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ACID BASE AND SALT
(Notes)
Acid
The word ‘Acid’ came from Latin word ‘Acidus or Acere’ which means sour
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e
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curd, tamarind, lemon, etc
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Natural Acid or organic acid:
Acids which are obtained from natural sources are called natural acid or organic acid
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g
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Chemical Properties of Acid
Reaction of acids with metal:
Acids give hydrogen gas along with respective salt when they react with a metal
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𝑍𝑛 + 2𝐻𝐶𝑙 → 𝑍𝑛𝐶𝑙2 + 𝐻2
Hydrogen gas and sodium chloride are formed when hydrochloric acid reacts with sodium metal
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𝐹𝑒 + 2𝐻𝐶𝑙 → 𝐹𝑒𝐶𝑙2 + 𝐻2
Hydrogen gas and zinc sulphate are formed when zinc metal reacts with sulphuric acid
𝑍𝑛 + 𝐻2 𝑆𝑂4 → 𝑍𝑛𝑆𝑂4 + 𝐻2

Test for hydrogen gas:
The gas evolved after reaction of acid with metal can be tested by bringing a lighted candle near it
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Burning with pop sound is the characteristic test for
hydrogen gas
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𝑀𝑒𝑡𝑎𝑙 𝑐𝑎𝑟𝑏𝑜𝑛𝑎𝑡𝑒 + 𝐴𝑐𝑖𝑑 → 𝑆𝑎𝑙𝑡 + 𝐶𝑎𝑟𝑏𝑜𝑛 𝑑𝑖𝑜𝑥𝑖𝑑𝑒 + 𝑊𝑎𝑡𝑒𝑟
Examples:



Hydrochloric acid gives carbon dioxide gas, sodium chloride along with water when reacts with sodium
carbonate
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𝑀𝑔𝐶𝑂3 + 2𝐻𝐶𝑙 → 𝑀𝑔𝐶𝑙2 + 𝐶𝑂2 + 𝐻2 𝑂






Hydrochloric acid gives carbon dioxide gas, calcium chloride and water when it reacts with calcium
carbonate
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o 𝐶𝑎𝐶𝑂3 + 𝐻2 𝑆𝑂4 → 𝐶𝑎𝑆𝑂4 + 𝐶𝑂2 + 𝐻2 𝑂
Sulphuric acid gives sodium sulphate, carbon dioxide gas and water when it reacts with sodium carbonate
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o 2𝐻𝑁𝑂3 + 𝑁𝑎2 𝐶𝑂3 → 𝑁𝑎𝑁𝑂3 + 2𝐻2 𝑂 + 𝐶𝑂2

Reaction of acid with hydrogen carbonates (bicarbonates):
Acids give carbon dioxide gas, respective salt and water when they react with metal hydrogen carbonate
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𝑁𝑎𝐻𝐶𝑂3 + 𝐻𝐶𝑙 → 𝑁𝑎𝐶𝑙 + 𝐶𝑂2 + 𝐻2 𝑂
Sulphuric acid gives sodium sulphate, carbon dioxide gas and water when it reacts with sodium bicarbonate
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Test for evolution of carbon dioxide gas:
 Carbon dioxide turns lime water milky when passed through it
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 The gas evolved because of reaction of acid with metal carbonate or metal hydrogen carbonate turns lime
water milky
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This happens because of formation of white
precipitate of calcium carbonate
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This happens because of formation of calcium hydrogen carbonate
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𝐶𝑎𝐶𝑂3 + 𝐶𝑂2 + 𝐻2 𝑂 → 𝐶𝑎(𝐻𝐶𝑂3 )2
Reaction of acid with marble and egg shell:
Since, marble and egg shell are made of calcium carbonate, hence when acid is poured over marble or egg shell,
bubbles of carbon dioxide are formed
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Nitrogen oxide and sulphur dioxide form nitric acid
and sulphuric acid on reaction with water
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Acid rain causes damage to the historical monuments and other buildings
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Marble is calcium carbonate which reacts with the
acid and thus gets corroded
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Acid and metal carbonate or bicarbonate are kept in separate chambers in a fire extinguisher
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The carbon dioxide gas so produce is poured over fire
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Base:
Bases are the substances which have bitter taste and feel soapy on touch
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Sodium hydroxide (caustic soda), calcium hydroxide, sodium carbonate (washing soda), lime (Calcium oxide),
potassium hydroxide (caustic potash), etc
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Types of base:
Base can be divided in two types – Water soluble and water insoluble
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These are also known as alkali
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Alkali is considered as strong base
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𝐴𝑙𝑘𝑎𝑙𝑖 + 𝑀𝑒𝑡𝑎𝑙 → 𝑆𝑎𝑙𝑡 + 𝐻𝑦𝑑𝑟𝑜𝑔𝑒𝑛



Example:
Sodium hydroxide gives hydrogen gas and sodium zincate when reacts with zinc metal
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2𝑁𝑎𝑂𝐻 + 2𝐴𝑙 + 2𝐻2 𝑂 → 2𝑁𝑎𝐴𝑙𝑂2 + 2𝐻2

Reaction of base with oxides of non-metals:
Non-metal oxides are acidic in nature
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When carbon dioxide is
dissolved in water it produces carbonic acid
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𝐵𝑎𝑠𝑒 + 𝑁𝑜𝑛 − 𝑚𝑒𝑡𝑎𝑙 𝑜𝑥𝑖𝑑𝑒 → 𝑆𝑎𝑙𝑡 + 𝑊𝑎𝑡𝑒𝑟
Example:



Sodium hydroxide gives sodium carbonate and water when it reacts with carbon dioxide
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𝐶𝑎(𝑂𝐻)2 + 𝐶𝑂2 → 𝐶𝑎𝐶𝑂3 + 𝐻2 𝑂

Neutralisation Reaction:
An acid neutralizes a base when they react with each other and respective salt and water are formed
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




Example:
Sodium chloride and water are formed when hydrochloric acid reacts with sodium hydroxide (a strong base)
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2𝐻𝐶𝑙 + 𝐶𝑎(𝑂𝐻)2 → 𝐶𝑎𝐶𝑙2 + 2𝐻2 𝑂
Sodium sulphate and water are formed when sulphuric acid reacts with sodium hydroxide (a base)
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𝐻𝑁𝑂3 + 𝑁𝑎𝑂𝐻 → 𝑁𝑎𝑁𝑂3 + 𝐻2 𝑂

Reaction of Acid with Metal Oxides:
Metal oxides are basic in nature
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In this
reaction, respective salt and water are formed
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2𝐻𝐶𝑙 + 𝐶𝑎𝑂 → 𝐶𝑎𝐶𝑙2 + 𝐻2 𝑂
Similarly, when sulphuric acid reacts with zinc oxide, zinc sulphate and water are formed
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𝐴𝑙2 𝑂3 + 6𝐻𝐶𝑙 → 2𝐴𝑙𝐶𝑙3 + 3𝐻2 𝑂

Common in Acid and Base
Acids give hydrogen gas when they react with metal
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For example:
Hydrochloric acid (HCl), sulphuric acid (H2SO4), nitric acid (HNO3), etc
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The dissociation of hydrogen ion in aqueous solution is
the common property in all acids
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𝐻𝐶𝑙 (𝑎𝑞) → 𝐻 + (𝑎𝑞) + 𝐶𝑙 − (𝑎𝑞)
 Sulphuric acid (H2SO4) gives hydrogen ion (H+) and sulphate ion (SO4− −) in water
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−
𝐻𝑁𝑂3 (𝑎𝑞) → 𝐻 + (𝑎𝑞) + 𝑁𝑂3 (𝑎𝑞)
−
 Acetic acid (CH3COOH) gives acetate ion (CH3COO ) and hydrogen ion (H+)
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That’s why hydrogen ion is always written with suffix (aq), such
as H+ (aq)
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 Acids conduct electricity in their aqueous solution because of dissociation of hydrogen ion
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 A dry acid, such as dry hydrochloric acid does not change the colour of blue litmus paper to red because a dry
acid does not dissociate hydrogen ion
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Acidic behavior of carbon dioxide gas:
Carbon dioxide gas produces carbonic acid when dissolved in water
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2−
𝐶𝑂2 + 𝐻2 𝑂 → 𝐻2 𝐶𝑂3 → 2𝐻 + + 𝐶𝑂3
Are all compounds which contain hydrogen, necessarily acids?
No, all compounds which contain hydrogen are not acid
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are not acid in spite of the fact that they contain hydrogen
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Common in all Base:
A base dissociates hydroxide ion in water, which is responsible for the basic behavior of a compound
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𝑁𝑎𝑂𝐻 (𝑎𝑞) → 𝑁𝑎+ (𝑎𝑞) + 𝑂𝐻 − (𝑎𝑞)
Similarly, when potassium hydroxide is dissolved in water, it dissociates hydroxide ion and potassium ion
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Neutralisation Reaction:
When an acid reacts with a base, the hydrogen ion of acid combines with the hydroxide ion of base and forms water
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𝑂𝐻 − + 𝐻 + → 𝐻2 𝑂
Example:
𝑁𝑎𝑂𝐻 + 𝐻𝐶𝑙 → 𝑂𝐻 − + 𝑁𝑎+ + 𝐻 + + 𝐶𝑙 − → 𝑁𝑎𝐶𝑙 + 𝐻2 𝑂
𝑂𝑅
𝑁𝑎𝑂𝐻 + 𝐻𝐶𝑙 → 𝑁𝑎𝐶𝑙 + 𝐻2 𝑂
Dilution of Acid and Base:
 The concentration of hydrogen ion in an acid and hydroxide ion in a base; per unit volume; shows the
concentration of acid or base
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Similarly, by
addition of base to water the concentration of hydroxide ion per unit volume decreases
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 The dilution of acid or base is exothermic
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If water is added to a concentrated acid or base a lot of heat is generated, which may
cause splashing out of acid or base and may cause severe damage as concentrated acid and base are highly
corrosive
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pH – Measurement of strength of Acid and Base





The strength of acid or base depends upon the hydrogen ion concentration
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If the concentration of hydrogen ion is smaller than the hydroxide ion, the solution is called basic
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 pH is a scale which quantifies the concentration of hydrogen ion in a solution
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 A neutral solution, such as distilled water has value of hydrogen ion concentration equal to 7 on pH scale
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The basic solution has
value of hydrogen ion concentration greater than 7 on pH scale
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Potenz is a German word which means ‘power’ or ‘potential’
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Thus, pH means the potential of hydrogen or power of hydrogen
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Indicator:
Substances which show the acidic or basic behavior of other substance by change in colour are known as indicator
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Some common types of indicators are
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



Natural
Olfactory Indicator
Synthetic Indicator
Universal Indicator

Natural Indicator:
Indicators obtained from natural sources are called natural indicators
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are some common natural indicators used widely to show the acidic or basic character of substances
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The solution of litmus is purple in colour
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


An acid turns blue litmus paper red
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Turmeric:
Turmeric is another natural indicator
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Turmeric solution or paper turns reddish brown
with base
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Red cabbage:
The juice of red cabbage is originally purple in colour
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Olfactory Indicators:
Substances which change their smell when mixed with acid or base are known as olfactory indicators
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Onion:
Paste or juice of onion loses its smell when added with base
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Vanilla:
The smell of vanilla vanishes with base, but it’s smell does not vanishes with an acid
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For example: phenolphthalein, methyl orange, etc
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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
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Universal indicator shows different colour over the range of pH value from 1 to 14 for a given solution
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Universal indicator is the combination of many
indicators, such as water, propanol, phelophthalein, sodium salt, sodium hydroxide, methyl red, bromothymol blue

monosodium salt, and thymol blue monosodium salt
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Salt
Salts are the ionic compounds which are produced after the neutralization reaction between acid and base
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There are number of salts but sodium chloride is the most common among them
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Sodium chloride is used to enhance the taste of food
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Example:
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


Sodium chloride (NaCl) and Calcium chloride (CaCl2) belong to chloride family
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Zinc chloride (ZnCl2) and Zinc sulphate (ZnSO4) belong to zinc family
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The pH of value of
such salts is equal to 7, i
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neutral
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



Sodium chloride (NaCl) is formed after the reaction between hydrochloric acid (a strong acid) and sodium
hydroxide (a strong base)
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2𝑁𝑎𝑂𝐻 + 𝐻2 𝑆𝑂4 → 𝑁𝑎2 𝑆𝑂4 + 2𝐻2 𝑂
Potassium chloride (KCl): It is formed after the reaction between potassium hydroxide (a strong base) and
hydrochloric acid (a strong acid)
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The pH value of
acidic salt is lower than 7
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


Ammonium chloride is formed after reaction between hydrochloric acid (a strong acid) and ammonium
hydroxide (a weak base)
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2𝑁𝐻4 𝑂𝐻 + 𝐻2 𝑆𝑂4 → (𝑁𝐻4 )2 𝑆𝑂4 + 2𝐻2 𝑂

Basic Salt:
Salts which are formed after the reaction between weak acid and strong base are called basic salt
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


Sodium carbonate is formed after the reaction between sodium hydroxide (a strong base) and carbonic acid
(a weak base)
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𝐶𝐻3 𝐶𝑂𝑂𝐻 + 𝑁𝑎𝑂𝐻 → 𝐶𝐻3 𝐶𝑂𝑂𝑁𝑎 + 𝐻2 𝑂

Cause of formation of acidic, basic and neutral salt:
 When a strong acid reacts with a weak base, the base is unable to fully neutralize the acid
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 When a strong base reacts with a weak acid, the acid is unable to fully neutralize the base
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 When equally strong acid and base react they fully neutralize each other
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pH value of salt:




Neutral salt: The pH value of a neutral salt is almost equal to 7
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Basic salt: The pH value of a basic salt is more than 7
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It is formed after the reaction between
sodium hydroxide and hydrochloric acid
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𝑁𝑎𝑂𝐻 + 𝐻𝐶𝑙 → 𝑁𝑎𝐶𝑙 + 𝐻2 𝑂
The pH value of sodium chloride is about 7
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Sodium
chloride is used in manufacturing of many chemicals
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It is also known as caustic soda
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 In the process of brine decomposes to form sodium hydroxide
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 This whole process is known as Chlor-Alkali process
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Chlorine gas is used in water treatment, manufacturing of PVC, disinfectants, CFC, pesticides
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Sodium hydroxide is used for de-greasing of metals, manufacturing of paper, soap, detergents, artificial
fibres, bleach, etc
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It is a solid and yellowish white in colour
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 When calcium hydroxide (slaked lime) reacts with chlorine, it gives calcium oxychloride (bleaching powder)
and water is formed
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 The term bleach means removal of colour
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 It works because of oxidation
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Use of bleaching powder:




Bleaching powder is used as disinfectant to clean water, moss remover, weed killers, etc
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Bleaching powder is used as oxidizing agent in many industries, such as textiles industry, paper industry, etc
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 Bread soda, cooking soda, bicarbonate of soda, sodium bicarb, bicarb of soda or simply bicarb, etc
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 Baking soda is obtained by the reaction of brine with carbon dioxide and ammonia
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 𝑁𝑎𝐶𝑙 + 𝐶𝑂2 + 𝑁𝐻3 + 𝐻2 𝑂 → 𝑁𝐻4 𝐶𝑙 + 𝑁𝑎𝐻𝐶𝑂3
In this process, calcium carbonate is used as the source of CO2 and the resultant calcium oxide is used to
recover ammonia from ammonium chloride
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Sodium hydrogen carbonate is amphoteric in nature
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Thermal decomposition of sodium hydrogen carbonate (baking soda)
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2𝑁𝑎𝐻𝐶𝑂3 + ℎ𝑒𝑎𝑡 → 𝑁𝑎2 𝐶𝑂3 + 𝐶𝑂2 + 𝐻2 𝑂
Sodium carbonate formed after thermal decomposition of sodium hydrogen carbonate; decomposes into
sodium oxide and carbon dioxide on further heating
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Baking soda is used as antacid
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Baking soda is used in cleansing of ornaments made of sliver
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Generally, tartaric acid is mixed with
baking soda to make baking powder
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 The smell of sodium tartarate is pleasant and taste is good
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 Baking powder produces carbon dioxide on heating, so it is used in cooking to make the batter spongy
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The sodium carbonate; thus
produced; makes the taste bitter
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𝑁𝑎𝐶𝑙 + 𝐶𝑂2 + 𝑁𝐻3 + 𝐻2 𝑂 → 𝑁𝐻4 𝐶𝑙 + 𝑁𝑎𝐻𝐶𝑂3
 The sodium carbonate obtained in this process is dry
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Washing soda is obtained by rehydration of anhydrous sodium carbonate
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10𝐻2 𝑂
 Since there are 10 water molecules in washing soda, hence it is known as Sodium bicarbonate decahydrate
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 On heating the washing soda all molecules of water are evaporate resulting 𝑁𝑎2 𝐶𝑂3 called soda ash
𝐻𝑒𝑎𝑡

𝑁𝑎2 𝐶𝑂3
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In making of detergent cake and powder
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It is used in glass and paper industries
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The water molecule present in salt is known as
water of crystallization
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5H2O):
Blue colour of copper sulphate is due to presence of 5 molecules of water
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After adding
water; anhydrous copper sulphate becomes blue again
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5𝐻2 𝑂 + ℎ𝑒𝑎𝑡 → 𝐶𝑢𝑆𝑂4
Plaster of Paris
 Plaster of Paris is obtained by heating of gypsum, a hydrated salt of calcium
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2𝐻2 𝑂 + 𝐻𝑒𝑎𝑡 → 𝐶𝑎𝑆𝑂4
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1
1
𝐶𝑎𝑆𝑂4
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2𝐻2 𝑂
2
2
 Plaster of Paris is used in making of toys, designer false ceiling, etc
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