BlueGas
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HSC 2012-2015 Chemistry Marathon (archive) (3 Viewers)
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Ekman
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BlueGas
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re: HSC Chemistry Marathon Archive
It's just the table I've learnt it's abit different, for example HCl is used to test for Pb2+, but the one I've memorised is testing Pb2+ with iodide ions.
Drsoccerball
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leehuan
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re: HSC Chemistry Marathon Archive
When it comes to solubility rules, it seriously helps to know SECONDARY tests, especially when you don't have a flow chart and you're using a table like my notes have. (note: I learnt using a flow chart)
Pb(2+) - Primary -> Cl(-), Secondary (typically preferred due to colour) -> I(-)
Ba(2+) - Primary -> SO4(2-), Secondary -> Apple-green flame
Cu(2+) - Primary -> Blue-green flame, Secondary -> OH(-) ppt is blue, Tertiary -> Add NH3 to OH(-) solution and it turns a darker blue because of a complex ion
Fe - Primary -> OH(-) ppt
Distinguishing:
Fe(2+)* - OH- ppt is always brown; decolourises MnO4
Fe(3+)* - OH- ppt is supposed to be brown... but whenever I perform the experiment it appears green; if you add KSCN it forms a blood red complex ion
Hg(2+) - Primary -> Cl(-), Secondary (typically preferred due to colour) -> I(-)
Ca(2+) - Primary -> SO4(2-), Secondary -> Red flame
Alternate means to distinguish between Ba(2+) and Ca(2+) -> Add F(-), Pretty sure only CaF2 precipitates as BaF2 is sparingly insoluble. Again might be reversed.
* - These two may have info reversed. If someone knows, please confirm
Also, dud test for Cu(2+) because it doesn't necessarily always work............ the solution is blue
___________
When choosing what type of Cl(-) or I(-) to add, just be logical about it. Typically HCl and HI do no harm in comparison to NaCl and NaI. Though, one could argue NaCl or NaI (or KCl, KI) are preferred because group I metals are always soluble and are neutral cations which do not effect results.
When it comes to solubility rules, it seriously helps to know SECONDARY tests, especially when you don't have a flow chart and you're using a table like my notes have. (note: I learnt using a flow chart)
Pb(2+) - Primary -> Cl(-), Secondary (typically preferred due to colour) -> I(-)
Ba(2+) - Primary -> SO4(2-), Secondary -> Apple-green flame
Cu(2+) - Primary -> Blue-green flame, Secondary -> OH(-) ppt is blue, Tertiary -> Add NH3 to OH(-) solution and it turns a darker blue because of a complex ion
Fe - Primary -> OH(-) ppt
Distinguishing:
Fe(2+)* - OH- ppt is always brown; decolourises MnO4
Fe(3+)* - OH- ppt is supposed to be brown... but whenever I perform the experiment it appears green; if you add KSCN it forms a blood red complex ion
Hg(2+) - Primary -> Cl(-), Secondary (typically preferred due to colour) -> I(-)
Ca(2+) - Primary -> SO4(2-), Secondary -> Red flame
Alternate means to distinguish between Ba(2+) and Ca(2+) -> Add F(-), Pretty sure only CaF2 precipitates as BaF2 is sparingly insoluble. Again might be reversed.
* - These two may have info reversed. If someone knows, please confirm
Also, dud test for Cu(2+) because it doesn't necessarily always work............ the solution is blue
___________
When choosing what type of Cl(-) or I(-) to add, just be logical about it. Typically HCl and HI do no harm in comparison to NaCl and NaI. Though, one could argue NaCl or NaI (or KCl, KI) are preferred because group I metals are always soluble and are neutral cations which do not effect results.
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re: HSC Chemistry Marathon Archive
Fe3+: Reacts with sodium hydroxide to produce a red brown precipitate. Also forms a brown preciptate with ammonia. Forms a deep red colour with thiocyanate (SCN-) indicator. Does not give a specific colour in a flame test
Fe2+: forms a pale green precipitate with hydroxide. The precipitate will turn brown on standing. Will react with acidified potassium permanganate solution to remove the pink colour
Fe3+: Reacts with sodium hydroxide to produce a red brown precipitate. Also forms a brown preciptate with ammonia. Forms a deep red colour with thiocyanate (SCN-) indicator. Does not give a specific colour in a flame test
leehuan
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re: HSC Chemistry Marathon Archive
Rightio. It's acidified permangenate, as can be detected on the table of standard reduction potentials.
I had suspicions that I had those two iron ions mixed up. I just couldn't be bothered to check my notes. Thanks.
_______________________________________________
1. With the aid of relevant equations, explain how one CFC is capable of removing a significant amount of ozone in the atmosphere, until the harmful molecule is deactivated. (4)
2. Why are CFCs particularly problematic to the ozone layer over Antarctica? (2)
3. Assess the impacts of various strategies to reduce CFC emissions over the last few decades. (5)
Rightio. It's acidified permangenate, as can be detected on the table of standard reduction potentials.
I had suspicions that I had those two iron ions mixed up. I just couldn't be bothered to check my notes. Thanks.
_______________________________________________
1. With the aid of relevant equations, explain how one CFC is capable of removing a significant amount of ozone in the atmosphere, until the harmful molecule is deactivated. (4)
2. Why are CFCs particularly problematic to the ozone layer over Antarctica? (2)
3. Assess the impacts of various strategies to reduce CFC emissions over the last few decades. (5)
The second mark to Q2 is referring to how said harmful molecule can be deactivated, and why the process of deactivation is halted. I'm not sure if it will necessarily appear in an HSC exam though.
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leehuan
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re: HSC Chemistry Marathon Archive
Past theories of acids and bases tend to purely rely on what was believed to be the chemical composition of all acids and their properties. Lavoisier's theory stated that acids were substances which contained hydrogen, as he found that when compounds involving oxygen dissolved in water, they produced acidic properties, such as CO2, NO2 and P4O10. This also meant that some acids were recognised to be acids, e.g. H2SO4. However, this is now known to be significantly flawed, as some substances containing oxygen are in fact basic (e.g. Na2CO3, Na2O) and why some other acids did not contain oxygen (e.g. HCl). Davy then proposed that acids were substances that contained hydrogen through the discovery of HCl, through means of dissolving gaseous hydrogen chloride into water and producing a highly acidic solution. Davy also found that metals could displace the hydrogen in acids: Metal + Acid -> Salt + Hydrogen gas. Yet, this was also flawed because other substances such as CH4 are not acidic, yet also contain hydrogen.
Arrhenius then developed a theory that was, at the time, much more revolutionary and a more accurate definition of acids, and bases. Arrhenius showed that acids were substances that when dissolved in water, ionised to form H+ ions, and similarly for bases albeit OH- ions. Arrhenius was also able to initiate the definitions of relative strengths of acids through his theory from an understanding of degrees of ionisation, and also demonstrated how acids and bases can undergo a neutralisation process: Acid + Base -> Salt + Water. This is reasonably accurate, and is sometimes taught as a simplified model of how acids and bases work, however it did not cater for other bases such a Na2CO3 and NH3.
The most accurate definition of acids and bases was proposed by Johannes Bronsted and Thomas Lowry. The Bronsted-Lowry theory defines acids and bases in terms of their chemical behaviour, that is, acids were substances that could donate a proton/protons, whereas bases could accept them. This theory focused much more on the properties of acids and bases rather than their chemical composition and an understanding of what conjugate acids and bases were. By consideration of the ability to donate/accept H+, it was then finally understood why substances were acidic, basic or neutral. (It also led into the identification of amphiprotic species with reference conjugate acids and bases.)
Past theories of acids and bases tend to purely rely on what was believed to be the chemical composition of all acids and their properties. Lavoisier's theory stated that acids were substances which contained hydrogen, as he found that when compounds involving oxygen dissolved in water, they produced acidic properties, such as CO2, NO2 and P4O10. This also meant that some acids were recognised to be acids, e.g. H2SO4. However, this is now known to be significantly flawed, as some substances containing oxygen are in fact basic (e.g. Na2CO3, Na2O) and why some other acids did not contain oxygen (e.g. HCl). Davy then proposed that acids were substances that contained hydrogen through the discovery of HCl, through means of dissolving gaseous hydrogen chloride into water and producing a highly acidic solution. Davy also found that metals could displace the hydrogen in acids: Metal + Acid -> Salt + Hydrogen gas. Yet, this was also flawed because other substances such as CH4 are not acidic, yet also contain hydrogen.
Arrhenius then developed a theory that was, at the time, much more revolutionary and a more accurate definition of acids, and bases. Arrhenius showed that acids were substances that when dissolved in water, ionised to form H+ ions, and similarly for bases albeit OH- ions. Arrhenius was also able to initiate the definitions of relative strengths of acids through his theory from an understanding of degrees of ionisation, and also demonstrated how acids and bases can undergo a neutralisation process: Acid + Base -> Salt + Water. This is reasonably accurate, and is sometimes taught as a simplified model of how acids and bases work, however it did not cater for other bases such a Na2CO3 and NH3.
The most accurate definition of acids and bases was proposed by Johannes Bronsted and Thomas Lowry. The Bronsted-Lowry theory defines acids and bases in terms of their chemical behaviour, that is, acids were substances that could donate a proton/protons, whereas bases could accept them. This theory focused much more on the properties of acids and bases rather than their chemical composition and an understanding of what conjugate acids and bases were. By consideration of the ability to donate/accept H+, it was then finally understood why substances were acidic, basic or neutral. (It also led into the identification of amphiprotic species with reference conjugate acids and bases.)
BlueGas
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re: HSC Chemistry Marathon Archive
Anyone wanna take a shot at this question?
Describe TWO possible sources of contamination in this catchment, and assess methods that could be used for purifying the water before it reaches the town. (7 marks)
Anyone wanna take a shot at this question?
Describe TWO possible sources of contamination in this catchment, and assess methods that could be used for purifying the water before it reaches the town. (7 marks)
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Drsoccerball
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re: HSC Chemistry Marathon Archive
As the lake is near a farm run-off from rain will cause loose particles from the farm to wash into the water. These particles can increase the turbidity of the water. Since the farm uses fertilizers with nitrates and phosphates content the increase in concentrations of nitrate/phosphates would cause a rise in eutrophocation and an increase in BOD. This would make the water contaminated and subject to bacteria algae etc... Furthermore the logged native forest has a lot more loose particles than the farm and by rain and floods these become suspended in the water contaminating it. Considering all these consequences before providing for the town the water must be treated. Firstly all the larger particles/ objects are stopped by screening. After the larger particles are "filtered" out chlorination takes place in order to kill all the bacteria and organisms brought by eutrophication or other forms of sources. From this point it is possible to use a membrane filter to filter out smaller particles. The pore size of a membrane filter is that of 0.2 microns and anything larger is filtered out by passing water over the filter. This or a settling tank can be used. After the settling tank sedimentation takes place and then water is obtained. The Post-treatment of water by adding things such as chlorine fluorine etc... is added to adjust the pH and make it cleaner.
Damn i need to revise D: should stop doing maths
As the lake is near a farm run-off from rain will cause loose particles from the farm to wash into the water. These particles can increase the turbidity of the water. Since the farm uses fertilizers with nitrates and phosphates content the increase in concentrations of nitrate/phosphates would cause a rise in eutrophocation and an increase in BOD. This would make the water contaminated and subject to bacteria algae etc... Furthermore the logged native forest has a lot more loose particles than the farm and by rain and floods these become suspended in the water contaminating it. Considering all these consequences before providing for the town the water must be treated. Firstly all the larger particles/ objects are stopped by screening. After the larger particles are "filtered" out chlorination takes place in order to kill all the bacteria and organisms brought by eutrophication or other forms of sources. From this point it is possible to use a membrane filter to filter out smaller particles. The pore size of a membrane filter is that of 0.2 microns and anything larger is filtered out by passing water over the filter. This or a settling tank can be used. After the settling tank sedimentation takes place and then water is obtained. The Post-treatment of water by adding things such as chlorine fluorine etc... is added to adjust the pH and make it cleaner.
Damn i need to revise D: should stop doing maths
re: HSC Chemistry Marathon Archive
draw them all out. lol. That's what I did for one of the past HSC multiple choice questions
BlueGas
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re: HSC Chemistry Marathon Archive
I don't know how to draw them out though, that's the problem. Is it hard to explain it words on how to do it?
Drsoccerball
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re: HSC Chemistry Marathon Archive
This is how 1st in chem explained it to me. Combinations. Since the structure is 3D don't count isomers twice.
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