Exp no 9 assay of boric acid

pc I

1. Pharmaceutical chemistry I lab (Assay of Boric Acid) Prepared by – Ankita V. Berde Lecturer Indira institute of Pharmacy,Sadavali . Questions and answers as on lab manual of PC I as per MSBTE

2. 1.Write the principle of boric acid assay. It is an alkalimetric titraion where boric acid(weak acid) is titrated with sodium hydroxide(strong alkali). But the drawback is,end point is not sharp.To overcome this glycerine is added to form glyceroboric acid complex,which acts as a strong monobasic acid and can be titrated against standard solution of sodium hydroxide using phenolphthalein as indicator.

3. 2.Write the procedure for standardization of sodium hydroxide. Potassium hydrogen phthalate mehod I.P.2010 Weigh accurately about 5g of potassium hydrogen phthalate,previously powdered and dried at 120 o for 2 hours. Dissolve in 75ml of carbon-dioxide free water. Add 0.1ml of phenolphthalein solution. Titrate with sodium hydroxide solution until permanent pink colour is produced.

4. 3.Write the formula for percentage purity calculation. Ans. Percentage purity of given sample is calculated using the formula V × m × F × 100 % purity =. M × W Where, V = Volume of the standard solution,i.e . burette reading m = Exact calculated molarity of the prepared standard solution. F = Factor. M = Standard molarity of the standard solution. W = Weight of the sample to be assayed used in the titrations.

5. 4.Write the factor calculation of boric acid. In the assay of boric acid,one molecule of boric acid(in the form of glyceroboric acid) reacts with one moolecule of sodium hydroxide.

6. 5.Write the uses of boric acid. Boric acid is used as anti infective in the form of dusting powder. It can be used as local antiseptic in the form of creams,ointments,lotions,etc . Aqueous solutions can be used as mouthwashes,eye lotions,skin lotions and as douches for irrigating the bladder and vagina.

7. 6.Write the assay procedure for boric acid. Weigh accurately about 2.0g of boric acid. Dissolve in a mixture of 50ml of water and 100ml of glycerin previously neutralised to phenolphthalein solution. Titrate with 1M sodium hydroxide using phenolphthalein solution as indicator.

8. 7.Write the use of glycerine in the boric acid assay. Boric acid is a very weak acid and thus it cannot be titrated accurately with an alkali. Glycerin reacts with boric acid to form glyceroboric acid which is a monobasic acid,strong enough to give a satisfactory end point when titrated with a strong base.

9. 8.Write the chemical reaction involved in boric acid assay.

10. 9.Write the standards of boric acid. Ans. As per I.P. 2010,boric acid should contain not less than 99.5% and not more than 100.5% of H3BO3. 10.Write the factor of boric acid assay. Ans.Each 1ml of 1M NaoH is corresponds to 0.06184 g of H3BO3.

11. Thank you! Happy learning!