Molar excess means using more than the theoretical 1:1 ratio of NMT to aspirin. Different molecules each have their own molecular weights (MW) according to the numbers and types of atoms they contain (as you probably know). A 1:1 molar ratio of NMT to aspirin for 'x' mg NMT would require:

'x' *(MW[aspirin]/MW[NMT]) mg aspirin (Let's call this equation 'A' for the moment) So, that's divide the MW of aspirin by the MW of NMT and multiply by the mass of NMT to be used.

- I'll let you do the maths. Remember to take the mass of the counter ion (e.g. fumarate, acetate) into account if weighing an NMT salt.

I'm not sure if the 1.2 molar excess means to use 2.2 times the theoretical 1:1 amount - i.e. 1 part NMT to 2.2 parts aspirin, or merely 1:1.2, I'll look back and check. Anyhow, to get the correct amount of aspirin required for the reaction, multiply the result of equation 'A' above by 2.2 (or 1.2).

EDIT: I've been and looked back through the thread. The original post refers to the 1.2 molar excess and there's no further clarification, so I'd take it to mean 2.2 times the theoretical amount of aspirin. In particular this greater amount of aspirin would drive the reaction nearer to completion.