Pharmaceutical Calculations (part 1), Exercises of Pharmacy

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Pharmaceutical

Calculations

How much solute is present in 80ml of 20% w/v

aqueous solution?

Solution: 100 ml contains 20gm 80 ml contains 20 × 80 100 = 16 gm Ans. 16 gm of solute is present in 80ml of 20% w/v aqueous solution.

How many milliliters of a 1:5000 w/v solution of the

preservative lauralkonium chloride can be made from

125 ml of a 0.2% w/v solution of the preservative?

Solution: V 1

S

1

= V

2

S

2

V

1 = 125 ml, S 1 = 0.2 % w/v V 2

125 × 0. 2

. 02

S

2

1 × 100 5000 = .02 %w/v = 1250 ml (Ans.)

How many milliliters of water should be added to 80 ml

of a 20% w/v aqueous solution of a drug to prepare a

3% w/v solution?

Solution: V 1

S

1

= V

2

S

2 V 1

× 3% = 80 × 20%

V

1 = 533.3 ml So, volume of added water should be = 533.3 – 80 = 453.3 ml (Ans.)

4 mg of NaCl is dissolved in 8 kg of solution. What is the concentration of

NaCl in ppm?

Solution: Ppm = 𝒈𝒎 (𝒔𝒐𝒍𝒖𝒕𝒆) 𝒈𝒎 (𝒔𝒐𝒍𝒖𝒕𝒊𝒐𝒏)

× 10

6

. 004 8000

× 10

6 = 0.5 ppm ( Ans.)

The concentration of KI is 150 ppm in a solution with a mass of 7500

gm. How many grams of KI is present in the solution?

Solution: 150 ppm = 𝑥 𝑔𝑚 7500 𝑔𝑚

6 = 1.125 gm KI.

If a commercially available insulin preparation contains

1 ppm of proinsulin, how many micrograms of proinsulin

would be contained in a 10 ml vial of insulin?

Solution: We know, Ppm = 𝒈𝒎 (𝒔𝒐𝒍𝒖𝒕𝒆) 𝒈𝒎 (𝒔𝒐𝒍𝒖𝒕𝒊𝒐𝒏)

× 10

6 Given, Concentration= 1 ppm 1 = 𝑥 𝑔𝑚 10 𝑔𝑚

× 10

6 Volume of solution= 10 ml = 10

• 5 g = 10 μ𝑔 Therefore, mass of solution= 10 g [since, 1ml= 1 gm for water and in this case, for water based solution]