Question

In the given synthesis of Aspirin, Both components react in 1:1 mole ratio. If we take 20 grams of Salicylic acid and 20 grams of Acetic anhydride in a reaction mixture. The limiting reagent would be

Answer 1

Molar Mass of Salicylic acid = (7 x 12) + (6 x 1) + (3 x 16) g/mol = 84 + 6 + 48 g/mol = 138 g/mol

Molar Mass of Acetic anhydride = (4 x 12) + (6 x 1) + (3 x 16) g/mol = 48 + 6 + 48 g/mol = 102 g/mol

Given that, salicylic acid and acetic anhydride reacts in 1:1 mole ratio,

Therefore, let's determine the moles of both the components:

We know,

Therefore,

Moles of Salicylic acid = (20 g/ 138 g/mol) = 0.145 mol

Moles of acetic anhydride = (20 g/ 102 g/mol) = 0.196 mol

Now, by definition, Limiting reagent is that species which is present in lesser amount and is therefore, completely consumed during a reaction.

Here, salicylic acid is present is lesser amount, therefore, it is the limiting reagent!