Predictions for Chemistry 2014 HSC? (9 Viewers)

[faisalabdul16]

New question :

Discuss the advantages and disadvantages of using models in chemistry. Use examples to illustrate your answer. 6 marks

 

[SuchSmallHands]

I would have done this totally differently to everyone (again, monitoring and management/water quality not my strong suit). Would this approach have been wrong?
Microscopic membrane filtration canbe used to remove unwanted species as small as ions from a water supply. As the membrane pore size decreases, the filter becomes more efficient at removing smaller contaminants, however the use of such filters becomes less cost effective as pore size decreases.
Microfiltration (100-1000 nm pore size) is effective at removing silt, colloids and a variety of bacteria. It is commonly used in rural treatment plants with less extensive purification facilities. It is the most economical form of MMF.
Ultrafiltration (100-5 nm pore size) is highly effective at removing a greater variety of microbes, including viruses, and improving water colour. The addition of a surfactant coating also enables removal of ions from the water. It is more costly than microfiltration, but also more effective in microbe removal, which makes water more suitable for human consumption. Thus it is effective in optimising the potability of water.
Nanofiltration(0.5-5 nm pore size) is effective in purifying water when that absence of contaminants is highly important (eg in renal dialysis). It is also effective in reducing concentration of Ca2+ and Mg2+ ions in hard water at a lower cost than reverse osmosis.
Reverse osmosis is an effective method for desalination purposes. Adequate pressure is applied to overcome osmotic pressure and force water through a semi permiable membrane of 0.1 to 1 nm from a region of high solute concentration to one of low solute concentration. While it is highly effective in removing ions from water, it is a less cost efficient mechanism of achieving this purpose than smaller pore MMF.
Thus, the degree of effectiveness of various forms of MMF vary depending upon pore size and desired expenditure or equipment access. However, MMF has the capacity to be an extremely efficient, if costly, mechanism of removing contaminants as small as ions from solution.

 

[faisalabdul16]

I would have done this totally differently to everyone (again, monitoring and management/water quality not my strong suit). Would this approach have been wrong?
Microscopic membrane filtration canbe used to remove unwanted species as small as ions from a water supply. As the membrane pore size decreases, the filter becomes more efficient at removing smaller contaminants, however the use of such filters becomes less cost effective as pore size decreases.
Microfiltration (100-1000 nm pore size) is effective at removing silt, colloids and a variety of bacteria. It is commonly used in rural treatment plants with less extensive purification facilities. It is the most economical form of MMF.
Ultrafiltration (100-5 nm pore size) is highly effective at removing a greater variety of microbes, including viruses, and improving water colour. The addition of a surfactant coating also enables removal of ions from the water. It is more costly than microfiltration, but also more effective in microbe removal, which makes water more suitable for human consumption. Thus it is effective in optimising the potability of water.
Nanofiltration(0.5-5 nm pore size) is effective in purifying water when that absence of contaminants is highly important (eg in renal dialysis). It is also effective in reducing concentration of Ca2+ and Mg2+ ions in hard water at a lower cost than reverse osmosis.
Reverse osmosis is an effective method for desalination purposes. Adequate pressure is applied to overcome osmotic pressure and force water through a semi permiable membrane of 0.1 to 1 nm from a region of high solute concentration to one of low solute concentration. While it is highly effective in removing ions from water, it is a less cost efficient mechanism of achieving this purpose than smaller pore MMF.
Thus, the degree of effectiveness of various forms of MMF vary depending upon pore size and desired expenditure or equipment access. However, MMF has the capacity to be an extremely efficient, if costly, mechanism of removing contaminants as small as ions from solution.

I think it's a good answer. 4/4

Give a question?

I want to write an answer too -.- I am also sitting the HSC this year hahahaha

 

[enigma_1]

I think it's a good answer. 4/4

Give a question?

I want to write an answer too -.- I am also sitting the HSC this year hahahaha

Also if you have time sketch a quick diagram of MMF next to it.

I'm trying to think of a really hard question for you coz your answers are beastly.

 

[faisalabdul16]

Also if you have time sketch a quick diagram of MMF next to it.

I'm trying to think of a really hard question for you coz your answers are beastly.

hahaha!
I've honestly realised that this thread has been the best chemistry study. Not only are we giving weird/long questions, we are critiquing the answers we provide and improving them.

 

[QZP]

What equations do you use to show ozone acting as a UV shield in stratosphere? My notes has 4 equations (2 for formation of ozone, 2 for destruction of ozone) which seems too much to write in an exam

 

[faisalabdul16]

What equations do you use to show ozone acting as a UV shield in stratosphere? My notes has 4 equations (2 for formation of ozone, 2 for destruction of ozone) which seems too much to write in an exam

Are you talking about these 2?

O3 + UV ----> O2 + O.

O. + O2 -----> O3

 

[QZP]

I learnt
- Formation of ozone:
O2 + UV --> 2O.
O2 + O. --> O3

- Destruction of ozone:
O3 + UV --> O2 + O.
O3 + O. --> 2O2

Both involve absorbing UV hence ozone is a UV radiation shield.

A relevant Q: Are we meant to put states on these!!??

 

[QZP]

Another quick Q: What is the significance of halons in the syllabus? Would you talk about them in an extended response? (I've only seen the discussion of CFC's, HCFC's and HFC's)

Anyone have questions relating to halons?

 

[faisalabdul16]

I learnt
- Formation of ozone:
O2 + UV --> 2O.
O2 + O. --> O3

- Destruction of ozone:
O3 + UV --> O2 + O.
O3 + O. --> 2O2

Both involve absorbing UV hence ozone is a UV radiation shield.

A relevant Q: Are we meant to put states on these!!??

well ozone and oxygen is just gases so there easy to put. The rest you don't for obvious reasons.

 

[QZP]

well ozone and oxygen is just gases so there easy to put. The rest you don't for obvious reasons.

Why not? I'm pretty sure we put gaseous state on all of them

 

[faisalabdul16]

Another quick Q: What is the significance of halons in the syllabus? Would you talk about them in an extended response? (I've only seen the discussion of CFC's, HCFC's and HFC's)

Anyone have questions relating to halons?

I don't think they directly ask you questions about halons because all they are, are brominated haloalkanes.

Halons are like any chlorofluorocarbons, they cause ozone depletion.

You don't really have to know this imo, but wouldn't kill just to know what a halon is.

 

[faisalabdul16]

Why not? I'm pretty sure we put gaseous state on all of them

Many papers (sample answers) only put the state for the ozone or the oxygen.

I've seen it in past hsc papers as well, they're not too pedantic about the states in these equations.

 

[SuchSmallHands]

Another quick Q: What is the significance of halons in the syllabus? Would you talk about them in an extended response? (I've only seen the discussion of CFC's, HCFC's and HFC's)

Anyone have questions relating to halons?

Here's what I have in my notes for halons: halons have been considered as replacements for CFCs as they act as effective propellants. However, their ozone depletion value exceeds that of CFCs, and this their use would act to the detriment of stratospheric ozone concentrations in an even greater degree than CFCs. (I wrote about halons for the dot point on an assesment of possible/debated alternatives to CFCs, so if talk about them only if the question was something along those lines).

 

[faisalabdul16]

Here's what I have in my notes for halons: halons have been considered as replacements for CFCs as they act as effective propellants. However, their ozone depletion value exceeds that of CFCs, and this their use would act to the detriment of stratospheric ozone concentrations in an even greater degree than CFCs. (I wrote about halons for the dot point on an assesment of possible/debated alternatives to CFCs, so if talk about them only if the question was something along those lines).

Just remember this, halons are like chlorofluorocarbons but also contain bromine. Now, in regards to strength or the most 'dangerous' form of ozone depletion is caused by bromine followed by chlorine. Fluorine, is ozone friendly.

The only part you really need to know is the definition of a halon and then everything else is the same. Bromine causes ozone depletion however to a greater extent than chlorine blah blah blah blah blah thats it.

 

[QZP]

I don't think halons were considered as replacements for CFC's... I only know they were used in fire extinguishers :S And also they have significantly higher ozone depleting potentials as f16 called out

 

[SuchSmallHands]

Just remember this, halons are like chlorofluorocarbons but also contain bromine. Now, in regards to strength or the most 'dangerous' form of ozone depletion is caused by bromine followed by chlorine. Fluorine, is ozone friendly.

The only part you really need to know is the definition of a halon and then everything else is the same. Bromine causes ozone depletion however to a greater extent than chlorine blah blah blah blah blah thats it.

I was under the impression that halons were halogenated, not necessarily brominated. Many don't contain bromine (eg Halon 10001)

 

[QZP]

There's a dotpoint about analysing information indicating changes in atmospheric ozone concentrations and describing the changes. Obviously there is a clear decrease in ozone concentration during the use of CFC's and stuff, but what is the general consensus today? (This relates to evaluate the effectiveness of steps taken to alleviate problems...)

I've heard people say that yes, high effectiveness and ozone layer is regenerating
BUT ALSO i've seen (and this is my stance also) that there is minimal regeneration of ozone layer due to the longevity of ozone depleting substances (recall regeneration of Cl. in CFC's)

 

[QZP]

I was under the impression that halons were halogenated, not necessarily brominated. Many don't contain bromine (eg Halon 10001)

Nice. So is CFC's a subset of halons?

 

[QZP]

How much do we have to know about the ozone hole at Antarctica during Spring e.g. its cause? I don't see any reference to it in the syllabus but all textbooks go into it...