If 1.20 grams of salicylic acid is reacted with excess methanol, what mass of ester should you expect to achieve theoretically?

Molar masses of..
salicylic acid is 138.13g/mol
methanol is 32.05g/mol
ester (methyl salicylate) is 152.16g/mol

Mole ratio
1:1

My work:
1. 1.20 g salicylic acid (1 mol salicylic acid/138.13 g salicylic acid) = 0.008687468 mol salicylic acid

2. 0.008687468 mol salicylic acid (1 mol ester/1 mol salicylic acid) = 0.008687468 mol ester

3. 0.008687468 mol ester (152.16 g ester/1 mol ester) = 1.32 g ester


so 1.32g of ester would be expected.

Is my work correct? or do I have to use the excess reagent to find the mass of the product?

No, you always use the limiting reagent. By definition, it is the component that limits the amount of product formed.

 

Using your molar masses and mass amounts, I get the same answer.