CBSE Class 10 Chemistry Acids Bases And Salts Notes

CBSE Class 10 Chemistry Acids Bases And Salts Notes. Learning the important concepts is very important for every student to get better marks in examinations. The concepts should be clear which will help in faster learning. The attached concepts made as per NCERT and CBSE pattern will help the student to understand the chapter and score better marks in the examinations. For more study material for Chemistry please click here - class 10 chemistry chapter 4 notes.

Chapter 2

Acids, Bases and Salts

Chapter Notes

Top concepts:

2. On the basis of origin, acids are classified as:

a). Organic acids: Acids derived from living organisms like plants and animals are called organic acids. They are weak acids and are not harmful for living organisms. For example: citric acid is present in fruits, acetic acid present in vinegar, oxalic acid present in tomato, tartaric acid present in tamarind, lactic acid present in sour milk and curd.

b). Mineral acids: They are also called inorganic acids. They are dangerous and corrosive. Special precautions have to be taken while handling them. For example: sulphuric acid (H₂SO₄), hydrochloric acid (HCl) etc.

3. On the basis of their strength, acids are classified as:

a. Strong acids: Strong acids are those acids which completely dissociate into its ions in aqueous solutions. Example: nitric acid (HNO₃) , sulphuric acid(H₂SO₄), hydrochloric acid(HCl)

b. Weak acids: Weak acids are those acids which do not completely dissociate into its ions in aqueous solutions. For example: carbonic acid (H₂CO₃), acetic acid (CH₃COOH)

4. On the basis of their concentration, acids are classified as:

a. Dilute acids: Have a low concentration of acids in aqueous solutions.

b. Concentrated acids: Have a high concentration of acids in aqueous solutions.

5. Alkalies: Water soluble bases are called alkalies. For example: Sodium hydroxide (NaOH), potassium hydroxide(KOH)

6. On the basis of their strength, bases are classified as: 

a. Strong bases: Strong bases are those bases which completely dissociate into its ions in aqueous solutions.

Example: sodium hydroxide (NaOH), potassium hydroxide (KOH) b. Weak bases: Weak bases are those bases which do not completely dissociate into its ions in aqueous solutions. For example: ammonium hydroxide (NH4OH) 7. On the basis of their concentration, bases are classified as: a. Dilute bases: Have a low concentration of alkali in aqueous solutions.

b. Concentrated bases: Have a high concentration of alkali in aqueous solutions. 8. Acids and bases conduct electricity because they produce ions in water. There is a flow of electric current through the solution by ions.

9. Indicators are those chemical substances which behave differently in acidic and basic medium and help in determining the chemical nature of the substance. Acid base indicators indicate the presence of an acid or a base by a change in their colour or smell.

10.Indicators can be natural or synthetic.

11.Olfactory indicators: These are those indicators whose odour changes in acidic or basic medium. Example: onion

12.Onion: Smell of onion diminishes in a base and remains as it is in an acid.

13.Vanilla essence: The odour of vanilla essence disappears when it is added to a base. The odour of vanilla essence persists when it is added to an acid.

14.Turmeric: In acids, yellow colour of turmeric remains yellow. In bases, yellow colour of turmeric turns red.

15.Litmus: Litmus is a natural indicator. Litmus solution is a purple dye which is extracted from lichen. Acids turn blue litmus red. Bases turn red litmus blue. Water is essential for acids and bases to change the colour of litmus paper. Remember that litmus paper will act as an indicator only if either the litmus paper is moist or the acid or base is in the form of aqueous solution. This is because acids and bases release H+ and OH- ions respectively in aqueous solutions.

16.Phenolphthalein: Phenolphthalein remains colourless in acids but turn pink in bases.

17.Methyl orange: Methyl orange turns pink in acids and becomes yellow in bases.

18.Reaction of acids and bases with water:

19.Reaction of acids and bases with metals:
Metals displace hydrogen from the acids and form salt and hydrogen gas. This is a displacement reaction. So, acids react with only those metals which are placed above hydrogen in the reactivity series so that metals can displace hydrogen from acids.

20.Reaction of acids and bases with metal carbonates:

Acids react with metal carbonate to form salt, water and release carbon dioxide.

21.Reaction of acids and bases with metal bicarbonates:
Acids react with metal bicarbonate to form salt, water and release carbon dioxide.

22. Reaction of acids with bases: Neutralisation reaction: Acids react with bases to form salt and water.

23.Reaction of acids with metallic oxides:

Metallic oxides are basic. Therefore, acids react with metallic oxides to form salt and water.

HCl + CuO ® CuCl₂ + H₂O

24.Reaction of bases with non-metallic oxides: Non – metallic oxides are acidic in nature. Bases react with non- metallic oxides to form salt and water. Example: CO₂

Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

25.Amphoteric oxides: Oxides which show acidic as well as basic properties. For example: ZnO, Al₂O₃

26.Neutral oxides: Oxides which are neither acidic nor basic are called neutral oxides. Example: CO

27.pH: It is used to find out the strength of acids and bases i.e., how strong or weak the acid or a base is. p in pH stands for ‘potenz’ in German. The strength of acids and bases depends on the number of H+ ions and OH- ions produced respectively.

28.pH scale: A scale for measuring hydrogen ion concentration in a solution is called pH scale.

29.On pH scale, we measure pH from 0 to 14. pH value:

30.More the hydrogen ion (or hydronium ion) concentration, lower is the pH value.

31.More the hydroxyl ion concentration, higher is the pH value.

32.Variation in pH:

33. Acids which produce more hydrogen ions are said to be strong acids and acids which produce less hydrogen ions are said to be weak acid In other words, strong acids have a lower pH value than weak acids.

34. Bases which produce more hydroxyl ions are said to be strong bases and bases which produce less hydroxyl ions are said to be weak base In other words, strong bases have a higher pH value than weak bases.

35. Living organisms are pH sensitive. Human body works within a pH range of 7.0 to 7.8.

36. Rain water with a pH less than 5.6 is called acid rai This acid rain if it flows into river water makes the survival of aquatic life difficult.

37. Plants also require a specific pH range of soil for their healthy growth.

38. pH of our digestive system: Our stomach produces hydrochloric acid for digestion of food. But during indigestion, excess of acid is produced in the stomach and therefore, the pH decrease This causes pain and irritation. So, to neutralise this excess acid, a mild base is used. This mild base works as an antacid. An antacid is any substance, generally a base or basic salt, which counteracts stomach acidity.

39. Tooth decay: Tooth decay starts when the pH of the mouth is lower than 5.5. Tooth enamel is made up of calcium phosphate which is the hardest substance in the body. It does not dissolve in water, but is corroded when the pH in the mouth is below 5.5. If food particles remain in the mouth after eating, bacteria present in our mouth produce acid by degradation of sugar. This decreases the pH of mouth and hence tooth decay occur The best way to prevent this is to clean the mouth after eating food. Using toothpastes, which are generally basic, for cleaning the teeth can neutralise the excess acid and prevent tooth decay.

40. pH is also significant as it is used in self defence by animals and plant Bees use acids in their sting. To neutralise the effect a mild base like baking soda can be used.

41. Sodium hydroxide (NaOH) Preparation:
Chlor Alkali process:

In this process, electricity is passed through an aqueous solution of Sodium chloride (called brine). Sodium chloride decomposes to form sodium hydroxide. Chlorine gas is formed at the anode, and hydrogen gas at the cathode. Sodium hydroxide solution is formed near the cathode.

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

42.Bleaching powder: Bleaching powder is represented as CaOCl₂, though the actual composition is quite complex.
Preparation: Bleaching powder is produced by the action of chlorine on dry slaked lime.
Ca(OH)₂ + Cl₂ → CaOCl₂+ H₂O

43.Baking soda: Sodium hydrogen carbonate (NaHCO₃)
Preparation:
NaCl + H₂O + CO₂+ NH₃ → NH₄Cl + NaHCO₃

44.Washing soda: Sodium carbonate Na₂CO₃ .10H₂O
Preparation:
In the first step, sodium carbonate is obtained by heating baking soda.
2NaHCO₃      Heat→    Na₂CO₃ + H₂O + CO₂
Then washing soda is produced by recrystallisation of sodium carbonate.
Na₂CO₃ + 10H₂O → Na₂CO₃ .10H₂O

45.Plaster of Paris: Calcium sulphate hemihydrate CaSO₄. ½ H₂O
Preparation: Plaster of Paris is prepared by heating Gypsum at 373K.
CaSO₄. 2H₂O     Heat at 373K →   CaSO₄. ½ H₂O + 1½ H₂O

46.Water of crystallisation: It is the fixed number of water molecules present in one formula unit of a salt.

ACIDS, BASES AND SALTS      

4.1 ACIDS :

Substances with sour taste are regarded as avoids. Lemon juice, vinegar, grape fruit juice and spoilt milk etc. taste sour since they are acidic. Many substances can be identified as acids based on their taste but some fo the acids like sulphuric acid have very strong action on the skin which means that they are corrosive in nature. In such case it would be according to modern definition-

An acid may be defined as a substance which release one or more H+ ions in aqueous solution.

Acids are mostly obtained from natural sources. One the basis of their source avids are of two types -

 (a) Mineral acids         (b) Organic acids

4.1 (a) Mineral Acids :

Acids which are obtained from rocks and minerals are called mineral acids.

4.1 (b) Organic Acids :

Acids which are present in animals and plants are known as organic acids. A list of commonly used acids along with their chemical formula and typical uses, is given below -

4.1 (c) Chemical Properties of Acids:

1.Action with metals: Dilute acids like dilute HCI and dilute H₂SO₄ react with certain active metals to evolve hydrogen gas.

Metals which can displace hydrogen from dilute acids are known as avtive metals. e.g. Na, K, Zn, Fe, Ca, Mg etc.

Zn(s) + H₂SO₄ (dilute) → ZnSO4(aq) + H₂(g)

The active metals which lie above hydrogen in the activity series are electropositive in nature. Their atoms lose electrons to form positive ions and these electrons are accepted by H+ ions of the acid. As a result, H₂ is evolved.

For e.g.

2.Action with metal oxides : Acids react with metal oxides to form salt and water. These reactions are mostly carried out upon heating.

For e.g.

3.Action with metal carbonates and metal bicarbonates : Both metal carbonates and bicarbonates react with acids to evolve CO2gas and form salts.

For e.g.

4.Action with bases : Acids react with bases to give salts and water.

4.1 (d) Strong and Weak Acids :

(i) Strong acids : Acids which are completely ionised in water are known as strong acids.

Hydrochloric acid (HCI), sulphuric acid (H2SO4), nitric acid (HNO3) etc. are all strong acids.

(ii) Weak acids: Acids which are weakly ionised in water are known as weak acids.

For e.g.

Carbonic acids (H2CO3), phosphoric acid (H3PO4), formic acid (HCOOH), acetic acid (CH3COOH) are weak acids.

CH₃COOH + Water → CH₃COO-(aq) + H⁺ (aq)

In general MINERAL acids are STRONG acids while ORGANIC acids are WEAK acids.

4.2  Base :

Substances with bitter taste and soapy touch are regarded as bases. Since many bases like sodium hydroxide and potassium hydroxide have corrosive action on the skin and can even harm the body, so according to the modern definition -

a base may be defined as a substance capable of releasing one or more OH- ions in aqueous solution.

4.2 (a) Alkalies :

Some bases like sodium hydroxide and potassium hydroxide are water soluble. These are known as alkalies. Therefore water soluble bases are known as alkalies eg. KOH, NaOH. A list of a few typical bases along with their chemical formulae and uses is given below-

4.2 (b) Chemical Properties :

1.Action with metals : Metals like zinc, tin and aluminum react with strong alkalies like NaOH (caustic soda), KOH (caustic potash) to evolve hydrogen gas.

2.Action with non-metallic oxides: Acids react with metal oxides, but bases react with oxides of non-metals to form salt and water.

For e.g.

4.2 (c) Strong and Weak Bases :

(i) Strong base : A base contains one or more hydroxyl (OH) groups which it releases in aqueous solution upon ionisation. Bases which are almost completely ionised in water, are known as strong bases.

For e.g.

Sodium hydroxide (NaOH), potassium hydroxide (OH) groups which it releases in aqueous solution upon ionisation. Bases which are almost completely ionised in water, are known as strong bases.

Both NaOH and KOH are deliquescent in nature which means that they absorb moisture from air and get liquefied.

(ii) Weak bases : Bases that are feebly ionised on dissolving in water and reduce a low concentration of hydroxyl ions are called weak bases.

4.3 CONDUCTING NATURE OF ACID AND BASE SOLUTIONS :

Acids are the substances which contain one or more hydrogen atoms in their molecules which they can release in water as H+ ions. Similarly, bases are the substances which contain one or more hydroxyl groups in their molecules which they an release in water as OH- ions. Since the ions are the carries of charge therefore, the aqueous solutions of both acids and bases are conductors of electricity.

Experiment :

In a glass beaker, take a dilute solution of hydrochloric acid (HCI). Fix two small nails of iron in a rubber cork in the beaker as shown in the figure. Connect the nails to the terminals of a 6 volt battery through a bulb. Switch on the current and bulb will start glowing. This shows that the electric current has passed through the acid solution. As the current is carried by the movement of ions, this shows that is solution HCI has ionised to give H+ and CI- ions. Current will also be in a position to pass if the beaker contains in it dilute H2SO4 (H+ ions are released in aqueous solution). Similarly, aqueous solutions containing NaOH or KOH will also be conducting due to release of OH- ions.

Bulb will not glow if glucose (C₆H₁₂O₆) or ethyl alcohol (C₂H₆O) solution is kept in the beaker. This means that both of them will not give any ions in solution.

4.4 COMPARISON BETWEEN PROPERTIES OF ACIDS AND BASES :

4.5 ROLE OF WATER IN THE INISATION OF ACIDS AND BASES :

Substances can act as acids and bases only in the presence of water in aqueous solution. In dry state which is also called anhydrous state, these characters cannot be shown Actually, water helps in the ionisation of acids or base by separating the ions. This is also known as dissociation and is explained on the basis of a theory called Arrhenius theory of acids and bases.

In the dry state, hydrochloric acid is known as hydrogen chloride gas i.e. HCI(g). It is not in the position to give any H+ ions. Therefore, the acidic character is not shown. Now, let us pass the gas through water taken in a beaker with the help of glass pipe. H₂O molecules are of polar nature which means that they have partial negative charge  (δ ⁺)on oxygen atom and partial positive charge (δ ^-) on hydrogen atoms. They will try to form a sort of envelope around the hydrogen atoms as well as chlorine atoms present in the acid and thus help in their separation as ions. These ions are said to be hydrated ions.

HCI(g) + Water → H+ (aq) + CI^- (aq)

                               (Hydrated ions)

The electrical current is carried through these ions. The same applied to other acids as well as bases. Thus we conclude that -

(i) acids can release H⁺ ions only in aqueous solution.

(ii) base can release OH^- ions only in aqueous solution.

(iii) hydration helps in the release of ions from acids and bases.

4.6 DILUTION OF ACIDS AND BASES :

Acids and bases are mostly water soluble and can be diluted by adding the required amount of water. With the addition of water the amount of acid or base per unit volume decrease and dilution occurs. The process is generally exothermic in nature. A concentrated acid like sulphuric acid or nitric acid is to be diluted with water. Acid should be added dropwise to water taken in the container with constant stirring.

5.1 INDICATORS:

Indicator indicated the nature of particular solution whether acidic, basic or neutral. Apart from this, indicator also represents the change in nature of the solution from acidic to basic and vice versa. Indicators are basically coloured organic substances extracted from different plants. A few common acid base indicators are

5.1 (a) Litmus :

Litmus is a purple dye which is extracted from ‘lichen’ a plant belonging to variety Thallophytic. It can also be applied on paper in the form of strips and is available as blue and red strips. A blue litmus strip, when dipped in an acid solution acquires red colour. Similarly a red strip when dipped in a base solution becomes blue.

5.1 (b) Phenolphthalein :

It is also an organic dye and acidic in nature. In neutral or acidic solution, it remains colourless while in the basic solution, the colour of indicator changes to pink.

5.1 (c) Methyl Orange :

Methyl orange is an orange coloured dye (yellow) and basis in nature. In the acidic medium the colour of indicator becomes red and in the basic or natural medium, it colour remains unchanged.

5.1 (d) Red Cabbage Juice :

It is purple in colour in natural medium and turns red or pink in the acidic medium. In the basic or alkaline medium, its colour changes to green.

5.1 (e) Turmeric Juice :

It is yellow in colour and remains as such in the neutral and acidic medium. In the basic medium its colour becomes reddish or deep brown.

Litmus is obtained from LICHEN plant.

5.2  NEUTRALISATION :

 It may be defined as a reaction between acid and base present in aqueous solution to form salt and water.

Basically neutralision is the combination between H⁺ ions of the acid with OH^- ions of the base to form H₂O.

For e.g

Neutralisation reaction involving an acid and base is of exothermic nature. Heat is evolved in all naturalisation reactions. If both acid and base are strong, the value of heat energy evolved remains same irrespective of their nature.

 For e.g

Strong acids and strong bases are completely ionised of their own in the solution. No energy is needed for their ionisation. Since the action of base and anion of acid on both sides of the equation cancels out completely, the heat evolved is given by the following reaction -

5.3 APPLICATIONS OF NEUTRALISATION :

(i) People particularly of old age suffer from acidity problems in the stomach which is caused mainly due to release of excessive gastric juices containing HCI. The acidity is neutralised by antacid tablets which contain sodium hydrogen carbonate (baking soda), magnesium hydroxide etc.

(ii) The sting of bees and ants contain formic acid. Its corrosive and poisonous effect can be neutralised by rubbing soap which contains NaOH (an alkali).

(iii) The stings of wasps contain an alkali and its poisonous effect can be neutralised by an acid like acetic acid (present in vinegar).

(iv) Farmers generally neutralise the effect of acidity in the soil caused by acid rain by adding slaked lime (Calcium hydroxide) to the soil.

5.4 pH SCALE :

A scale for measuring hydrogen ion concentration in a solution called pH scale, has been developed by S.P.L. sorrensen. The P in pH stands for potenz’ in German meaning power. On the pH scale we can measure pH from O (very acidic) to 14 (very alkaline). pH should be thought of simply as a number which indicates the acidic or basic nature of solution. Higher the hydrogen ion concentration, Lower is the pH scale.

Characteristic of pH scale are -

(i) For acidic solution,    pH < 7

(ii) For alkaline solution, pH > 7

(iii) For neutral solution, pH = 7

5.4 (a) Universal Indicator Papers for pH Values :

Indicators like litmus, phenolphthalein and methyl orange are used in predicting the acidic and basic characters of the solutions. However universal indicator papers have been developed to predict the pH of different solutions. Such papers represent specified colours for different concentrations in terms of pH values.

The exact pH of the solution can be measured with the help of pH meter which gives instant reading and it can be relied upon.

pH values of a few common solutions are given below -

5.4 (b) Significance of pH in daily life :

(i) pH i our digestive system : Dilute hydrochloric acid produced in our stomach helps in the digestion of food. However, excess of acid causes indigestion and leads to pain as well as irritation. The pH of the digestive system in the stomach will decrease. The excessive acid can be neutralised with the help of antacid which are recommended by the doctors. Actually, these are group of compounds (basic in nature) and have hardly and side effects. A very popular antacid is ‘Milk of Magnesia’ which is insoluble magnesium hydroxide. Aluminum hydroxide and sodium hydrogen carbonate can also be used for the same purpose. These antacids will bring the pH of the system back to its normal value. The pH of human blood varies between 7.36 to 7.42. it is maintained by the soluble bicarbonates and carbonic acid present in the blood. These are known as buffers.

(ii) pH change leads to tooth decay : The white enamel coating on our teeth is of insoluble calcium phosphate which is quite hard. It is not affected by water. However, when the pH in the mouth falls below 5.5 the enamel gets corroded. Water will have a direct access to the roots and decay of teeth will occur. The bacteria present in the mouth break down the sugar that we eat in one form or the other to acids, Lactic acid is one these. The formation of these acids causes decrease in pH. It is therefore advisable to avoid eating surgery foods and also to keep the mouth clean so that sugar and food particles may not be present. The tooth pastes contain in them some basic ingredients and they help in neutralising the effect of the acids and also increasing the pH in the mouth.

(iii) Role of pH in curing stings by insects: The stings of bees and ants contain methanoic acid (or formic acid). When stung, they cause lot of pain and irritation. The cure is in rubbing the affected area with soap. Sodium hydroxide present in the soap neutralises acid injected in the body and thus brings the pH back to its original level bringing relief to the person who has been stung. Similarly, the effect of stings by wasps containing alkali is neutralised by the application of vinegar which is ethanoic acid (or acetic acid)

(iv) Soil pH and plant growth : The growth of plants in a particular soil is also related to its pH. Actually, different plants prefer different pH range for their growth. it is therefore, quite important to provide the soil with proper pH for their healthy growth. Soils with high iron minerals or with vegetation tend to become acidic. This soil pH can reach as lows as 4. The acidic effect can be neutralised by ‘liming the soil’ which is carried by adding calcium hydroxide. These are all basic in nature and have neutralising effect. Similarly, the soil with excess of lime stone or chalk is usually alkaline. Sometimes, its pH reaches as high as 8.3 and is quite harmful for the plant growth. In order to reduce the alkaline effect, it is better to add some decaying organic matter (compost or manure). The soil pH is also affected by the acid rain and the use of fertilizers. Therefore soil treatment is quite essential.

6.1 SALTS :

 A substance formed by neutralization of an acid with a base is called a salt.

For e.g.

6.2 CLASIFFICATION OF SALTS:

Salts have been classified on the basis of chemical formulae as well as pH values.

6.2 (a) Classification Based on Chemical Formulae :

(i) Normal salts : A normal salt is the one which does not contain any ionsable hydrogen atom or hydroxyl group. This means that it has been formed by the complete neutralisation of an acid by a base.

 For e.g. NaCI, KCI, NaNO₂, K₂ SO₄ etc.

(ii) Acidic salts : an acidic salt still contains some replaceable hydrogen atoms, This means that the neutralisation of acid by the base is no complete. For example, sodium hydrogen sulphate (NaHCO₄), sodium hydrogen carbonate (NaHCI₃) etc.

(iii) Basic salts : A basic salt still contains some replaceable hydroxyl groups. This means that the neutralisation of base by the acid is not complete. For example, basic lead nitrate Pb (OH) NO₃. basic lead chloride, Pb(OH)CI etc.

6.2 (b) Classification Based on pH Values :

Salts are formed by the reaction between acids and bases. Depending upon the nature of the acids and bases or upon the pH values, the salt solutions are of three types.

(i) Neutral salt solutions : Salt solutions of strong acids and strong bases are neutral and have pH equal to 7. They do not change the colour of litmus solution.

 For e.g. : NaCI, NaNO₃, Na₂SO₄ etc.

(ii) Acidic salt solutions : Salt solutions of strong acids and weak bases are of acidic nature and have pH less than 7. They change the colour of blue litmus solution to red.

For e.g. (NH₄)₂SO₄, NH₄CI etc.

In both these salts, the base NH₄OH is weak while the acids H₂SO₄ and HCI are strong.

(iii) Basic salt solutions : Salt solutions of strong bases and weak acids are of basic nature and have pH more than 7. They change the colour of red litmus solution to blue.

For e.g. Na₂CO₃,K₃PO₄ etc.

In both the salts, bases NaOH and KOH are strong while the acids H₂CO₃ and H₃PO₄ are weak.

6.3 USES OF SALTS :

 (i)  As a table salt,

(ii) In the manufacture of butter and cheese.

(iii) In leather Industry.

(iv) In the manufacturing of washing soda and baking soda.

(v) For the preparation of sodium hydroxide by electrolysis of brine.

(vi) Rock salt is spread on ice to melt it in cold countries.

SOME IMPORTANT CHEMICAL COMPOUNDS :

6.4 SODIUM CHLORIDE - COMMON SALT (TABLE SALT) :

Sodium chloride (NaCI) also called common salt or table salt is the most essential part of our diet. Chemically it is formed by the reaction between solutions of sodium hydroxide and hydrochloric acid. Sea water is the major source of sodium chloride where it is present in disserved form along with other soluble salts such as chlorides and sulphates of calcium and magnesium. it is separated by some suitable methods. Deposits of the salts are found in different part of the world and is known as rock salt. When pure, it is a white crystalline solid, However, it is often brown due to the presence of impurities.

6.4 (a) Uses :

(i) Essential for life : Sodium chloride is quite essential for life. Biologically, it has a number of function to perform such as in muscle contraction, in conduction of nerve impulse in the nervous system and is also converted in hydrochloric acid which helps in the digestion of food in the stomach. When we sweat, there is loss  of sodium chloride along with water. It leads to muscle cramps. Its loss has to be compensated suitably by giving certain salt preparations to the patient. Electrol powder is an important substitute of common salt.

(ii) Raw material for chemical: Sodium chloride is also a very useful raw material for different chemical. A few out of these are hydrochloric acid (HCI), washing soda (Na₂CO₃.10H₂O), baking soda (NaHCO₃) etc. Upon electrolysis of a strong solution of the salt (brine), sodium hydroxide, chlorine and hydrogen are obtained. Apart from these, it is used in leather industry for the leather tanning. In severe cold, rock salt is spread on icy roads to melt ice. it is also used as fertilizer for sugar beet.

6.4 (b) Electrolysis of aqueous solution of NaCI :

6.5  WASHING SODA :

Chemical name :

Sodium carbonate decahydrate 

Chemical formula : Na₂CO₃, 10H₂O

6.5 (a) Recrystallization of sodium carbonate:

 Sodium carbonate is recrystallized by dissolving in water to get washing soda it is a basic salt.

            Na2CO3 + 10H2O→  Na₂CO₃, 10H₂O

            Sodium                         Washing soda

            carbonate

6.5 (b) Uses :

(i)  It is used as cleansing agent for domestic purposes.

(ii) It is used in softening hard water and controlling the pH of water.

(iii) It is used in manufacture of glass.

(iv) Due to its detergent properties, it is used as a constituent of several dry soap powders.

(v) It also finds use in photography, textile and paper industries etc.

(vi) It is used in the manufacture of borax (Na₂B₄O₇. 10H₂O)

6.6 BAKING SODA :

Baking soda is sodium hydrogen carbonate or sodium bicarbonate (NaCHO₃).

6.6 (a) Preparation :

It is obtained as an intermediate product in the preparation of sodium carbonate by Solvay process. In this process, a saturated solution of sodium chloride in water is saturated with ammonia and then carbon dioxide gas is passed into the liquid. Sodium chloride is converted into sodium bicarbonate which, being less soluble, separates out from the solution.

6.6 (b) Properties :

(i) It is a white, crystalline substance that forms an alkaline solution with water. The aqueous solution of sodium bicarbonate is neutral to methyl orange but gives pink colour with phenolphthalein orange. (Phenolphthalein and methyl orange are dyes used as acid-base indicators.)

(ii) When heated above 543 K, it is converted into sodium carbonate.

 2NaHCO₃ (s) →Na₂CO₃ (s) + CO₂ (g) + H₂O

6.6 (c) Uses:

(i) It is used in the manufacture of baking powder. Baking powder is a mixture or potassium hydrogen tartar ate and sodium bicarbonate. During the preparation of bread the evolution of carbon dioxide causes bread the evolution of carbon dioxide causes bread to rise (swell).

(ii) It is largely used in the treatment of acid spillage and in medicine as soda bicarb, which acts as an antacid.

(iii) It is an important chemical in th textile, tanning, paper and ceramic industries.

(iv) It is also used in a particular type of fire extinguishers. The following diagram shows a fire extinguisher that uses NaHCI₃ and H₂SO₄ to produce CO₂ gas. The extinguisher consists of a conical metallic container (A) with a nozzle (Z) at one end. A strong solution of NaHCO₃ is kept in the container. A glass ampoule (P) containing H₂SO₄ is attached to a knob (K) and placed inside the NaHCO₃ solution. The ampoule can be broken by hitting the knob. As soon as the acid comes in contact with the NaHCO3 solution, CO2 gas is formed. When enough pressure in built up inside the container, CO2 gas rushes out through the nozzle (A). Since CO2 does not support combustion, a small fire can be put out by pointing the nozzle towards the fire. The gas is produced according to the following reaction.

6.7 BLEACHING POWDER :

Bleaching powder is commercially called ‘chloride of lime or’ chlorinated lime’. It is principally calcium oxychloride having the following formula :

Bleaching powder is prepared by passing chlorine over slaked lime at 313 K.

Actually beaching powder is not a compound but a mixture of compounds :

CaOCI₂, 4H₂O, CaCI₂. Ca(OH)₂. H₂O

6.7 (a) Uses :

(i) It is commonly used as a bleaching agent in paper and textile industries.

(ii) It is also used for disinfecting water to make water free from germs.

(iii) It is used to prepare chloroform.

(iv) It is also used to make wool shrink-proof.

6.8 PLASTER OF PARIS :

6.8 (a) Preparation :

It is prepared by heating gypsum (CaSO₄. 2H₂O) at about 373 k in large seel pots with mechanical stirrer ,or in a revolving furnace .

The temperature is carefully controlled, as at higher temperature   gypsum is fully dehydrated. The properties of dehydrated gypsum are completely different from those of plaster of Paris.

6.8 (b)   Properties :

(i) Action with water : When it    is dissolved in water , it gets crystallized and forms gypsum

6.8 (c) Uses :

When finely powered Plaster of Parries is mixed with water and made into a paste, it quickly sets into a hard mass. In the process, its volume also increases slightly. These properties find a number of uses. Addition of water turns Plaster of Parries back into gypsum.

(i) It is used in the laboratories for sealing gaps where airtight arrangement is required.

(ii) It is also used for making toys, cosmetic and casts of statues.        

(iii) It is used as a cast for setting broken bones.           

(iv) It also find use in making moulds in pottery.           

(iv) It is also used for making surfaces smooth and for making designs on walls and ceilings. 

6.9 HYDRATED SATLS - SALTS CONTAINING WATER OF CRYSTALLISATION:

Certain salts contain definite amount of some H₂O molecules loosely attached to their own molecules. These are known as hydrated salts and are of crystalline nature. The molecules of H₂O present are known as ‘water of crystallisation’.

In colourd crystalline and hydrated salts, the molecules of water of crystallisation also account for their characteristic colours. Thus, upon heating of hydrated salt, its colour changes since molecules of water of crystallisation are removed and the salt becomes anhydrous, For example, take a few crystals of blue vitriol i.e. hydrated copper sulphate in a dry test tube or boiling tube. Heat the tube from below. The salt will change to a white anhydrous powder and water droplet will appear on the walls of the tube. Cool the tube and add a few droops of water again. The white anhydrous powder will again acquire blue colour.

Some Naturally occuring acids

Vinegar                   – AceticAcid
Orange                   – CitricAcid
Lemon                    – CitricAcid
Tamarind                – TartaricAcid
Tomato                   – OxalicAcid
Sour milk (Curd)     – LacticAcid
Ant and Nettle sting – MethanoicAcid

♦ Acid – Base Indicators – Indicate the presence of an acid or base in a solution.
♦ Litmus solution – It is a natural indicator. It is a purple day extracted from Lichens. Other examples are Red Cabbage and coloured petals of Petunia and turmeric.
♦ Olfactory indicators – Show odour changes in acidic or basic media. eg. onion and clove.

♦ Acid – Base Indicators 

♦ DiluteAcid : Contains only a small amounts of acid and a large amount of water.
♦ ConcentratedAcid : Aconcentrated acid contains a large amount of acid and  a small amount of water.

♦ Chemical Properties of Acids and Bases
Acid + Metal → Salt + Hydrogen
2HCl + Zn → ZnCl₂ + H₂
2HNO₃ + Zn → Zn (NO₃)₂ + H₂
H₂SO₄ + Zn → ZnSO₄ + H₂
2CH₃COOH + Zn → (CH₃COO)₂ Zn + H₂
♦ Pop test : When a buring candle is brought near a test tube containing hydrogen gas it burns with a ‘Pop’ sound. This test is conducted for examining the presence of hydrogen gas.
♦ Base + Metal → Salt + Hydrogen
NaOH + Zn → Na₂ZnO₂ + H₂
                     Sodium Zincate
Note – Such reactions are not possible with all the metals.

Action of Acids with metal Carbonates and metal bicarbonates

Metal Carbonate + Acid → Salt + Carbondioxide + Water
Na₂CO_3(s) + 2HCl_(aq) → 2NaCl_(aq) + H₂O(l) + CO_2(g)
Metal bicarbonate + Acid → Salt + Carbondioxide + Water
NaHCO₃ + HCl → NaCl + CO₂ + H₂O

Lime water Test : On passing the CO₂ gas evolved through lime water,

Ca(OH)₂ (aq) + CO_2(g) → CaCO_3(s) + H₂O(l)
Lime water                         White precipitate
On passing excess CO₂ the following reaction takes place
CaCO_3(s) + H₂O(l) + CO_2(g) → Ca(HCO₃)2 aq
                                              Soluble in water

Neutralisation Reactions

Base + Acid → Salt + Water
NaOH_(aq) + HCl_(aq) → NaCl_(aq) + H₂O(l)
Neutralisation reacton takes place when the effect of a base is nullified by an acid and vice versa to give salt and water.

Reactions of metal oxides with acids

Metal Oxide + Acid → Salt + Water
CuO               +  HCl       →     CuCl₂     +     H₂O
Copperoxide     Hydrochloric   Copper    +    Water
                         acid             chloride
Note : Appearance of blue green colour of the solution because of formation of CuCl₂.
Metallic oxides are said to be basic oxides because they give salt and water on reacting with acids.

Reaction of Non Metallic Oxide with Base

Non metallic oxide + Base → Salt + Water
Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

Note : NonMetallic oxides are said to be acidic in nature because on reacting with a base they produce Salt and Water.
All acidic solutions conduct electricity
– Glowing of bulb indicates that there is a flow of electric current through the solution.

Acids or bases in a Water Solution

Acids produce H+ions in the presence of water
HCl + H₂O → H₃O⁺ + Cl–
H₃O⁺ – Hydronium ion.
– H⁺ion cannot exist alone. It exists as H⁺_(aq) or (H₃O⁺) hydronium ion.
H⁺ + H₂O → H₃O⁺
– Bases provide (OH^–) ions in the presence of water 

Alkalis

All bases donot dissolve in water.An alkali is a base that dissolves in water.
Common alkalis are
NaOH Sodiumhydroxide
KOH Potassiumhydroxide
Ca(OH)₂ Calciumhydroxide
NH₄OH :Ammonium hydroxide
Note : All alkalis are bases but all bases are not alkalis.
♦ Precaution must be taken while mixing acid or base with water. The acid must always be added to water with constant stirring as it is highly exothermic reaction.
When an acid or a base is mixed with water they become dilute. This results in the decrease in the concentration of H₃O⁺ or OH^– per unit volume in acids and bases respectively.

Strength of an Acid or Base

Strength of acids and bases depends on the no. of H+ions and OH^–ions produced respectively.
With the help of a universal indicator we can find the strength of an acid or base. This indicator is called PH scale.
pH = Potenz in German means power.
This scale measures from 0 (very acidic) to 14 (very alkaline) 7 Neutral (water in Neutral).
pH paper : Is a paper which is used for measuring PH.
Variation of PH 

– strongAcids give rise to more H⁺ions.
eg. HCl, H₂SO₄ and HNO₃.
– Weak Acids give rise to less H⁺ ions
eg. CH₃ COOH, H₂ CO₃ (Carbonic acid)
– Strong Bases – Strong bases give rise to more OH^– ions.
eg. NaOH, KOH, Ca(OH)₂
– Weak Bases : give rise to less OH^– ions.
eg. NH₄OH

More about Salts

Salts and their derivation 

Note : NaCl and Na₂ SO₄ belong to the family of sodium salts as they have the same radicals. Similarly NaCl and KCl belong to the family of chloride salts.

Importance of pH in our daily life

♦ Importance of pH in our digestive system – pH level of our body regulates our digestive system. In case of indigestion our stomach produces acid in a very large quantity because of which we feel pain and irritation in our stomach.
To get relief from this pain antacids are used. These antacids neutralises the excess acid and we get relief.
♦ pH of Acid Rain : When pH of rain water is less than 5.6 it is called Acid Rain.When this acidic rain flows into rivers these also get acidic, which causes a threat to the survival of aquatic life.
♦ pH of Soil : Plants require a specific range of pH for their healthy growth. If pH of soil of any particular place is less or more than normal than the farmers add suitable fertilizers to it.
♦ Our body functions between the range of 7.0 to 7.8 living organisms can survive only in the narrow range of pH change.
♦ Tooth decay and pH : Bacteria present in the mouth produce acids by degredation of sugar and food particles remaining in themouth.Using toothpaste which is generally basic can neutralise the excess acid and prevent tooth decay.
♦ Bee sting or Nettle sting contains methanoic acid which causes pain and irritation. When we use a weak base like baking soda on it we get relief.

Neutral Salts : Strong Acid + Strong base
pH value is 7
eg. NaCl, CaSO₄
Acidic Salts : Strong Acid + weak base
pH value is less than 7
eq. NH₄Cl, NH₄ NO₃
Basic Salts : Strong base + weak acid
pH value is more than 7
eg. CaCO₃, CH₃ COONa

Chemicals from Common Salt

– Sodium chloride is called as common salt used in our food. It is derived from seawater.
– Rock Salt is the brown coloured large crystals. This s mined like coal.
– Common Salt is an important raw material for manymaterials of daily use such as.
Sodiumhydroxide
Washing Soda
Bleaching Power.

SodiumHydroxide

Preparation : Prepared by the method called chlor-alkali Called chlor-alkali because we get chlorine and a base in this.
2NaCl_(aq) + 2H₂O(l) → 2NaOH_(aq) + Cl_2(g) + H_2(g)  

Bleaching Power

Preparation →     Ca(OH)₂      +     Cl₂    →     CaOCl₂    +    H₂O
                  calcium hydroxide     chlorine       bleaching      water
                                                                     power

uses in textile, factories and laundry, used as disinfectant

Baking Soda 
– Common name – Sodium Hydrogen Carbonate

Uses
– Used in glass, soap and paper industry
– Cleaning agent for domestic purposes.
– Removal of hardness of water.
– Manufacturere of borax.

Water of crystallisation : Fixed no. of water molecules present in one formula unit of a salt.
– On heating copper sulphate crystals water droplets appear, formula of hydrated copper sulphate – CuSO₄. 5H₂O.
– gypsum also contains water of crystallisation.
– Formula of gypsum – CaSO₄.2H₂O
– On heating gypsum at 373k it becomes CaSO₄.½H₂O is plaster of paris.
– Plaster of Paris is used as plaster for fractured bones.
– When plaster of Paris is mixed with water it changes to gypsum.
CaSO₄.½ H₂O + 1½ H₂O → CaSO₄.2H₂O
Uses of plaster of Paris :Making toys, decorativematerial and smooth surfaces.

GIST OF THE LESSON

1) Acids are sour in taste, turn blue litmus red, and dissolve in water to release H+ ions e.g. HCl, H₂SO₄, HNO₃ etc.

2) Bases are bitter in taste, have soapy touch, turn red litmus blue and give hydroxide ions in solution.
e.g. NaOH, KOH etc.

3) A salt is a compound which is formed by neutralization reaction between an acid and base. e.g. sodium chloride.

3) Indicators – Indicators are substances which indicate the acidic or basic nature of the solution by their colour change.

The colour of some acid – base indicators in acidic and basic medium are given below 

5) Chemical properties of acids:

i) Acids react with active metals to give hydrogen gas.

Zn + H₂SO₄→ZnSO₄ + H₂

ii) Acids react with metal carbonate and metal hydrogen carbonate to give carbon dioxide.

NaHCO₃ +HCl →NaCl + H₂O + CO₂

iii) Acids react with bases to give salt and water. This reaction is called as neutralization reaction.

NaOH + HCl → NaCl +H₂O

iv) Acids react with metals oxides to give salt and water.

CuO + H₂SO₄→CuSO₄ + H₂O

6) Chemical properties of Bases:

i) Reaction with Metals - Certain reactive metals such as Zinc, Aluminium, and Tin react with alkali solutions on heating and hydrogen gas is evolved.

2NaOH + Zn → Na₂ZnO₂ +H₂

ii) Reaction with acids -Bases react with acids to form salt and water.

KOH +HCl → KCl +H₂O

iii) Reaction with Non -metallic oxides – These oxides are generally acidic in nature. They react with bases to form salt and water.

2NaOH + CO₂ → Na₂CO₃ + H₂O

7) PH Scale: The concentration of hydrogen ion in solution is expressed in terms of pH. The pH of a solution is defined as the negative logarithm of hydrogen ion concentration in moles per liter.

pH = - log [H⁺]

For water or neutral solutions, pH = 7 ; For acidic solutions, pH < 7; For basic solutions, pH > 7

8) Some Important Chemical Compounds:

a) Common Salt (NaCl)
Sodium chloride is known as common salt. Its main source is sea water. It is also exists in the form of rocks and is called rock salt.

Common salt is an important component of our food. It is also used for preparing sodium hydroxide, baking soda, washing soda etc.

b) Sodium Hydroxide or Caustic Soda (NaOH)

It is prepared by passing electricity through an aqueous solution of sodium chloride also known as brine.

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

This process is known as chlor-alkali process.

Properties:

1. It is white translucent solid.

2. Crystals of sodium hydroxide are deliquescent.

3. It is readily soluble in water and gives strong alkaline solution.

c) Bleaching Powder (CaOCl₂)
Its chemical name is calcium oxychloride. It is prepared by passing chlorine gas through dry slaked
lime.
Ca (OH)₂ + Cl₂ → CaOCl₂ + H₂O

Uses –
1. For bleaching cotton and linen in textile industry and wood pulp in paper industry
2. For disinfecting drinking water.
d) Baking Soda (NaHCO3)
Chemical name is Sodium hydrogen carbonate.
It is prepared by passing CO2 gas through brine solution saturated with ammonia.
NaCl + H₂O +CO₂ +NH_3  ^→  NH₄Cl + NaHCO₃

Properties:
1. It is white crystalline solid and sparingly soluble in water at room temperature.
2. On heating it decomposes to give sodium carbonate and carbon dioxide.
3. It reacts with acids to give carbon dioxide gas.
4. It aqueous solution is weak alkaline due to hydrolysis.

Uses:
1. It is used in soda – acid fire extinguisher.
2. It acts as mild antiseptic and antacid.
3. It is used as a component of baking powder. In addition to sodium hydrogen carbonate baking soda contains tartaric acid.
e) Washing Soda (Na2CO3.10 H2O)
Chemical name is sodium carbonate decahydrate.
It is prepared by heating baking soda. Recrystallisation of sodium carbonate gives washing soda.
2NaHCO₃ →  Na₂CO₃ +H₂O +CO₂
Na₂CO₃ +10 H₂O →  Na₂CO₃. 10 H₂O

Uses:
1. It is used for removing permanent hardness of water.
2. It is used in glass, soap and paper industries.
3. It can be used as a cleaning agent for domestic purposes.
f) Plaster of Paris (CaSO₄.1/2H₂O)
Its chemical name is calcium sulphate hemihydrates. It is obtained by heating Gypsum upto 373K.
CaSO₄.2H₂O →  CaSO₄.1/2H₂O + 11/2H₂O
On treatment with water it is again converted into gypsum and sets as a hard mass.
CaSO₄.1/2H₂O+11/2H₂O  →  CaSO₄.2H₂O

Uses:-
1. It is used by doctors for setting fractured bones.
2. It is used for making statues, models and other decorative materials.

MIND MAP