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Aspirin (C9H8O4) is synthesized by the re-
action of salicylic acid (C7H6O3) with acetic
anhydride, C4H6O3.

2C7H6O3 + C4H6O3 →2C9H8O4 + H2O

When 12 g of C7H6O3 and 12 g of C4H6O3
react, How much of the excess reactant is used
when the reaction is complete?

Answer in units of mol.

Respuesta :

1 Calculate the molar mass of salicylic acid (C7H6O3):
Molar mass of C7H6O3 = (7 x atomic mass of C) + (6 x atomic mass of H) + (3 x atomic mass of O)
= (7 x 12.01) + (6 x 1.008) + (3 x 16.00)
= 91.08 + 6.048 + 48.00
= 145.128 g/mol

2 Calculate the molar mass of acetic anhydride (C4H6O3):
Molar mass of C4H6O3 = (4 x atomic mass of C) + (6 x atomic mass of H) + (3 x atomic mass of O)
= (4 x 12.01) + (6 x 1.008) + (3 x 16.00)
= 48.04 + 6.048 + 48.00
= 102.088 g/mol

3 Calculate the number of moles of salicylic acid (C7H6O3) and acetic anhydride (C4H6O3) used:
Number of moles of C7H6O3 = 12 g / 145.128 g/mol
= 0.0827 mol
Number of moles of C4H6O3 = 12 g / 102.088 g/mol
= 0.1176 mol

4 Determine the limiting reactant by comparing the moles of each reactant used. The reactant that produces the least amount of product is the limiting reactant.
From the balanced equation, 2 moles of C7H6O3 react with 1 mole of C4H6O3.
Since the molar ratio is 2:1, C4H6O3 is the limiting reactant.

5 Calculate the amount of excess salicylic acid (C7H6O3) used:
Amount of excess C7H6O3 used = 0.0827 mol - (0.1176 mol / 2)
= 0.0239 mol

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