HSC 2012-2015 Chemistry Marathon (archive) (1 Viewer)

[Mr_Kap]

re: HSC Chemistry Marathon Archive

Outline the processes used to determine the amount of sulfate present in a sample of lawn fertilizer. (5 marks)

An outline like this wouldn't be worth 5 marks. Maybe 4 marks.


The question should be,

"Outline the processes used to determine the amount of sulfate present in a sample of lawn fertiliser, and justify the use of 2 of these processes." (5 marks)

 

[BlueGas]

re: HSC Chemistry Marathon Archive

An outline like this wouldn't be worth 5 marks. Maybe 4 marks.


The question should be,

"Outline the processes used to determine the amount of sulfate present in a sample of lawn fertiliser, and justify the use of 2 of these processes." (5 marks)

Fair enough, I'd like to see someone answer this.

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

Fair enough, I'd like to see someone answer this.

Yeah its one thing i didnt pay attention too...

 

[Mr_Kap]

re: HSC Chemistry Marathon Archive

Yeah its one thing i didnt pay attention too...

*to

 

[BlueGas]

re: HSC Chemistry Marathon Archive

Yeah its one thing i didnt pay attention too...

So you're just ignoring this experiment? lol.

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

Post your answer -.-

 

[BlueGas]

re: HSC Chemistry Marathon Archive

Post your answer -.-

I put this question up for a reason lol, so I can know the answer.

 

[Mr_Kap]

re: HSC Chemistry Marathon Archive

I put this question up for a reason lol, so I can know the answer.

We need ekman.

 

[Kaido]

re: HSC Chemistry Marathon Archive

Weighed out 1.0 g of fertiliser into a beaker, added dilute hydrochloric acid solution and then stirred. 50.0 mL of 0.350 mol L-1 barium chloride solution was then added. A white precipitate of barium sulfate formed. Washed the precipitate, filtered it, left it to dry and then determined the weight of the precipitate to be ___
Ba2+ (aq) + SO42- (aq) -> BaSO4 (s)

Justfication: HCl coz u wanna get rid of the other ions and shit, all the washing/filtering/drying coz u want it to be valid (i.e. no extra goddamn water to affect ur calc)

And your usual calculations

Oh fk, this was a question ages ago ahahaha

 

[Fizzy_Cyst]

re: HSC Chemistry Marathon Archive

*to

Irony that the 'your' should be 'you're' ?

 

[BlueGas]

re: HSC Chemistry Marathon Archive

Weighed out 1.0 g of fertiliser into a beaker, added dilute hydrochloric acid solution and then stirred. 50.0 mL of 0.350 mol L-1 barium chloride solution was then added. A white precipitate of barium sulfate formed. Washed the precipitate, filtered it, left it to dry and then determined the weight of the precipitate to be ___
Ba2+ (aq) + SO42- (aq) -> BaSO4 (s)

Justfication: HCl coz u wanna get rid of the other ions and shit, all the washing/filtering/drying coz u want it to be valid (i.e. no extra goddamn water to affect ur calc)

And your usual calculations

Oh fk, this was a question ages ago ahahaha

Can someone word this in a better way?

 

[BlueGas]

re: HSC Chemistry Marathon Archive

Quick question, when cellulose is insoluble, does that mean cellulose is insoluble in water only?

 

[Mr_Kap]

re: HSC Chemistry Marathon Archive

Quick question, when cellulose is insoluble, does that mean cellulose is insoluble in water only?

insoluble in everything because it has strong intermolecular forces (h-bonds), and it is a large chained molecule,
meaning it cannot be dissolved.

IDK that's why i think.

 

[Kaido]

re: HSC Chemistry Marathon Archive

Quick question, when cellulose is insoluble, does that mean cellulose is insoluble in water only?

In the context of HSC, you will only be posed the solubility of cellulose in water
(Althoguh, if you do shipwrecks, you learn about wooden structures (complex structure material) and how it will "rot" in water and stuff)

 

[Kaido]

re: HSC Chemistry Marathon Archive

Can someone word this in a better way?

It's a pretty good explanation imo

 

[BlueGas]

re: HSC Chemistry Marathon Archive

Quick question, how to test for the presence of phosphate in a solution?

 

[BlueGas]

re: HSC Chemistry Marathon Archive

Another quick question, is the answer A for this question?

 

[rand_althor]

re: HSC Chemistry Marathon Archive

Another quick question, is the answer A for this question?

I think it isn't, as you want the chloride to form a precipitate after everything else has been removed. If you add Silver nitrate first, it will react with the chloride to form Silver chloride, a white precipitate. Not sure what adding Sulfuric acid does besides adding more sulfate ions, but adding Barium sulfate, another precipitate, to the solution would then cause problems in determining the amount of Silver chloride present.

I would say the answer is D. Adding Nitric acid allows you to remove carbonate ions through effervescence. Adding Barium nitrate then causes Barium sulfate to form, which can be filtered out. Finally adding Silver nitrate would cause Silver chloride to form, which can be filtered out, weighed etc.

 

[BlueGas]

re: HSC Chemistry Marathon Archive

I think it isn't, as you want the chloride to form a precipitate after everything else has been removed. If you add Silver nitrate first, it will react with the chloride to form Silver chloride, a white precipitate. Not sure what adding Sulfuric acid does besides adding more sulfate ions, but adding Barium sulfate, another precipitate, to the solution would then cause problems in determining the amount of Silver chloride present.

I would say the answer is D. Adding Nitric acid allows you to remove carbonate ions through effervescence. Adding Barium nitrate then causes Barium sulfate to form, which can be filtered out. Finally adding Silver nitrate would cause Silver chloride to form, which can be filtered out, weighed etc.

Reading over the answer I chose, I'm not sure why I actually chose A lol, why would you want to add barium sulfate to sulfate? haha.

 

[leehuan]

re: HSC Chemistry Marathon Archive

Quick question, how to test for the presence of phosphate in a solution?

When performing anion tests, always add HNO3 to expel off any CO3(2-) which may affect results.

However, after that, firstly add Ba(NO3)2 to the solution. There should be no reaction, as BaHPO4 is soluble.

Now, consider the following acid and conjugate base.
HPO4(2-) + H2O <--> PO4(3-) + H3O(+)

Note that in acidic solution (acidic due to the HNO3 in the mixture), the concentrations of HPO4(2-) will increase. However conversely, in alkaline solution the concentrations of PO4(3-) will increase. [Le Chatelier's principle states that if a system at equilibrium is disturbed, it will seek to shift its equilibrium in an attempt to minimise the disturbance.] If we basify the solution by adding NH3, then the concentrations of PO4(3-) will increase, which is good. This is because Ba3(PO4)2 is relatively insoluble.

Therefore addition of ammonia will show the precipitate (experimentally I've found it to be pale blue) and this is a test for PO4(3-)