Ncert class 10 - science - chapter 2 - acids, bases and salts

This presentation contains the important points for NCERT - Class 10 - Science - Chapter 2 - Acids, Bases and Salts

1. Acids, Bases and Salts Class X – Science Chapter 2 Chemistry

2. Acids and Bases Acids: Acids are those substances which release hydrogen ions ( H + ) when dissolved in water. Hydrogen ions ( H + ) cannot exist alone. Hydrogen ions ( H + ) combine with water molecule (H 2 O) to form H 3 O + (hydronium ions). e.g. Hydrochloric Acid, Nitric Acid. Bases Bases are those substances which release hydroxyl ions ( OH - ) when dissolved in water. Bases soluble in water is called Alkalis. e.g. Sodium Hydroxide, Calcium Hydroxide

3. Ions in Acids / Bases

4. Properties of Acids / Bases Properties of Acids Properties of Bases Sour in taste Bitter in taste Conducts electricity when dissolved in water Conducts electricity when dissolved in water Turns blue litmus red Turns red litmus blue Dilute Acids Dilute Bases Decrease in Hydronium ion ( H 3 O + ) concentration per unit volume results in formation of dilute acids Decrease in Hydroxyl ion ( OH - ) concentration per unit volume results in formation of dilute bases. Highly exothermic reaction. Exothermic reaction

5. Strength of Acids / Bases Common Acids Strong Acid Weak Acid Release more H + ions Release less H + ions e.g. HCl Acetic acid Strong Base Weak Base Release more OH - ions Release less OH - ions e.g. NaOH Ammonium Hydroxide (NH 4 OH) Source Acid Source Acid Vinegar Acetic acid Lemon Citric Acid Tomato Oxalic Acid Tamarind Tartaric Acid Orange Citric Acid Curd Lactic Acid

6. Indicators Indicators : Substances that tell us whether a substance is acidic or basic by change in colour , smell etc. e.g. Litmus solution Types of Indicators Olfactory Indicators : Subtances that changes its odour in acidic or basic media. Natural Indicators : Turmeric, Litmus (obtained from lichen) Synthetic Indicators : Methyl Orange, Phenolphthalein

7. Indicators Indicator Natural Colour Acids Bases Red Litmus Red Remains red Turns Blue Blue Litmus Blue Turns Red Remains Blue Phenolphthalein Colourless Colourless Pink Methyl Orange Reddish Orange Red Yellow

8. Litmus Test

9. Chemical properties of Acids

10. Chemical properties of Bases

11. Neutralization Reaction Neutralization Acids and bases react with each other to produce salt and water. Acid + Base Salt + Water HCl + NaOH NaCl + H 2 O Salts Salt is obtained when hydrogen of acids is replaced by the metal. e.g. NaCl , Na 2 SO 4 Common Salt: Sodium Chloride salt obtained from sea.

12. Fact Check Metallic Oxides are Basic Oxides: Metallic oxides react with acids to give salt and water, similar to the reaction of a base with an acid. Non-metallic Oxides are Acidic Oxides: Non-Metallic oxides react with bases to give salt and water, similar to the reaction of an acid with a base.

13. pH pH Scale: Denotes Hydrogen ion concentration in a solution. This number indicates if a solution is acidic or basic. The scale ranges from 0 to 14. pH of Salts Acid Base Salt Type pH of Salt Strong Strong Neutral pH = 7 Strong Weak Acidic pH < 7 Weak Strong Basic pH > 7 pH Value Inference = 7 Neutral Solution < 7 Acidic Solution > 7 Basic Solution

14. pH in Daily life Our body works within pH range of 7.0 to 7.8 Acid rain has a pH of 5.6 which affects aquatic animals. Plants need specific range of pH for Soil. Acids produced by stomach helps in digestion. Tooth decay starts when the pH in mouth is lower than 5.5 . Bacteria present in mouth produce acids by degradation of Sugar. Bee strings produce acids which causes pain and irritation.

15. Sodium Hydroxide preparation Chlor -alkali process: Aqueous solution of sodium chloride (brine) is electrolysed . Products are Chlorine, Hydrogen and Alkaline NaOH . Hydrogen is released at Cathode Chlorine is released at anode 2NaCl ( aq ) + 2H 2 O (l) electrolysis 2NaOH ( aq ) + Cl 2 (g) + H 2 (g)

16. Sodium Hydroxide preparation Uses of Products

17. Bleaching Powder preparation Bleaching Power (Calcium Oxychloride ): Prepared by action of chlorine on dry slaked lime Ca (OH) 2 . Ca (OH) 2 + Cl 2 373K CaOCl 2 + H 2 O Uses

18. Baking Soda Preparation Baking Soda (Sodium Hydrogen Carbonate): Prepared from the raw materials NaCl , NH 3 , H 2 O, CO 2 NaCl + H 2 O + CO 2 + NH 3 NH 4 Cl + NaHCO 3 Properties It is a mild non-corrosive basic salt. When it is heated during cooking following reaction takes place 2NaHCO 3 heat Na 2 CO 3 + H 2 O + CO 2 Washing Soda (Na 2 CO 3 ) is bitter in taste.

19. Baking Soda Preparation Uses Used as an antacid. As it is alkaline, it neutralizes excess acid in stomach. Used in soda-acid fire extinguisher. For making baking powder (mixture of baking soda + mild edible acid like tartaric acid) NaHCO 3 + H + (from acid) CO 2 + H 2 O + Sodium salt of acid CO 2 gas produced in the reaction makes the cake fluffy, soft and spongy.

20. Washing Soda Preparation Washing Soda (Na 2 CO 3 .10H 2 O - Sodium Carbonate): Prepared by heating baking soda. It is crystallized on adding water. 2NaHCO 3 heat Na 2 CO 3 + H 2 O + CO 2 Na 2 CO 3 + 10 H 2 O Na 2 CO 3 .10H 2 O ( 10 H 2 O is water of crystallization)

21. Water of Crystallisation What is water of crystallisation ? Fixed number of water molecules present in one formula unit of a salt. CuSO 4 .5H 2 O on heating CuSO 4 + 5H 2 O decrystallise (blue crystals of (white powder) copper sulphate ) CuSO 4 + 5H 2 O on adding water CuSO 4 .10H 2 O re- crystallise (white powder) (blue crystals)

22. Plaster of Paris Plaster of Paris (CaSO 4 . ½ H 2 O – Calcium Sulphate hemihydrate): On heating Gypsum at fixed temperature POP (Plaster of Paris) is obtained. (One molecule of CaSO 4 is attached to ½ molecule of water. Hence 2 molecules of CaSO 4 shares one molecule of water i.e. 2CaSO 4 .H 2 O) CaSO 4 .2H 2 O 373K CaSO 4 . ½ H 2 O + 1 ½ H 2 O (Gypsum) (POP)

23. Activity 2.1 - Changes in color Sample Solution Red Litmus Solution Blue Litmus Solution Phenolphthal ein Solution Methyl Orange Solution HCl No change Red Colourless Red H 2 SO 4 No change Red Colourless Red H N O 3 No change Red Colourless Red CH 3 C OOH No change Red Colourless Red NaOH Blue No change Pink Yellow Ca (OH) 2 Blue No change Pink Yellow KOH Blue No change Pink Yellow Mg(OH ) 2 Blue No change Pink Yellow NH 4 OH Blue No change Pink Becomes colorless after sometime Yellow Becomes colorless after sometime

24. Activity for Olfactory Indicators and Natural Indicators Example1: Cloth strips when kept in a bag with finely chopped onions and left overnight in the fridge the strips would smell of onion. Cloth Strip + dilute HCl Solution → We can smell Onion, red colour of cloth strip changes to pale red Cloth Strip + dilute NaOH Solution → Red colour of cloth strip changes to green Activity 2.2

25. Activity for Olfactory Indicators and Natural Indicators Example2: Odour Test Vanilla Essence + dilute HCl Solution → Smell of Vanilla essence exists Vanilla Essence + dilute NaOH Solution → no smell Clove Oil + dilute HCl Solution → Smell of Clove exists Clove Oil + dilute NaOH Solution → Smell of Clove does not exist Activity 2.2

26. Activity – 2.3 Reaction between acid and metal. When Zinc reacts with dilute Hydrochloric acid, Zinc chloride is formed and bubbles of hydrogen gas are observed. Zn (s) + 2HCl ( aq ) ZnCl 2 ( aq ) + H 2 (g) + Δ (Dilute) Inference: Hydrogen gas is formed On passing hydrogen gas evolved through a soap solution, bubbles are formed. A burning candle near gas filled bubbles causes a pop sound.

27. Activity – 2.4 Reaction between base and metal. When granulated Zinc reacts with sodium hydroxide, sodium zincate is formed and bubbles of hydrogen gas are observed. Zn + 2NaOH Zn 2 ZnO 2 + H 2 (g) + Δ Inference: Hydrogen gas is formed On passing hydrogen gas evolved through a soap solution, bubbles are formed. A burning candle near gas filled bubbles causes a pop sound.

28. Activity – 2.5 Reaction of Acids with Metal carbonates and Metal Hydrogen Carbonates When acid reacts with Metal carbonate or Metal Hydrogen carbonate, salt of the metal, Carbon dioxide and water are formed. Test Tube A: Na 2 CO 3 + 2HCl 2NaCl + H 2 O + CO 2 Test Tube B: NaHCO 3 + 2HCl NaCl + H 2 O + CO 2

29. Activity – 2.5 – continued.. Testing of Carbon dioxide On passing the CO 2 gas through lime water, it turns milky because insoluble precipitate CaCO 3 is formed as shown below. Ca (OH) 2 ( aq ) + CO 2 ( aq ) CaCO 3 (s) + H 2 O (l) (Lime water) (white ppt.) On passing excess CO 2 gas through lime water, it becomes colourless . CaCO 3 (s) + H 2 O (l) + CO 2 (g) Ca (HCO 3 ) 2 ( aq ) (soluble in water)

30. Activity – 2.6 Reaction between acids and bases Acids and bases nullify each other’s effect. Acids and bases react with each other to form salt and water. NaOH + HCl NaCl + H 2 O NaOH (Base) + Phenolphthalein Pink + HCl (Acid) Colourless (Neutralized) + NaOH (Base) Pink

31. Activity – 2.7 Reaction between Metal Oxide and Acid Metal oxides react with Acid to form Salt and water. Metal Oxides acts as a base here. Metal + Acid Salt + Water Oxide

32. Conduction of Electricity by acids and bases Activity 2.8

33. Activity 2.8 Conduction of Electricity by acids and bases Inference: Acids and Bases release ions in aqueous form and hence conduct electricity. Solution Bulb Reason HCl Glows H + ions released H 2 SO 4 Glows H + ions released Glucose C 6 H 12 O 6 Does not glow H + or OH - ions released Alcohol C 2 H 5 OH Does not glow H + or OH - ions released NaOH Glows OH - ions released Ca (OH) 2 Glows OH - ions released

34. Acidic property of Acids Only in Aqueous solution. When concentrated Sulphuric acid is added to dry Sodium chloride in a test tube, it emits Hydrochloric Acid in gaseous form. When gaseous HCl is exposed to dry blue litmus, it does not change colour . When gaseous HCl is exposed to moist blue litmus, it changes its colour from blue to red. H 2 SO 4 + 2NaCl Na 2 SO 4 + 2HCl ↑ Inference Acids release H + ions in aqueous solution. Acidic property of acids is exhibited only in aqueous form. i.e. only when H + ions are present. Activity 2.9

35. Dilution of Acid or Base When concentrated Sulphuric acid is added to water or when Sodium Hydroxide pellets are added to water, the beaker comes hot. H 2 SO 4 + Water Heat NaOH + Water Heat Inference Dilution of Acid is an exothermic reaction. Dilution of Base is an exothermic reaction. Activity 2.10

36. pH Values of solutions: Activity 2.11 Solution Colour of pH Paper Approximate pH Value Nature of Substance Saliva (Before Meal) Light green 7.4 Base Saliva (After Meal) Pale Yellow 5.8 Acid Lemon Juice Pink Red 2.5 Acid Colourless Aerated drink Pale Yellow 6 Acid Carrot Juice Light Orange 4 Acid Coffee Orange Yellow 5 Acid Tomato Juice Dark Orange 4.1 Acid Tap Water Green 7 Neutral 1M NaOH Dark blue, Violet 13 -14 Base 1M HCl Red 1 Acid

37. Activity 2.12 pH Values of Soil: pH Value Nature Result = 7 Neutral Plants grow well > 7 Basic Plants are affected < 7 Acidic Plants are affected Take 2g of Soil in a Test Tube Filter the contents Add 5 ml Water Check pH value of the Filtrate

38. Formulae of Salts Activity 2.13 Salt Formula Acid Used Base Used Potassium Sulphate K 2 SO 4 H 2 SO 4 KOH Sodium Sulphate Na 2 SO 4 H 2 SO 4 NaOH Calcium Sulphate CaSO 4 H 2 SO 4 Ca (OH) 2 Magnesium Sulphate MgSO 4 H 2 SO 4 Mg(OH) 2 Copper Sulphate CuSO 4 H 2 SO 4 Cu(OH) 2 Sodium Chloride NaCl HCl NaOH Sodium Nitrate NaNO 3 HNO 3 NaOH Sodium Carbonate Na 2 C O 3 H 2 C O 3 NaOH Ammonium Chloride NH 4 Cl HCl NH 4 OH

39. Nature of Salt Solution Activity 2.14 Salt Solution Acidic/ Basic/Neutral Acid Used Base Used Sodium Chloride Neutral HCl NaOH Potassium Nitrate Neutral HNO 3 KOH Ammonium Chloride Acidic HCl NH 4 OH Zinc Sulphate Acidic H 2 SO 4 Zn(OH) 2 Copper Sulphate Acidic H 2 SO 4 Cu(OH) 2 Sodium Acetate Basic CH 3 COOH NaOH Sodium Carbonate Basic H 2 C O 3 NaOH Sodium Hydrogen Carbonate Basic H 2 C O 3 NaOH

40. Activity 2.15 Water of Crystallisation CuSO 4 .5H 2 O Δ CuSO 4 + 5H 2 O (blue crystal) (White) CuSO 4 + 5H 2 O CuSO 4 .5H 2 O (white) (blue crystal) Blue coloured Copper Sulphate in a Test Tube Heat it White Powder Drops of Water on Test tube Add Water drops Blue colour re - appears

41. Thank you