# Thread: HSC 2012-2015 Chemistry Marathon (archive)

1. ## Re: HSC 2012 Chemistry Marathon

Originally Posted by nightweaver066
Content sounds pretty good, expression could be better (but this isn't english so i'm not going to criticise that lol).

Lavoisier defined acids as containing oxygen as he found non-metal oxides which reacted to form acids in water, e.g. sulfuric acid. Then provide the equation of sulfur trioxide reacting with water.

Stay consistent in your response! Unsure if this is that important but you said acids dissolve to form hydrogen ions, but in your chemical equation, you had sulfuric acid forming hydronium ions.

The rest looks fine though.

Comment on my answer whether it's worthy 6 marks or not?
ahhh thankss im tryinng to improve that already let me check yours

hmm yeap that should get you the 6, though in the answers iv got they structure it out so they explain how it works as both an acid and a base then give the equations respectively underneath, but it really doesnt matter nice

2. ## Re: HSC 2012 Chemistry Marathon

Originally Posted by zeebobDD
ahhh thankss im tryinng to improve that already let me check yours

hmm yeap that should get you the 6, though in the answers iv got they structure it out so they explain how it works as both an acid and a base then give the equations respectively underneath, but it really doesnt matter nice
Sweet, thanks for the feedback.

New question:

3. ## Re: HSC 2012 Chemistry Marathon

Originally Posted by nightweaver066
(a) The use of beta rays to gauge the thickness of cardboard is most efficient. Beta rays are able to pass through (penetrate) the cardboard, and hence be detected - determining its thickness.
(b) Geiger-Muller Counter
(c)The Geiger-Muller counter has countless advantages compared to mechanical instruments such as callipers. They minimise exposure to the radiation, hence lowering the risk of cell mutilation and cancer. They also electronically convert the readings to a simple readable value, making it easy to compare and note thickness levels.

More depth needed?

4. ## Re: HSC 2012 Chemistry Marathon

NEW QUESTION:

Discuss problems associated with the use of CFCs and analyse their effect on the atmosphere using appropriate chemical equations

5. ## Re: HSC 2012 Chemistry Marathon

Originally Posted by kingkong123
(a) The use of beta rays to gauge the thickness of cardboard is most efficient. Beta rays are able to pass through (penetrate) the cardboard, and hence be detected - determining its thickness.
(b) Geiger-Muller Counter
(c)The Geiger-Muller counter has countless advantages compared to mechanical instruments such as callipers. They minimise exposure to the radiation, hence lowering the risk of cell mutilation and cancer. They also electronically convert the readings to a simple readable value, making it easy to compare and note thickness levels.

More depth needed?
In (a), explain what you mean by 'efficient'.

The rest is fine though.

zeebobDD, i doubt many people have started chemical monitoring and management lol.

6. ## Re: HSC 2012 Chemistry Marathon

Hi guys, this is a question from the 2009 HSC -
Question 20:
Calculate the mass of ethanol that must be burnt to increase the temp of 210g of water by 65 degrees celsius if exactly half of teh heat released by this combustion is lost to its surroundings.
Heat of combustion = 1367 kj/mol/L

7. ## Re: HSC 2012 Chemistry Marathon

Originally Posted by ziaa
Hi guys, this is a question from the 2009 HSC -
Question 20:
Calculate the mass of ethanol that must be burnt to increase the temp of 210g of water by 65 degrees celsius if exactly half of teh heat released by this combustion is lost to its surroundings.
Heat of combustion = 1367 kj/mol/L

If half the heat is lost to the surroundings, you'll need to produce double the amount of heat.

That means you'll need $c = (210 \times 4.18 \times 2)J$ of energy

$n(ethanol) = \frac{m}{46.068}$

Finding molar heat of combustion of ethanol:

$H_c = \frac{(210 \times 4.18 \times 2)}{\frac{m}{46.068} \times 1000}kJ$

$= \frac{210 \times 4.18 \times 2 \times 46.068}{m \times 1000}$

As we know this is 1367kJ/mol,

$1367 = \frac{210 \times 4.18 \times 2 \times 46.068}{m \times 1000}$

Rearrange and solve for m.

Question:

8. ## Re: HSC 2012 Chemistry Marathon

Question:
(i) According to the Bronsted-Lowry Theory of acids and bases, an acid is a proton donor and a base is a proton acceptor.
(ii) In reaction (1), $HCO_3^-$ acts as a base. It accepts a proton from $H_3O^+$, resulting in the $H_2CO_3$. In reaction (2) $HCO_3^-$ acts as an acid, it donates a proton to $H_2O$, resulting in the $H_3O^+$ in the reactants.

9. ## Re: HSC 2012 Chemistry Marathon

In reaction 1, HCO3- acts as a bronsted-lowry base; it accepts a proton from the hydronium ion on the RHS to form H2CO3

*revive*

Bump

12. ## Re: HSC 2012 Chemistry Marathon

a) butyl ethanoate.png

b) both of these steps increase the efficiency of the esterification reaction. The concentrated sulfuric acid acts as a catalyst to reduce the activation energy for the reactants, and the refluxing process allows the reaction to occur at a higher temperature, and increases the rate of reaction. The condenser in the process ensures that reactants and products are kept within the flask.

13. ## Re: HSC 2012 Chemistry Marathon

question.JPG

how do u attach photos properly?

14. ## Re: HSC 2012 Chemistry Marathon

Originally Posted by barbernator
a) butyl ethanoate.png

b) both of these steps increase the efficiency of the esterification reaction. The concentrated sulfuric acid acts as a catalyst to reduce the activation energy for the reactants, and the refluxing process allows the reaction to occur at a higher temperature, and increases the rate of reaction. The condenser in the process ensures that reactants and products are kept within the flask.
Since it says justify, you should include that the esterification process is very slow.

For the last point you made, mention how the reactants and products are volatile.

Other than that, good

15. ## Re: HSC 2012 Chemistry Marathon

Originally Posted by barbernator
question.JPG

how do u attach photos properly?
Use [IMG] link [./IMG] without the dot

$NH_4Cl is the product of ammonium hydroxide and hydrochloric acid\\NH_4OH_{(aq)} + HCl_({aq)} \rightarrow NH_4Cl_{(aq)}\\As it is a product of a weak base and strong acid, the product must be acidic, i.e. it forms an acidic salt such that:\\ NH^+_{4(aq)} + H_2O_{(l)} \rightarrow NH_3{(aq)} + H_3O_{(aq)}^+$

16. ## Re: HSC 2012 Chemistry Marathon

Chem notes uploaded onto year 12 chit chat

17. ## Re: HSC 2012 Chemistry Marathon

^^^
Check it out if you guys need it.

New question:

18. ## Re: HSC 2012 Chemistry Marathon

[tex]NH_4OH_{(aq)} + HCl_({aq)}
u should probably include water as a product in this equation as well but all good

19. ## Re: HSC 2012 Chemistry Marathon

Originally Posted by barbernator
u should probably include water as a product in this equation as well but all good
Oops.. Main point was gotten across though :P

20. ## Re: HSC 2012 Chemistry Marathon

ethene is produced through the dehydration of ethanol, as well as cracking, both catalytic and thermal. A variety of petrochemical feedstocks can be converted into ethanol. Biomass, containing cellulose is broken down into glucose monomers through using bacteria or sulfuric acid catalysts. This can then be processed into ethanol through fermentation by yeast. Yeast is then dehydrated (insert equation here) using (a concentrated sulfuric acid catalyst i think....) into ethylene. Long chain alkanes, sourced from crude oil, are cracked into smaller alkanes and alkenes. Thermal cracking and catalytic cracking both produce these products, (equation pentane -- ethene and propane). I think i have missed heaps in this answer, but hopefully it covers the two main processed for the production of ethanol. Im surprised it isnt worth more marks actually

Edit: I think i've interpretted "petrochemical feedstocks" incorrectly not sure...

21. ## Re: HSC 2012 Chemistry Marathon

Originally Posted by barbernator
ethene is produced through the dehydration of ethanol, as well as cracking, both catalytic and thermal. A variety of petrochemical feedstocks can be converted into ethanol. Biomass, containing cellulose is broken down into glucose monomers through using bacteria or sulfuric acid catalysts. This can then be processed into ethanol through fermentation by yeast. Yeast is then dehydrated (insert equation here) using (a concentrated sulfuric acid catalyst i think....) into ethylene. Long chain alkanes, sourced from crude oil, are cracked into smaller alkanes and alkenes. Thermal cracking and catalytic cracking both produce these products, (equation pentane -- ethene and propane). I think i have missed heaps in this answer, but hopefully it covers the two main processed for the production of ethanol. Im surprised it isnt worth more marks actually

Edit: I think i've interpretted "petrochemical feedstocks" incorrectly not sure...
I think you have as well.

"Petrochemical feedstocks" = petroleum.

Maybe reattempt the question with a focus on catalytic/thermal cracking? (Go through the process and provide balanced chemical equations)

Good attempt though if it was simply ways of attaining ethene :P

22. ## Re: HSC 2012 Chemistry Marathon

heres an abstract one [img] 24875 [img]

lol fail attachment again

23. ## Re: HSC 2012 Chemistry Marathon

1. Explain why the equivalence point of a reaction doesn't necessarily result in the pH of the solution being 7 at that point. (2)
2. From this, write a balanced equation for an acid-base neutralisation reaction with a equivalence point of pH>7 and state the indicator which is used to show this point in this reaction. (2)

24. ## Re: HSC 2012 Chemistry Marathon

Your first question. I don't have time so i'll just run over a few points.
- Petroleum is a finite resource and we are consuming it quicker than we're excavating it
- Experts predict it will run out in the next 50 years
- Oxidation-reduction reactions are able to produce a voltage and supply electricity and with further scientific development has the potential to substitute petroleum for energy
- Lead-acid cells is one important battery used today
- Used to jump-start cars and as a power source for rural areas
- Oxidation reaction & reduction equation formula
- Petroleum running out -> alternative needed -> batteries using oxidation-reduction reactions are becoming more important -> must improve technology so that batteries can be more efficient and can be used for more large scale applications

1. The equivalence point of a reaction depends upon the titrant and the titre. A reaction between a strong base and strong acid or a weak acid and weak base will yield a neutral solution, i.e. pH of 7. However reactions between a strong base and weak acid or weak base and strong acid will yield either pH < 7 or pH > 7 respectively. Therefore the equivalence point of a reaction doesn't necessarily result in the pH of the solution being 7 at that point.

2. Using NaOH and acetic acid,
$NaOH_{(s)} + CH_3COOH_{(aq)} \rightarrow NaCH_3COO_{(aq)} + H_2O_{(l)}$

Use phenolphthalein to determine the equivalence point.

25. ## Re: HSC 2012 Chemistry Marathon

Question:

Page 4 of 81 First ... 234561454 ... Last

There are currently 1 users browsing this thread. (0 members and 1 guests)

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•