!! HL Chemistry 2015 - discussion, guesses, predictions, explosions, etc.

OMGeary

What's the probability of there being 2 experiments in 1 question, because they did it with physics and biology this year?

Chocolalla

OMGeary wrote: »

What's the probability of there being 2 experiments in 1 question, because they did it with physics and biology this year?

I don't understand what you mean , of course there's going to be one not even one three experiments ???

OMGeary

What I mean is there's three experiment questions in chemistry. In physics there are 4 experiment questions, but today Q4. was made up of 2 experiments. Is it possible that lets say Q3. will be on 2 experiments as opposed to one

m.xvii

Anyone in an institute have any predictions, seem to have been pretty accurate up to now. Have most things covered, just want to know what to look over this final night.

Jason_H

OMGeary wrote: »

What I mean is there's three experiment questions in chemistry. In physics there are 4 experiment questions, but today Q4. was made up of 2 experiments. Is it possible that lets say Q3. will be on 2 experiments as opposed to one

They did that for organic in 2013!

Chocolalla

OMGeary wrote: »

What I mean is there's three experiment questions in chemistry. In physics there are 4 experiment questions, but today Q4. was made up of 2 experiments. Is it possible that lets say Q3. will be on 2 experiments as opposed to one

Ohh , well chromatography and clove oil came up as Q2 in 2008

dazzadazza

EaSwe wrote: »

Mandatory Experiment 15: To investigate Le Chatelier's Principle using the reaction between iron (III) chloride and potassium thiocynate

There are videos of all the experiements on Folens' website, if you sign up and add the chemistry live videos to your bag and checkout (it's free for everyone regardless of your book) https://www.folens.ie/digital-products/lc-chemistry-live-experiment-videos

I just did this can you view the videos now online? Or do they have to get sent to my house?

EaSwe

dazzadazza wrote: »

I just did this can you view the videos now online? Or do they have to get sent to my house?

Yep you can view them straight away..
There's instructions here
It's a bit cumbersome but the videos and explanations are great

Notsolovely

Would it be alright to go for all 11 answers? And leave the markers to pick the best 8. Or would you think that going over the original 8 answers is always the best strategy?

Doctorhopeful

Notsolovely wrote: »

Would it be alright to go for all 11 answers? And leave the markers to pick the best 8. Or would you think that going over the original 8 answers is always the best strategy?

My class did all past papers up to 2002 so I'm in the same boat of *probably* being able to answer all the questions. Normally I just do nine which gives me a buffer because there's usually one question I accidentally misinterpret :P going for all 11 seems like overkill to me but by all means go for it if you feel confident doing that!

Doctorhopeful

How many people actually bothered doing an option? Can't find any motivation whatsoever to do one and i've had since march :L they're both so boring, and i'm so indecisive....

Cheerios

Notsolovely wrote: »

Would it be alright to go for all 11 answers? And leave the markers to pick the best 8. Or would you think that going over the original 8 answers is always the best strategy?

My teacher said not to go into the exam thinking that you're going to do all 11 questions. Do the 8 that you think you can answer best and read over them after you have finished. If you are 100% confident with your work and have spare time, only then should you answer the remaining 3 questions.

Chocolalla

Doctorhopeful wrote: »

How many people actually bothered doing an option? Can't find any motivation whatsoever to do one and i've had since march :L they're both so boring, and i'm so indecisive....

i didn't but I'm staying up until i have mastered the option and equilibrium

The_N4sir

Hopefully a full questions on water and equilibrium come up in section B. Absolutely love them. The short questions are much more consistent than physics for example IMO. Hopefully Iron tablet, ethene/ethyne and benzoic acid come up.

Going for an A1 myself so hopefully the exam goes well

Fiona G

Anyone know the purpose of adding sulfuric acid to the conical flask in the sodium thiosulfate/iodine titration? Can't find an explanation and they love throwing up those sort of questions.

Is it just to supply H+ for the reaction?

Deranged96

Ok lads, 11th hour section A predictions, lay em on me!

MmmPancakes

Deranged96 wrote: »

Ok lads, 11th hour section A predictions, lay em on me!

Just taking a look at the front of my papers,
Ethyne
Vinegar
Iodine - Thiosulfate Titration
Rate of production of oxygen
Clove Oil
New one: Preparation of Benzoic Acid
Free Chlorine/Suspended Solids?

What comes up every year in Section b?

Deranged96

MmmPancakes wrote: »

Just taking a look at the front of my papers,
Ethyne
Vinegar
Iodine - Thiosulfate Titration
Rate of production of oxygen
Clove Oil
New one: Preparation of Benzoic Acid
Free Chlorine/Suspended Solids?

What comes up every year in Section b?

Water came up every year bar last year so that'll be up no question.

Q5 is always atomic theory.

Rates and Equilibrium are two chapters that are staples of section B, I think they've always featured but not sure.

Always a heat of reaction question.

Nearly always an organic chemistry reaction mechanism and last year it was a substitution reaction so this year it's expected to be an addition mechanism.

Chocolalla

Deranged96 wrote: »

Ok lads, 11th hour section A predictions, lay em on me!

Chromatography

123mad

Deranged96 wrote: »

Ok lads, 11th hour section A predictions, lay em on me!

Iron tablet

Niamhjkl

Fiona G wrote: »

Anyone know the purpose of adding sulfuric acid to the conical flask in the sodium thiosulfate/iodine titration? Can't find an explanation and they love throwing up those sort of questions.

Is it just to supply H+ for the reaction?

Yes, the use of the dilute sulfuric acid is to provide enough H+ ions for the complete reduction of the MnO4 ( excuse the large 4) to Mn^2+.
Best of luck

lc2015x

Last minute question lads! Is it too risky to leave out all of organic chemistry? I didn't attempt any of those questions in the mocks & still got myself a C1 (aiming for a B1 now) I know the other chapters in great detail. Should I practice organic questions for the next few hours or just leave it altogether and just have a look over the main topics? Thanks!

Deranged96

lc2015x wrote: »

Last minute question lads! Is it too risky to leave out all of organic chemistry? I didn't attempt any of those questions in the mocks & still got myself a C1 (aiming for a B1 now) I know the other chapters in great detail. Should I practice organic questions for the next few hours or just leave it altogether and just have a look over the main topics? Thanks!

If I were you anyway I'd go over heats of reactions (if you're including that in organic chem) and C2H2 experiment, prep of benzoic acid and the clove oil experiment.

lc2015x

Deranged96 wrote: »

If I were you anyway I'd go over heats of reactions (if you're including that in organic chem) and C2H2 experiment, prep of benzoic acid and the clove oil experiment.

have benzoic studied anyway, and as far as clove oil, I've the jist of it, thanks!
I kind of meant the theory here, bit late too study all the definitions, structures and mechanisms associated with organic?

Deranged96

lc2015x wrote: »

have benzoic studied anyway, and as far as clove oil, I've the jist of it, thanks!
I kind of meant the theory here, bit late too study all the definitions, structures and mechanisms associated with organic?

Well I don't know what your abilities are, but I wouldn't be able to learn enough theory to be able to attempt an extra question in the three or so hours that are left.

If you were going to study anything though I'd go addition mechanism

seinstein1

can anyone here pleasee send me some notes on the new benzoic acid experiment. i am desperate...

Dawn96

seinstein1 wrote: »

can anyone here pleasee send me some notes on the new benzoic acid experiment. i am desperate...

If you put 'preparation of benzoic acid' into google, the second result (Gill McMahon) has AMAZING notes on the experiment

Cheerios

seinstein1 wrote: »

can anyone here pleasee send me some notes on the new benzoic acid experiment. i am desperate...

Here are the notes my teacher gave us.

Procedure:
1. A known mass of phenylmethanol (benzyl alcohol), a saturated solution of potassium permanganate, and a solution of sodium carbonate are heated in a concial flask for approximately 20 minutes in a boiling water bath.

Observation:
- The purple colour changes to brown.
- A brown percipitate is formed.

Explanation:
- The potassium permanganate solution is saturated to ensure that sufficient is present to oxidise all the phenylmethanol completely to benzoic acid.
- The sodium carbonate ensures that the solution is alkaline as this oxidation reaction works best at an alkaline pH, i.e. the rate of reaction is greatest under alkaline conditions.
- As the reaction proceeds, the colour changes from purple (the colour of the manganese ion in an oxidation state of +7) to brown (the colour of the manganese ion in an oxidation state of +4), i.e. there is a reduction of Mn(VII) to Mn(IV) and the phenylmethanol is oxidised to benzoic acid.
- The brown percipitate is manganese dioxide (MnO2), which is not soluble in water.


Procedure:
2. The conical flask and its contents are cooled by running cold water over the outside of the conical flask.
3. In the fume cupboard, concentrated hydrochloric acid is added to the conical flask.
4. A glass rod is dipped in the solution and touched against a piece of damp blue litmus paper to check that the contents of the conical flask are acidic.

Explanation:
- A compound called sodium benzoate is produced as an intermediate in this reaction. It is necessary to add concentrated hydrochloric acid in order to convert sodium benzoate to benzoic acid. Since benzoic acid is only slightly soluble in cold water, this helps to percipitate out the benzoic acid. In addition, the hydrochloric acid neutralises any excess sodium carbonate added and the potassium hydroxide produced in the reaction. The third reason for adding the HCl is to provide an acidic medium to enable the Mn4+ ions in manganese dioxide to be reduced to soluble Mn2+ ions.


Procedure:
5. Using a dropper, sodium thiosulfate solution (Na2SO3) is added to the conical flask until the brown percipitate reacts fully with it.

Observation:
- Brown percipitate disappears.
- White crystals are now visible in the flask.

Explanation:
- Sodium sulfite is a reducing agent and reduces Mn4+ ions (insoluble) to Mn2+ ions (soluble). It is necessary to reduce the insoluble solid specks of brown manganese dioxide (MnO2) before filtering off the benzoic acid crystals as these brown specks would contaminate the benzoic acid.
- The half reactions are:
Mn4+ (insoluble) + 2e- ====> Mn2+ (soluble)
SO32- + H2O ====> SO42- + 2H+ + 2e-
- The white crystals of benzoic acid become visible as the brown percipitate disappears.


Procedure:
6. The conical flask is placed in ice.
7. The white crystals formed are filtered off using a Buchner flask , Buchner funnel and filter paper.
8. The conical flask is washed out with the clear liquid from the Buchner flask, i.e. with the liquid obtained by filtration (the filtrate).
9. The crystals are washed with ice-cold water.
10. The damp crystals are allowed to air dry overnight and then placed in a desiccator.
11. The mass of crystals formed is measured.

Explanation:
- Since benzoic acid has low solubility in cold water, the conical flask is placed in ice to maximise the yield of crystals.
- The crystals are filtered off using suction filtration with the aid of a Buchner flask and Buchner funnel since this type of filtration speedsu p the filtration process. In addition, it helps to dry the crystals.
- The conical flask is rinsed out with the filtrate from the Buchner flask to remove any crystals of benzoic acid that remain in the conical flask.
- The crystals are washed with ice-cold water to remove any soluble impurities that may be present on the filter paper or adhering to the crystals.

Sorry if there are any spelling mistakes I was tryna type fast. :P

seinstein1

Dawn96 wrote: »

If you put 'preparation of benzoic acid' into google, the second result (Gill McMahon) has AMAZING notes on the experiment [/QUOTE

seinstein1

Thanks a lot cheerios

Quarks

Best of luck lads