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:
o Acids are those substances which release hydrogen ions
(H+) when dissolved in water.
o Hydrogen ions (H+) cannot exist alone.
o Hydrogen ions (H+) combine with water molecule (H2O) to
form H3O+ (hydronium ions).
e.g. Hydrochloric Acid, Nitric Acid.
• Bases
o Bases are those substances which release hydroxyl ions
(OH-) when dissolved in water.
o 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
(H3O+) 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
(NH4OH)
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
1. Olfactory Indicators: Subtances that changes its
odour in acidic or basic media.
2. Natural Indicators: Turmeric, Litmus (obtained
from lichen)
3. 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
With
Metals
• Acid + Metal → Salt + Hydrogen gas
• 2HCl + Zn → ZnCl2 + H2
With
Metal
Carbonate
• Acid + Metal Carbonate → Salt + CO2 + H2O
• 2HCl + Na2CO3 → 2NaCl + CO2 + H2O
With Metal
Hydrogen
Carbonate
•Acid + Metal hydrogen Carbonate → Salt + CO2 + H2O
•HCl + NaHCO3 → NaCl + CO2 + H2O
With
Metallic
Oxide
•Acid + Metal Oxide → Salt + Water
• 2HCl + CaO → CaCl2 + H2O

10. Chemical properties of Bases
With Metals
• Base + Metal → Salt + Hydrogen gas
• 2NaOH + Zn → Na2ZnO2 + H2
• Sodium Zincate
With Non-Metallic
Oxide
•Base + Non-Metallic Oxide → Salt + Water
• Ca(OH)2 + CO2 → CaCO3 + H2O

11. Neutralization Reaction
• Neutralization
o Acids and bases react with each other to produce
salt and water.
Acid + Base Salt + Water
HCl + NaOH NaCl + H2O
• Salts
o Salt is obtained when hydrogen of acids is replaced
by the metal.
e.g. NaCl, Na2SO4
o Common Salt: Sodium Chloride salt obtained from
sea.

12. Fact Check
• Metallic Oxides are Basic Oxides:
o 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:
o 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:
o Denotes Hydrogen ion concentration in a solution.
o This number indicates if a solution is acidic or basic.
o 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:
o Aqueous solution of sodium chloride (brine) is
electrolysed.
o Products are Chlorine, Hydrogen and Alkaline NaOH.
o Hydrogen is released at Cathode
o Chlorine is released at anode
2NaCl (aq) + 2H2O (l) electrolysis 2NaOH (aq) + Cl2 (g) + H2 (g)

16. Sodium Hydroxide preparation
• Uses of Products
H2
•Fuels
•Margarine
•Ammonia for
Fertilisers
Cl2
•Water
Treatment
•Swimming
pools
•PVC
•Disinfectants
•CFCs
•Pesticides
NaOH
•De-greasing
metals
• Soaps and
detergents
•Paper making
•Artificial
fibre
Hydrochloric
Acid (H2 + Cl2)
•Cleaning
Steel
•Ammonium
Chloride
medicines
•Cosmetics
Bleach (NaOH
and Cl2)
•Household
Bleach
•Bleaching
fabrics

17. Bleaching Powder preparation
• Bleaching Power (Calcium Oxychloride):
o Prepared by action of chlorine on dry slaked lime
Ca(OH)2.
Ca(OH)2 + Cl2
373K CaOCl2 + H2O
• Uses
Bleaching
Cotton and
Linen in Textile
Industry
Bleaching
Wood pulp in
Paper Industry
Bleaching
washed clothes
in Laundry
Bleach
ing
Used as
Oxidising agent
in Chemical
Industries
Oxidising
agent
Used for
Disinfecting
drinking water
Disinfe-
ctant

18. Baking Soda Preparation
• Baking Soda (Sodium Hydrogen Carbonate):
o Prepared from the raw materials NaCl, NH3, H2O, CO2
NaCl + H2O + CO2 + NH3 NH4Cl + NaHCO3
• Properties
o It is a mild non-corrosive basic salt.
o When it is heated during cooking following reaction takes
place
2NaHCO3
heat Na2CO3 + H2O + CO2
o Washing Soda (Na2CO3) is bitter in taste.

19. Baking Soda Preparation
• Uses
o Used as an antacid. As it is alkaline, it neutralizes
excess acid in stomach.
o Used in soda-acid fire extinguisher.
o For making baking powder (mixture of baking soda +
mild edible acid like tartaric acid)
NaHCO3 + H+ (from acid) CO2 + H2O + Sodium salt of acid
CO2 gas produced in the reaction makes the cake
fluffy, soft and spongy.

20. Washing Soda Preparation
• Washing Soda (Na2CO3.10H2O - Sodium Carbonate):
o Prepared by heating baking soda.
o It is crystallized on adding water.
2NaHCO3
heat Na2CO3 + H2O + CO2
Na2CO3 + 10 H2O Na2CO3.10H2O
(10 H2O is water of crystallization)
• Making glass, soap and water
• Manufacture of Sodium compounds
such as borax
• Domestic Cleansing agent
• Remove Permanent Hardness of water
Uses of Washing Soda

21. Water of Crystallisation
• What is water of crystallisation?
o Fixed number of water molecules present in one
formula unit of a salt.
CuSO4.5H2O on heating CuSO4 + 5H2O
decrystallise
(blue crystals of (white powder)
copper sulphate)
CuSO4 + 5H2O on adding water CuSO4.10H2O
re-crystallise
(white powder) (blue crystals)

22. Plaster of Paris
• Plaster of Paris (CaSO4.½H2O – Calcium Sulphate
hemihydrate):
o On heating Gypsum at fixed temperature POP (Plaster of
Paris) is obtained.
(One molecule of CaSO4 is attached to ½ molecule of water. Hence 2
molecules of CaSO4 shares one molecule of water i.e. 2CaSO4.H2O)
CaSO4.2H2O 373K CaSO4.½H2O+ 1½H2O
(Gypsum) (POP)
• Plastering fractured bone. POP on mixing
with water turns into Gypsum and sets into
hard solid mass.
• Making toys, decoration materials.
• To make rough surface smooth.
Uses of Plaster of Paris

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
H2SO4 No change Red Colourless Red
HNO3 No change Red Colourless Red
CH3COOH 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
NH4OH Blue No change Pink
Becomes
colorless after
sometime
Yellow
Becomes
colorless after
sometime

24. • Activity for Olfactory Indicators and Natural
Indicators
o 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
o 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.
o When Zinc reacts with dilute Hydrochloric acid, Zinc
chloride is formed and bubbles of hydrogen gas are
observed.
Zn (s) + 2HCl (aq) ZnCl2 (aq) + H2 (g) + Δ
(Dilute)
Inference:
o Hydrogen gas is formed
o On passing hydrogen gas evolved through a soap solution,
bubbles are formed.
o A burning candle near gas filled bubbles causes a pop
sound.

27. Activity – 2.4
• Reaction between base and metal.
o When granulated Zinc reacts with sodium hydroxide,
sodium zincate is formed and bubbles of hydrogen gas are
observed.
Zn + 2NaOH Zn2ZnO2 + H2 (g) + Δ
Inference:
o Hydrogen gas is formed
o On passing hydrogen gas evolved through a soap solution,
bubbles are formed.
o 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
o When acid reacts with Metal carbonate or Metal Hydrogen
carbonate, salt of the metal, Carbon dioxide and water are
formed.
Test Tube A:
Na2CO3 + 2HCl 2NaCl + H2O + CO2
Test Tube B:
NaHCO3 + 2HCl NaCl + H2O + CO2

29. Activity – 2.5 – continued..
• Testing of Carbon dioxide
o On passing the CO2 gas through lime water, it turns milky
because insoluble precipitate CaCO3 is formed as shown
below.
Ca(OH)2 (aq) + CO2 (aq) CaCO3 (s) + H2O (l)
(Lime water) (white ppt.)
o On passing excess CO2 gas through lime water, it becomes
colourless.
CaCO3 (s) + H2O (l) + CO2 (g) Ca(HCO3)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 + H2O
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
Due to Copper Chloride
CuO + 2HCl → CuCl2 + H2O
Stir it
Blue Green Colour forms
Copper Oxide in a Beaker
Add dilute HCl

32. • Conduction of Electricity by acids and bases
Activity 2.8

33. Activity 2.8
• Conduction of Electricity by acids and bases
• Inference:
o Acids and Bases release ions in aqueous form and hence
conduct electricity.
Solution Bulb Reason
HCl Glows H+ ions released
H2SO4 Glows H+ ions released
Glucose C6H12O6 Does not glow H+ or OH- ions released
Alcohol C2H5OH 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.
o When concentrated Sulphuric acid is added to dry Sodium
chloride in a test tube, it emits Hydrochloric Acid in gaseous
form.
o When gaseous HCl is exposed to dry blue litmus, it does not
change colour.
o When gaseous HCl is exposed to moist blue litmus, it
changes its colour from blue to red.
H2SO4 + 2NaCl Na2SO4 + 2HCl ↑
• Inference
o Acids release H+ ions in aqueous solution.
o 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
o When concentrated Sulphuric acid is added to water or when
Sodium Hydroxide pellets are added to water, the beaker
comes hot.
H2SO4 + Water Heat
NaOH + Water Heat
• Inference
o Dilution of Acid is an exothermic reaction.
o Dilution of Base is an exothermic reaction.
Activity 2.10

36. • pH Values of solutions:
Activity 2.11
Solution Colour of pH
Paper
Approxim
ate 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 K2SO4 H2SO4 KOH
Sodium Sulphate Na2SO4 H2SO4 NaOH
Calcium Sulphate CaSO4 H2SO4 Ca(OH)2
Magnesium Sulphate MgSO4 H2SO4 Mg(OH)2
Copper Sulphate CuSO4 H2SO4 Cu(OH)2
Sodium Chloride NaCl HCl NaOH
Sodium Nitrate NaNO3 HNO3 NaOH
Sodium Carbonate Na2CO3 H2CO3 NaOH
Ammonium Chloride NH4Cl HCl NH4OH

39. • Nature of Salt Solution
Activity 2.14
Salt Solution Acidic/
Basic/Neut
ral
Acid Used Base Used
Sodium Chloride Neutral HCl NaOH
Potassium Nitrate Neutral HNO3 KOH
Ammonium Chloride Acidic HCl NH4OH
Zinc Sulphate Acidic H2SO4 Zn(OH)2
Copper Sulphate Acidic H2SO4 Cu(OH)2
Sodium Acetate Basic CH3COOH NaOH
Sodium Carbonate Basic H2CO3 NaOH
Sodium Hydrogen
Carbonate
Basic H2CO3 NaOH

40. Activity 2.15
Water of Crystallisation
CuSO4.5H2O Δ CuSO4 + 5H2O
(blue crystal) (White)
CuSO4 + 5H2O CuSO4.5H2O
(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