ACID -BASE:
- Acids are SOUR while bases are Bitter in taste.
- Without tasting, we can check them by LITMUS Test as acids turn blue litmus to RED and bases turn red litmus to BLUE [we have studied in previous classes]
- If someone is suffering from ACIDITY, what will you give to that person, Lemon Juice,Vinegar or Baking Soda solution?......[ we know that Acids and Bases Neutralise each other]
Acids Bases
–
Sour in taste –
Bitter in taste
–
Change the blue litmus to red –
Change red litmus to blue
–
eg.Hydrochloric Acid (HCl) eg. Sodium hydroxide (NaOH)
–
Sulphuric Acid (H2SO4 ) Potassium
hydroxide (KOH)
–
Nitric Acid (HNO3) Calcium
hydroxide Ca(OH)2
– Acetic Acid (CH3 COOH) –
Ammonium hydroxide (NH4OH)
Some Naturally
occurring acids
Vinegar – Acetic Acid
Orange – Citric Acid
Lemon – Citric Acid
Tamarind – Tartaric Acid
Tomato – Oxalic Acid
Sour milk (Curd)
– Lactic Acid
Ant and Nettle
sting – Methanoic Acid
ACID-BASE INDICATORS:
NATURAL INDICATORS
( 1. Litmus Solution : A purple dye obtained from Lichen (symbiotic association of fungus and algae).
2. Turmeric (turn reddish brown with base & unchanged with acids).
3. Red cabbage leaves (originally purple, turns reddish in acid, greenish in base)
4. Some other examples are petals of Petunia, Hibiscus (China rose), Geranium and Hydrangea. Grape Juice
OLFACTORY INDICATORS
2. Turmeric (turn reddish brown with base & unchanged with acids).
3. Red cabbage leaves (originally purple, turns reddish in acid, greenish in base)
4. Some other examples are petals of Petunia, Hibiscus (China rose), Geranium and Hydrangea. Grape Juice
OLFACTORY INDICATORS
( Olfactory indicators –
Show odour/smell changes when mixed in acidic or basic media.
1. ONION ( Paste or juice of onion loses its smell when added with base. It does not change its smell with acid)
2. Vanilla ( The smell of vanilla vanishes with base, but it’s smell does not vanishes with an acid)
3. CLOVE OIL (smell same in acidic medium but didn't smell in base)
SYNTHETIC INDICATORS
Indicators that are synthesized in laboratory are known as synthetic indicators.
Eg. Methyl Orange, Phenolphthalein
1. Phenolphthalein is a colourless liquid. It remains colourless with acid but turns into pink with a base.
2. Methyl orange is originally orange in colour. It turns into red with acid and turns into yellow with base.
2. Vanilla ( The smell of vanilla vanishes with base, but it’s smell does not vanishes with an acid)
3. CLOVE OIL (smell same in acidic medium but didn't smell in base)
SYNTHETIC INDICATORS
Indicators that are synthesized in laboratory are known as synthetic indicators.
Eg. Methyl Orange, Phenolphthalein
1. Phenolphthalein is a colourless liquid. It remains colourless with acid but turns into pink with a base.
2. Methyl orange is originally orange in colour. It turns into red with acid and turns into yellow with base.
UNIVERSAL INDICATORS
Using a litmus paper, phenolphthalein, methyl orange, etc. only the acidic or basic character of a solution can be determined, but use of these indicators does not give the idea about the strength of acid or base. So, to get the strength as well as acidic and basic nature of a given solution universal indicator is used.
Universal indicator shows different colour over the range of pH value from 1 to 14 for a given solution. Universal indicator is available both in the form of strips and solution. Universal indicator is the combination of many indicators [such as water, propanol, phenolphthalein, sodium salt, sodium hydroxide, methyl red, bromothymol blue monosodium salt, and thymol blue monosodium salt ] The colour matching chart is supplied with universal indicator which shows the different colours for different values of pH.
 |
| (pH OF SOME EDIBLE INDICATORS FROM THE KITCHEN) |
Chemical
Properties of Acids and Bases
1. REACTION WITH METALS:
1. REACTION WITH METALS:
Acid + Metal gives Salt + Hydrogen [ video ]
(Refer activity 2.3 on page No. 19 of NCERT Book)
2HCl + Zn è ZnCl2 + H2
2HNO3 + Zn è Zn (NO3)2 + H2
H2SO4 + Zn è ZnSO4 + H2
2CH3COOH + Zn è (CH3COO)2 Zn
+ H2
NaOH(aq.) + Zn(s) è Na2ZnO2(s) + H2 (g)
(Sodium Zincate)
2. Action of Acids with metal Carbonates and metal
bicarbonates/ Hydrogencarbonates
[ NCERT text book Activity 2.5 for class X ]
Take 0.5g Sodium Carbonate in test tube -A and 0.5g Sodium Hydrogen Carbonate in test tube - B, Add 2 ml of dilute Hydrochloric Acid in it. Pass the produced gas through Lime Water (NaOH) or Calcium Hydroxide or Potassium Hydroxide solution and Observe.
Test-Tube-A:
Na2CO3(s) +
2HCl (aq) è 2NaCl(aq) + H2O(l)
+ CO2(g)
Test-Tube-B:
NaHCO3(s) + HCl (aq) è NaCl(aq) + H2O(l)
+ CO2(g)
On passing evolved gas through lime water:
Ca(OH)2
(aq.) + CO2(g) è CaCo3(s) + H2O(l)
[white ppt]
On passing excess gas, following reaction takes place:
CaCo3(s) + H2O (l) + CO2(g) è Ca(HCO3)2(aq.)
[soluble in water]
Neutralisation Reactions [Acid Base Reactions]
Base + Acid forms Salt + Water
NaOH(aq) + HCl(aq) will give NaCl(aq) + H2O(l)
Neutralisation
reaction takes place when the effect of a base is nullified by an acid and vice
versa to give salt and water.
(A)Reactions
of metal oxides with acids [ video ]
Metal Oxide + Acid forms Salt + Water
ACTIVITY: Take small amount of Copper Oxide in a beaker and add dilute HCl slowly while stirring. Note the colour change. [ Metal oxides are BASIC in nature]
CuO + HCl will give CuCl2 + H2O
(B)
Reaction of Non Metallic Oxide with Base
Non metallic oxide + Base gives Salt + Water
Ca(OH)2 + CO2 è CaCO3 + H2O
[Refer activity 2.5 of NCERT Book]
Alkalis:
All bases do not
dissolve in water. An alkali is a base that dissolves in water.
Common alkalis
are:
NaOH Sodium
hydroxide
KOH Potassium
hydroxide
Ca(OH)2 Calcium
hydroxide
NH4OH :Ammonium hydroxide
[Note : All
alkalis are bases but all bases are not alkalis.]
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)
S. No. PH Value Colour of the
Paper Nature of Solution H+ion Conc. OH-ion
1. 0 Dark red highly acidic very high very low
2. 4 Orange
or
yellow Acidic high
low
3.
7 Green Neutral Equal Equal
4. 10 Bluish green or blue Alkaline low high
5. 14 Dark blue
or violet highly basic very
low very high
– strongAcids
give rise to more H+ions.
eg. HCl, H2SO4 and
HNO3
– Weak Acids
give rise to less H+ ions
eg. CH3 COOH, H2CO3 (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)
S. No Name of Salt Formula Derived
from
1. Potassium
Sulphate K2SO4
KOH + H2SO4
2. Sodium Sulphate Na2SO4
NaOH + H2SO4
3. Sodium Chloride NaCl
NaOH + HCl
4. Ammonium Chloride NH4Cl
NH4OH +
HCl
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
(1)
Importance of pH in our digestive
system – pH level of our body regulates
our digestive
system (digestive enzymes acts at specific pH). In case of indigestion our
stomach produces acid in a very large quantity because of which we feel pain
and irritation in our stomach (Acidity). To get relief from this pain antacids
are used. These antacids neutralizes the excess acid and we get relief.
(2)
pH of Acid Rain :
When pH of rain water is less than 5.6 it is called Acid
Rain. When this
acidic rain enters rivers and soil, decreasing their pH, which causes
threat to the survival of plants & animals
present there. It also causes Marble and skin cancer.
(3)
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. Indiscriminate use of fertilizer can cause pH shift
and poor yield.
(4)
Tooth decay and pH :
Bacteria present in the mouth produce acids by degradation of sugar and food
particles remaining in the mouth. Using toothpaste which is generally basic can
neutralize the excess acid and prevent tooth decay.
(5)
INSECT bite or 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.
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 is mined like coal.
– Common Salt is
an important raw ingredient for many materials of daily use
such as:
(a)
Sodium hydroxide
(b)
Washing Soda
(c )Bleaching Powder.
Sodium Hydroxide
Preparation :Prepared
by the method called chlor-alkali (when electricity is passed through aqueous solution of NaCl or BRINE, it Decomposes to form NaOH)
It is Called chlor-alkali
because we get chlorine and a base in this.
2NaCl(aq) + 2H2O(l) è2NaOH(aq) + Cl2(g) +
H2(g)
 |
| (Chlor-Alkali Process) |
BLEACHING - POWDER [ CaOCl2 ]
Preparation:
Ca(OH)2 + Cl2 è CaOCl2 + H2
calcium hydroxide chlorine bleaching powder
( Dry Slaked Lime)
Ca(OH)2 + Cl2 è CaOCl2 + H2
calcium hydroxide chlorine bleaching powder
( Dry Slaked Lime)
USES:
1. For Bleaching Cotton & Linen in Textile Industry, bleaching wood pulp in paper factories & for bleaching washed clothes in washing industries.
2. As an Oxidizing agent in chemical industries.
3. Purification of Drinking water.
1. For Bleaching Cotton & Linen in Textile Industry, bleaching wood pulp in paper factories & for bleaching washed clothes in washing industries.
2. As an Oxidizing agent in chemical industries.
3. Purification of Drinking water.
Baking Soda [ NaHCO3 ]
– Common
name – Sodium Hydrogen Carbonate
Preparation:
NaCl
+ H2O
+ CO2 +
NH3 èNH4Cl
+ NaHCO3
(Sodiumhydrogen carbonate)
On heating NaHCO3 produces
:
NaHCO3 è HeatèNa2CO3 +
H2O
+ CO2
CO2 produced
causes dough to rise and make cakes, pastries spongy.
Uses :
1.
In household, ingredients of antacid
2.
In making baking powder
3.
On heating baking powder produces
NaHCO3 + H+ èCO2 + H2O + Sodium
Salt of acid
Washing Soda [ Na2CO3.10H2O ]
Preparation : Re-crystallization
of sodium carbonate
Na2CO3 + 10H2O è Heat è Na2CO3. 10H2O
Uses
1.
Used in glass, soap and paper industry
2.
Cleaning agent for domestic purposes.
3.
Removal of hardness of water.
4.
Manufacture
of borax.
Water of
crystallisation :
Fixed number 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.
Plaster Of Paris
Plaster Of Paris
( 1. Gypsum
also contains water of crystallization.
( 2. Formula of gypsum – CaSO4.2H2O
( 3. On heating gypsum at 373 K it becomes CaSO4.½H2O is
plaster of Paris.
4. Plaster of Paris is used as plaster for
fractured bones.
5. When plaster of Paris is mixed with water it
changes to gypsum.
CaSO4.½ H2O +
1½ H2O èCaSO4.2H2O
Uses of plaster of Paris
:
Making toys, decorative material and smooth surfaces.
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