fuels vs biofuels, coal vs petrol or petrodiesel vs biodiesel.
Knowing the energy efficiency of different methods of energy production is also something that often gets questioned, for example the energy efficiency of a coal or gas-fired powerplant vs a fuel cell, so having a rough grasp of those percentages is often helpful.

[cutiepie30]

Hi Guys,

Could you please explain to me as to why Carbon-12 and Carbon-13 have the same amount of particles that is (6.02 x 10^23) when Carbon-13 has a greater mass than Carbon-12?

It is briefly explained in the attached document, but I don't exactly get as to why 12 grams was chosen to analyse the number of particles in a mole

Thanks so much

[Erutepa]

Hi Guys,

Could you please explain to me as to why Carbon-12 and Carbon-13 have the same amount of particles that is (6.02 x 10^23) when Carbon-13 has a greater mass than Carbon-12?

It is briefly explained in the attached document, but I don't exactly get as to why 12 grams was chosen to analyse the number of particles in a mole

Thanks so much

I think what this attached documents is saying is that the mole is defined as the amount of carbon-12 atoms in 12g of carbon 12. The document is saying that 12g of carbon 12 was chosen as 12g is the same number as its mas number and isotopic mass (basically 12 was a nice number to pick).
Since there are aprox. 6.02X10^23 atoms in 12g of carbon-12, this is the definition of the mole. That is to say, 1 mole of a element is 6.02X10^23 atoms.
For carbon-13, each atom has a greater mass due to the additional neutron, as such one mole of carbon-13 (which is the same number of atoms as 1 mole of carbon-12) will have a greater mass. If this is confusing, it can help to substitute the concept of a mole with the concept of a dozen. A dozen 10g balls will have a greater collective mass than a dozen 9g balls. Here a mole is essentially functioning the same a 'a dozen' it is simply a particular number of things. Where a dozen is 12 things - a mole is 6.02X10^23 things.

As an interesting side note, this is no longer how the mole is defined! You do not need to know this however for VCE chem

[cutiepie30]

I think what this attached documents is saying is that the mole is defined as the amount of carbon-12 atoms in 12g of carbon 12. The document is saying that 12g of carbon 12 was chosen as 12g is the same number as its mas number and isotopic mass (basically 12 was a nice number to pick).
Since there are aprox. 6.02X10^23 atoms in 12g of carbon-12, this is the definition of the mole. That is to say, 1 mole of a element is 6.02X10^23 atoms.
For carbon-13, each atom has a greater mass due to the additional neutron, as such one mole of carbon-13 (which is the same number of atoms as 1 mole of carbon-12) will have a greater mass. If this is confusing, it can help to substitute the concept of a mole with the concept of a dozen. A dozen 10g balls will have a greater collective mass than a dozen 9g balls. Here a mole is essentially functioning the same a 'a dozen' it is simply a particular number of things. Where a dozen is 12 things - a mole is 6.02X10^23 things.

As an interesting side note, this is no longer how the mole is defined! You do not need to know this however for VCE chem

Thanks So Much, its makes so much sense now