HSC Chemistry Question Thread

[mxrylyn]

Hey,
So I know how to write a cyclohexene + Bromine Water reaction equation, but I'm not sure how I would write the same reaction equation with cyclohexane is apposed to cyclohexene.

[Natasha.97]

Hey,
So I know how to write a cyclohexene + Bromine Water reaction equation, but I'm not sure how I would write the same reaction equation with cyclohexane is apposed to cyclohexene.

Hi!
Even though BrOH is technically more scientifically correct, Br_2(aq) is accepted. This would result in the following equations:

Cyclohexane + Bromine Water
- C₆H_12(aq) + Br_2(aq) → C₆H₁₁Br_(aq) + HBr_(aq)
- Cyclohexane + Bromine → 1-bromohexane + Hydrogen bromide

Cyclohexene + Bromine Water
- C₆H_10(aq) + Br_2(aq) → C₆H₁₀Br_2(aq)
- Cyclohexene + Bromine → 1,2-dibromohexane

Hope this helps

[justwannawish]

I’ve always used 300 for hydration and 170 for dehydration without any issues. :)An error I once made in titration was not reading the miniscus properly. Make sure it is read from the bottom of the concave at eye level. Don’t force out the liquid at the tip of the pipette because it has been calibrated to account for the lost volume. Rinse everything with the solution that is going to be used in it except for the conical flask (water). Don’t use a beaker to measure volume in titrations because its markings are estimated, use that tall beaker. Do the titration on top of a white surface like paper so that changes of the indicator colour are easier to see. Don’t put too much indicator (I did this lol) because they can skew the titration results if you overdo it as they’re slightly acidic/basic themselves. When the titration is approaching the end point, open the burette drop by drop and swirl the flask after every drop. If the drop of titre is clinging onto the top of the burette, don’t risk opening the burette anymore because you might end up adding multiple drops, which could exceed the end point. Instead, spray the droplet off with distilled water from one of those plastic bottles with the long tube. It doesn’t matter if concentration of the conical flask changes because the moles are still the same. The end point is reached when the colour change stays when you swirl the beaker. For example, titration NaOH with a weak acid you would use phenolphthalein. When the phenolphthalein keeps a slight pink shade even after you swirl the flask, that would be the end point.
Hope this helps

Thank you so much! I totally missed this. But could you please explain how to get the appropriate indicator for each standard solution and acid? I don't really get the conjugate acid/ base theorem

[Natasha.97]

Thank you so much! I totally missed this. But could you please explain how to get the appropriate indicator for each standard solution and acid? I don't really get the conjugate acid/ base theorem

Hi!

The indicator is chosen by predicting the acidity/basicity of the produced salt. There are 3 probabilities:
- Strong acid + Strong base = Neutral [Use litmus (purple) or bromothymol blue(green)]
- Strong acid + Weak base = Acidic [Use methyl orange(red)/bromothymol blue (yellow)]
- Weak acid + Strong base = Basic [Use phenolphthalein(pink)]

Hope this helps

[mxrylyn]

Hi!
Even though BrOH is technically more scientifically correct, Br_2(aq) is accepted. This would result in the following equations:

Cyclohexane + Bromine Water
- C₆H_12(aq) + Br_2(aq) → C₆H₁₁Br_(aq) + HBr_(aq)
- Cyclohexane + Bromine → 1-bromohexane + Hydrogen bromide

Cyclohexene + Bromine Water
- C₆H_10(aq) + Br_2(aq) → C₆H₁₀Br_2(aq)
- Cyclohexene + Bromine → 1,2-dibromohexane

Hope this helps

Thank you!
How would I then show the reaction between cyclohexane and cyclohexene with acidified potassium permanganate (KMnO4)?

[Natasha.97]

Thank you!
How would I then show the reaction between cyclohexane and cyclohexene with acidified potassium permanganate (KMnO4)?

Hi!
Cyclohexene will decolourise the potassium permanganate solution, while cyclohexane will not. The permanganate ions are reduced to manganese (II) ions (Mn²⁺). The reaction is as follows:

- 3C₆H₁₀ + 2KMnO₄ + 4H₂O → 3C₆H₁₂O₂ + 2MnO₂ + 2KOH
- Cyclohexene + potassium permanganate + water → 1,2-cyclohexanediol + manganese dioxide + potassium hydroxide

Hope this helps

[Mate2425]

Hi, Jake I was just wondering if you could please help me with explaining the manufacturing of the radioisotope "Technetium - 99m" and the process required to obtain the Technetium 99m for medical use. Thanks Heaps 

[Natasha.97]

Hi, Jake I was just wondering if you could please help me with explaining the manufacturing of the radioisotope "Technetium - 99m" and the process required to obtain the Technetium 99m for medical use. Thanks Heaps 

Hi!

Firstly,  Molybdenum-98 undergoes neutron bombardment in a nuclear reactor to produce the Molybdenum-99:


Then, Molybdenum-99 (half life of 66 hours) is transported to hospitals where it undergoes beta decay to form Technetium-99m:


Technetium-99m decays to form Technetium-99, releasing gamma rays in the process:


Hope this helps

[Mate2425]

Hi!

Firstly,  Molybdenum-98 undergoes neutron bombardment in a nuclear reactor to produce the Molybdenum-99:
(Image removed from quote.)

Then, Molybdenum-99 (half life of 66 hours) is transported to hospitals where it undergoes beta decay to form Technetium-99m:
(Image removed from quote.)

Technetium-99m decays to form Technetium-99, releasing gamma rays in the process:
(Image removed from quote.)

Hope this helps

Thank you it helps alot 😃

[cnimm2000]

Hey,
In the chemistry syllabus there is a dot point which asks you to identify a practising male and female Australian chemist. I was struggling finding an Australian female research chemist. it would be great if you had any suggestions.
thanks

[mary123987]

Hey,
In the chemistry syllabus there is a dot point which asks you to identify a practising male and female Australian chemist. I was struggling finding an Australian female research chemist. it would be great if you had any suggestions.
thanks

Hey welcome to the forums!
did a quick search you can use :
Professor Michelle Coote
This website has some good info http://rsc.anu.edu.au/~mcoote/
But quite frankly if you are looking for more info use a male chemist.
Anyways goodluck if you need help let me know

[justwannawish]

How do I do this question:
Calculate the pH of the solution produced by mixing 50ml of 0.1M HCl with 20mL of 0.05M NaOH

[Natasha.97]

How do I do this question:
Calculate the pH of the solution produced by mixing 50ml of 0.1M HCl with 20mL of 0.05M NaOH

Hi!

1. Write out the balanced equation between the reactants
2. Calculate the moles of H⁺ and OH^- by using the formula c=nv (make sure that the volume is in L!)
3. Calculate the difference between the two values to determine the excess H⁺ moles
4. Calculate the concentration of H^-: divide moles by the total volume
5. Use the formula pH = -log₁₀[H⁺] to find the pH.

I’ve attached my working in case you get stuck, hope this helps

Edit: Fixed superscript

[JaredMayo]

Hey do any of you think you could describe the processes of complete ionisation (dissociation) and incomplete ionisation (dissociation) (using balanced  equations with states of matter)

[Natasha.97]

Hey do any of you think you could describe the processes of complete ionisation (dissociation) and incomplete ionisation (dissociation) (using balanced  equations with states of matter)

Hi!

Strong acids such as Hydrochloric Acid (HCl) undergo complete ionisation (all acid molecules have ionised to hydronium ions).
HCl_(g) + H₂O(l) → H₃O⁺_(aq) + Cl^-_(aq)

Weak acids such as Acetic Acid (CH₃COOH) undergo incomplete ionisation (some acid molecules have ionised to hydronium ions).
CH₃COOH_(aq) + H₂O_(l)  ⇌  H₃O⁺_(aq) + CH₃COO^-_(aq)

Here is a diagram to illustrate:


Hope this helps

Edit: Added states