Unit 3 Questions MEGATHREAD :)

[RobM8]

Why can't non-metals be analysed by AAS?

They absorb and emit light/radiation that is not in the visible part of the electromagnetic spectrum.

[scocliffe09]

Why can't non-metals be analysed by AAS?

They absorb and emit light/radiation that is not in the visible part of the electromagnetic spectrum.

That's not necessarily true...
It's more to do with the fact that we can't produce Hollow Cathode Lamps for them (and this is the hallmark of AAS that gives it specificity and accuracy) and that we might not be able to vaporise them successfully. e.g. most organic chemicals will be combusted by a flame!

[RobM8]

Why can't non-metals be analysed by AAS?

They absorb and emit light/radiation that is not in the visible part of the electromagnetic spectrum.

That's not necessarily true...
It's more to do with the fact that we can't produce Hollow Cathode Lamps for them (and this is the hallmark of AAS that gives it specificity and accuracy) and that we might not be able to vaporise them successfully. e.g. most organic chemicals will be combusted by a flame!

I always was told that they didn't produce visible light by our teacher - that is a worry.
Why is it that we can't produce Hollow Cathode Lamps for non-metals ?

[nacho]

Why can't non-metals be analysed by AAS?

They absorb and emit light/radiation that is not in the visible part of the electromagnetic spectrum.

That's not necessarily true...
It's more to do with the fact that we can't produce Hollow Cathode Lamps for them (and this is the hallmark of AAS that gives it specificity and accuracy) and that we might not be able to vaporise them successfully. e.g. most organic chemicals will be combusted by a flame!

I always was told that they didn't produce visible light by our teacher - that is a worry.
Why is it that we can't produce Hollow Cathode Lamps for non-metals ?

I think it may have something to do with electrical conductivity, pretty sure we don't need to know why though, it would seem like we're dwelling back into unit 1 and 2 and going ahead to 4..

edit:
Why is the light in AAS pulsed?

[jane1234]

Why can't non-metals be analysed by AAS?

They absorb and emit light/radiation that is not in the visible part of the electromagnetic spectrum.

That's not necessarily true...
It's more to do with the fact that we can't produce Hollow Cathode Lamps for them (and this is the hallmark of AAS that gives it specificity and accuracy) and that we might not be able to vaporise them successfully. e.g. most organic chemicals will be combusted by a flame!

I always was told that they didn't produce visible light by our teacher - that is a worry.
Why is it that we can't produce Hollow Cathode Lamps for non-metals ?

I think it may have something to do with electrical conductivity, pretty sure we don't need to know why though, it would seem like we're dwelling back into unit 1 and 2 and going ahead to 4..

edit:
Why is the light in AAS pulsed?

To differentiate between the light absorbed by the sample and the light emitted from the sample, as they will be of the same wavelength.

[tony3272]

Why can't non-metals be analysed by AAS?

They absorb and emit light/radiation that is not in the visible part of the electromagnetic spectrum.

That's not necessarily true...
It's more to do with the fact that we can't produce Hollow Cathode Lamps for them (and this is the hallmark of AAS that gives it specificity and accuracy) and that we might not be able to vaporise them successfully. e.g. most organic chemicals will be combusted by a flame!

I always was told that they didn't produce visible light by our teacher - that is a worry.
Why is it that we can't produce Hollow Cathode Lamps for non-metals ?

I think it may have something to do with electrical conductivity, pretty sure we don't need to know why though, it would seem like we're dwelling back into unit 1 and 2 and going ahead to 4..

edit:
Why is the light in AAS pulsed?

It's pulsed so that light which is emitted when the electron moves back from it's excited state is not read by the detector, I think.

[nacho]

thanks,
did we need to know that each amino acid is coded by 3 bases?
It came up in a neap exam

[luken93]

thanks,
did we need to know that each amino acid is coded by 3 bases?
It came up in a neap exam

Pretty sure we don't, I thought the exact same thing!

[tony3272]

thanks,
did we need to know that each amino acid is coded by 3 bases?
It came up in a neap exam

Lol i have no idea what that is...
It seems more bio than chem. (btw which neap exam? I don't think i've seen that question)

[nacho]

thanks,
did we need to know that each amino acid is coded by 3 bases?
It came up in a neap exam

Pretty sure we don't, I thought the exact same thing!

these exam companies should never ever put things outside the syllabus.. it's completely demotivating and makes you think that you've missed out on some major aspect, or which wasnt covered by the textbook..

[Keo]

thanks,
did we need to know that each amino acid is coded by 3 bases?
It came up in a neap exam

Pretty sure we don't, I thought the exact same thing!

these exam companies should never ever put things outside the syllabus.. it's completely demotivating and makes you think that you've missed out on some major aspect, or which wasnt covered by the textbook..

I guess that's how these companies make money, make students think that harder questions which are totally irrelevant to the study design are actually better  :tickedoff:

[jane1234]

- (Yet another sig fig question): When working out volumes of gases, does the number of significant figures in the temperature matter (using the nRT=PV formula)??

- Also, when writing combustion equations, is it acceptable to write the organic compound in the gaseous (g) state?

[luken93]

- (Yet another sig fig question): When working out volumes of gases, does the number of significant figures in the temperature matter (using the nRT=PV formula)??

- Also, when writing combustion equations, is it acceptable to write the organic compound in the gaseous (g) state?

Ummm, well I suppose it does, however when you are converting from celcius to kelvin, it'll be say 25 + 273 = 298. Addition means to the least number of DECIMAL places...

As for combustion, I thought all of the reactants and products were (g) ? Grr I hate states!

[scocliffe09]

- (Yet another sig fig question): When working out volumes of gases, does the number of significant figures in the temperature matter (using the nRT=PV formula)??

- Also, when writing combustion equations, is it acceptable to write the organic compound in the gaseous (g) state?

Ummm, well I suppose it does, however when you are converting from celcius to kelvin, it'll be say 25 + 273 = 298. Addition means to the least number of DECIMAL places...

As for combustion, I thought all of the reactants and products were (g) ? Grr I hate states!

Seriously guys, chill about sig figs. In the sf question, VCAA should make it pretty clear what's going on. And temperature is a bit of a contentious topic. My advice would be include it in your considerations but don't forget Luke's point.
Combustion is safest when written with gaseous states. depending on other reaction conditions, other states might be acceptable. For example, it is common for liquid water to form on the inside of a test tube so I don't see why writing (l) for water would be wrong.

[thatricksta]

- (Yet another sig fig question): When working out volumes of gases, does the number of significant figures in the temperature matter (using the nRT=PV formula)??

- Also, when writing combustion equations, is it acceptable to write the organic compound in the gaseous (g) state?

Just DO NOT write aqueous and you should be ok.
Also, it's unlikely something like this would be asked, but if you were asked for the combustion of glucose (organic molecule), it would be solid, but that is common sense and I am sure you wouldn't write glucose as a gaseous state before combustion... xD

Question:
Do we need to include heat above the arrow of our equation for combustion reactions?