Class 10 Science Compounds of Common Use Exam Notes

Class 10 Science Compounds of Common Use Exam Notes. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.

Introduction

Class 10 Science: Some Important Chemical Compounds Exam Notes

INTRODUCTION

Types of Salt: When a cation replaces H⁺ of an acid, a salt is formed. There are various types of salts.(i) Sulphates: Those salts which are obtained by replacing the hydrogen of sulphuric acid are called sulphates, e.g.,

Name	Formula
Sodium sulphate	Na2SO4
Potassium sulphate	K2SO4
Zinc sulphate	ZnSO4
Copper sulphate	CuSO4
Magnesium sulphate	MgSO4
Calcium sulphate	CaSO4
Ferrous sulphate or Iron (II) sulphate	FeSO4
Stannous sulphate	SnSO4
Ferric sulphate or Iron (III) sulphate	Fe2(SO4)3
Aluminium sulphate	Al2(SO4)3
Chromium sulphate	Cr2(SO4)3
Nickel sulphate	NiSO4
Manganese sulphate	MnSO4
Barium sulphate	BaSO4
Cobalt sulphate	CoSO4
Mercury (II) sulphate	HgSO4
Lead sulphate	PbSO4

(ii) Chlorides: When the hydrogen of hydrochloric acid is replaced by a cation, chloride salts are formed, e.g.,

Name	Formula
Sodium chloride	NaCl
Calcium chloride	CaCl2
Aluminium chloride	AlCl3
Copper chloride	CuCl2
Nickel chloride	NiCl2
Potassium chloride	KCl
Magnesium chloride	MgCl2
Iron (III) chloride	FeCl3
Arsenic chloride	AsCl3
Antimony chloride	SbCl3

(iii) Nitrates: Those salts which are obtained by replacing the hydrogen of nitric acid by a cation are called nitrate salts, e.g.,

Name	Formula
Sodium nitrate	NaNO3
Potassium nitrate	KNO3
Ammonium nitrate	NH4NO3
Lead nitrate	Pb(NO3)2
Calcium nitrate	Ca(NO3)2
Magnesium nitrate	Mg(NO3)2
Aluminium nitrate	Al(NO3)3
Copper nitrate	Cu(NO3)2

(iv) Carbonates: When the hydrogen of carbonic acid is replaced by a metal ion, carbonate salts are formed, e.g.,

Name	Formula
Sodium carbonate	Na2CO3
Zinc carbonate	ZnCO3
Iron (II) carbonate	FeCO3
Potassium carbonate	K2CO3
Copper carbonate	CuCO3
Lead carbonate	PbCO3

2. Salts. Salts are also obtained by the reaction of an acid with a base. The cation is derived from the base and the anion is derived from the acid. The salts derived from sodium hydroxide are called sodium salts. The salts derived from potassium hydroxide are called potassium salts. Calcium hydroxide gives calcium salts, magnesium hydroxide gives magnesium salts, copper hydroxide gives copper salts and so on.3. Displacement Reactions. Those reactions in which a more reactive metal can displace a less reactive metal from its salt solution.4. Hydrogen Carbonates. Those salts which are obtained by replacement of one hydrogen of H₂CO₃ are called hydrogen carbonates or bicarbonates, e.g.,

Name	Formula
Sodium hydrogen carbonate	NaHCO3
Potassium hydrogen carbonate	KHCO3
Calcium hydrogen carbonate	Ca(HCO3)2
Magnesium hydrogen carbonate	Mg(HCO3)2

5. Hydrogen Sulphates. Those salts which are formed by replacement of one atom of hydrogen of sulphuric acid by a metal ion are called hydrogen sulphates, e.g.,

Name	Formula
Sodium hydrogen sulphate	NaHSO4
Calcium hydrogen sulphate	Ca(HSO4)2
Potassium hydrogen sulphate	KHSO4
Magnesium hydrogen sulphate	Mg(HSO4)2

6. Monoprotic Acids. Those acids which give one H⁺ ion in aqueous solution are called monoprotic acids, e.g., HCl, HBr, HI, HNO₃, HNO₂ (nitrous acid), CH₃COOH (acetic acid), HCOOH (formic acid). They form only one type of salts.7. Diprotic Acids. Those acids which give two H⁺ ions in aqueous solution are called diprotic acids, e.g., H₂SO₄, H₂CO₃ (carbonic acid), H₂SO₃ (sulphurous acid), (COOH)₂ (oxalic acid). They form two series of salts, one by replacing one hydrogen and another by replacing both the hydrogen atoms.8. Triprotic Acids. Those acids which give three protons, i.e. three H⁺ ions, in aqueous solution are called triprotic acids, e.g., H₃PO₄ (phosphoric acid). They form three series of salts:

Name	Formula
Sodium dihydrogen phosphate	NaH2PO4
Disodium hydrogen phosphate	Na2HPO4
Sodium phosphate	Na3PO4

9. Chemical in Common Salt. The main chemical present in common salt is sodium chloride. It is obtained by the neutralisation reaction of sodium hydroxide with HCl (hydrochloric acid). It is obtained on a large scale from sea water. It is found in large deposits called rock salt.

10. Uses of Common Salt.

1. It is used in daily food.
2. It is used as a preservative.
3. It is used for manufacture of Na metal and Cl₂(g) by electrolysis in the molten state.
4. It is used for manufacture of caustic soda.
5. It is used for manufacture of baking soda and washing soda by the Solvay process.

11. Manufacture of Sodium Hydroxide. Sodium hydroxide is the most important alkali and is made commercially by electrolysis of saturated brine solution (sodium chloride). Three kinds of cells are used:Castner–Kellner Cell. In this cell, mercury flows along the bottom of the cell and is made the cathode in the outer compartments as shown in the figure. The anode consists of a number of graphite blocks.

The electrolysis of brine solution takes place. Since hydrogen has an over-voltage (i.e. more energy is required to discharge H⁺ ions) at the mercury cathode, sodium is preferentially discharged at the cathode, forming an amalgam with mercury. Sodium amalgam flows out and is reacted with H₂O to give NaOH.

2NaHg + 2H₂O → 2NaOH + 2Hg + H₂

The mercury is recirculated in the cell. H₂ and Cl₂ are two important by-products.

12. Properties of Sodium Hydroxide.

1. It is a deliquescent solid and absorbs moisture and CO₂, finally forming solid hydrated carbonate.
2. It can precipitate cations like Zn²⁺, Al³⁺, Pb²⁺, Sn²⁺, but these precipitates get dissolved in excess of NaOH.

Zn(OH)₂ + 2OH⁻ → [Zn(OH)₄]²⁻ (Zincate ion)

Al(OH)₃ + 3OH⁻ → [Al(OH)₆]³⁻ (Aluminate ion)

Sn(OH)₂ + 4OH⁻ → [Sn(OH)₆]⁴⁻ (Stannate ion)

Pb(OH)₂ + 2OH⁻ → [Pb(OH)₄]²⁻ (Plumbate ion)

13. Uses of Sodium Hydroxide.

1. It is used in the soap industry.
2. It is used in the paper industry.
3. It is used in the textile industry.
4. It is used for preparation of pure fats and oils.
5. It is used in preparation of artificial silk (rayon).
6. It is used in the petroleum industry.
7. It is used in absorbing poisonous gases.
8. It is used as a reagent in the laboratory.

14. Washing Soda. Its chemical formula is Na₂CO₃·10H₂O, i.e. sodium carbonate decahydrate; one mole of Na₂CO₃ contains 10 moles of water of crystallisation. Anhydrous sodium carbonate is called soda ash.15. Solvay Process. It is used for manufacture of washing soda. It is also called the Ammonia Soda process.Raw materials. Sodium chloride (NaCl), ammonia (NH₃) and limestone (CaCO₃).Process.

1. In this process a cold and concentrated solution of sodium chloride (called brine) is saturated with ammonia.
2. The ammoniacal brine is fed from the top of the carbonating tower packed with perforated plates.
3. Carbon dioxide (CO₂) is introduced from the base of the tower, which reacts with NH₃ and H₂O to form ammonium bicarbonate (ammonium hydrogen carbonate).

NH₃ + H₂O + CO₂ → (NH₄)HCO₃     ...(i)

4. Ammonium hydrogen carbonate reacts with sodium chloride (NaCl) to form sodium hydrogen carbonate and ammonium chloride.

(NH₄)HCO₃ + NaCl → NaHCO₃ + NH₄Cl     ...(ii)

(Ammonium hydrogen carbonate + Sodium chloride → Sodium hydrogen carbonate + Ammonium chloride)

5. CO₂ used in the first reaction is produced by heating limestone in a lime kiln (furnace).

CaCO₃ → CaO + CO₂  (on heating)

(Limestone → Quicklime + Carbon dioxide)

6. Quicklime reacts with H₂O to form slaked lime.

CaO + H₂O → Ca(OH)₂

(Calcium oxide + Water → Calcium hydroxide)

7. Slaked lime reacts with ammonium chloride produced in reaction (ii) to generate ammonia, which can be used again in reaction (i).

Ca(OH)₂ + 2NH₄Cl → CaCl₂ + 2NH₃ + 2H₂O

(Calcium hydroxide + Ammonium chloride → Calcium chloride + Ammonia + Water.) Thus, most of the ammonia can be recovered and reused; therefore, this process is economical. Secondly, calcium chloride is obtained as a by-product.

8. Sodium hydrogen carbonate formed in reaction (ii) is sparingly (partially) soluble in water and can be separated by filtration.
9. Sodium hydrogen carbonate is heated to form sodium carbonate.

2NaHCO₃ → Na₂CO₃ + H₂O + CO₂  (on heating)

CO₂ formed is recirculated, i.e. used again in reaction (i).

10. Sodium carbonate is recrystallised by dissolving in water to get washing soda.

Na₂CO₃ + 10H₂O → Na₂CO₃·10H₂O

(Sodium carbonate (anhydrous) + Water → Washing soda)

16. Properties of Washing Soda

1. It is a transparent crystalline solid.
2. It contains ten molecules of water of crystallisation.
3. It is an efflorescent substance (i.e. loses water of crystallisation) when exposed to air. It loses nine molecules of water and forms the monohydrate.

Na₂CO₃·10H₂O → Na₂CO₃·H₂O + 9H₂O

4. Washing soda loses all the water of crystallisation on heating and becomes anhydrous (which does not contain water of crystallisation). It does not decompose on heating.

Na₂CO₃·10H₂O → Na₂CO₃ + 10H₂O  (heat)   ...(iii)

(Sodium carbonate decahydrate → Soda ash (anhydrous sodium carbonate) + Water)

5. Washing soda dissolves in water to form an alkaline solution which turns red litmus blue. It shows that its aqueous solution is alkaline in nature.

Na₂CO₃ + 2H₂O ⇌ 2NaOH + H₂CO₃   ...(iv)

6. When treated with HCl or H₂SO₄, it liberates CO₂ gas.

Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂   ...(v)

Na₂CO₃ + H₂SO₄ → Na₂SO₄ + H₂O + CO₂   ...(vi)

7. When CO₂ gas is passed through an aqueous solution of sodium carbonate, sodium hydrogen carbonate gets precipitated.

Na₂CO₃ + CO₂ + H₂O → 2NaHCO₃   ...(vii)

17. Uses of Sodium Carbonate.

1. It is used in manufacture of glass, soap, paper and other sodium compounds like borax, caustic soda, etc.
2. It is used in softening of hard water.
3. It is used as washing soda in laundries.
4. It is used as a cleaning agent for domestic purposes.
5. It is used as a laboratory reagent.
6. It is used in textile and petroleum refining.
7. It is used for preparation of carbonates of metals.
8. It is used in fusion mixture (Na₂CO₃ + K₂CO₃), which helps in qualitative analysis, i.e. in preparation of soda extract in the case of insoluble salts.

18. Baking Soda (NaHCO₃). Baking soda, chemically, is sodium hydrogen carbonate. It is obtained as the first product in the Solvay process as shown in reaction (ii). It can also be obtained by passing CO₂ gas through an aqueous solution of sodium carbonate as shown in reaction (vii).19. Properties of Sodium Hydrogen Carbonate.

1. It is a white crystalline solid.
2. It is sparingly soluble in water.
3. Its aqueous solution is alkaline in nature due to hydrolysis. The solution is weakly basic.

NaHCO₃ + H₂O ⇌ NaOH + H₂CO₃

This solution gives a yellow colour with methyl orange (indicator) but no colour with phenolphthalein.

4. On heating, it loses carbon dioxide and water, forming sodium carbonate.

2NaHCO₃ → Na₂CO₃ + CO₂ + H₂O  (heat)

5. When it comes in contact with H₂SO₄, it gives CO₂, which is used in fire extinguishers.

2NaHCO₃ + H₂SO₄ → Na₂SO₄ + 2H₂O + 2CO₂

20. Uses of Sodium Hydrogen Carbonate.

1. It is used as an antacid (medicine) under the name soda bicarbonate to neutralise excess acidity (hyperacidity) in the stomach.
2. It is an ingredient of baking powder, which contains NaHCO₃ and tartaric acid. When baking powder is heated, sodium hydrogen carbonate decomposes to give CO₂ and sodium carbonate. CO₂ causes bread and cake to rise. Tartaric acid helps to remove the bitter taste due to formation of Na₂CO₃.
3. It is used as an additive in foods.
4. It is used in making aerated soft drinks.
5. It is used in fire extinguishers because it forms CO₂ when reacted with H₂SO₄. CO₂ surrounds the combustible substance, which helps in extinguishing fire.
6. It is used for production of carbon dioxide.

21. Bleaching Powder (CaOCl₂). Chemically, it is called calcium oxychloride. It is also called chloride of lime.Manufacture. It is manufactured in Hasenclever’s plant or in Bachmann’s plant by the reaction of dry slaked lime with chlorine gas.

Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O

(Slaked lime + Chlorine → Bleaching powder + Water)

22. Properties of Bleaching Powder (Calcium oxychloride).

1. It is a pale yellow powder. It has a strong smell of chlorine.
2. It is soluble in water but a clear solution is never formed due to the presence of impurities.
3. It loses chlorine by the action of carbon dioxide.

CaOCl₂ + CO₂ → CaCO₃ + Cl₂

23. Uses of Bleaching Powder.

1. It is used for bleaching cotton and linen in textile industries, and for bleaching washed clothes in laundry.
2. It is used as an oxidising agent in many chemical industries.
3. It is used for disinfecting drinking water to make water free from micro-organisms.
4. It is used for manufacture of chloroform.
5. It makes wool unshrinkable.

24. Plaster of Paris (CaSO₄·½H₂O). Chemically, Plaster of Paris is calcium sulphate hemihydrate. It is called Plaster of Paris because it is obtained from gypsum, which is mainly found in Paris.Preparation. Plaster of Paris is obtained by heating gypsum (CaSO₄·2H₂O) at 373 K in a kiln. Heating should be done carefully.

CaSO₄·2H₂O → CaSO₄·&frac₁₂;H₂O + 3/2 H₂O  (373 K)

(Gypsum → Plaster of Paris + Water)

25. Properties of Plaster of Paris.

1. It is a white powder.
2. When it is mixed with water, crystals of gypsum are produced and set into a hard mass.

CaSO₄·&frac₁₂;H₂O + 3/2 H₂O → CaSO₄·2H₂O

(Plaster of Paris + Water → Gypsum.) The setting process is exothermic, i.e. heat is evolved. The setting process may be catalysed by sodium chloride, while it can be retarded by borax or alum.

3. When Plaster of Paris is heated at 473 K, it forms anhydrous calcium sulphate, which is known as dead burnt Plaster of Paris. It has no setting property as it takes up water very slowly.

CaSO₄·&frac₁₂;H₂O → CaSO₄ + &frac₁₂;H₂O  (473 K)

26. Uses of Plaster of Paris.

1. It is used for plastering fractured bones and dislocated bones so as to set them in the proper place.
2. It is used in making toys and decorative materials.
3. It is used in making casts for statues, toys, surgical instruments, etc.
4. It is used in making blackboard chalks.
5. It is used in dentistry.
6. It is used for making smooth surfaces and ornate designs on walls and ceilings.
7. It is used in laboratories for sealing air gaps in apparatus so as to make it airtight.

27. Uses of Mild Bases.

1. Washing soda is used as a cleaning agent.
2. NaHCO₃ acts as an antacid.
3. Sodium carbonate is used in removing permanent as well as temporary hardness of water.

28. Water of Crystallisation. It is the fixed number of water molecules present in a crystalline salt, e.g.,

Common name	Formula
Blue vitriol	CuSO4·5H2O
Glauber’s salt	Na2SO4·10H2O
Gypsum	CaSO4·2H2O
Green vitriol	FeSO4·7H2O
White vitriol	ZnSO4·7H2O
Epsom salt	MgSO4·7H2O

2NaHg + 2H2O –2NaOH + 2Hg + H2