HSC 2012-2015 Chemistry Marathon (archive) (3 Viewers)

[Drsoccerball]

re: HSC Chemistry Marathon Archive

Describe how acid rain is bad for the environment include a chemical equation. 5 marks

 

[gada1]

re: HSC Chemistry Marathon Archive

I feel deeply ashamed. Hello.

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

I feel deeply ashamed. Hello.

Start with answering my prervious question

 

[Kaido]

re: HSC Chemistry Marathon Archive

Include 'a' chemical equation and 4 marks for theory? gg
Let's start with some obvious:
- can cause decrease in pH levels in water-ways (e.g. lakes), hence increasing the acidity -> causing detrimental effects on the local ecosystem (fish die)
- crops and forests that are not suited to acidic environments will break down and thus large forests can be cleared by acid rain -> causing both ecosystems and habitats to break down
- can erode calcium carbonate structures such as those found in caves (H2SO4(aq)+CaCO3(s) -->CaSO4(aq)+CO2(g)+H2O(l))
- can also mention a more complex nitrogen deposition process that can lead to eutrophication (topic 3)

 

[someth1ng]

re: HSC Chemistry Marathon Archive

The cell would no longer be neutralised and the cell would become incomplete as the salt bridge reacted. This would stop the ions from each cell from moving to the other cell and hence the cell would no longer give a voltage.

The problem is more to do with the ions reacting causing precipitation. If that's happening, the ions may no longer available in solution, and without enough ions in solution, you have no battery. When the salt bridge ions are used up, you get no neutralisation (what you said) but if the half cell ions are used up, you have no half cell. In either case, it's a real mess, as you can imagine.

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

Explain how a nuclear reactor can be used to produce technecium 99m? 3 marks

 

[Kaido]

re: HSC Chemistry Marathon Archive

- fission of Uranium to get Mo-99 -> decays into tc-99m
- neutron bombardment of the already produced mo-98 to get mo-99 -> decays again
+ w/e equation you choose e.g. 98Mo+1n-->99Mo

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

What is a conjugate base? 2 marks

 

[Kaido]

re: HSC Chemistry Marathon Archive

B-L stated: when an acid donates a proton, the resultant molecule is known as the conj. base
e.g. HCl --> H+ Cl- (Cl- is the conj. base)

 

[someth1ng]

re: HSC Chemistry Marathon Archive

B-L stated: when an acid donates a proton, the resultant molecule is known as the conj. base
e.g. HCl --> H+ Cl- (Cl- is the conj. base)

That would probably get 0 since it's pretty ambiguous. Which resultant molecule? The one that gained or the one that lost the proton.

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

That would probably get 0 since it's pretty ambiguous. Which resultant molecule? The one that gained or the one that lost the proton.

Whats wrong with the answer?

 

[suika]

re: HSC Chemistry Marathon Archive

Whats wrong with the answer?

Like someth1ng said, it's pretty ambiguous/vague.

Also markers want you to get straight to the point - not dance around the subject (meaning using words that won't even make sense in your answer). Keep your answer simple and straight to the point and you will get your two marks.

Sorry for intruding btw, just thought I'd share my piece.

 

[zhertec]

re: HSC Chemistry Marathon Archive

What is a conjugate base? 2 marks

A conjugate base is the resultant compound of an acid that has donated a proton to a proton acceptor.

...would that get it? lol

 

[Kaido]

re: HSC Chemistry Marathon Archive

a 0? ok, could you explain the marking criteria that you used to critique my answer and perhaps add a response?
I'm an esl student and only recently came to Aus (2011), so yeah i'm not sure how to explain very well, haha. niggas be telling me to improve my skills

 

[someth1ng]

re: HSC Chemistry Marathon Archive

My response would be like this, I provided a general equation for clarity:
The conjugate base is what is formed when an acid donates a proton.

HA (acid) --> H+ (proton) + A- (conjugate base)

In your answers, the idea is definitely there but the wording is poor. Be careful when you use words like "compound" and "molecule". The conjugate base may not be a molecule nor a compound. A molecule, by definition, is a structure of atoms that is neutral (that's key!) - when talking about the conjugate base, in many (most) cases, it won't be neutral. As for compounds, it's something that is pure, in this context, it's not really accurate to refer to the conjugate as a compound.

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

How does the concentration of hydronium ions affect the acidity of a substance? 2 marks

 

[siggy]

re: HSC Chemistry Marathon Archive

How does the concentration of hydronium ions affect the acidity of a substance? 2 marks

Hydronium Ions, H30+, are positively charged ions that results from the presence of an acid in water, where a hydrogen ion reacts with the water molecule to form Hydronium ions. Due to their charge they increase the acidity of a substance by a lot as they are donating 3 protons, instead of 1 as with an H+ ion.

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

Hydronium Ions, H30+, are positively charged ions that results from the presence of an acid in water, where a hydrogen ion reacts with the water molecule to form Hydronium ions. Due to their charge they increase the acidity of a substance by a lot as they are donating 3 protons, instead of 1 as with an H+ ion.

What if the acid can't fully donate its proton ? You missed that point

 

[siggy]

re: HSC Chemistry Marathon Archive

What if the acid can't fully donate its proton ? You missed that point

I'm not sure If I've learnt that yet. Would that be when there is a weak acid - hence it couldn't fully ionise?

 

[enigma_1]

re: HSC Chemistry Marathon Archive

wat