What is salts | Chemistry class 10 notes

Types of Salts

What is salt ? It is most important topic of NCERT Acids bases salt chapter 2 in Class 10. Questions are frequently asked in the CBSE board , ICSE Board and other competitive exam ( IIT JEE, NEET, AIMS, State Engineering exam from salt chemistry.

“ Salt in Chemistry and Salt formula : class 10 notes “ will be very beneficial for the students who are engaged in the preparation of upcoming board exam and Competitive exam .

In Salt Chemistry topic, the following terms will be illustrated.

Contents :

* 1. What is salt

* 2. Family of Salt class 10

* 3. Characteristics Of Salts

* 4. Types of Salt According its pH value : Neutral Salt , Acidic Salt, Basic Salt

* 5. Some Important Salts: Common Salt ( NaCl ), Washing soda, Baking Soda , Baking Powder, Bleaching powder , Plaster of Paris

* 6. Water of crystallization

What is Salt:

* Salt is the ionic compound obtained from reaction between acid and base.

* Salt is formed due to replacement of Hydrogen ions ( H⁺ ) of Acid by cation present in base .

* Normal salt consists two part : Cation and Anion

* Cation is part of Base and Anion is part of Acid

Family of Salt:

* The Salts of ' Hydrochloric Acid ' are called ' Metal chloride.

* The salts of Sulfuric Acid are called Metal Sulphate.

* The Salt of Sulfurous Acid are called Metal Sulphite.

* The Salts of Nitric Acid are called Metal Nitrate.

* The Salts of Carbonic Acid are called Metal bicarbonate or Metal Carbonate .

* The Salts of Acetic Acid are called Metal Acetate. and so on.

Characteristics Of Salts:

* Salts are mostly solid.

* They have high melting and boiling point due to strong electrovalent bond.

* Salts are usually soluble in water . some salts are Insoluble.

* Soluble salts are good conductor of electricity.

* Water Soluble salts are Electrolyte.

* Salts are Ionic compounds.

Types of Salt According its pH value:

1. Neutral Salt:

Neutral Salt is formed when Strong Acid React with Strong Base. its aqueous solution is neutral and hence pH of solution is 7

* Strong Acid + Strong Base = Neutral salt + water

e.g , HCl + NaOH = NaCl + H₂O

2. Acidic Salt:

Acidic Salt is formed when Strong Acid react with Weak Base. its aqueous solution is Acidic . pH of solution is less than 7.

* Strong Acid + Weak Base = Acidic salt + water

e.g , HCl + NH₄ OH → NH₄ Cl + H₂O

3. Basic Salt:

Basic salt is formed when Strong base react with strong Acid. its aqueous solution is Basic. pH of solution is More than 7.

* Weak Acid + Strong Base = Basic salt + water

e.g. H₂CO₃ + NaOH → Na₂CO₃ + H₂O

Some Important Salts:

1. Common Salt ( NaCl )

* Common salt is neutral salt.

* It is white powder which is used in preparing food.

* Its chemical name is Sodium Chloride.

How Common Salt Is Obtained:

( a) . In Laboratory:

* Sodium Chloride can be made in Laboratory by the combination of sodium hydroxide and Hydrochloric Acid.

NaOH ( aq) + HCl (aq) → NaCl (aq) + H₂O(l)

* The Sodium Chloride solution formed in this method is evaporated to obtain solid Sodium Chloride.

* But Sodium Chloride is never made in this way on a large scale because it is present in nature in abundance.

( b ) . From Sea Water:

* Sea Water contains many dissolved salts in it. The major salt present in sea water is common salt.

* Common salt is obtained from sea water by the process of evaporation.

( c ) . From Underground Deposit:

* The large crystals of common salt found in underground deposits are called rock salts.

* Rock salt was formed when the ancient seas dried up by evaporation, thousand of year ago.

Uses of Common Salt:

* Common salt is used as a raw material for making a large number of useful chemicals in industry such as : Caustic Soda ( NaOH ) , Sodium Carbonate, Baking Soda ( NaHCO₃ ), HCl, Hydrogen, Chlorine, and sodium metal etc.

* It is used in cooking foods.

* It is used as a preservative in pickles.

* It is used in the manufacture of soap.

Formation of Sodium Hydroxide ( NaOH )

* Its common name is Caustic soda.

* It is used for making large number of useful chemicals.

Preparation:

Chlor-Alkali Process:

* Sodium Hydroxide is produced by the electrolysis of Concentrated aqueous solution of sodium chloride ( brine )

2 NaCl (aq) + 2H₂O (l) → 2 NaOH (aq) + Cl₂ (g) + H₂ (g)

* During electrolysis , Chlorine gas is produced at the Anode ( Positive electrode ).

* Hydrogen gas is produced at the cathode ( Negative electrode )

* This process is called Chlor- alkali process because chlorine gas and alkali are formed in this reaction.

Uses Of Sodium Hydroxide:

* It is used for making soap and detergent.

* It is used for making artificial textile fiber like rayon.

* It is used in manufacture of paper.

* It is used for making dyes and bleaches .

* It is used in de-greasing metals and oil refining.

2. Washing Soda ( Na₂CO₃ . 10 H₂O )

* Washing soda is sodium carbonate containing 10 Molecules of water of Crystallization.

* formula of washing soda is Na₂CO₃ . 10 H₂O and also called sodium carbonate decahydrate.

Preparation:

when ammonia and carbon dioxide gases pass through the solution of cold and concentrated sodium chloride ( Brine ) then sodium hydrogen carbonate and ammonium chloride are formed.

NaCl + H₂O + NH₃ + CO₂ → NaHCO₃ + NH₄ Cl

* Sodium hydrogen carbonate is slightly soluble in water so its precipitate are formed.

* Sodium Hydrogen Carbonate is separated by filtration, dried and heated.

* On heating , Sodium Hydrogen Carbonate decomposes to form anhydrous Sodium Carbonate.

2 NaHCO₃ → Na₂ CO₃ + CO₂ + H₂O

* Anhydrous sodium carbonate is also called Soda ash .

* Soda ash is dissolved in water and re-crystallized to get washing soda.

Na₂CO₃+ 10 H₂O → Na₂CO₃ . 10 H₂O

Properties of Washing Soda:

* It is a transparent crystalline solid.

* Washing soda is soluble in water .

* Washing soda is basic salt so its aqueous solution turn red litmus to blue.

* It has cleansing property. so it remove dirt and oils from dirty clothes.

Uses of sodium carbonate :

* It is used as a cleansing agent.

* It is used to remove permanent hardness of water.

* It is used in the manufacture of glass, soap and paper.

* It is used in manufacture of sodium compound such as borax.

3. Baking Soda ( NaHCO₃ )

* Its chemical name is sodium hydrogen carbonate or sodium bi carbonate.

* Its chemical formula is NaHCO₃

* It is slightly soluble in water.

Preparation:

* When ammonia and carbon dioxide gases pass through the solution of cold and concentrated sodium chloride ( Brine ) then sodium hydrogen carbonate and ammonium chloride are formed.

* NaCl + H₂O + NH₃ + CO₂ → NaHCO₃ + NH₄ Cl

* Sodium hydrogen carbonate is slightly soluble in water so its precipitate are formed.

Properties of Baking soda:

* it consist of white crystals which are sparingly soluble in water.

* it is basic in nature . it is non-corrosive base.

* On heating , Sodium Hydrogen Carbonate decomposes to form anhydrous Sodium Carbonate.

2 NaHCO₃ → Na₂ CO₃ + CO₂ + H₂O

Uses of Baking soda:

* Baking soda is used as an antacid in medicine to remove acidity of the stomach.

* It is used in fire extinguisher.

* It is used in making Baking powder

Baking Powder:

* Baking powder is a mixture of baking soda and a mild edible acid such as Tartaric acid.

* when baking powder is mixed with water then sodium bicarbonate reacts with tartaric acid to evolve carbon dioxide gas.

Sodium hydrogen carbonate + tartaric acid → sodium tartarate + CO₂ + H₂O

* When baking powder is used in making cake or bread , carbon dioxide gas come out slowly from the cake or bread and make the cake soft ant spongy.

* Sodium tartarate has pleasant taste and smell .

* If only sodium bicarbonate ( baking soda ) is used in making cake , then sodium carbonate formed from it by the action of heat will give bitter taste to cake.

4. Bleaching Powder ( CaOCl₂ )

* Its chemical name is calcium oxy-chloride.

* The chemical formula of bleaching powder is CaOCl₂ .

* It is also called chloride of lime

* The real bleaching agent present in bleaching powder is chlorine .

* The bleaching action of chlorine is due to its oxidizing property .

Preparation of Bleaching Powder

* Bleaching powder is prepared by passing chlorine gas over dry slaked lime Ca(OH)₂ .

Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O

Properties of Bleaching Powder

* Bleaching powder is a white powder which gives a strong smell of chlorine

* Bleaching powder is soluble in cold water.

* Bleaching powder reacts with dilute acids to produce chlorine.

CaOCI₂ + H₂SO₄ → CaSO₄ + H₂O + Cl₂

* The chlorine produced by the action of a dilute acid on bleaching powder acts as a bleaching agent .

Uses of Bleaching Powder

* Bleaching powder is used for bleaching cotton and linen in textile industry and for bleaching wood pulp in paper industry.

* It is used for bleaching washed clothes in laundry .

* Bleaching powder is used for disinfecting drinking water supply. i.e for making drinking water free from germs.

* Bleaching powder is used for the manufacture of chloroform (CHCI₃ ).

* Bleaching powder is used for making wool un-shrinkable.

* Bleaching powder is used as an oxidizing agent in many chemical industries.

5. Plaster of Paris (CaSO₄ .½ H₂O )

* Plaster of Paris is calcium sulfate hemihydrates.

* The formula of plaster of Paris is CaSO₄ .½ H₂O.

* Plaster of Paris is commonly known as P.O.P.

* It was obtained by heating gypsum which was mainly found in Paris. So it is called plaster of Paris .

Preparation of Plaster of Paris

* Plaster of Paris is prepared by heating gypsum ( CaSO₄ .2H₂O ) to a temperature of 100°C .

* When gypsum is heated to a temperature of 100°C (373 K) , it loses three-fourths of its water of crystallization to forms plaster of Paris ( CaSO₄ .½ H₂O ) .

CaSO₄ .2H₂O = CaSO₄ .½ H₂O + ¾ H₂O

* In the preparation of plaster of Paris, heating of gypsum should be controlled carefully.

* The temperature during the heating of gypsum should not above 160°C.

* Above temp 160⁰C , it losses complete water of crystallization to form dead burnt plaster ( CaSO₄ ) .

Properties of Plaster of Paris

* Plaster of Paris is a white powder.

* When water is added to plaster of Paris, it converts into hard mass in about half an hour.

* Hardness is occurred due to formation of gypsum .

CaSO₄ . ½ H₂O + 3/2 H₂O = CaSO₄ . 2 H₂O

Or,

2CaSO₄ . ½ H₂O + 3 H₂O = 2CaSO₄ . 2 H₂O ( gypsum )

Uses of Plaster of Paris

* Plaster of Paris is used in hospitals for setting fractured bones .

* Plaster of Paris is used in making toys, decorative materials, cheap ornaments, cosmetics, black-board chalk.

* Plaster of Paris is used as a fire-proofing material.

* Plaster of Paris is used in chemistry laboratories for sealing air-gaps in apparatus where air-tight arrangement is required.

* Plaster of Paris is used for making surfaces smooth before painting them

WATER OF CRYSTALLISATION

* Water present in salt molecule to form crystal structure is called water of crystallization.

* The salts which contain water of crystallisation are called hydrated salts.

e.g , CuSO₄.5H₂O is hydrated salt . It is called copper sulphate pentahydrate

Na₂CO₃.10H₂O - sodium carbonate decahydrate

* Water of crystallization is a part of 'crystal structure' of a salt.

* Since water of crystallisation is not free water, it does not wet the salt.

* The water of crystallisation is responsible for shape and color of crystals of the salts .

For example,

Water of crystallisation makes copper sulphate crystals blue in color. Thus, CuSO₄.5H₂O is blue in colour.

Ferrous sulfate crystals ( FeSO₄.7H₂O ) - green

Sodium carbonate crystals (Na₂CO₃.10H₂O) - white

calcium sulphate crystals (CaSO₄. 2H₂O) - white.

Action of Heat on Hydrated Salts

* When hydrated salts are heated strongly, then water of crystallization is removed .

* By losing water of crystallisation, the hydrated salts lose their regular shape and colour, and become colourless powdery substances.

* The salts which have lost their water of crystallisation are called anhydrous salts.

* When water is added to an anhydrous salt, it becomes hydrated once again, and regains its colour.

For example.

* Copper sulphate crystals (CuSO_4.5H₂O) are blue in colour. When copper sulphate crystals are heated strongly, they lose all the water of crystallisation and form anhydrous copper sulphate (which is white):

* The dehydration of copper sulphate crystals is a reversible process. So, when water is added to anhydrous copper sulphate, it gets hydrated and turns blue due to the formation of hydrated copper sulphate: (CuSO_4.5H₂O)

* This property of anhydrous copper sulphate is used to detect the presence of moisture (water) in a liquid. A few drops of the liquid are added to white anhydrous copper sulphate powder. The appearance of blue colour in anhydrous copper sulphate indicates the presence of moisture (water) in the liquid.

Sunday, July 4, 2021