HSC Chemistry Question Thread

[justwannawish]

What are the disadvantages of biopol, other than being expensive and inefficient to produce at a large scale?

Also it has poorer properties, such as low thermal stability and it's brittle.

[josephmalicdem]

How do I do Question 14: HSC Chemistry 2012?
Requesting help for Questions 15-16. I got both wrong.

Mod Edit: Use the "modify" button to add more than one post.

[anotherworld2b]

I have been working on this question but I'm sure what to do about the bromine

[MisterNeo]

How do I do Question 14: HSC Chemistry 2012?
Requesting help for Questions 15-16. I got both wrong.

From the previous question, you would have identified dichromate as the oxidising agent that undergoes reduction. The iron (II) undergoes oxidation. Using the data sheet values, you can find the E^o value. Remember that you do not multiply these data values according to stoichiometric moles, and use them as they are on the sheet.
For Q15, a pH increase of 1 indicates a tenfold decrease in H⁺ concentration, according to the pH formula. The question has a pH increase of 2, so the concentration must have been reduced by 100x. So the original volume plus the added water must equal 100x the original volume. The only one there is C because 10+990 is 1000, which is 100x 10.
For Q16, the answer is B because H₃O⁺ has a coordinate bond between that extra hydrogen with oxygen's lone pair.
For these questions, I'd memorise the common compounds that have these bonds.

[josephmalicdem]

(Image removed from quote.)
From the previous question, you would have identified dichromate as the oxidising agent that undergoes reduction. The iron (II) undergoes oxidation. Using the data sheet values, you can find the E^o value. Remember that you do not multiply these data values according to stoichiometric moles, and use them as they are on the sheet.
For Q15, a pH increase of 1 indicates a tenfold decrease in H⁺ concentration, according to the pH formula. The question has a pH increase of 2, so the concentration must have been reduced by 100x. So the original volume plus the added water must equal 100x the original volume. The only one there is C because 10+990 is 1000, which is 100x 10.
For Q16, the answer is B because H₃O⁺ has a coordinate bond between that extra hydrogen with oxygen's lone pair.
(Image removed from quote.) For these questions, I'd memorise the common compounds that have these bonds.

Thank you so much. Those are really great explanations. 👍🏻

[justwannawish]

Can someone please compare industrial chemistry and shipwrecks and corrosion? Our teacher wants to do the latter but our school has usually done  Industrial chem, and we have to vote on what to do before the break's over.

Advantages of either, the types of questions, anything is good

[MisterNeo]

Can someone please compare industrial chemistry and shipwrecks and corrosion? Our teacher wants to do the latter but our school has usually done  Industrial chem, and we have to vote on what to do before the break's over.

Advantages of either, the types of questions, anything is good

I'm currently doing Industrial, and I have to say that it is pretty much a revision of the 3 core topics.
It's mainly equilibriums, maximising yields, electrochemistry (galvanic/electrolysis), environmental issues.
Common questions include:
-Calculate the K-constant of this equilibrium (very easy).
-What is the role of this chemical in this process.
-Draw the diagram of soap and explan why it cleans stuff.
-Outline a prac you did in school about this process.
-Assess the environmental risks of these two processes. (mini essay)
The first few questions are very easy, but the last few are quite time consuming because you need to write a mini essay and/or diagrams included. There is only every 1-2 calculation questions about "If X-moles of this is used, how much of Y is produced?" and "Calculate the equilibrium concentration of chemical Y if chemical X was 1M initially".
Industrial is the most common choice for option, and I'd recommend it since it's basically revision.
I'm not sure about Shipwrecks, so you may want to ask someone who does. (Jake does)

[winstondarmawan]

Can someone please compare industrial chemistry and shipwrecks and corrosion? Our teacher wants to do the latter but our school has usually done  Industrial chem, and we have to vote on what to do before the break's over.

Advantages of either, the types of questions, anything is good

Shipwrecks is basically a superstudy of the Redox topic in Preliminary.
- The earlier stuff is content dumping - no need to worry much about that.
- Electrolytic cells, basically the opposite of galvanic cells.
- Corrosion of metals, particularly iron. Just a redox reaction between iron and water+oxygen.
- Artefacts topic at the end is also memorisation and content dumping.
ALSO THERE IS A SHITLOAD OF EQUATIONS YOU NEED TO MEMORISE.
Overall, from what I've heard from peers, Industrial seems easier.

[Arvacado]

Hiii!
Can someone help me with this question: What is the process of AAS?

1.How does soap act as an emulsifier?
2.What is the Solvay process?
Thank you! 

Mod Edit: Posts merged, use the 'Modify' post button to avoid chain posting

[bsdfjnlkasn]

Hiii!
Can someone help me with this question: What is the process of AAS?

Hey there!

So in addition to the method below, I recommend you memorise how to draw the diagram (it's not too difficult )

Process of AAS

1. Several standard solutions of the ion being tested for are prepared (i.e. solutions of which the concentration is known).
•   Range of concentrations of the standard solutions must include the anticipated concentration of the sample being tested, this is important for when we graph the absorbance values

2. Sample of the element being tested for is burnt in a hollow cathode ray lamp. Its electrons are momentarily excited and then fall back to ground state, emitting a unique pattern of light frequencies.

3. One by one, the standard solutions are pumped into a nearby flame, so that they vaporise into a mist that the lamplight must passes through. Ions absorb the same frequencies of light that they are able to emit
•   The more ions there are in the sample that match the burning element, the more light will be absorbed and the less intense the beam will become.

4. After passing through the flame, the light beam is focused by a lens, and a chosen wavelength of it is refracted through prism into the photomultiplier. (The light beam is restricted to one wavelength to improve accuracy).

5. The photomultiplier detects the light intensity, and uses this to calculate the absorbance of the sample (in units A).

The absorbances of the different standard solutions are plotted against their concentration, to form a calibration curve. This should be a straight increasing line and so its equation can be found as A = kc

6. Steps 3-5 are repeated using the sample being tested, to find an absorbance value.

7. The point with the given absorbance value is located on the graph, and its concentration co-ordinate is identified as the concentration of the sample.

1.How does soap act as an emulsifier?
2.What is the Solvay process?
Thank you! 

Soap acts as an emulsifier (i.e. it is an emulsifying agent) because it has both non-polar and polar parts. Looking at the example of water and oil (and why when you add soap, the two can suddenly mix):

The non-polar tails of soap molecules gather around oil droplets, so that the negatively charged polar ends face outwards. This creates a negative charge on the droplet of oil which repels other negatively charged soap and oil droplets, preventing the formation of large clumps of oil. Now, water can interact with the oil i.e. they can mix.

Mod edit: Merged posts

[MisterNeo]

1.How does soap act as an emulsifier?

To add onto bsdfjnlkasn's answer, soap acts as an emulsifying agent (emulsifier) by allowing two usually immiscible liquids to become miscible.
If that were a question in an exam, you must define what an emulsifying agent is, then address soap's structure like in the previous post

2.What is the Solvay process?

The Solvay process is the industrial method of producing Na₂CO₃ from brine (NaCl) and limestone (CaCO₃) with the use of ammonia.

[justwannawish]

Shipwrecks is basically a superstudy of the Redox topic in Preliminary.
- The earlier stuff is content dumping - no need to worry much about that.
- Electrolytic cells, basically the opposite of galvanic cells.
- Corrosion of metals, particularly iron. Just a redox reaction between iron and water+oxygen.
- Artefacts topic at the end is also memorisation and content dumping.
ALSO THERE IS A SHITLOAD OF EQUATIONS YOU NEED TO MEMORISE.
Overall, from what I've heard from peers, Industrial seems easier.

I'm currently doing Industrial, and I have to say that it is pretty much a revision of the 3 core topics.
It's mainly equilibriums, maximising yields, electrochemistry (galvanic/electrolysis), environmental issues.
Common questions include:
-Calculate the K-constant of this equilibrium (very easy).
-What is the role of this chemical in this process.
-Draw the diagram of soap and explan why it cleans stuff.
-Outline a prac you did in school about this process.
-Assess the environmental risks of these two processes. (mini essay)
The first few questions are very easy, but the last few are quite time consuming because you need to write a mini essay and/or diagrams included. There is only every 1-2 calculation questions about "If X-moles of this is used, how much of Y is produced?" and "Calculate the equilibrium concentration of chemical Y if chemical X was 1M initially".
Industrial is the most common choice for option, and I'd recommend it since it's basically revision.
I'm not sure about Shipwrecks, so you may want to ask someone who does. (Jake does)

Thank you both for your answers. I think I'm going to go for industrial, it seems like it's more related to the rest of the syllabus

[anotherworld2b]

would this be the correct highest solubility to lowest solubility? carboxlyic, alcohol, aldehyde and ketone, alkanes/alkenes/alkynes

[J.B]

For states in chemical reactions, are they for the chemical at standard conditions or state in the reaction?

For eg.
Hydration of ethene, is the water and ethanol gas or liquid?

Thank you

[Wordswurth]

For states in chemical reactions, are they for the chemical at standard conditions or state in the reaction?

For eg.
Hydration of ethene, is the water and ethanol gas or liquid?

Thank you

State in the reaction. Not standard condition I would say. I'd have thought water is liquid and ethene gas. Depends on the question.