Question

A solution of oleic acid has a concentration of 3.50 x 10-4 M. The following operations are carried out. i) A 1 mL sample of this solution is diluted with 9 mL of petroleum ether forming solution A. ii) Two milliliters of this solution A is taken and further diluted with 8mL of petroleum ether, forming solution B. How many grams of oleic acid are contained in 5 mL of solution B? (molar mass for oleic acid is 282 grams/mole)

Answer 1

A solution of oleic acid has a concentration of 3.50 x 10-4 M. The following operations are carried out.

i) A 1 mL sample of this solution is diluted with 9 mL of petroleum ether forming solution A.

M1V1 = M2 V2

3.50 x 10-4* 1 ml = M2* 9 ml

M2 = 3.89*10^-5 M

ii) Two milliliters of this solution A is taken and further diluted with 8mL of petroleum ether, forming solution B.

M2V2 = M3V3

3.89*10^-5 M *2 ml = M3 * 8 ml

M3 =9.72*10^-6 M

How many grams of oleic acid are contained in 5 mL of solution B? (molar mass for oleic acid is 282 grams/mole)

Now calculate the moles of oleic acid in 5 ml

Number of moles = molarity * volume in L

= 9.72*10^-6 M * 5 ml *1 L/1000 ml

= 4.86*10^-8 moles

Amount in g = number of mole s* molar mass

= 4.86*10^-8 moles * 282 grams/mole

= 1.37*10^-5 g

= 0.0137 mg