Question

Can someone show me how to calculate theoretical yield using glacial acetic acid as an example?

Answer 1

Solution:

The yield calculation that you perform for most synthetic procedures is based on the comparision of moles of product isolated and moles of product that you can theoretically obtain based on the the limiting reagent.

Let's look at one simple example. Suppose, a student reacts 30.0 g acetic acid and 100 mL of ethanol in the presence of 2 mL of concentrated sulfuric acid and he obtains 42 g of the crude ester and 39.5 g after purification (distillation).

Step 1: Write balanced equation ( in presence of H2SO4)

CH3COOH + CH3CH2OH = CH3COOCH2CH3

MW 60g 46g 88g

Step 2:Identify limitiing reagent- For this calculate the no of moles of each reagent, and in this case we find the minimum no of moles of H2SO4 and hence it is limiting reagent.

Step 3: Calculation of yield

Firstly, How many moles of the product did he isolate?

This is calculated by weight divided by MW.

Crude: 42 g/(88 g/mol)= 0.47 mol

Purified: 39.5 g/(88 g/mol)=0.45 mol

b. Yields:

Calculate the moles of CH3COOH= weight/ MW = 30g / 60g = 0.50 mol

Then, Yield = [actual number of moles ( moles of ester )/theoretical number of moles (moles of acetic acid)x100%]

Crude yeild = (0.47 mol/0.50 mol) x100% = 94%

Purified yeild = (0.45 mol/0.50 mol) x 100% = 90 %