Acid base

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Acids, Bases

& BuffersPresented By:

Purvi Soni

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Hydrochloric Acid Formula: HCl Mol.weight : 36.46 g/mol Synonym: Muriatic acid, Acidum hydrochloricum, Spirit of salt.

Hydrochloric acid is commonly known as spirit of salt because it was first of all prepared by distilling sea salt with sulphuric acid.

Standard Value:- It is an aqueous solution of hydrogen chloride in water and is having not less than 35%w/w and not more than 38%w/w of HCl.

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Preparation.

(1)It is manufactured by the action of

sulphuric acid on sodium chloride (common salt).

Calculated quantities of concentrated sulphuric acid and sodium chloride are heated in the cast iron pans of a salt cake furnace.

NaCl + H2SO4 → NaHSO4 + HCl

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Salt Cake Furnance It consists of:- The cast-iron

pan (A) The reverberatory hearth (C). The salt and sulphuric acid are put into the pan

(A), and are moderately heated by a coke fire the grate (E).

Hydrochloric acid vapors escape through the earthenware pipe (B).

Then the fuse mass of sodium & sulphate and undecomposed salt is raked up o the (C),

where it is exposed to the high temperature of the flame from (D).

This completes the second reaction and a pasty mass of normal sodium sulphate is formed.

The hydrochloric acid vapors, set free during the reaction, mix with the furnace gases from (D),

and escape through the pipe (F) to the absorbing apparatus.

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Lunge-Rohrmann plate tower The hydrochloric acid gas is

formed which is passed in a tower, which is sprayed with water.

A stream of water or dilute acid from the tower will flow through them in a direction opposite to that in which the gas is moving.

The dilute hydrochloric acid is collected at the bottom.

It is again circulated to the tower to absorb more hydrogen chloride so that it gets concentrated.

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Muffle FurnanceThe acid so produced is

then purified. NaHSO4 formed in the

process is mixed with some more quantity of sodium chloride, and heated strongly in the muffle furnace to get more hydrogen chloride gas.

NaHSO4 + NaCl → Na2SO4 + HCl

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The overall equation may be put as follows:

2NaCl + H2SO4 →Na2SO4 + 2HCl

(2)During the manufacture of caustic soda by the electrolysis

of sodium chloride solution, large quantities of hydrogen and chlorine are obtained as

by-products. These gases are combined to yield hydrogen chloride.

H2 + Cl2 → 2HCl

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Properties. It is a colourless, fuming liquid having a pungent odour. It is miscible with water, alcohol.Specific gravity:- 1.18. It is a strong acid and attacks metals, forming their

hydrochlorides with the evolution of hydrogen gas. Even in high diluted form it is very strongly acidic to

litmus.Qualitatively, it can be recognized by the formation of a

white ppt of silver chloride with silver nitrate. AgNO3 + HCl → AgCl + HNO3

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Storage: It should be stored in well closed containers of glass or other material at a

temperature not exceeding 30°C.

Pharmaceutical Uses. It is mainly used as a pharmaceutical aid or especially, as an acidifying agent

(acidifier).

Dilute hydrochloric acid (10% w/w of HCl; limits 9.5-10.5%), when further diluted, with 25 to 50 volumes of water may be used as gastric acidifier when levels of hydrochloric acid in gastric juice are low (achlorhydria).

Uses. It is extensively used as a Solvent, Catalyst in basic pharmaceuticals and also an acidifier. (As it is used as an acidifier, it is a pharmaceutical necessity for preparing

dilute hydrochloric acid.)

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Sodium HydroxideFormula: NaOHMol. Weight : 40 g/molSynonym : Caustic SodaStandard Value:- It

contains not less than 95 % of total alkali calculated as NaOH including not more than 3% of Na2CO3

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Preparation:

(1) It is obtained by the soda-lime process in

which sodium carbonate (Na2CO3) is heated with milk of lime Ca(OH)2 in large tanks.

Na2CO3 + Ca(OH)2→ CaCO3 ↓ + 2NaOHThe reaction is reversible, but more than 90%

of Na2CO3 is converted into NaOH, when correct quantities are used.

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(2) By Electrolysis of NaCl solution:NaOH is manufactured in large quantities by

electrolysis of NaCl solution.Different types of cells are used for this purposes. Most of them employ Carbon-anodes and Metallic

Cathodes with some special device by which NaOH is produced in an isolated, brine free, cathode compartment.

This method is simple and cheap.H2 and Cl2 gases are also obtained as useful by-

products.(In the preparation of HCl)

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At Cathode:Na+ + e_ → Na

2 Na + 2H2O → 2NaOH + H2

At anode:Cl → Cl + e_

Cl + Cl → Cl2

Overall Rxn:NaCl ↔ Na+ + Cl-

(Ionization)

Carbon Anode

Metallic Cathode

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Properties:-It occurs in the form of flakes, sticks, or pellets.It is very deliquescent.It is strongly alkaline & corrosive.It absorbs CO2 gas & gets partially converted into

sodium carbonate.It is soluble in water & is freely soluble in alcohol &

glycerin with the evolution of heat. H2O+CO2 →H2CO3

2NaOH+H2CO3 → Na2CO3+2H2O

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Storage:Sodium hydroxide must be stored in tightly

closed containers as it absorbs moisture and carbon dioxide.

Uses:As it is a strong alkali, it is not used

therapeutically. It finds use as a disinfectant for veterinary

purposes and as a chemical in laboratories and industries.

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Ammonium Hydroxide

Formula: NH4OH Synonym:- Ammonia water, Ammonical liquor, Aqua ammonia. Molecular weight:- 35.04 g/mol Standard Value:- It contains not less than

27% w/v and not more than 30% w/v of ammonia.

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Preparation:-

(1) Ammonia is obtained commercially by synthesis of

its constituent element, nitogen and hydrogen combined under high pressure and at high temperature in the presence of catalyst.

N2+3H2→ 2NH3

Ammonia produced may be stored in liquid form in metallic cylinder or absorbed in water or converted into ammonium salts by combination with acids.

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(2) It can be also be obtained by the cyanamide process. Nitrogen is passed over calcium carbide heated to a

high temperature in an electric furnance, to produce calcium cyanamide.

CaC2+N2 → CaN.CN+CCalcium cyanamide Is used as fertilizer but ammonia

can be produced from it by heating with water under pressure.

CaN.CN+3H2O →CaCO3+2NH3

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PropertiesColourless, Transparent liquid.Have pungent characteristic odour.It is miscible with alcohol & its solution is strongly

alkaline to litmus.Ammonia forms ammonia basic salt on reaction with

mercuric chloride (ammonolysis). HgCl2+NH3 → Hg(NH2)Cl+HClWhen ammonia is passed over heated sodium or

potassium at 300˚C, amides are formed. 2NH3+2Na → 2NaNH2+H2

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Uses:It is only used for chemical and

pharmaceutical purposes.It is used primarily in making dilute ammonia

solution, which contains 9.5 to 10.5% ammonia.

It is too strong for internal administration.It is an ingredient of aromatic spirit of

ammonia preparation(IP’66), used as respiratory stimulant.

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