perthhigh.co.uk

[EuanHunter]

If you have any problems please post your questions here. I'll be checking it regularly with it being the run up to the exam.

[RobynAKidd]

How would you work out question 6.b) from the 2000 paper:

6CO2 + 6H20 = C6H12O6

If 200Kg of Carbon Dioxide were removed by algae, calculate the mass of oxygen that would be produced.

[EuanHunter]

Step 1: write out the information from the question above the relevant bits of the equation:

200kg . . . . . . . . . . . . . . . . . . . ?
6CO2 + 6H2O --> C6H12O6 + 6O2

step 2: use the triangle

no. of moles of CO2 = mass/ RFM ........ RFM= C + 2xO = 12+ 2x16 = 44
.............................= 200kg/44
.............................. = 4.55 moles of CO2

step 3: use the equation

From eqn 6moles of CO2 --> 6 moles O2
therefore 1 mole of CO2 --> 1 mole O2
therefore 4.55 moles of CO2 --> 4.55 moles O2

step 4:use the triangle again

mass of O2 = nm x RFM ....................... RFM O2 = 2x O = 2 x16 = 32
................. = 4.55 x 32
.................. = 145.45 kg of O2


You are almost garanteed to get a question like this in the exam. However they always follow the exact same pattern: triangle, use equation, use triangle again. My step 1 here is just a technique I use to make sure I've read the question properly and have picked out all the relevant information and put it in order.

[KellyMMcIntosh]

I'm totally confused about esters!! Does the functional group(coo) point towards the acid or the alcohol?

Please help!!!

[EuanHunter]

no worries, its the alcohol.

[KellyMMcIntosh]

i found out the answer on evans2chemweb but is there anything else specific that i need to know for the exam-there isn't much in my notes!!

[EuanHunter]

about esters?

[KellyMMcIntosh]

yes

[EuanHunter]

what to know about esters:

1) identifying a compound as an ester --> look for COO group
2) naming esters --> remember alachol before acid
3) drawing the structure of an ester --> from the name or by being given the structure of alcohol and acid, condensation reaction.

4) know how to make them --> its a PPA so more likely to come up

5) hydrolysis of esters --> be able to draw the alcohol and acid formed

6) uses --> they generally smell nice (dont know about the ones yous made mind you!!!) so are used in foods and perfumes

7) fats and oils are natural esters

polyesters --> formed from condensation reactions of a diol and a diacid

think that's it!!!

[KellyMMcIntosh]

Thanks!!

[EuanHunter]

no problem