Sodium bicarbonate

                                       Sodium bicarbonate

Definition :- a white, crystalline, water-soluble solid, in powder or granules, NaHCO₃  , usually prepared by the reaction of soda ash with carbon dioxide or obtained from the intermediate product of the Solvay process by purification: used chiefly in the manufacture of sodium salts, baking powder, and beverages, as a laboratory reagent, as a fire extinguisher, and in medicine as an antacid.

Also called bicarbonate of soda, baking soda, sodium acid carbonate.

Definition :- NaHCO3 White, water-soluble crystals with an alkaline taste; loses carbon dioxide at 270°C; used as a medicine and a butter preservative, in food preparation, in effervescent salts and beverages, in ceramics, and to prevent timber mold. Also known as baking soda; bicarbonate of soda; sodium acid carbonate.

Definition :-  a white crystalline weakly alkaline salt NaHCO₃ used in baking powders and in medicine especially as an antacid—called also baking soda, bicarb, bicarbonate of soda, sodium acid carbonate .

Preparation :

1.    Sodium bicarbonate is prepared from ammonium bicarbonate and sodium chloride.

2.    Sodium carbonate is converted into the bicarbonate by passing carbon dioxide through a saturated solution.

Na₂CO₃ + H₂O + CO₃ -------->  2NaHCO₃

Physical and chemical properties\Characters

Appearance : White crystals .

pH : 8.3 (0.1 mol)

Odor : odorless .

Molecular weight : 84.01 g / mole.

Molecular formula : NaHCO₃.

Density :- 2.20 g cm−3

Boiling point : 851 ° c.

Malting point :  50 °C, 323 K, 122 °F.

Solubility :  Soluble in water and acetone.

Insoluble :- in ethanol.

Chemical Characters

       i.             

           When sodium bicarbonate is heated , it is decomposed into the normal carbonate CO and water.

2NaHCO₃ -------->  Na₂CO₃ + H₂O + CO₃

    ii.            Asolution of sodium bicarbonate is alkaline dune to hydrolysis (Ph-8.2).

NaHCO₃ + H₂O ß-------------------à Na⁺ + H₂CO₃ + ^-OH

Sodium bicarbonate is slightly alkaline and faile to trun phenolphthalein red. On the other hand , in sodium carbonate the carbonate ion is so extensively hydrolyzed that the solution is quite alkaline (Ph is 11.6)

CO₃^-2 + H₂O ß--------------------à HCO₃^- + ^-OH

 iii.            When a mercuric chloride solution is added to a solution of sodium bicarbonate there is no immediate formation of a precipitate. After some time a reddish precipitate of HgO is formed.

2NaHCO₃ + HgCl₂ -----------------------à 2NaCl + Hg ( HCO₃)₂

Hg (HCO₃)₂  --------------------------à HgO + H₂O +2CO₂

 iv.            When the bicarbonate is treated with an acid , carbon dioxide is liberated.

NaHCO + HCl ------------------à NaCl + CO + H O

     Test for purity

1)   Tests for alkalinity , aluminum , calcium , insoluble matter , arsenic , iron , lead , chloride , sulphate , ammonium compounds.

2)   For detecting the presence of aluminum , calcium and insoluble matter an aqueous solution is boiled with ammonia solution and filtered . the residue is ignited and weighed.

3)   An aqueous solution after addition of nitric acid complies with the limit test for chloride.

4)   An aqueous solution after addition of hydrochloric acid complies with the limit test for sulphate.

5)   Evolution of ammonia on heating the substance with sodium hydroxide indicates the presence of ammonium compound.

6)   An aqueous solution after addition of hydrochloric acid complies with the limit test for iron.

Test for identification : It gives the reactions of sodium and of bicarbonates.

Assay : Titrate with 0.5 N hydrochloric or sulphuric acid , using methyl orange as indicator

HCl + NaHCO₃ -------------------------------------à NaCl + H₂O + CO₂

2NaHCO₃ +H₂SO₄ --------------------------------à Na₂SO₄ + 2H₂O + 2CO₂

Each ml of 0.5 N hydrochloric acid is equivalent to 0.042 g of NaHCO₃.

It is a direct titration method. The end point in yellow to pink. The equivalence point of this titration is at about _PH 3.6 which corresponds to the colour change methyl orange ( _PH 2.8 – 4.0 red yellow ). The reaction at the equivalence point is acidic because of the presence of carbonic acid.

CO₂ + H₂O --------------------------------à H₂CO₃

Storage :

Medical and Pharmaceutical Uses :-

                                                                               i.            Treat acid indigestion and heartburn.

                                                                            ii.            Uric acid renal stones.

                                                                         iii.            Cardio pulmonary resuscitation.

                                                                         iv.            Used as soda-mint tablet preparation.

                                                                            v.            Renal tubular acidosis.

                                                                         vi.            For the treatment of aspirin over dose.

                                                                      vii.            Chronic renal failure.

                                                                   viii.            Used as an antacid preparation.

                                                                         ix.            Medicinal ingredient in gripe water for infant.

                                                                            x.            Antiseptic properties.