Dilution and Concentration

Dilution and Concentration - Pharmaceutical preparations can be diluted by: 1- The addition of diluent. 2- Admixture with solutions of lower strength. Pharmaceutical preparations can be concentrated by: 1- The addition of active ingredient. 2- Admixture with solutions of greater strength. 3- Evaporation of the diluent. - Stock solutions: They are strong solutions from which weaker ones may be made.

Dilution and Concentration (quantity) x (concentration) (Concentrated mixture) = (quantity) x (concentration) (Diluted mixture) Example How many milliliters of a 1:5000 (w/v) solution of phenylmercuric acetate can be made from 125 ml of a 0.2% solution ?? Answer 1:5000 = 1 x 100 = 0.02 % 5000 X 0.2 = quantity of diluted solution x 0.02 Quantity of diluted solution = 1250 ml

Alligation Definition: is an arithmetical method of solving problems that involve the mixing of solutions or mixtures of solids possessing different percentage strengths. Alligation medial: is a method by which the percentage strength of a mixture of two or more substances whose quantities and concentrations are known may be calculated. Alligation alternate: is a method by which we may calculate the number of parts of two or more components of a given strength when they are to be mixed to prepare a mixture of desired strength.

Alligation Examples 1- What is the percentage (v/v) of alcohol in a cough mixture containing 500 ml of terpin hydrate elixir, 100 ml of chloroform spirit, and enough hydriodic acid syrup to make 1000 ml? Terpin hydrate elixir contains 40% (v/v) of alcohol, and chloroform spirit contains 90% (v/v) of alcohol? Answer X 500 = 20000 90 x 100 = 9000 0 x 400 = 0 Totals: 1000 29000 % = 29000 / 1000 = 29%

Alligation 2- A hospital pharmacist wants to use three lots of ichthammol ointment containing respectively 50%, 20% and 5% of ichthammol. In what proportion should they be mixed to prepare a 10% ichthammol ointment ?? Answer 50% 5 parts of 50% ointment 20% 5 parts of 20% ointment 10% 5% 40 + 10 parts of 5% ointment