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Preparation of ethyl ethanoate, stuck on one part

Hi all. Youve been really great helping me out before, hope someone can help me with this :smile:

One of our practicals involve the preparation of this ester. Then we have to do some calculations, and I get stuck on one part I dont understand. So here is the setup:

1. Place 20cm3 of pure ethanoic acid and 12 cm3 of ethanol in a round bottom flask
2. Add carefully 8cm3 of conc H2SO4
3. Arrange the apparatus for reflux and heat gently for 25-30 minutes
4. After cooling, rearrange the apparatus for distillation and distill off about 20cm3 of distillate
5. place the distillate in a separating funnel and wash the product twice with 10cm3 portions of sodium hydrogen carbonate solution
6. Dry the ester over anhydrous calcium chloride
7. Finally distill collecting the distillate which boils over the range 99-103

The question is to calculate theoretical yield from actual yield. Actual yield was 7.16

So, guided points have us starting calculating the RMM of ethanol and ethyl ethanoate (46 and 88 respectively). No problem, I understand that.

The next step though, has us calculating the moles in "12cm3 (0.8 m/cm3 density)"

I have written down this is 9.6/46 = 0.21, and my notes proceed from there. But I dont understand where this 9.6 comes from, or what 0.8 density means. (or where the 0.8 figure comes from) Could somebody be so kind as to talk me through this procedure please?

Thanks

Reply 1

skribble

just bumping this, got an exam tomorrow and think this will come up so any help is appreciated :biggrin:

Reply 2

NiceToMeetYou

An exam tomorrow in half term? That sucks :frown:

Percentage yield is just actual yield/theoretical yield

Now, to work out the theoretical yield, you need 2 things.
1. The balanced equation
2. The Mr of each reactant/product

From the balanced equation, work out in moles how much of each reactant you used, as you have volumes you'll need to use number of moles = concentration times volume (in dm)

From this use the balanced equation to work out the ratio that they reactant in
i.e if 1 mole of reactants produced 2 moles of ester the ration is 1:2

From this, times the moles you used by the ratio, this is the theoretical number of moles
Use Moles = mass/mr to convert this into a mass of ester and you have a theoretical yield

I don't know how clear this is, I'm not too good at explaining :frown:

EDIT:
Totally misread your post, ignore this haha

(edited 10 years ago)

Reply 3

username878045

Original post by skribble

just bumping this, got an exam tomorrow and think this will come up so any help is appreciated :biggrin:

I think the 9.6 comes from 12x0.8. The concentration is 0.8 mol/cm^3 and there are 12 cm^3, so simply multiplying them together gets the number of moles (moles = conc x volume).

The value of 0.8 is based upon the chemical you used - it was specifically made up to that concentration.