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

         Preparation of Acids

 

• By direct combination of a non metal with hydrogen

e.g.   \[{{H}_{2}}+\,C{{l}_{2}}\,\to 2HCl;\,\,{{H}_{2}}+S\to {{H}_{2}}S;\,\,{{H}_{2}}+B{{r}_{2}}\to 2HBr\]

• By reaction between salt and the less concentrated acid

e.g. \[KCl+{{H}_{2}}S{{O}_{4}}\to {{H}_{2}}S{{O}_{4}}+HCl;\,\,NaCl+{{H}_{2}}S{{O}_{4}}\to NaHO{{S}_{4}}+HCl\]

• By action of concentrated nitric acid on non metals.

e.g.   \[S+6HN{{O}_{3}}(con)\to {{H}_{2}}S{{O}_{4}}+2{{H}_{2}}O+6N{{O}_{2}}\]

• By dissolving non-metal oxides in water

e.g. \[S{{O}_{3}}+{{H}_{2}}O\to {{H}_{2}}S{{O}_{4}};\,{{N}_{2}}{{O}_{5}}+{{H}_{2}}O\to 2NH{{O}_{3}};\,C{{O}_{2}}+{{H}_{2}}O\to \,{{H}_{2}}C{{O}_{3}}\]

• By action of dilute mineral acids on salts such as chlorides, carbonates sulphates etc.

e.g. \[{{K}_{2}}{{O}_{3}}+{{H}_{2}}S{{O}_{4}}\,(dil)\to {{K}_{2}}S{{O}_{4}}+{{H}_{2}}S{{O}_{4}};\,FeS+{{H}_{2}}S{{O}_{4}}\,(dil)\to FeS{{O}_{4}}+{{H}_{2}}S\]

 

         Properties of Acids

1. They have sour taste
2. They turns blue litmus red

III. Dilute mineral acids reacts with metals, above hydrogen in the activity series to liberate hydrogen gas.

\[2Na+2HCl\,(dil)\to 2NaCl+{{H}_{2}}\]

\[Zn+{{H}_{2}}S{{O}_{4}}(dil)\to ZnS{{O}_{4}}+{{H}_{2}}\]

(4) Reaction of Na, K, Ca with acid is explosive.

(5) Hydrogen gas evolved produces "POP" sound on burning.

• Nitric acid is an oxidizing agent so it oxidizes hydrogen to \[{{H}_{2}}O\] & itself get reduced.

But \[Mg\And Mn\] react with very dilute \[HN{{O}_{3}}\] to produce hydrogen gas.

\[Mg+2HN{{O}_{3}}\to Mg{{(N{{O}_{3}})}_{2}}+{{H}_{2}}\,(1%)\]

• Metal oxides are basic in nature. They react with acids to form salt and water.

\[{{K}_{2}}O+2HCl\to 2KCl+{{H}_{2}}O\]

\[MgO+{{H}_{2}}S{{O}_{4}}\to MgS{{O}_{4}}+\,{{H}_{2}}O\]

• Metal hydroxides react with acids to form salt and water.

\[2\,KOH+{{H}_{2}}S{{O}_{4}}\to {{K}_{2}}S{{O}_{4}}+2{{H}_{2}}O\]

\[NaOH+HCl\to MgS{{O}_{4}}+{{H}_{2}}O\]

• Acids reacts with metal carbonates and hydrogen carbonates to form salt, water and liberate carbon dioxide gas.

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

\[Zn\,C{{O}_{3}}+2HCl\to ZN\,C{{l}_{2}}+{{H}_{2}}O+C{{O}_{2}}\]

Carbon dioxide gas when passed through line water, turns it to milky due to the formation of calcium carbonate.               

 \[Ca{{(OH)}_{2}}+C{{O}_{2}}\to CaC{{O}_{3}}+{{H}_{2}}O\]

Acids react with sulphites and hydrogen sulphites to form salt, water and sulphurdioxide            

\[{{K}_{2}}S{{O}_{3}}+{{H}_{2}}S{{O}_{4}}\to {{K}_{2}}S{{O}_{4}}+{{H}_{2}}O+S{{O}_{2}}\]

\[NaHS{{O}_{3}}+NaCl\to NaCl+{{H}_{2}}O+S{{O}_{2}}\]

Sulphur dioxide gas also turn lime water milky when passed through it, but is not permanent.   

• Acids react with metal sulphides to form salt and hydrogen sulphide gas. |

 \[MgS+{{H}_{2}}S{{O}_{4}}\to MgS{{O}_{4}}+{{H}_{2}}S\]

\[FeS+2HCl\to FeC{{l}_{2}}+{{H}_{2}}S\]

Hydrogen sulphide gas smells like rotten egg.

 

           Uses of Some Common Acids

• Acetic acid - For Cooking
• Oxalic acid - For removing stain off
• Citric acid - Food preservative
• Tartaric acid - For baking power
• Boric acid - For washing eyes
• Carbonic acid - In soft drinks
• Preparation of Bases

 

       Preparation of Bases

• By direct combination of metal and oxygen

\[2Mg+{{O}_{2}}\to 2MgO\]

\[4Na+{{O}_{2}}\to 2N{{a}_{2}}O\]

• By dissolving basic oxides in water

\[N{{a}_{2}}O+{{H}_{2}}O\to 2NaOH\]

\[MgO+{{H}_{2}}O\to Mg{{(OH)}_{2}}\]

• By reacting active metals with water

\[2K+2{{H}_{2}}O\to 2KOH+{{H}_{2}}\]

\[Ca+2{{H}_{2}}O\to Ca{{(OH)}_{2}}+{{H}_{2}}\]

• By thermal decomposition of metal

\[ZnC{{O}_{3}}\to ZnO+C{{O}_{2}}\]

\[CuC{{O}_{3}}\to CuO+C{{O}_{2}}\]

Sodium and potassium carbonates do not give this reaction

• By thermal decomposition of metal nitrates

\[2Al(N{{O}_{3}})\to A{{l}_{2}}{{O}_{3}}+6N{{O}_{2}}+3{{O}_{2}}\]

\[CuC{{l}_{2}}+NaOH\to NaCl+Cu{{(OH)}_{2}}\]

• By treating aqueous salt solution of certain metal with strong base.

\[ZnS{{O}_{4}}+2KOH\to {{K}_{2}}S{{O}_{4}}+Zn{{(OH)}_{2}}\]

\[CuC{{l}_{2}}+NaOH\to NaCl+Cu{{(OH)}_{2}}\]

 

            Properties of Base

1. They have bitter taste
2. They are soapy to touch

III. They react with carbon dioxide in air to form respective carbonate

\[2KOH+C{{O}_{2}}\to {{K}_{2}}C{{O}_{3}}+{{H}_{2}}O\]

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

The lime water containing \[Ca{{(OH)}_{2}}\], is used for white washing. When left for some time, it reacts with \[C{{O}_{2}}\] in air to form a shiny layer of \[CaC{{O}_{3}}\].

1. Bases react with acids to form salt and water

\[NaOH+HN{{O}_{3}}\to NaN{{O}_{3}}+{{H}_{2}}O\]

\[Ca{{(OH)}_{2}}+{{H}_{2}}S{{O}_{4}}\to CaS{{O}_{4}}+2{{H}_{2}}O\]

1. Bases react with ammonium salts to liberate ammonia gas:

\[NaOH+N{{H}_{4}}Cl\to NaCl+{{H}_{2}}O+N{{H}_{3}}\]

\[2KOH+{{(N{{H}_{4}})}_{2}}C{{O}_{3}}\to {{K}_{2}}C{{O}_{3}}+2{{H}_{2}}O+N{{H}_{3}}\]

Ammonia has pungent odour. When a glass rod dipped in dilute hydrochloric acid is brought near the mouth of the test tube containing ammonia and white fumes of ammonium chloride is termed.

Hydroxides of zinc, lead and aluminium are amphoteric in nature i.e. they behave both as acids as well as base.

\[Zn{{(OH)}_{2}}+{{H}_{2}}S{{O}_{4}}\to ZnS{{O}_{4}}+2{{H}_{2}}O\]

\[Al{{(OH)}_{3}}+3HN{{O}_{3}}\to Al(N{{O}_{3}})+3{{H}_{2}}O\]

\[Pb{{(OH)}_{2}}+NaOH\to N{{a}_{2}}Pb{{O}_{2}}+2{{H}_{2}}O\]

\[Zn{{(OH)}_{2}}+NaOH\to N{{a}_{2}}Zn{{O}_{2}}+2{{H}_{2}}O\]

 

            Use of Some Common Bases

• \[Al\,{{(OH)}_{3}}:\] As a foaming agent in extinguishing fire.
• \[NaOH:\] For removing stains from cloths.
• \[KOH:\] For manufacturing soaps and in alkaline batteries.
• \[Mg\,{{(OH)}_{2}}:\] As an antacids.
• \[Ca{{(OH)}_{2}}:\] For white washing and for softening of hard water.

 

          Preparation of Salts

• Anhydrous salts can be prepared by direct combination method.

\[Fe+S\to FeS\] (Iron (ll) Sulphide)

\[Fe+3C{{l}_{2}}\to 2FeC{{l}_{3}}\] (Iron (III) chloride)

\[2Na+C{{l}_{2}}\to 2NaCl\] (sodium chloride)

• Hydrated soluble salts can be prepared by the action of acids on the metals.

\[Zn+{{H}_{2}}S{{O}_{4}}\to ZnS{{O}_{4}}+{{H}_{2}}\]

\[Fe+{{H}_{2}}S{{O}_{4}}\to ZnS{{O}_{4}}+{{H}_{2}}\]

\[3Ca+8HN{{O}_{3}}\to 3Cu{{(NaO)}_{2}}+4{{H}_{2}}O+2NO\]  (Copper (II) nitrate)

• Soluble salts can be prepared by the action of acids on metal oxides, metal hydroxides, metal carbonates and bicarbonates and metal sulphides.

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

\[ZnC{{O}_{3}}+2HN{{O}_{3}}\to Zn(N{{O}_{3}})+{{H}_{2}}O+C{{O}_{2}}\]

\[Pb{{(OH)}_{2}}+2HN{{O}_{3}}\to Pb{{(N{{O}_{3}})}_{2}}+2{{H}_{2}}O\]

\[ZnS+2HCl\to ZnC{{l}_{2}}+{{H}_{2}}S\]

\[KHC{{O}_{3}}+HCl\to KCl+{{H}_{2}}O+C{{O}_{2}}\]

\[CaC{{O}_{3}}+{{H}_{2}}S{{O}_{4}}\to CaS{{O}_{4}}+{{H}_{2}}O+C{{O}_{2}}\]

• Insoluble salts can be prepared by precipitation from soluble salts.

\[CaC{{l}_{2}}+{{K}_{2}}C{{O}_{3}}\to KCl+CaC{{O}_{3}}\]

\[BaS{{O}_{4}}+2NaCl\to BlC{{l}_{2}}+N{{a}_{2}}S{{O}_{4}}\]

 

           Properties of Salts

• Hygroscopy: It is the phenomenon due to which certain salts absorb water vapours from air. Such salts are called hygroscopic salts.

e.g. Quick lime \[(CaO)\], Concentrated sulphuric acid. Anhydrous calcium chloride etc.

• Deliquescence: It is the phenomenon due to which certain substances absorb water vapours form atmosphere and completely dissolves in it to form a saturated solution.

e.g. Sodium Hydroxide \[(NaOH)\], Potassium Hydroxide (KOH), Anhydrous Calcium Chloride.

• Efflorescence: Certain hydrated salts loose their water of crystallization partially or completely when exposed to air.

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

Such substances are called efflorescent substances.

• Water of crystallization: It is the number of water molecules which enter into lattice structure of a salt during its crystallization. Such salts are called hydrous or hydrated salts.

e.g.

1. Calcium chloride \[(CaC{{l}_{2}}.6{{H}_{2}}O)\]
2. Gypsum or Calcium sulphate \[CaS{{O}_{4}}.2{{H}_{2}}O\]
3. Plaster of Paris or calcium sulphate hemihydrate \[CaS{{O}_{4}}.\frac{1}{2}{{H}_{2}}O\]
4. Blue nitrate or copper sulphate \[CuS{{O}_{4}}.5{{H}_{2}}O\]
5. Green vitriol or Ferrous sulphate \[FeS{{O}_{4}}.7{{H}_{2}}O\]
6. Washing soda or Sodium carbonate decca hydrate \[N{{a}_{2}}C{{O}_{3}}.10{{H}_{2}}O\]
7. White nitrol or Zinc sulphate \[ZnS{{O}_{4}}.7{{H}_{2}}O\]
8. Glaubers salt or Sodium Sulphate \[N{{a}_{2}}S{{O}_{4}}.10{{H}_{2}}O\]
9. Epsom salt or Magnesium Susphate \[MgS{{O}_{4}}.7{{H}_{2}}O\]

Common salt turns watery in rainy season. It is because it contains magnesium chloride in traces which is hygroscopic substance.