Preparation and standardization of various molar and normal solutions

Preparation and standardization of various molar and normal solutions

1. PREPARATION AND STANDARDISATION OF VARIOUS MOLAR AND NORMAL SOLUTIONS NEHLA P DEPARTMENT OF PHARMACEUTICAL CHEMISTRY MOULANA COLLEGE OF PHARMACY

2. OXALIC ACID

3. STANDARD N/10 OXALIC ACID SOLUTION (PRIMARY STANDARD) PREPARATION Weigh 6.3 gm of oxalic acid & dissolve in distilled water &finally make up the volume to one liter in a volumetric flask. The standard solution of oxalic acid (Primary standard) is used to find the strength of solutions of alkalies like NaOH , KOH (Secondary standards) whose standard solutions can not be made by direct weighing . SINCE IT IS A PRIMARY STANDARD THERE IS NO NEED TO STANDARDIZE IT

4. SODIUM HYDROXIDE

5. SODIUM HYDROXIDE PRINCIPLE Sodium hydroxide is deliquescent (absorbs moisture from the atmosphere) solid. It cannot be weighed accurately. Therefore, it is not possible to prepare a standard solution of sodium hydroxide of accurately known concentration by weighing NaOH . A sodium hydroxide solution of approximate concentration (0.2 M) is to be prepared. It is then standardized by titrating it against an accurately weighed sample of potassium acid phthalate (KHP), HOOC-C6H4-COOK , which is a primary standard acidic substance. A primary standard substance can be weighed accurately because it is stable (does not decompose) and not hygroscopic (does not absorb moisture from the atmosphere).

6. The reaction between NaOH and KHP (molar mass 204.23 g/mole) is as follows: NaOH + HOOC-C6H4-COOK  NaOOC-C6H4-COOK + H2O By measuring the volume of the ~0.2M NaOH solution dispensed from the buret that is necessary to react completely with a weighed sample of KHP, the exact concentration of NaOH solution is calculated.

7. PREPARATION 1 Normal solution we need to know the, equivalent of NaOH , which is calculated by dividing Molecular weight by 1, that is 40 divided by 1= 40. So the equivalent weight of NaOH is 40. To make 1 N solution, dissolve 40.00 g of sodium hydroxide in water to make volume 1 liter. For a 0.1 N solution (used for wine analysis) 4.00 g of NaOH per liter is needed.

8. METHOD OF STANDARDIZATION Weigh accurately about 2.0 g of potassium hydrogen phthalate, previously powdered and dried at 120 o  for 2 hours, and dissolve in 75 ml of carbon dioxide-free distilled water. Add 0.1 ml of phenolphthalein solution and titrate with the sodium hydroxide solution until a permanent pink colour is produced. Each ml of 1M sodium hydroxide is equivalent to 0.2042 g of C 8 H 5 KO 4 .

9. 1.0 M HYDROCHLORIC ACID

10. 1.0 M HYDROCHLORIC ACID PRINCIPLE Hydrochloric acid is produced in solutions up to 38% HCl (concentrated grade). Higher concentrations up to just over 40% are chemically possible, but the evaporation rate is then so high that storage and handling need extra precautions, such as pressure and low temperature . Laboratory grade hydrochloric acid is not sufficiently pure to be used as a primary standard, because it evaporates easily. A standard solution of sodium carbonate is used to determine the exact concentration of a hydrochloric acid solution. The neutralization reaction that occurs is as follows: Na2CO3 + 2HCl  2NaCl + H2O + CO2 Methyl orange indicator solution is used. At the end-point – when neutralization just occurs – the indicator changes color from yellow to peachpink

11. METHOD OF PREPARATION : Dilute 85.0 ml of concentrate hydrochloric acid with purified water to produce 1000 ml . METHOD OF STANDARDIZATION : Weigh accurately about 1.5 g of anhydrous sodium carbonate, previously heated at about 270° for 1 hour. Dissolve it in 100 ml of distilled water and add 0.1 ml of methyl red solution Add the acid slowly from a burette, with constant stirring, until the solution becomes faintly pink. Heat the solution to boiling, cool and continue the titration. Heat again to boiling and titrate further as necessary until the faint pink colour is no longer affected by continued boiling. Each ml of 1 M hydrochloric acid is equivalent to 0.05299 g of Na 2 CO 3 .

12. SODIUM THIOSULPHATE

13. SODIUM THIOSULPHATE PRINCIPLE The principle of standardization of sodium thiosulphate is based on redox iodometric titration with potassium iodate (primary standard). Potassium iodate is a strong oxidizing agent, it is treated with excess potassium iodide in acidic media which liberates iodine which is back titrated with sodium thioslphate . Uniformity of reactions between iodine and sodium thiosulphate forms basis for utilizing the standard solution of iodine in the analysis of sodium thiosulphate . Sodium thiosulphate is used in the analysis of iodine. In the analysis of iodine starch solution is used as indicator . KIO3 + 5KI + 3H2SO4→ 3K2SO4+3I2+3H2O 3I2+2Na2S2O3 → 2NaI + Na2S4O6

14. METHOD OF PREPARATION : Dissolve 25 g of sodium thiosulphate  and 0.2 g of sodium carbonate in carbon dioxide-free distilled water and dilute to 1000 ml with the distilled water STANDARDISATION OF 0.1N SODIUM THIOSULPHATE Take 10 ml of Potassium Iodate solution .Add 2 gm of Potassium Iodide and 5 ml of dilute H2SO4,keep it in dark for 10 minutes, add 2 to 3 drops of starch indicator and titrate with sodium thiosulphte using starch solution as indicator until the blue colour is disappeared . N 1V 1=N 2V2 N 2 = N 1V1 V 2

15. 1.0 M SULPHURIC ACID (H 2 SO 4 )

16. PRINCIPLE Sulphuric acid is a diprotic acid and 1 N solution contain 98.08/2 = 49.04 g H2SO4. It is an example of alkalimetry . When a strong acid is titrated with a strong base, the salt produced in the reaction is not hydrolysed and therefore the ph of the resultant solution at the end point is exactly 7.0. sulphuric acid is a strong acid, is standardized by titrating with a strong base i.e. sodium carbonate (primary standard). The following reaction takes place when sodium carbonate is titrated with sulphuric acid. In this titration, end point detection is carried out by using methyl orange indicator. Na2CO3 + H2SO4 --  H2O + CO2 + Na2SO4 1.0 M SULPHURIC ACID (H 2 SO 4 )

17. 1.0 M SULPHURIC ACID (H 2 SO 4 ) METHOD OF STANDARDIZATION : Take about 3.0 gm of anhydrous Na 2 CO 3  dried previously at 270ºC for one hour. Dissolve it in 100 ml of distilled water, add 0.1 ml of methyl red as indicator & titrate with 1 M H 2 SO 4  with constant stirring until the solution becomes faintly pink . Heat the solution to boiling cool & continue the titration until the faint pink colour is no longer affected by continue boiling. Each ml of 1 M H 2 SO 4  is equivalent to 0.10598 gm of Na 2 CO 3  (Sodium Carbonate). METHOD OF PREPARATION : Take 54 ml of conc. H 2 SO 4  in about 600 ml of H 2 O in 1000 ml of volumetric flask; cool & finally make the volume to 1000 ml with distilled water.

18. 0.1 M CERIC AMMONIUM SULPHATE

19. PRINCIPLE It is a redox titration. Ceric ammonium sulphate is titrated with Arsenic trioxide solution (Primary standard) in presence of sodium hydroxide, and osmic acid solution. As 2O 3+ 2NaOH → 2NaAsO2+ H2O NaAsO2 + 2H 2O→ NaH2AsO4+ 2H ++ 4e Ce 4+ + e- → Ce3+ 0.1 M CERIC AMMONIUM SULPHATE

20. 0.1 M CERIC AMMONIUM SULPHATE METHOD OF PREPARATION : Dissolve 65 g of  ceric ammonium sulphate ,  with the aid of gentle heat, in a mixture of 30.0 ml of  sulphuric acid   and 500 ml of distilled water.  Cool , filter the solution, if turbid, and dilute to 1000 ml with distilled water. METHOD OF STANDARDIZATION : Weigh accurately about 0.2 g of arsenic trioxide, previously dried at 105 ° for 1 hour, and transferred to a 500- ml conical flask . Wash down the inner walls of the flask with 25 ml of a 8.0% w/v solution of sodium hydroxide, swirl to dissolve, add 100 ml of distilled water and mix. Add 30 ml of dilute sulphuric acid, 0.15 ml of  osmic acid solution, 0.1 ml of  ferrroin sulphate solution and slowly titrate with the ceric ammonium sulphate solution until the pink colour is changed to a very pale blue, adding the titrant slowly towards the end- point.  Each ml of 0.1 M ceric ammonium sulphate  is equivalent to 0.004946 g of As 2 O 3.

21. POTASSIUM PERMANGANATE

22. POTASSIUM PERMANGANATE PRINCIPLE The principle of standardization of potassium permanganate is based upon redox titration in which strength of an oxidizing agent is estimated by titrating it with a reducing agent and viceversa . Potassium permanganate acts as an strong oxidizing agent in acidic medium that oxidizers oxalic acid in to carbondioxide . Known strength of oxalic acid is titrated directly with potassium permanganate . End point can be detected with appearance of permanent pink colour potassium permanganate acts as selfindicator 2KMnO4+5H2C2O4+3H2SO4 →K2SO4+2MnSO4+8H2O +10CO2 PREPARATION PROCEDURE : Dissolve 3.2g of potassium permanganate in 1000ml of water, heat on a water bath for 1 hour, allow to stand for 2 days. Filter the solution through glass wool.

23. STANDARDISATION Take 20 ml of Oxalic acid solution .add 5 ml of 1m sulphuric acid. Warm the mixture to about 70oC .titrate with potassium permanganate solution taken in the burette. End point is appearance of pink colour that persist for 30sec. N 1V 1=N 2V 2 N 2 = N 1V 1 /V 2

24. THANK YOU