Predictions for Chemistry 2014 HSC? (8 Viewers)

[SuchSmallHands]

Anyone can answer bold?

Another Q: Describe how hydrogen and nitrogen gas is obtained for the Haber Process (3)

Nitrogen: fixed from air
Hydrogen: don't know, could be the same. Either way I don't think this is on our syllabus.

For colloids, I assume they're talking hydrocolloids (hydrophilic polymers in water). Polymers can act as a film-like surface coating.

 

[faisalabdul16]

Nitrogen: fixed from air
Hydrogen: don't know, could be the same. Either way I don't think this is on our syllabus.

For colloids, I assume they're talking hydrocolloids (hydrophilic polymers in water). Polymers can act as a film-like surface coating.

I also couldn't find specific dot points targeting where and how hydrogen and nitrogen is extracted.

 

[QZP]

Yeah but its weird how all textbooks go into it :{ Probably should know it as extra info to cover grounds

 

[SuchSmallHands]

Yeah but its weird how all textbooks go into it :{ Probably should know it as extra info to cover grounds

Can't see how it would hurt, but it will never be asked directly as it was in that question (inb4 that exact question appears on our HSC). Out of curiosity, where do we get the hydrogen from? Is it from factional distillation of liquefied air like the nitrogen?

 

[faisalabdul16]

Did anyone do my calculation question?
hydrogen is obtained by reacting natural gas with steam, or from cracking oil fractions

 

[QZP]

Can't see how it would hurt, but it will never be asked directly as it was in that question (inb4 that exact question appears on our HSC). Out of curiosity, where do we get the hydrogen from? Is it from factional distillation of liquefied air like the nitrogen?

Simple version is that N2 is sourced from air via chemical filtration (air passed through chemicals such that O2, etc. is removed) and CO2 is sourced by methane + steam --> CO + H2 (the CO undergoes a further catalytic conversion to CO2).

Jacaranda says its expensive (implying lacking economic feasibility) to extract N2 from air using fractional distillation of liquefied air so avoid it

 

[SuchSmallHands]

Did anyone do my calculation question?
hydrogen is obtained by reacting natural gas with steam, or from cracking oil fractions

No, I'll try it now

 

[SuchSmallHands]

Okay the way I worked that out seems a little unusual. I got 71.9%w/w but I probably got it wrong

 

[SuchSmallHands]

Do you have an answer for the calc?

 

[faisalabdul16]

Do you have an answer for the calc?

What you got is correct.
And I'm sure you did it my way because I also found it very unusual

 

[SuchSmallHands]

What you got is correct.
And I'm sure you did it my way because I also found it very unusual

What a weird question... All that stuff about the precipitate was totally unnecessary, you just played with a little stoichiometry and got the answer in like 2 minutes. That would have totally thrown me in the HSC, because I was not at all confident in that answer.

 

[faisalabdul16]

What a weird question... All that stuff about the precipitate was totally unnecessary, you just played with a little stoichiometry and got the answer in like 2 minutes. That would have totally thrown me in the HSC, because I was not at all confident in that answer.

Yeah me too! Very strange

hmmmm new question....

What is the principle behind atomic absorption spectroscopy? Discuss advantages and disadvantages associated with the use of this technology.

 

[QZP]

In AAS, the hollow cathode lamp is made with the metal being analysed. Is this validity or accuracy?

 

[faisalabdul16]

In AAS, the hollow cathode lamp is made with the metal being analysed. Is this validity or accuracy?

Validity deals with the design of the experiment, whether all variables were kept constant except for the one changing and whether it was a suitable experiment. Thereby, not having an appropriate hollow cathode lamp renders the experiment futile. Hence, it is validity.

 

[SuchSmallHands]

Yeah me too! Very strange

hmmmm new question....

What is the principle behind atomic absorption spectroscopy? Discuss advantages and disadvantages associated with the use of this technology.

This will be dodgy, apologies in advance. I hate monitoring and management and have made no notes/done no past paper questions on it (top student)

Underpinning principle: atoms will absorb quanta of light energy (photons) of particular energies, which correspond to certain wavelengths of light, in order to promote an electron from the ground state to the excited state. In AAS, an atomised sample is irradiated with light of a frequency specific to that ion emitted by a hollow cathode lamp which is similarly particular to that ion. Absorption of the frequency is detected and compared to a calibration curve in order to deduce ion concentration.

Positives
- sensitive to ppm (can be up to ppb depending on equipment quality), thus effective in accurately determining concentration of trace metals.
- idk, could be portable. seems pretty small. (warned this would be dodgy haha)

Negatives
- pain in the ass to change that bloody lamp every time you want to test for the presence of a new ion
- my school tried to see one working and we couldn't work out how to use the machine. Clearly not very user friendly and they should do something about that.

 

[QZP]

This will be dodgy, apologies in advance. I hate monitoring and management and have made no notes/done no past paper questions on it (top student)

Underpinning principle: atoms will absorb quanta of light energy (photons) of particular energies, which correspond to certain wavelengths of light, in order to promote an electron from the ground state to the excited state. In AAS, an atomised sample is irradiated with light of a frequency specific to that ion emitted by a hollow cathode lamp which is similarly particular to that ion. Absorption of the frequency is detected and compared to a calibration curve in order to deduce ion concentration.

Positives
- sensitive to ppm (can be up to ppb depending on equipment quality), thus effective in accurately determining concentration of trace metals.
- idk, could be portable. seems pretty small. (warned this would be dodgy haha)

Negatives
- pain in the ass to change that bloody lamp every time you want to test for the presence of a new ion
- my school tried to see one working and we couldn't work out how to use the machine. Clearly not very user friendly and they should do something about that.

Is this depth even needed? (My teacher warned me before about overreaching depth) I believe it is sufficient to say elements have characteristic wavelengths of light which they can absorb/emit.

 

[SuchSmallHands]

In AAS, the hollow cathode lamp is made with the metal being analysed. Is this validity or accuracy?

Well I mean it has to be both. The hollow cathode lamp contains the metal being analysed because that metal is excited in the lamp and emits light of the frequency which will be absorbed by the metal sample. If you used a different metal it just wouldn't work, so your result wouldn't be at all accurate and the test wouldn't have been valid. The 'jumps' between energy levels are quantised, the same frequency which excited one metal won't do it to another. I hope this isn't a HSC question, because it's seriously like if the question was 'In the combustion of magnesium, we perform the experiment using a bunsen burner that is turned on. Does this improve validity or accuracy?' there's seriously no other way to do it haha

 

[faisalabdul16]

This will be dodgy, apologies in advance. I hate monitoring and management and have made no notes/done no past paper questions on it (top student)

Underpinning principle: atoms will absorb quanta of light energy (photons) of particular energies, which correspond to certain wavelengths of light, in order to promote an electron from the ground state to the excited state. In AAS, an atomised sample is irradiated with light of a frequency specific to that ion emitted by a hollow cathode lamp which is similarly particular to that ion. Absorption of the frequency is detected and compared to a calibration curve in order to deduce ion concentration.

Positives
- sensitive to ppm (can be up to ppb depending on equipment quality), thus effective in accurately determining concentration of trace metals.
- idk, could be portable. seems pretty small. (warned this would be dodgy haha)

Negatives
- pain in the ass to change that bloody lamp every time you want to test for the presence of a new ion
- my school tried to see one working and we couldn't work out how to use the machine. Clearly not very user friendly and they should do something about that.

It's not portable.
Other advantages include -
- Measure the concentration of metal up to parts per billion
- Can measure the concentration of heavy metals such as lead, cadmium, mercury in water, air or soil. Results could be used by individuals to determine the severity of the pollution and to act on it accordingly.
- The advent of this technology has provided information about trace elements, which was something scientists did not fathom as gravimetric analysis (wet methods) was innaccurate.
- The advent of this technology has not only saved the lives of humans, but also the Australian agricultural industry, estimated to be worth $32 billion. AAS, has enabled scientists to comprehend that soil also require trace elements such as cobalt and other essential nutrients in order to allow for crop growth.
- other metal ions in a solution will not interfere

Disadvantages -
- The use of this technology is expensive
- scientists must know what metal they are testing for before using the machine
- very long process
- involves making numerous standard solutions to calibrate the machine
- can only test one metal at a time.
- scientists must know

 

[SuchSmallHands]

Is this depth even needed? (My teacher warned me before about overreaching depth) I believe it is sufficient to say elements have characteristic wavelengths of light which they can absorb/emit.

Oh I don't know, my teacher gives me shit for going over the top on stuff like this all the time so it might not be necessary. Your statement sounds fine to me.

 

[QZP]

goodnight friends. i will hibernate now