CLASS X
SCIENCE
ACIDS BASES AND SALTS (CHAPTER-2)
INTRODUCTION
• ACIDS are
- Sour in taste & non-soapy to touch
-Changes the blue colour of blue litmus to red
- Common examples are citric acid, lactic acid
• BASES are
- Bitter in taste & soapy to touch
- Changes the blue colour of red litmus to blue
- Common examples are washing soda, baking soda
NATURALLY OCCURING ACIDS
NATURAL SOURCE ACID
Vinegar Acetic acid
Orange & Lemon Citric acid
Tamarind Tartaric acid
Tomato Oxalic acid
Curd Lactic acid
Antsting Methanoic acid/Formic acid
Acid –base INDICATORS/
indicators
Substances that change their colour or odour when added into an
acid or an alkaline(base) solution to indicate the presence of acid or
base.
Classified in the following ways-
a)Natural indicators
b) Synthetic indicators
c) Olfactory indicators
UNIVERSAL
INDICATORS
INDICATORS NATURAL
SYNTHETIC INDICATORS
INDICATORS
OLFACTORY
INDICATORS
NATURAL INDICATORS
Found in nature in the plants.
Eg- Litmus solution( a purple colour dye extracted from lichen plant belonging to
the division “Thallophyta”
INDICATOR COLOUR IN ACIDIC MEDIUM COLOUR IN ALKALINE MEDIUM
Litmus(Purple in Red Blue
neutral)
Red Cabbage Red Green
juice(from leaves)
Turmeric Yellow Reddish brown
Flowers of Hydrangea blue pink
plant
SYNTHETIC INDICATORS
Indicators which are synthesised in the laboratory or industry.
INDICATOR COLOUR IN COLOUR IB BASIC COLOUR IN
ACIDIC SOLUTION NEUTRAL
SOLUTION SOLUTION
Phenolphthalein Colourless Pink Colourless
Methyl Orange Red Yellow Orange
OLFACTORY INDICATORS
Those substances whose odour changes in acidic or basic medium.
INDICATOR ODOUR IN ACIDIC ODOUR IN BASIC
MEDIUM MEDIUM
Vanilla extract Smell detected No smell
Onion Smell detected No smell
UNIVERSAL INDICATOR
To check how strong a given acid or base is,a universal indicator ,which is
amixture of several indicators.
It shows different colours at different concentrations of hydrogen ion in a
solution.
Example-pH scale
CHEMICAL PROPERTIES OF ACIDS
1) Reaction with Metals-Acids react with metals to form salt and hydrogen gas
ACID + METAL SALT + HYDROGEN GAS
• eg:- Zn + 2HCl--------------- ZnCl2 + H2
• Fe + H2SO4----------- FeSO4 +H2
• Hydrogen gas burns with a pop sound.
•
Metal carbonates/Bicarbonates + Acid Salt +Water+ Carbon dioxide
• Na2CO3 + 2HCl 2NaCl + H2O + CO2
• NaHCO3 +HCl NaCl + H2O + CO2
•
CHEMICAL PROPERTIES OF BASES
1) Reaction with Metals -Bases also react with metal to form hydrogen
BASE + METAL-------------- SALT + HYDROGEN GAS
Eg:- 2NaOH +Zn ------------- Na2 ZnO2 + H2
Sodium Zincate
2) Reaction with Non-metallic oxide- Bases react with non-metallic oxides(acidic oxides) to produce salt and water.
BASE + NON-METALLIC → SALT+ WATER
Ca(OH)2 (aq) + CO2 (g) --------- CaCO3 (s) + H2 O (l)
Base non-metallic oxide (Calcium carbonate)Salt
This reaction shows that Non- Metallic oxides are ACIDIC in nature.
ACIDS IN WATER SOLUTION
All acids produce hydrogen ion (H+) or H3O+ (Hydronium ion) in the presence of
water.
As H+ ion cannot exist alone so it combines with water molecules and forms H3O+
(Hydronium ion).
HCl + H2O -------------- Cl- + H3O+
H+ + H2O -------------- H3O+
H+/H3O+ is responsible for the electrical conductivity of acidic solutions
Some substances do not form H+ ions in aqueous solution even though element
hydrogen is present in the compound. They are not acids. Example glucose, alcohol
etc
BASES IN WATER SOLUTION
All bases produce hydroxide ion (OH-) or hydroxyl
ion in the presence of water
NaOH(aq) -------------- OH-(aq) + Na+(aq)
Ca(OH)2(aq) ------------ 2OH-(aq) +Ca2+ (aq)
Hydroxide ion is responsible for the electrical
conductivity of basic solutions.
NOTE- All bases do not dissolves in water.An alkali is abase that dissolves in water.
Both acids and bases conduct electric current in their aqueous solution due to the
presence of free ions.
Dilution of acids
• Acid must be slowly added to water, Since dilution is exothermic
• Otherwise it may cause burns due to acid splash and can cause breakage of
glass containers.
• Mixing an acid or base with water decreases the
concentration of ions per unit volume
pH scale
• It is a scale for measuring hydrogen ion concentration in a solution
Importance of pH in everyday life
• Our body pH is 7.0 to 7.8
• When rain water has pH less than 5.6 it is acid rain
• Plants need a specific pH for the growth. So we need to check the soil pH
• Our stomach produces hydrochloric acid. Too much of acid causes
indigestion, pain and irritation.
To get rid of the acidity bases called ANTACIDS are used.eg:-milk of magnesia.
• Tooth enamel (calcium phosphate) gets corroded by acids produced by bacteria
which acts on food particles remaining in our mouth.
• To prevent this we use tooth pastes which are basic
• Bees and ants inject acid when they sting. So a mild base on the stung area gives
relief. You can use soap / tooth paste/ baking soda
Some naturally occurring acids
pH of salts
• An acid is formed by the reaction between an acid and a base.
• The pH of salts depends on the strength of original acid and base
Chemicals from common salt
• Common salt( Sodium chloride) is an important raw material for substances
like sodium hydroxide, bleaching powder, baking soda, washing soda and many
more
Sodium hydroxide (NaOH)
• When electricity is passed through brine(aq solution of sodium chloride), chlorine
is formed at cathode and hydrogen at anode. NaOH is formed near cathode. This
process is known as CHLOR-ALKALI process.
• 2NaCl +2H2O---------------- 2NaOH + H2+Cl2
Bleaching powder- calcium oxy chloride-
CaOCl2
• It is formed by the action of chlorine on dry slaked lime
• Ca(OH) 2 + Cl2-------------- CaOCl2 + H2O
• Uses
• For bleaching cotton, linen, wood pulp
• As an oxidizing agent
• For disinfecting
Baking soda- sodium bicarbonate-
NaHCO3
• Preparation : NaCl +H2O +NH3 +CO2----------------NH4Cl + NaHCO3
• On heating it produces large amount of carbon dioxide
2NaHCO3 ---------------------- Na2CO3 +H2O +CO2
Uses
For making baking powder (a mixture of baking soda + edible acid like tartaric acid) .
Uses of baking soda
• Cake becomes soft and spongy because baking powder when mixed in water
or heated the following reaction takes place
• NaHCO3 + H+---------------- CO2 +H2O + sodium salt of acid
• As an antacid against acidity
• In fire extinguishers
Washing soda- Sodium carbonate deca
hydrate
Na
• Preparation : Recrystallisation
2 CO
of sodium 3 10
carbonate H 2O
• Na2CO3 +10 H2O ------------- Na2CO310H2O
• Uses
• In the manufacture of glass, cement, soap, borax
• Cleaning agent
• For removing permanent hardness of water
Are the crystals of salts really dry?
• Water of crystallization is fixed number of water molecules chemically attached to
each formula unit of a salt
• Blue Copper sulphate crystals (CuSO4.5H2O)
seems to be dry contain water of crystallization
On heating, water is removed and it turns
White.(CuSO4)
Plaster of Paris- Calcium sulphate
hemihydrate
- CaSO4 1/2H2O or (CaSO4) 2H2O
• On mixing with water Plaster of Paris becomes hard solid mass of gypsum
• CaSO4 1/2H2O +3/2H2O------------- CaSO42H2O (gypsum)
• One molecule of water is shared by 2 water molecules in POP
• Uses
• In making toys, decoration materials
• In making surface smooth
• For immobilizing broken bone
IMPORTANT LINKS FOR RESOURCE
MATERIALS
• https://diksha.gov.in/play/collection/do_31289123241963520013913?
contentType=TextBook
• https://bit.ly/term-10science
• https://www.khanacademy.org/science/in-in-class-10-chemistry-india/
x87dd2847d57ee419:in-in-acids-bases-and-salts
• https://nroer.gov.in/55ab34ff81fccb4f1d806025/
file/56cd6fbb81fccb54223d832f
• https://nroer.gov.in/55ab34ff81fccb4f1d806025/
page/58870b46472d4a1fef810919
• https://nroer.gov.in/55ab34ff81fccb4f1d806025/
file/5886e852472d4a1fef80f9cd
Assignment questions
• Define olfactory indicators. Give example
• What is neutralization reaction?
• Why do acids not show acidic behavior in the absence of water?
• Why does distilled water not conduct electricity where as rain water does?
• What do you mean by water of crystallization?
• Write the equation of “chlor alkali “ process.
• What happens when a solution of sodium bicarbonate is heated?
Thank you
