MedVision ad

Predictions for Chemistry 2014 HSC? (8 Viewers)

MrBeefJerky

Member
Joined
Jul 10, 2013
Messages
62
Gender
Undisclosed
HSC
2014
why are these questions so easy :(

sorry but like yeah. NO shipwrecks is easier than industrial by far. No calculations, nothing. All rote and stuff.

Since no one is answering,

btw how many marks?
I find calculations much easier than rote learning stuff
 

enigma_1

~~~~ Miss Cricket ~~~~
Joined
Feb 27, 2013
Messages
4,281
Location
Lords
Gender
Female
HSC
2014
produce ester: let's make ethyl butanoate

1) Add 30 ml Ethanol and 20 ml butanoic acid to a round bottomed flask. Excess of the ethanol is added coz it's cheaper #cheapos

2) Add 5ml of concentrated sulphuric acid (as a dehydrating agent to shift the equilibrium in the forward direction --> increas yield of ester AND it's a catalyst so it increases the rate of the reaction making it go faster) and add some ceramic boiling chips (anti bumping granules to allow the even heating of the liquid and to increase surface area for vaporisation to occur on)

3) Attach a condenser to the the round bottomed flask with the reactants and stuff in it (used because the system is in equilibrium and if the reactants evaporate then like the equilibrium will shift in the reverse direction and reduce yield of ester which is bad). The round bottomed flask is placed in a water bath to allow even heating of water BUT a better thing to use is the heat plate because the reactants are volatile. I think in hsc we should write that we used a heat plate lol. cheap schools.

4) Anyway next put the Bunsen Burner on top of a heat mat and put it under the reaction vessel. (or use the heat plate)

5) Pass the cooling water through the condenser so it condenses the reactants, preventing evaporation and preventing the equilibrium from shifting to the left. Turn on Bunsen burner and the reaction occurs for half an hour at 100 degrees Celsius.

6) then after 30 mins, turn off the Bunsen burner and let the cooling water pass through for a while. after it's cooled, take the round bottomed flask and pour the ester mixture into a separating funnel. 20 ml of NAHCO3 was added to the separaring funnel, this is because NaHCO3 is amphiprotic and it acts as a base :. neutralising the excess butanoic acid which may remain unused in the reaction. The mixture was shaken and left to stand. The lower aqueous layer was drained off.

7) then add 20ml of DISTILLED WATER to the separating funnel. Since water is a polar substance, it would dissolve the excess polar ethanol if there is any because likes dissolve likes. Again shake it and drain off the lower aqueous layer leaving only the ester and you've successfully purified the ester ethyl butanoate (I hope ;) )

Pretend I drew the diagram and the equilibrium equation for refluxing

k done

now mark it
 
Last edited:

SuchSmallHands

Well-Known Member
Joined
Nov 13, 2012
Messages
1,391
Gender
Female
HSC
2014
Industrial dominated m8.

Industrial > Shipwrecks.

PRODUCTION OF OCTYL ETHANOATE
- Add 30mL octanol and 15 mL ethanoic acid to a round bottomed flask. An alkanol and an alkanoic acid are the required reactants in esterification.
- Add 2mL of concentrated H2SO4 to act as a catalyst, pushing the equilibrium to the right, for the reaction and a boiling chip to act as a bubble nucleation point and in so doing prevent bumping
- Place reaction vessel in a heating mantle. Attach a condenser which in turn is attached to a tap flowing cool water via one hose, and allows water to flow out of the condenser into a sink via a second hose. Turn the heating mantle on
- Reflux the mixture for a minimum of one hour before allowing it to cool.

REACTION EQUATION
- CH3(CH2)7OH (g) + CH3COOH (g) <---(conc H2SO4)---> CH3(CH2)7CH3COO (g) + H2O (g)
 
Last edited:

SuchSmallHands

Well-Known Member
Joined
Nov 13, 2012
Messages
1,391
Gender
Female
HSC
2014
lol that's effectively the same as me. 2 two hour exams on one day. so we can both bitch. haha besides 3u English doesn't have to count. for me 2u English paper 2 has to count
I actually got my own timetable wrong, 3U isn't until Nov 5. It's 2U on the same day as EE1. And EE1 might not have to count, but come on, it's harder. But then again, Latin extension sounds harder than French, so we're probably about equal in misfortune.
 
Last edited:
Joined
Feb 16, 2014
Messages
2,258
Gender
Male
HSC
2014
produce ester: let's make ethyl butanoate

1) Add 30 ml Ethanol and 20 ml butanoic acid to a round bottomed flask. Excess of the ethanol is added coz it's cheaper #cheapos

2) Add 5ml of concentrated sulphuric acid (as a dehydrating agent to shift the equilibrium in the forward direction --> increas yield of ester AND it's a catalyst so it increases the rate of the reaction making it go faster) and add some ceramic boiling chips (anti bumping granules to allow the even heating of the liquid and to increase surface area for vaporisation to occur on)

3) Attach a condenser to the the round bottomed flask with the reactants and stuff in it (used because the system is in equilibrium and if the reactants evaporate then like the equilibrium will shift in the reverse direction and reduce yield of ester which is bad). The round bottomed flask is placed in a water bath to allow even heating of water BUT a better thing to use is the heat plate because the reactants are volatile. I think in hsc we should write that we used a heat plate lol. cheap schools.

4) Anyway next put the Bunsen Burner on top of a heat mat and put it under the reaction vessel. (or use the heat plate)

5) Pass the cooling water through the condenser so it condenses the reactants, preventing evaporation and preventing the equilibrium from shifting to the left. Turn on Bunsen burner and the reaction occurs for half an hour at 100 degrees Celsius.

6) then after 30 mins, turn off the Bunsen burner and let the cooling water pass through for a while. after it's cooled, take the round bottomed flask and pour the ester mixture into a separating funnel. 20 ml of NAHCO3 was added to the separaring funnel, this is because NaHCO3 is amphiprotic and it acts as a base :. neutralising the excess butanoic acid which may remain unused in the reaction. The mixture was shaken and left to stand. The lower aqueous layer was drained off.

7) then add 20ml of DISTILLED WATER to the separating funnel. Since water is a polar substance, it would dissolve the excess polar ethanol if there is any because likes dissolve likes. Again shake it and drain off the lower aqueous layer leaving only the ester and you've successfully purified the ester ethyl butanoate (I hope ;) )

Pretend I drew the diagram and the equilibrium equation for refluxing

k done

now mark it
- Did not explain importance of reflux, keeps volatile products and reactants in the flask.
- Did not mention that the top of the flask is open, to prevent a pressure build up.

6/7
 

SuchSmallHands

Well-Known Member
Joined
Nov 13, 2012
Messages
1,391
Gender
Female
HSC
2014
- Did not explain importance of reflux, keeps volatile products and reactants in the flask.
- Did not mention that the top of the flask is open, to prevent a pressure build up.

6/7
The question
- did not say to justify safety procedures
- did not say to justify use of reflux
2/7 for correlation between marking criteria and content of question
 

enigma_1

~~~~ Miss Cricket ~~~~
Joined
Feb 27, 2013
Messages
4,281
Location
Lords
Gender
Female
HSC
2014
The question
- did not say to justify safety procedures
- did not say to justify use of reflux
2/7 for correlation between marking criteria and content of question
bs how can you give me 2/7 for that?
 

SuchSmallHands

Well-Known Member
Joined
Nov 13, 2012
Messages
1,391
Gender
Female
HSC
2014
produce ester: let's make ethyl butanoate

1) Add 30 ml Ethanol and 20 ml butanoic acid to a round bottomed flask. Excess of the ethanol is added coz it's cheaper #cheapos

2) Add 5ml of concentrated sulphuric acid (as a dehydrating agent to shift the equilibrium in the forward direction --> increas yield of ester AND it's a catalyst so it increases the rate of the reaction making it go faster) and add some ceramic boiling chips (anti bumping granules to allow the even heating of the liquid and to increase surface area for vaporisation to occur on)

3) Attach a condenser to the the round bottomed flask with the reactants and stuff in it (used because the system is in equilibrium and if the reactants evaporate then like the equilibrium will shift in the reverse direction and reduce yield of ester which is bad). The round bottomed flask is placed in a water bath to allow even heating of water BUT a better thing to use is the heat plate because the reactants are volatile. I think in hsc we should write that we used a heat plate lol. cheap schools.

4) Anyway next put the Bunsen Burner on top of a heat mat and put it under the reaction vessel. (or use the heat plate)

5) Pass the cooling water through the condenser so it condenses the reactants, preventing evaporation and preventing the equilibrium from shifting to the left. Turn on Bunsen burner and the reaction occurs for half an hour at 100 degrees Celsius.

6) then after 30 mins, turn off the Bunsen burner and let the cooling water pass through for a while. after it's cooled, take the round bottomed flask and pour the ester mixture into a separating funnel. 20 ml of NAHCO3 was added to the separaring funnel, this is because NaHCO3 is amphiprotic and it acts as a base :. neutralising the excess butanoic acid which may remain unused in the reaction. The mixture was shaken and left to stand. The lower aqueous layer was drained off.

7) then add 20ml of DISTILLED WATER to the separating funnel. Since water is a polar substance, it would dissolve the excess polar ethanol if there is any because likes dissolve likes. Again shake it and drain off the lower aqueous layer leaving only the ester and you've successfully purified the ester ethyl butanoate (I hope ;) )

Pretend I drew the diagram and the equilibrium equation for refluxing

k done

now mark it
I never did this part and I didn't even realise we were supposed to. You say that you use an amphiprotic solution to act as a base, is the reason you do this instead of just using a base so you can add it in excess without disrupting the pH excessively?
 
Joined
Feb 16, 2014
Messages
2,258
Gender
Male
HSC
2014
Industrial dominated m8.

Industrial > Shipwrecks.

.
The question
- did not say to justify safety procedures
- did not say to justify use of reflux
2/7 for correlation between marking criteria and content of question
For 7 marks, that's what they're looking for. Chemistry is like that, they go way out of the question and require you to write additional info.

For instance in the 7 marker, if you say i used reflux and that's it. Markers will be like wtf is reflux and why did you use it? Hence why you pretty much have to write everything and justify everything.
 

enigma_1

~~~~ Miss Cricket ~~~~
Joined
Feb 27, 2013
Messages
4,281
Location
Lords
Gender
Female
HSC
2014
I never did this part and I didn't even realise we were supposed to. You say that you use an amphiprotic solution to act as a base, is the reason you do this instead of just using a base so you can add it in excess without disrupting the pH excessively?
Potentially yes. I never paid much attention to why it is used but yeah I'm assuming it's also because it produces CO2 (fizzing) since acid + carbonate gives you salt + CO2 + water, and by using NaHCO3 as amphiprotic/amphoteric substance, the heat released in the exothermic neutralisation reaction is much less than if a strong base were used so it is safer in a sense, I suppose.
 

Users Who Are Viewing This Thread (Users: 0, Guests: 8)

Top