When 20.0 g of C7H6O3and 20.0g of C4H6O3 react, which is the limiting reagent?

Question

Aspirin, C9H8O4, is synthesized by the reaction of salicylic acid, C7H6O3, with acetic anhydride, C4H6O3. 2C7H6O3 + C4H6O3 → 2 C9H8O4 + H2O

 

A) When 20.0 g of C7H6O3and 20.0g of C4H6O3 react, which is the limiting reagent? 

 B) If 19.7 g of aspirin were produced in an experiment, what is the percent yield?

Answer 1

Hi Ciarra Z.,

Your strategy on this type of problem is cut-and-dried.

1) Convert any masses to moles of material, using molar masses of each material (you may have to calculate these, or they may be given you).

2) Convert the moles values into reaction-equivalents. What I mean by that is, if you had 2 moles of something, but the reaction was for a coefficient of 2 in that material in the balanced equation, you would have only 1 reaction-equivalent of that material (2/2=1)

3) Compare across the equation for your various reaction-equivalent values. (Note: you will usually be comparing 1 reactant and 1 product, or 1 reactant and another reactant.) The lowest of these values is the "limiting material", and the reaction can only proceed based on using that material completely and any other reactants (typically) in proportion to that, as the reaction coefficients indicate.

4) You can also figure from the limiting reaction-equivalent reactant, over to the products generated in proportion as in (3).

5) If required, convert the product reaction-equivalents into moles and then into masses.

-- Cheers, --Mr. d.

Remember: the purpose of these problems is to learn the technique above. It's both a procedure, and a way of thinking about matter. Master the technique, and the problems are easily solved thereafter. Just go through the motions of solving, without thinking about what you are doing, and the problems remain hard thereafter. Your choice!