Predictions for Chemistry 2014 HSC? (6 Viewers)

[iStudent]

Secchi disk looks like this http://friendsofgulfstvincent.org.au/wp-content/uploads/2012/10/Secchi-disk.jpg

You pretty much lower the disk until the 4 quadrants are no longer visible/distinguishable and then you measure the length of the rope required to achieve this and hence turbidity is determined quantitatively

I agree. I would say turbidity qualitative tests is just looking at a sample of water lol. (and classifying as turbid, not turbid clear etc)

 

[SuchSmallHands]

So all I need to do is change mine to Br2 (aq) ?

or is it a different molecule?

Nope, just change the state (you can change the molecule but it gets harder to remember, and HSC markers accept either, so it's much easier to just put aq).

 

[SuchSmallHands]

I agree. I would say turbidity qualitative tests is just looking at a sample of water lol. (and classifying as turbid, not turbid clear etc)

That was all I could think of too, that's so funny though.

 

[enigma_1]

LOL ok someone have fun with this:

QZP have a go or something if you want.

Explain the procedure of measuring Biochemical Oxygen Demand in waterways and reasons for monitoring BOD (4 marks)

 

[QZP]

Alright. Cools!

I have some stuff to clear up: "Discuss the potential of cellulose as a raw material in the petrochemical industry"
So focusing on the cellulose decomposition to glucose --> fermentation to ethanol --> dehydration to ethylene
I know first and 3rd step is uneconomical due to amounts of energy required (is that right for the 3rd step?)
What about fermentation? Is there also a limiting factor there

 

[GOsie]

guys no it's actually a quantitative test, please see the above explanation.
I can understand why it would be deemed as qualitative however realistically the only qualitative test is if the water looks brown or murky. But secchi disk is quantitative

Isn't it qualitative because different people will see it at different lengths. It requires the human eye to determine how deep it should go. To me that sounds like a quality. You may be right though.

 

[enigma_1]

Alright. Cools!

I have some stuff to clear up: "Discuss the potential of cellulose as a raw material in the petrochemical industry"So focusing on the cellulose decomposition to glucose --> fermentation to ethanol --> dehydration to ethylene
I know first and 3rd step is uneconomical due to amounts of energy required (is that right for the 3rd step?)
What about fermentation? Is there also a limiting factor there

Yes as SSH corrected me previously, there is the requirement of maintaining the conditions for fermentation which require energy which is presently obtained from fossil fuels, furthermore for crop harvesting - the energy is also required. Since this is obtained from the burning of fossil fuels (non-renewable resource) it's technically bad and not really helping the environment. Also, the distillation of ethanol after fermentation to obtain concentrations of ~95% requires the same energy, so hence making it not economically viable.

Btw iff you get that question in an exam you would have to go through the advantages and disadvantages. Does someone wanna have a crack at it whilst we're on the topic anyway? ))

 

[SuchSmallHands]

LOL ok someone have fun with this:

QZP have a go or something if you want.

Explain the procedure of measuring Biochemical Oxygen Demand in waterways and reasons for monitoring BOD (4 marks)

It's actually really sweet of you to underline key terms for us, thanks

BOD is measured using the BOD 5 day standard, which determines the amount (in milligrams) of oxygen consumed by one litre of water during 5 days in the dark at 20 degrees celsius. Dissolved oxygen (DO) is measured at the start and end of the period, with the difference between the two values being cited as the BOD. It is important to monitor BOD as it is an indication of the amount of organic waste which pollutes a waterway. A high BOD value indicates high levels of such pollution, and thus the water must be filtered before it is fit for human consumption. High levels of organic pollution, as indicated by a high BOD, can also cause waterways to become hypoxic, and thus not conducive to the lives of aquatic organisms. Thus, to preserve the habitats of such organisms it is important that BOD is monitored and and managed.

 

[QZP]

Yes as SSH corrected me previously, there is the requirement of maintaining the conditions for fermentation which require energy which is presently obtained from fossil fuels, furthermore for crop harvesting - the energy is also required. Since this is obtained from the burning of fossil fuels (non-renewable resource) it's technically bad and not really helping the environment. Also, the distillation of ethanol after fermentation to obtain concentrations of ~95% requires the same energy, so hence making it not economically viable.

Btw iff you get that question in an exam you would have to go through the advantages and disadvantages. Does someone wanna have a crack at it whilst we're on the topic anyway? ))

- Energy of fermentation from fossil fuels? What!? It isn't an energy intensive process
- What do you mean crop harvesting involves burning fossil fuels lol

 

[SuchSmallHands]

I do not type fast enough to keep up with you guys haha

 

[SuchSmallHands]

- Energy of fermentation from fossil fuels? What!? It isn't an energy intensive process
- What do you mean crop harvesting involves burning fossil fuels lol

Well I mean if you want to go out with your sickle and manually harvest corn be my guest man. And it requires some energy to maintain conditions at 37 degrees celsius, since that's not exactly the average room temperature.

 

[enigma_1]

- Energy of fermentation from fossil fuels? What!? It isn't an energy intensive process
- What do you mean crop harvesting involves burning fossil fuels lol

Well I mean if you want to go out with your sickle and manually harvest corn be my guest man. And it requires some energy to maintain conditions at 37 degrees celsius, since that's not exactly the average room temperature.

yeah defs.

But QZP bro don't go too much out of the syllabus.
Do you wanna try writing a model answer?

Or anyone??

 

[QZP]

LOL ok someone have fun with this:

QZP have a go or something if you want.

Explain the procedure of measuring Biochemical Oxygen Demand in waterways and reasons for monitoring BOD (4 marks)

- BOD measures the biological activity of aerobic organisms (e.g. bacterial decomposition of organic waste) and is affected by many factors including TDS, pH, etc.
- Thus, BOD provides an evaluation of water quality as an optimally BOD indicates a healthy aquatic ecosystem. Excessively high BOD may indicate eutrophication or contamination from agricultural run-off. Hence the importance of monitoring BOD

BOD5 test:
- 2 samples of water taken
- The DO of one is immediately measured (e.g. using oxygen sensor), whilst the other is stored in a dark location @ 20deg.
- After 5 days, the DO of the second sample is measured to give a measurement of BOD in used DO/5days

 

[QZP]

Well I mean if you want to go out with your sickle and manually harvest corn be my guest man. And it requires some energy to maintain conditions at 37 degrees celsius, since that's not exactly the average room temperature.

What's with the tone? Genuine question how do you harvest crops? I thought it was all mechanical...

 

[SuchSmallHands]

Isn't it qualitative because different people will see it at different lengths. It requires the human eye to determine how deep it should go. To me that sounds like a quality. You may be right though.

Yo get a result in units though, a numerical result that indicates the degree to which the water is turbid. It's not just 'yes, the water is turbid' or 'no, the water is not turbid'. It's a (crappy) quantitative test that is prone to inaccuracy (I have crap eyesight ad couldn't see the damn mark after like 2mL of water was added in class) but it's still a quantitative test.

 

[SuchSmallHands]

What's with the tone? Genuine question how do you harvest crops? I thought it was all mechanical...

The engines that run those machines (tractors, etc.) use fossil fuels. Sorry if I sounded rude, I just thought it wasn't nice to indicate that you were laughing at someone else's answer when what they said was actually completely correct.

 

[enigma_1]

- BOD measures the biological activity of aerobic organisms (e.g. bacterial decomposition of organic waste) and is affected by many factors including TDS, pH, etc.
- Thus, BOD provides an evaluation of water quality as an optimally BOD indicates a healthy aquatic ecosystem. Excessively high BOD may indicate eutrophication or contamination from agricultural run-off. Hence the importance of monitoring BOD

BOD5 test:
- 2 samples of water taken
- The DO of one is immediately measured (e.g. using oxygen sensor), whilst the other is stored in a dark location @ 20deg.
- After 5 days, the DO of the second sample is measured to give a measurement of BOD in DO/5days

Yeah that's pretty good 4/4

You can also add in stuff lyk why high BOD is bad. eg a high BOD is indicative of a low dissolved oxygen content in the water because it is quickly used up by bacteria/organisms which use respire/use oxygen. This can lead to a eutrophication (containing nitrates and phosphates) and cyanobacteria which has a high BOD making the water unusable for any purposes.
Unpolluted water has BOD of less than 5 ppm and can be used.

 

[QZP]

Yeah definitely needed why high BOD is bad

 

[enigma_1]

anyone got questions to post?

 

[QZP]

Describe the nebulisation of the prepared solution and explain the need for the flame in AAS (3)