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

[leesh95]

re: HSC Chemistry Marathon Archive

Explain the process of electroplating?

 

[psychotropic]

re: HSC Chemistry Marathon Archive

Explain the process of electroplating?

electroplating is to coat or cover with a thin layer of metal using the basic principles of an electrolytic cell (i assume this question is for industrial chemistry)
so we have a gold anode, the glass/frame to be painted as the cathode, and a solution containing Au3+. Through the input of a voltage, we have created an electrolytic cell. At the anode
Au ----> Au3+ + 3e-
These electrons flow through an external wire connecting the anode and cathode. The negatively charged cathode now attracts the Au3+ ions.
the cathode reduces these by:
Au3+ + 3e- ----> Au.
Hence we have formed a solid gold coat on the surface of glass/another material we wanted to plate.

 

[psychotropic]

re: HSC Chemistry Marathon Archive

What are the advantages and the disadvantages of the Bronsted-Lowry theory of acids and bases?

 

[superSAIyan2]

re: HSC Chemistry Marathon Archive

AdvantageS:
- The BL theory recognised the importance of the ionising role of the solvent in determining the acidic/basic character of chemicals. Hence it could explain why hydrochloric acid is strong in aqueous soln but weak when dissolved in other solvents (E.g. diethyl)
- Also it could explain the amphiprotic nature of the hydrogen sulfate ion and the amphoteric nature of oxides such as Al2O3.
- The BL theory was based on proton exchange (acids donate p+, bases accept) and could explain why carbonates and ammonia (Which contain no hydroxide ions) exhibit basic behaviour. e.g. NH3 + H20 <----> NH4+ + OH- in this case the ammonia accepts a proton from the water molecule and is a base

Disadvantage: cant explain why substances like Al(Cl3) behaves as an acid when it cants donate protons

 

[leesh95]

re: HSC Chemistry Marathon Archive

electroplating is to coat or cover with a thin layer of metal using the basic principles of an electrolytic cell (i assume this question is for industrial chemistry)
so we have a gold anode, the glass/frame to be painted as the cathode, and a solution containing Au3+. Through the input of a voltage, we have created an electrolytic cell. At the anode
Au ----> Au3+ + 3e-
These electrons flow through an external wire connecting the anode and cathode. The negatively charged cathode now attracts the Au3+ ions.
the cathode reduces these by:
Au3+ + 3e- ----> Au.
Hence we have formed a solid gold coat on the surface of glass/another material we wanted to plate.

Is this in the industrial chemistry option?

 

[iSplicer]

re: HSC Chemistry Marathon Archive

All questions provided without a target mark value are a spectacular waste of time. Advantages/disadvantages of acid/base models can range from 2-7 marks (3~ and ~18 minutes) respectively.

Please try and keep this in mind unless you guys are doing extremely general revision and are struggling with underlying concepts to begin with.

 

[bangladesh]

re: HSC Chemistry Marathon Archive

All questions provided without a target mark value are a spectacular waste of time. Advantages/disadvantages of acid/base models can range from 2-7 marks (3~ and ~18 minutes) respectively.

Please try and keep this in mind unless you guys are doing extremely general revision and are struggling with underlying concepts to begin with.

Wouldn't call it a 'spectacular waste of time'. Most answers include dot points meaning you can expand on them if it's a 7 marker.
Plus. It's still fairly good revision.

 

[HeroicPandas]

re: HSC Chemistry Marathon Archive

Explain why ionic solids tend to be insoluble in water.

.

 

[someth1ng]

re: HSC Chemistry Marathon Archive

.

 

[albertcamus]

re: HSC Chemistry Marathon Archive

A student claims that the change in enthalpy of all neutralisation reactions is close to -57 kJ/mol. Evaluate the extent to which this is true.

Mark value?

But in terms of general stuffs

That only applies to neutralisation reactions where the net ionic eqn is h+ + oh- --> h20

If it's neutralisation according to my mateS Brownsted/Lowry then this neutralisation can also occur in a gaseous state or with carbonates etc.

So student's statement aint tru

 

[Youi_]

re: HSC Chemistry Marathon Archive

One week to Chemistry shall we make this thread more active?

 

[Menomaths]

re: HSC Chemistry Marathon Archive

Why not, although I'm doing Physics until Friday.

 

[HeroicPandas]

re: HSC Chemistry Marathon Archive

 

[bangladesh]

re: HSC Chemistry Marathon Archive

I'd totally write up answers for this if i didn't have to study 3u lols
feelsbadman

 

[hayabusaboston]

re: HSC Chemistry Marathon Archive

I'd totally write up answers for this if i didn't have to study 3u lols
feelsbadman

but 3u..... is 3u.... its relatively easy to have a solid grasp of the entire course in your head at any point in time.....

 

[bangladesh]

re: HSC Chemistry Marathon Archive

but 3u..... is 3u.... its relatively easy to have a solid grasp of the entire course in your head at any point in time.....

yeah, But I'm just doing past papers so that everything is fresh in my mind before the exam. From tomorrow arvo, CHEM 24/7. lols i love chemistry.

 

[abdog]

re: HSC Chemistry Marathon Archive

The pH of a 0.1 mol L-1 solution of a monoprotic acid was measured by a student and found to be close to 3. What proportion of the acid molecules remains unconverted to ions?

 

[bangladesh]

re: HSC Chemistry Marathon Archive

The pH of a 0.1 mol L-1 solution of a monoprotic acid was measured by a student and found to be close to 3. What proportion of the acid molecules remains unconverted to ions?

99/100?

 

[abdog]

re: HSC Chemistry Marathon Archive

99/1000?

Actually, it's per 100 but I know it's a typo
Yea it is. But tell me how you get it, otherwise it"s pointless

 

[bangladesh]

re: HSC Chemistry Marathon Archive

Find the H+ conc. Minus it from the molarity of the solution. then divide it by 0.1 because that's the original number of moles to find the ratio.