Chemistry Exam Revision Questions

[kenhung123]

(Excuse the spamming of questions)
4. Can fractional distillation extract pure compounds?
5. Do we need to know about the laboratory fractional distillation or industrial?

[Martoman]

4. In the industrial one its usually a mixture of hydrocarbons with similar bioling points.

5. Both. Although I have never seen a question on the laboratory one. (*waits to be corrected*)

[kenhung123]

6. When decreasing particle size - heinemann claims that there is better separation as there is more frequent adsorption and desorption. Now, does this mean reduce retention time? Also, how does frequent adsorption and desorption allow better separation if it does not reduce retention time?

[Martoman]

No no. Decreasing particle size = more can be packed in = more spots for adsorbsion to the stionary phase = longer retention time.

[kenhung123]

Thanks for that! These things are very confusing increase/decrease causes increase/decrease in other!

OK another question: Can water (H2O can form H+ and OH- right) be considered a reagent for reaction of chloroalkane to product alkanol? E.g. CH3CH2Cl+H2O=>Ch3CH2OH commonly the exams say NaOH or KOH but does it mean H2O is wrong?

[Martoman]

You need at least 300-400 degrees of heat and a solid catalyst to do so. It really involves a lot of effort.

[olly_s15]

4. In the industrial one its usually a mixture of hydrocarbons with similar bioling points.

5. Both. Although I have never seen a question on the laboratory one. (*waits to be corrected*)

laboratory one was on VCAA 2009 Q19 MC

you stand corrected

[Martoman]

eh, i did that exam! wow, my memory is failing bad.

[kenhung123]

You need at least 300-400 degrees of heat and a solid catalyst to do so. It really involves a lot of effort.

I think that is the condition+catalyst for addition of water to ethene not substitution?

1. I thought if products where Acid+metal=Salt+H2 or Salt+H2O or salt+H2O+CO2 is an acid-base?
Perhaps it can be acid and base and redox? But why would redox be a more accurate one?
2. Is the OH in carboxy group considered a hydroxy group i.e. can OH (hydroxy) be ionised in basic solution to form O-?
3. Do I need to use words to describe an organic pathway e.g. oxidise ethanol to form ethanoic acid with the use of dichromate oxidising agent
4. In organic reactions, quite a lot of the time we may deal with small molecules in (g) state. When forming bromo- and alcohols, do we retain the (g) state or would it be silly to say a gaseous alcohol is produced?
5. Is fermentation oxidation or a reduction reaction?

[Mao]

1. I thought if products where Acid+metal=Salt+H2 or Salt+H2O or salt+H2O+CO2 is an acid-base?
Perhaps it can be acid and base and redox? But why would redox be a more accurate one?

False. Acid + metal --> salt + H2 is always a redox reaction at VCE level.
base/carbonate/hydrogen carbonate + acid --> salt + h2O [ + CO2 ] are acid/base reactions

2. Is the OH in carboxy group considered a hydroxy group i.e. can OH (hydroxy) be ionised in basic solution to form O-?

No, it does not ionise (at VCE level). In reality, it can ionise, but you require a VERY strong base (pH > 14 if I remember correctly)

4. In organic reactions, quite a lot of the time we may deal with small molecules in (g) state. When forming bromo- and alcohols, do we retain the (g) state or would it be silly to say a gaseous alcohol is produced?

Depends on what temperature. Generally, light alcohols become gaseous at temperatures above 100 degrees (they boil before water does).

5. Is fermentation oxidation or a reduction reaction?

C6H6O6 --> 2CO2 + 2C2H6O
It is both an oxidation and a reduction reaction, where glucose is both the oxidant and the reductant.
If that is a bit of a leap:

Redox reactions usually concern only two atoms, one of them accepting electrons, one of them donating electrons. these two atoms may be bonded to a range of other things, thus making two molecules reacting together, when it is essentially two centers exchanging electrons.
In large organic molecules, redox reaction may occur between different parts of the molecule. E.g. the 1' C acts as an oxidant and the 3' C acts as a reductant (just an example, this may not be true for fermentation of glucose). the actual reaction pathway for fermentation of glucose is quite complicated with NADH and ATP floating around everywhere, but the key is, different parts of the sugar have different chemical properties, and may react with each other.

[kenhung123]

Oh my god! You are so awesome. Thank you thank you thank you!

[kenhung123]

1. I thought if products where Acid+metal=Salt+H2 or Salt+H2O or salt+H2O+CO2 is an acid-base?
Perhaps it can be acid and base and redox? But why would redox be a more accurate one?

False. Acid + metal --> salt + H2 is always a redox reaction at VCE level.
base/carbonate/hydrogen carbonate + acid --> salt + h2O [ + CO2 ] are acid/base reactions

Does that mean metal+acid=>salt +H2O [+CO2] is not acid-base?

6. Given that each carbon has at least 1 hydrogen, would the number of carbon and hydrogen environments be same for the molecule?
7. Is bromine used in bromine tests in state (g) (l) or (aq)

[Mao]

1. I thought if products where Acid+metal=Salt+H2 or Salt+H2O or salt+H2O+CO2 is an acid-base?
Perhaps it can be acid and base and redox? But why would redox be a more accurate one?

False. Acid + metal --> salt + H2 is always a redox reaction at VCE level.
base/carbonate/hydrogen carbonate + acid --> salt + h2O [ + CO2 ] are acid/base reactions

Does that mean metal+acid=>salt +H2O [+CO2] is not acid-base?

Correct, it is not acid/base.

6. Given that each carbon has at least 1 hydrogen, would the number of carbon and hydrogen environments be same for the molecule?
Not necessarily, OH and NH groups would increase the number of H environment. E.g. for ethanol, 2 C environment, 3 H environments.

7. Is bromine used in bromine tests in state (g) (l) or (aq)
usually (aq) [or in an organic solvent such as CH2Cl2 (aka DCM), commonly used in organic chemistry]

[kenhung123]

Thanks once again Mao!

Another question I encountered:
If CH3CH(OH)CH3 reacted with CH3CH2CH2COOH (Is esterification possible when there is no primary alkanol?)
Isn't this meant to be the product:

[m@tty]

Yeah, that's possible. I believe it is named 2-propyl butanoate.