HSC Chemistry Question Thread

[Natasha.97]

Hiii. Just revising biopolymers right now, and I was just wondering, how much of the history do I need to know? I was thinking just the date when it started being produced and whatnot but jake's notes have a whole para on them and its stressing me out because i hate remembering historical detail RIP. does anyone happen to have a short + effective summary on phbs? thanks!

Hi!

Personally, I'm not really sure if you need the historical development, but the current developments of PHB.
Here's my summary for PHB, hope this helps

[beau77bro]

Hiii. Just revising biopolymers right now, and I was just wondering, how much of the history do I need to know? I was thinking just the date when it started being produced and whatnot but jake's notes have a whole para on them and its stressing me out because i hate remembering historical detail RIP. does anyone happen to have a short + effective summary on phbs? thanks!

It does say "progress in recent development of a named biopolymer", so maybe just the basic outline would be useful to note, but definitely more focus on the potential of use based on properties. From my summary:

[necromantic]

Hi!
How do you identify/explain if a salt is acidic/basic/neutral and whether it's weak/strong? (Acidic environment, dotpoint 4.4)

[MisterNeo]

Hi!
How do you identify/explain if a salt is acidic/basic/neutral and whether it's weak/strong? (Acidic environment, dotpoint 4.4)

Hey
You can identify salt pH by looking at the cation and anion it is made of.
Acidic Salt
Anion is the from a strong acid, and cation is from a weak base.
Eg. NH₄Cl is an acidic salt because ammonium is from a weak base (ammonia) and the chloride is from a strong acid (hydrochloric).

Basic Salt
Anion is from a weak acid, and cation is from a strong base.
Eg. CH₃COONa (sodium acetate) is a basic salt because the sodium ion is from a strong base (NaOH), and the acetate ion is from a weak acid (acetic acid).

Neutral Salt
Anion is from a strong acid, and cation is from a strong base.
OR
Anion is from a weak acid, and cation is from a weak base.
Eg. NH₄HCO₃ OR NaCl because ammonium and bicarbonate are both from weak species (NH₃ H₂CO₃), and sodium and chloride are from strong species (NaOH HCl).

The ions are usually a conjugate of a base or an acid. Hope this helps

[Natasha.97]

Hi!
How do you identify/explain if a salt is acidic/basic/neutral and whether it's weak/strong? (Acidic environment, dotpoint 4.4)

Hi!

Salts
Basic salt (pH>7.0)
   - Formed from a weak acid and a strong base
   - Example: Sodium Acetate (acetic acid and sodium hydroxide)
      ○ CH₃COOH_(aq) + NaOH_(aq) → CH₃COONa_(aq) + H₂O_(l)
      ○ CH₃COONa_(aq) + H₂O_(l) → CH₃COO^–_(aq) + Na⁺_(aq)
      ○ CH₃COO^-_(aq) + H₂O_(l)  ←→ CH₃COOH_(aq) + OH^-_(aq)
      ○ Acetate ion accepts H⁺ from H₂O, resulting in the formation of the OH^- ion which makes the pH > 7.0
Acidic salt (pH<7.0)
   - Formed from a weak base and a strong acid
   - Example: Ammonium Chloride (ammonia and hydrochloric acid
      ○ NH₄OH_(aq) + HCl_(aq) → NH₄Cl_(aq) + H₂O_(l)
      ○ NH₄Cl_(aq) + H₂O_(l) → NH₄⁺_(aq) + Cl^-_(aq)
      ○ NH₄⁺_(aq) + H₂O_(l) ←→ NH_3(aq) + H₃O⁺_(aq)
      ○ Ammonium ion donates H⁺ to H₂O, resulting in the formation of the H₃O⁺ ion which makes pH < 7.0
Neutral salt (pH=7.0)
   - Formed from either a strong acid and strong base, or a weak acid and weak base
   - Example: Hydrochloric Acid and Sodium Hydroxide
      ○ HCl_(aq) + NaOH → NaCl_(aq) + H₂O_(l)
      ○ NaCl_(aq) + H₂O_(l) → Na⁺_(aq) + Cl^-_(aq)
      ○ Na⁺ stays as an ion (metal)
      ○ Cl^- is a very weak base, so it does not accept protons
   - Example: Ethanoic Acid and Ammonia
      ○ CH₃COOH_(aq) + NH_3(aq) → (CH₃COO)NH_4(aq)
      ○ (CH₃COO)NH_4(aq) →CH₃COO^-_(aq) + NH₄⁺_(aq)
      ○ CH₃COO^-_(aq) + H₂O_(l) → CH₃COOH_(aq) + OH^-_(aq)
      ○ NH₄⁺_(aq) + H₂O_(l) → NH_3(aq) + H₃O⁺_(aq)
      ○ The hydroxide ions formed by CH₃COO^- and the hydronium ions formed by NH₃ cancel each other, so the salt is neutral

Hope this helps

[Mathew587]

For the IUPAC nomenclature, is the accepted method the lowest sum or is alphabetical order?

[Sine]

For the IUPAC nomenclature, is the accepted method the lowest sum or is alphabetical order?

alphabetical order

[Mathew587]

cos q11 from 2016 hsc had D as the answer when I would have thought it'd be A. Can someone pls explain why?
thnx

[Natasha.97]

cos q11 from 2016 hsc had D as the answer when I would have thought it'd be A. Can someone pls explain why?
thnx

Hi!

There is a "lowest sum of locants" rule, and when calculated, the sum of locants on D is 7 (2+2+1+1+1), as opposed to 8 (1+1+2+2+2) for A

Hope this helps

[RuiAce]

alphabetical order

For reasons unknown, they do not teach this in the HSC.

[VanillaRice]

For the IUPAC nomenclature, is the accepted method the lowest sum or is alphabetical order?

alphabetical order

Hi!

There is a "lowest sum of locants" rule, and when calculated, the sum of locants on D is 7 (2+2+1+1+1), as opposed to 8 (1+1+2+2+2) for A

Hope this helps

I feel there might be a misunderstanding here, so to clarify:
When numbering substituents, you want the lowest numbers.
When listing substituents, you want alphabetical order.

[Mathew587]

Hi!

There is a "lowest sum of locants" rule, and when calculated, the sum of locants on D is 7 (2+2+1+1+1), as opposed to 8 (1+1+2+2+2) for A

Hope this helps

thanks jess. i've heard of that that but it felt dodgy in that both the locant rule and alphabetical order must be followed.

[J.B]

Hi,
I just wanted to clarify that I have interpreted this correctly.
So hydrogen bonds are intermolecular forces between hydrogen and either O, F, or N.
So in this image, even though there is a possibility of molecules forming hydrogen bonds in "C" between a H of one molecule & an O of another molecule. Is it considered to not have any hydrogen bonds as intramolecularly the Hydrogen and Oxygen aren't bonded together, so they don't have strong enough positive and negative dipoles to form the H-bonds intermolecularly?
I hope this makes sense. Thank you.

[VanillaRice]

Hi,
I just wanted to clarify that I have interpreted this correctly.
So hydrogen bonds are intermolecular forces between hydrogen and either O, F, or N.
So in this image, even though there is a possibility of molecules forming hydrogen bonds in "C" between a H of one molecule & an O of another molecule. Is it considered to not have any hydrogen bonds as intramolecularly the Hydrogen and Oxygen aren't bonded together, so they don't have strong enough positive and negative dipoles to form the H-bonds intermolecularly?
I hope this makes sense. Thank you.

Are you referring to compound Z? If so, the oxygen indeed is not close enough to the hydrogen to have a large electron pulling effect to form a large enough delta positive region around the hydrogen for hydrogen bonding.

Hope this helps

[angelahchan]

Hi,
Does anyone have recent developments for polylactic acid? The online thing I found was something about improving crystallisation rates but I have no clue what it means. Where can I find more info, and should I switch to a different biopolymer if I can't find a development?