aCalculate the amount of acetyl salicylic acid ASA MW180158g

a)Calculate the amount of acetyl salicylic acid (ASA; MW180.158g/mol) to prepare 100 mLof a 0.013 M stock solution.

b)In measuring exactly about the amount in part “a”, you actually weigh 0.2150 g. This sample is then hydrolyzed with NaOH (to convert it to salicylic acid, SA), and

quantitatively transferred to a 100 mL volumetric flask. Calculate the actual concentration of the SA stock solution.

Solution

Ans a. M = 0.013 moles/L

Molarity of a solution is given by the relation = number of moles of solute/volume in L = n/V

n = w/m.w, m.w = 180.158 g/mol and V = 0.1 L

So w = M x L x m.w = 0.013 x 0.1 x 180.158 = 0.2342 g

Ans b,

1 mole of acetyl salicylic acid (180.158) will give 1 mole of Salicylic acid (138.121)

Hence 0.2150 g of acetyl salicylic acid will give = (138.121/180.158) x 0.2150 = 0.1648 g of salicylic acid

Hence molarity of SA solution will be

n = 0.1648/138.121 = 1.193x10(-3)

V = 0.1 L

M = n/V = 0.0119 moles/L