10th Class Science Acids, Bases and Salts / अम्ल, क्षार एवं लवण Family of Salts

         Family of Salts

 

Washing Soda - \[N{{a}_{2}}C{{O}_{3}}.10{{H}_{2}}O\] (Sodium Carbonate Decahydrate)

It is manufactured by Solvay's process also known as ammonia soda process.

 

Raw Materials Required

• Brine (concentrated sodium chloride solution).
• Ammonia gas
• Carbon dioxide

 

Steps Involved

\[N{{H}_{3}}+{{H}_{2}}O+C{{O}_{2}}\to N{{H}_{4}}HC{{O}_{3}}\]

Ammonium hydrogen carbonate

\[N{{H}_{4}}HC{{O}_{3}}+NaCl\to N{{H}_{4}}Cl+NaHC{{O}_{3}}\]

\[2NaHC{{O}_{3}}\to N{{a}_{2}}C{{O}_{3}}+C{{O}_{2}}+{{H}_{2}}O\]

\[N{{a}_{2}}C{{O}_{3}}+10{{H}_{2}}O\to N{{a}_{2}}C{{O}_{3}}.10{{H}_{2}}O\]

(Washing soda)

 

            Properties of Washing Soda

• It is white transparent crystalline solid.
• It contains ten molecules of water of crystallization.
• It shows efflorescence.

\[N{{a}_{2}}C{{O}_{3}}.10{{H}_{2}}O\to N{{a}_{2}}C{{O}_{3}}.{{H}_{2}}O+9{{H}_{2}}O\]

• Its aqueous solution is alkaline.
• On heating it undergoes following changes

\[N{{a}_{2}}C{{O}_{3}}.10{{H}_{2}}O\to N{{a}_{2}}C{{O}_{3}}.{{H}_{2}}O\to N{{a}_{2}}C{{O}_{3}}\to C{{O}_{3}}(l)\]

• It reacts with dilute acids to give effervescence of carbon dioxide

\[N{{a}_{2}}C{{O}_{3}}+2HCl\to NaCl+{{H}_{2}}O+C{{O}_{2}}\]

 

            Uses

• In manufacture of glass, soap and papers.
• Used as a laboratory agent.
• Used as a cleansing agent.
• For removing permanent hardness of water.
• For manufacturing caustic soda, borax water glass etc.

 

              Baking Soda (NaHCO₃) (Sodium hydrogen carbonate)

• Laboratory method of preparation of sodium bicarbonate is by passing carbon-dioxide through cold saturated solution of sodium carbonate

\[N{{a}_{2}}C{{O}_{3}}+{{H}_{2}}O+C{{O}_{2}}\to 2NaHC{{O}_{3}}\] .

• On large scale it is obtained as an intermediate in the Solvay's process

\[N{{H}_{3}}+{{H}_{2}}O+C{{O}_{2}}\to N{{H}_{4}}HC{{O}_{3}}\]

\[N{{H}_{4}}HC{{O}_{3}}+NaCl\to NaHC{{O}_{3}}+N{{H}_{4}}Cl\]

 

            Properties of Sodium Hydrogen Carbonate

• It is white solid.
• On heating to 573 k, it is converted to sodium carbonate and carbon dioxide.

 \[2NaHC{{O}_{3}}\to N{{a}_{2}}C{{O}_{3}}+C{{O}_{3}}+C{{O}_{2}}+{{H}_{2}}O\]

• It is sparingly soluble in water. Its aqueous solution is basic. It reacts with acids to form salt, water and carbon dioxide.

\[NaHC{{O}_{3}}+HCl\to NaCl+{{H}_{2}}O+C{{O}_{2}}\]

 

              Uses

• For neutralizing acidity in stomach.
• As a mild antiseptic.
• Baking soda is a mixture of sodium hydrogen carbonate and tartaric acid. On heating it reacts to produce carbon dioxide gas which escapes and makes the food stuffs spongy.
• In soda acid fire extinguisher baking soda is used with sulphuric acid. When the extinguisher is used, sulphuric acid reacts with baking soda to produce carbondioxide and water which cuts off the supply of air and stops fire.

\[{{H}_{2}}S{{O}_{4}}+2NaHC{{O}_{3}}\to N{{a}_{2}}S{{O}_{4}}+2C{{O}_{2}}+2{{H}_{2}}O\]

 

              Bleaching Powder \[(CaOC{{l}_{2}})\] (Calcium Oxychloride)

It is prepared by the action of chlorine gas on dry slaked lime.

\[Ca{{(OH)}_{2(S)}}+C{{l}_{2(g)}}\to CaC{{l}_{2(s)}}+{{H}_{2}}{{O}_{(l)}}\]

Because of this reaction bleaching powder is also called chloride of lime.

 

               Properties

• Yellowish white powder of calcium oxychloride has a strong smell of chlorine.
• When left open in air, it decomposes slowly and liberate chlorine gas.
• \[CaC{{l}_{2}}+C{{O}_{2}}\to CaC{{O}_{3}}+C{{l}_{2}}\]
• On reaction with dilute acids it liberates chlorine gas.

\[CaOC{{l}_{2}}+2HCl\to CaC{{l}_{2}}+C{{l}_{2}}+{{H}_{2}}O\]

\[CaOC{{l}_{2}}+{{H}_{2}}S{{O}_{4}}\to CaS{{O}_{4}}+{{H}_{2}}O+C{{l}_{2}}\]

 

             Uses

• For bleaching cotton, linen and wood palp.
• For making wool unshrinkalbe.
• In manufacture of chloroform.
• For disinfecting drainages and ditches.
• For sterilizing the drinking water.

 

              Plaster of Paris \[(CaS{{O}_{4}}.\frac{1}{2}{{H}_{2}}O)\] (Calcium Sulphate Hemi hydrate)

It is prepared by heating gypsum at 390 k in a kiln.

\[2CaS{{O}_{4}}.2{{H}_{2}}{{O}_{(s)}}\to {{(CaS{{O}_{4}})}_{2}}{{H}_{2}}O+3{{H}_{2}}O\]

OR

\[CaS{{O}_{4}}.2{{H}_{2}}O\to CaS{{O}_{4}}.\frac{1}{2}{{H}_{2}}O+\frac{1}{2}{{H}_{2}}O\]

During manufacturing of plaster paris heating should be done carefully. Temperature should not exceed 390 k, else gypsum will loose all water molecule and anhydrous calcium sulphate will be formed.

 

            Properties

• It is a white powder                      
• It absorbs water at room temperature and large amount of heat is liberated.
• On mixing with water it forms a slurry which crystallizes rapidly into gypsum.

\[CaS{{O}_{4}}\frac{1}{2}{{H}_{2}}O+\frac{1}{2}{{H}_{2}}O\to CaS{{O}_{4}}.2{{H}_{2}}O\]

 

           

• Uses
• As a fire proofing material.                                 
• For making chalks.
• For making casts and patterns for moulds and statues.
• As cement in ornamental casting.
• In hospitals for immobilizing the affected part in case of sprain or fracture.

For filling small gaps in walls and on roofs.

 

 

 

         The water of crystallization of washing soda is:

(a) 10

(b) 9

(c) 5 

(d) 1

(e) None of these

 

Answer: (a)

 

 

         A salt on treatment with excess of ammonium hydroxide produces a complex tetraammine copper (II) ions. the salt contains:

(a) Cuprous ions

(b) Cupric ions

(c) Calcium ions

(d) Chloride ions

(e) None of these                                                     

 

Answer: (b)                                      

Explanation 

Cupric ions, as they react with excess of ammonia solution to form

\[{{[Cu{{(N{{H}_{3}})}_{4}}]}^{2+}}\]

 

 

           When dilute hydrochloric acid is poured over powdered calcium carbonate, efflorescence are formed. It is because:

(a) Acids are corrosive

(b) Calicum carbonate is very reactive

(c) Calcium oxide in formed

(d) Carbon dioxide is evolved

(e) None of these

 

Answer: (d)

 

 

         When sodium hydroxide is added to ammonium carbonate salt and then a glass rod dipped in dilute hydrochloric acid is brought near the test tube, we observe:

(a) Brisk efflorescence

(b) Dense white firms

(c) Yellowish green vapours

(d) Reddish brown gas

(e) None of these

 

Answer: (b)

 

 

        A solution when reacts with zinc metal liberates a gas which burn with a pop sound. The pH of the solution is

(a) Equal to 7

(b) Less than 7

(c) Greaterthan7

(d) Between 8 and 14

(e) None of these

 

Answer: (b)

 

 

           

What is pH of a solution whose hydrogen ion concentration is \[1\times {{10}^{-3}}\] modes?

(a) 3

(b) 2           

(c) 7

(d) 0-3

(e) None of these

 

Answer: (a)

Explanation 

\[pH=-\log \,[{{H}^{+}}]\]

\[-\log \,[1\times {{10}^{-3}}]=-(-3)\log \,10=3\]

 

 

          Aqueous solution of common salt is                           

(a) Acidic

(b) Alkaline       

(c) Basic

(d) Neutral

(e) None of these

 

Answer: (d)

 

 

• The term acid, comes from the Latin term acere, which means "sour".
• The word "alkali" comes from the Arabic al-qili, which refers to the ashes of the seawort plant.

 

 

• The word acid is derived from the latin word soru. As per Aerhenius, an acid is a substance which furnish hydronium ion in its aqueous solution. On the basis of strength the acids can be classified as strong and weak acid, on the basic of concentration acids can be classified as dilute or concentrated acid, on the basis of basicity acids can be monobasic, dibasic ortribasic.
• The base is a substance which combines with acids to form salt and water. The water soluble base are called alkalis. Bases may be classified as week or strong base on the basis of strength, monoacidic or diacidic or triacidic on the basis of their activity. The bases have bitter taste and are soapy to touch.
• Salt is a compound which is formed by the neutralization of an acid by a base. The salts can be classified as normal salt, acidic salt, basic salt, double salt, mixed salt, binary salt or complex salt.
• Symbols used

\[[{{H}^{+}}]=\] Concentration of hydrogen ion

\[{{H}_{3}}{{O}^{+}}=\] hydronium ion a = heat.