Question

0.3926 g of salicylic acid is dissolved in water and made up to 250.0 mL in a volumetric flask. Then, 4.00 mL of this solution is pipetted into a 50.0 mL volumetric flask and diluted with water to the mark. What is the final salicylic acid concentration?

Answer 1

salicyclic acid formula is C7H6O3

Molar mass of C7H6O3,

MM = 7*MM(C) + 6*MM(H) + 3*MM(O)

= 7*12.01 + 6*1.008 + 3*16.0

= 138.118 g/mol

mass(C7H6O3)= 0.3926 g

use:

number of mol of C7H6O3,

n = mass of C7H6O3/molar mass of C7H6O3

=(0.3926 g)/(1.381*10^2 g/mol)

= 2.842*10^-3 mol

volume , V = 2.5*10^2 mL

= 0.25 L

use:

Molarity,

M = number of mol / volume in L

= 2.842*10^-3/0.25

= 1.137*10^-2 M

use dilution formula

M1*V1 = M2*V2

1---> is for stock solution

2---> is for diluted solution

Given:

M1 = 1.137*10^-2 M

V1 = 4 mL

V2 = 50 mL

use:

M1*V1 = M2*V2

M2 = (M1*V1)/V2

M2 = (1.137*10^-2*4)/50

M2 = 9.096*10^-4 M

Answer: 9.096*10^-4 M