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Your structure for acetic acid is correct and so is your balanced equation.
To find theoretical yield, you will first need to find the limiting reactant. First convert everything to moles.
Salicylic acid (138 g/mol):
185 kg = 185000g
185000 g / (138 g/mol) = 1341 moles (wow, large scale!)
Acetic Anhydride (102 g/mol):
125kg = 125000g
125000g / (102 g/mol) = 1225 moles
Based on your balanced equation, there is a one to one mole ration between salicylic acid and acetic anhydride, which makes things easier. Basically, you need to determine which reactant runs out first (limiting reactant). Because the mole ratio is 1:1, in this case the limiting reagent is the one with the least number of moles (acetic anhydride).
Because there is a 1:1 mole ratio between acetic anhydride and aspirin (every 1 mole of acetic anhydride that you use up produces one mole of aspirin), your theoretical yield of aspirin (in moles) is 1225 moles. Theoretical yields are normally reported in grams, so you'll need to convert 1225 moles of aspirin to gram of aspirin (144 g/mol).
I get 220500g. Based on significant figures, it would be 221kg. That's a lot of aspirin.
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