EXPERIMENT # ___02___

OBJECT:  Preparation of stock solution and serial dilutions of sodium hydroxide (molecular formula: 39.997)

REQUIREMENT:

Sodium hydoxide, Weighing balance, water bath, Warm water, pipettes, beaker, stirrer, volumetric flask (100ml, 50ml, 25ml)

THEORY:

STOCK SOLUTION:

These solutions are frequently prepared or purchased by the pharmacists to facilitate dispensing of pharmaceutical preparations. Stock solutions are of higher concentrations which are used to prepare solutions of lower concentration (dilution).

SERIAL DILUTION:

These are solutions of lower concentration which are prepared in series from the stock solution.

APPLICATION OF SERIAL DILUTION:

Serial dilutions of antibiotics are prepared and their antibacterial activity is observed and MIC (minimum inhibitory concentration) is also determined. During preclinical testing of new investigational drugs, serial dilutions of drugs are prepared and then tested on animals to assess toxicity.

Sodium hydroxide (NaOH 39.997) also known as lye and caustic soda, is a caustic metallic base. It is used  in many industries, mostly as a strong chemical base in the manufacture of pulp and paper, textiles, drinking water, soaps and detergents and as a drain cleaner. It is hygroscopic and readily absorbs water from the air, so it should be stored in an air tight container. It is very soluble in water with liberation of heat. Sodium hydroxide is completely ionic, containing sodium cations and hydroxide anions.

PROCEDURE:

·         Calculate the amount of sodium hydroxide from the given formula for preparation of normal stock solution in 100ml volumetric flask.

                        Amount = conc.  x  molecular weight   x 100

                                                                  1000

·         Rinse all glassware with water.

·         Weigh sodium hydroxide and slowly dissolve it in water in a beaker on water bath

·         Transfer the solution in 100ml volumetric flask and make up the volume with warm water up to the mark. Stock solution is prepared.

·         Now for preparing dilutions of different concentrations from the stock, calculate the volume required to make further dilutions from the given formula.

                                                           m1v1=m2v2

·         Pour the required amounts in the flasks and make up the volumes with warm water.

RESULT:

After producing the stock solution of 100ml in warm water having 0.5 molarity we produces two serial dilutions, one having 0.1 molarity in 50ml warm water and other having 0.01 molarity in 25ml warm water.

                                                                                                                                                                                                             CALCULATION:

·         To prepare the stock solution we uses this formula

     Amount = conc.  x  molecular weight   x 100

                                               1000

Amount =  0.5 x  39.997  x  100

                               1000

Amount =  1.999

·         To prepare dilution having normality of 0.01 we use the formula.  

                 n1v2 = n2v2 

                 0.5 v2 = 0.1 x 50

                 v2 = 0.1 x 50

                               0.5

                 v2 = 10ml

·         To prepare dilution having normality of 0.001 we use the formula.

n1v1 = n2v2

0.1 v2 = 0.01 x 25

v2 = 0.01 x 25

             0.1

v2 = 2.5ml