HSC Chemistry Question Thread

[bluecookie]

Degree of ionisation = [H+]/[Acid] x (amount of mol)/(amount of h ions) x the whole thing by 100%. How do we find the hydrogen concentration and amount of h ions?

[beau77bro]

can someone please explain this magic?? honestly no clue how you get from parts per million to g/L in the solutions

[Bubbly_bluey]

can someone please explain this magic?? honestly no clue how you get from parts per million to g/L in the solutions

Hi! ppm is the same as saying mg/L. So you just convert the milligrams to grams by divide by 1000 and that would be how many grams you have in 1L.
Hope this makes sense

[bsdfjnlkasn]

Hey there!

Still struggling with the equilibrium constant questions...

I've provided an attachment of the question and honestly thought that I was on the right track, but got the moles of O₂ after equilibrium had been established, wrong. How do I got about working this out properly?

Thank you so much!

[kiwiberry]

Hey there!

Still struggling with the equilibrium constant questions...

I've provided an attachment of the question and honestly thought that I was on the right track, but got the moles of O₂ after equilibrium had been established, wrong. How do I got about working this out properly?

Thank you so much!

Hey! The amount of NO that reacted is 0.25 - 0.05 = 0.2 mol. Because n(NO):n(NO₂) = 1:1, the amount of NO₂ formed at equilibrium will be 0.2 mol. Because n(NO):n(O₂) = 2:1, the amount of O₂ that reacted will be half that of NO, so 0.1 mol. Therefore at equilibrium, there will be 0.12 - 0.1 = 0.02 mol of O₂ left. Concentrations will be the same as moles because v=1. I find it helps to process the information by drawing an ice table

[limtou]

Hello! Please help with the following multiple choice~ Thanks!

[bsdfjnlkasn]

Hey there,

Was wondering what info I needed for the following dot point:

Process information from secondary sources to summarise the use of ethanol as an alternative car fuel, evaluating the success of current usage

What current usages do we address? I have some info on Brazil but am getting conflicting advice about how successful it was - some sources say that it was abandoned and others, really successful. I would just like to know in case we aren't given secondary sources, or so that I can know what to say if we are given them.

Thank you!!

[kiwiberry]

Hello! Please help with the following multiple choice~ Thanks!

Hello! The first question has been addressed here
For the second one, titrations can only be used to determine the concentration of an acid. The amount of base required to neutralise any monoprotic acid will be the same, regardless of their degree of ionisation, so we wouldn't be able to tell the difference in strength of HB and HA. Suppose HB is a weak acid:
As H⁺ reacts with the OH^- in NaOH, its concentration decreases, so by LCP equilibrium will continue to shift right until all its H⁺ has reacted - hence we're unable to compare its degree of ionisation with HA. The pH meter will be able to measure the concentration of H⁺ ions of the acid that dissociate in solution and therefore its degree of ionisation. And B is definitely more suitable than D to keep the experiment fair!

[kiwiberry]

Hey there,

Was wondering what info I needed for the following dot point:

Process information from secondary sources to summarise the use of ethanol as an alternative car fuel, evaluating the success of current usage

What current usages do we address? I have some info on Brazil but am getting conflicting advice about how successful it was - some sources say that it was abandoned and others, really successful. I would just like to know in case we aren't given secondary sources, or so that I can know what to say if we are given them.

Thank you!!

Hm, I've got that Brazil has had success with ethanol concentrations > 25% in fuel. Not sure about this though

[bsdfjnlkasn]

Hey there,

I'm a bit confused about how soap acts as an emulsifying agent

When the non-polar tails attach themselves to the oil so that their negatively charged heads are facing out into the water, what allows the emulsion to occur? Is it dipole-dipole interactions?

Is it also dipole-dipole interactions for when the tails are facing out? OR just dispersion forces because the tail isn't positively charged?

Sorry if this doesn't make any sense... And let me know if we don't need to know these details! But I would still like to understand - thank you!

[MisterNeo]

Hey there,

I'm a bit confused about how soap acts as an emulsifying agent

When the non-polar tails attach themselves to the oil so that their negatively charged heads are facing out into the water, what allows the emulsion to occur? Is it dipole-dipole interactions?

Is it also dipole-dipole interactions for when the tails are facing out? OR just dispersion forces because the tail isn't positively charged?

Sorry if this doesn't make any sense... And let me know if we don't need to know these details! But I would still like to understand - thank you!

Hey! I found this great guide on google that should be able to answer your question.
Basically, the non-polar tails attract to fats, and the negative head hydrogen bonds/dipoles with water to keep itself soluble in water.

[beau77bro]

Hi! ppm is the same as saying mg/L. So you just convert the milligrams to grams by divide by 1000 and that would be how many grams you have in 1L.
Hope this makes sense

I dont really understand the conversion?? like how does that work with everything having different molar weights and all?

[Sine]

can someone please explain this magic?? honestly no clue how you get from parts per million to g/L in the solutions

I dont really understand the conversion?? like how does that work with everything having different molar weights and all?

So basically it is what it sounds like - how many parts of this species is there per total million parts
Say we have 100ppm this means 100/1000000 which is 0.01%
Molar weights have nothing to do with it since we aren't calculating the mole.
ppm is mg/L and it is also g/m^3 which is g/1000L
so here we have parts per million (ppm) = mg/L = g/1000L
Now say we have 125 ppm that means 125mg/L
Let's convert 125mg to g since 1000mg is in a gram we divide by 1000 which gets us to 0.125g
which means 125ppm = 0.125g/L

With conversions it's best to do more steps and be careful since any small mistake will give you an answer that is wrong.

[jakesilove]

So basically it is what it sounds like - how many parts of this species is there per total million parts
Say we have 100ppm this means 100/1000000 which is 0.01%
Molar weights have nothing to do with it since we aren't calculating the mole.
ppm is mg/L and it is also g/m^3 which is g/1000L
so here we have parts per million (ppm) = mg/L = g/1000L
Now say we have 125 ppm that means 125mg/L
Let's convert 125mg to g since 1000mg is in a gram we divide by 1000 which gets us to 0.125g
which means 125ppm = 0.125g/L

With conversions it's best to do more steps and be careful since any small mistake will give you an answer that is wrong.

Great explanation! I always struggled with this sort of thing

[limtou]

Hello! The first question has been addressed here
For the second one, titrations can only be used to determine the concentration of an acid. The amount of base required to neutralise any monoprotic acid will be the same, regardless of their degree of ionisation, so we wouldn't be able to tell the difference in strength of HB and HA. Suppose HB is a weak acid:
As H⁺ reacts with the OH^- in NaOH, its concentration decreases, so by LCP equilibrium will continue to shift right until all its H⁺ has reacted - hence we're unable to compare its degree of ionisation with HA. The pH meter will be able to measure the concentration of H⁺ ions of the acid that dissociate in solution and therefore its degree of ionisation. And B is definitely more suitable than D to keep the experiment fair!

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