Acid Base and Salt by techrinser.business

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Learn more about the physical and chemical properties of acid base and salt.

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									                           CHAPTER 13
                       ACID, BASE AND SALT

Acid is a substance which gives hydrogen ion when dissolved in water.
Eg: HCl, HNO3.

Weak acids: Acids which produce low concentration of hydrogen ion in
aqueous solution due to partial dissociation are called weak acids. Eg:
Acetic acid, Formic acid, etc.

Strong acids: Acids which produce high concentration of hydrogen ion
in aqueous solution due to maximum ionization are called strong acids.
Eg: Hydrochloric acid, Nitric acid, etc.

Organic acids: Acids obtained from plants and animals are called
organic acids. Eg: Acetic acid, Citric acid, etc.

Inorganic acids: Acids derived from minerals are called inorganic acids
or mineral acids. Eg: Hydrochloric acid, Nitric acid, etc.

Concentrated acid: An acid in which very little or no water is present is
called concentrated acid.

Dilute acid: An acid in which is diluted by addition of water is called a
dilute acid.

Uses of acids:
    1. Sulphuric acid and nitric acid are used in making chemical
        fertilizers.
    2. Acetic acid is used in pickles in the name of vinegar.
    3. Citric acid is used for flavouring drink.
    4. Carbonic acid is used in soda water and soft drink.
Bases are metallic oxides or hydroxides which react with acids to give
salt and water. Eg: Magnesium oxide, Calcium hydroxide, Sodium
hydroxide, Ammonium hydroxide, etc.

Bases which are soluble in water are called alkali. Alkali produces
hydroxyl ion (OH) when dissolved in water.
CaO + H2O = Ca++ + 2OH-
Na2O + H2O = 2Na+ + 2OH-

Bases which dissociate almost completely in aqueous solution producing
high concentration of hydroxyl ions (OH) are called strong bases. Eg:
Potassium hydroxide, Sodium hydroxide, etc.

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Bases which dissociate partially in aqueous solution producing low
concentration of hydroxyl ions (OH) are called weak bases. Eg:
Ammonium hydroxide.

Uses of Base
   1. Sodium hydroxide is used in the manufacture of soap.
   2. Calcium hydroxide is used to soften hard water.
   3. Magnesium hydroxide is used as an antacid to neutralize acidity
       in stomach.
   4. Ammonium hydroxide is used in the manufacture of chemical
       fertilizer.

Salt is a neutral compound formed by the neutralization of acid with a
base. Eg: NaCl, K2SO4, MgSO4, Na2SO4, etc.

Acidic salt: The salt formed by the incomplete displacement of hydrogen
of an acid by a metal or electropositive radical is called acid salt. Eg:
NaHSO4, KHSO4, etc.

Basic salt: The salt formed by the incomplete neutralization of a base
with an acid or by partial replacement of hydroxyl ion of base is called
basic salt. Eg: Cu(OH)NO3, Mg(OH)Cl, etc.

Normal salt: The salt formed by the complete displacement of hydrogen
of an acid by a metal or electropositive radical is called normal salt. Eg:
NaCl, KNO3, KCl, etc.

Uses of salt
   1. Sodium chloride is used in cooking. It is also known as common
       salt.
   2. Sodium carbonate is used in the preparation of glass, detergent,
       soap, etc.
   3. Sodium bi-carbonate is used in fire extinguisher.
   4. Calcium sulphate is used for plastering of fractured bones, for
       white washing.

Solubility of salts
All salts of sodium, potassium and ammonium are soluble in water.
All nitrates are soluble.
All carbonates are soluble.
All chlorides are soluble except Lead chloride and Silver chloride.
All sulphates are except Lead and Barium sulphate.



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Indicators are chemical compounds which show the termination of a
chemical reaction by changing its colour. It is also used to identify
whether the substance is an acid or a base. Eg: Methyl orange,
phenolpthalein, litmus paper, etc.

Universal indicator is a mixture of several simple indicators of different
colour. It is used to determine the strength of an acid or a base.

pH is defined as the percentage of hydrogen ion in a solution of a given
substance.

pH scale is a scale which is used to determine the relative strength of an
acidic or alkaline solutions. pH value 1 represents strong acid and pH
value 14 represents a strong base.

Colour change in different indicators

 Indicators                Colour in Acid           Colour in Base
 Litmus paper              Blue to Red              Red to Blue
 Methyl orange             Red                      Yellow
 Phenolpthalein            Colourless               Pink


                         Important Questions

1) A compound has pH value 10. What will be the change in colour
   of phenolpthalein if it is added to that compound?
   pH value 10 shows that the compound is basic in nature. Hence the
   phenolpthalein solution will turn pink when mixed with that compound.

2) Two solution A and B have pH values 2 and 10 respectively.
     Which one of these two will give pink colour with
     phenolpthalein?
   pH value 2 means the compound is an acid and pH value 10 means
   the compound is a base. Since acid shows no colour change with
   phenolpthalein, the compound B will give pink colour with
   phenolpthalein.

3) Write down the name and molecular formula of a compound
   which gives hydrogen ion and chloride ion in the solution state.
   In which colour is the methyl orange changed after treating it
   with this compound. Why? Write the name of salt when this


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   compound is treated with lime water. Write down the chemical
   equation also.
   The name of the compound is Hydrochloric acid and its molecular
   formula is HCl. The change in colour of methyl orange when treated
   with this compound is red. This is because, the compound is acid
   and acid converts methyl orange into red.
   When this compound is treated with lime water, Calcium chloride is
   formed. The chemical equation is shown below.
   2HCl + Ca(OH)2                      CaCl2 + 2H2O

4) How could a Magnesium ribbon be changed into alkali? Write its
   reaction also.
   When magnesium ribbon is burnt in air, it forms white ash of
   magnesium oxide. This oxide is mixed with water to form magnesium
   hydroxide, which is an alkali.
   2Mg + O2              2MgO

  MgO + H2O                Mg(OH)2

5) How does the pH goes on changing while alkali is added on acid?
   When alkali is added on acid, the pH value of the solution starts
   increasing. This is because the addition of alkali to an acid will
   decrease the acidity of the solution and after all the acid has been
   neutralized by alkali, the alkalinity of the solution will increase
   gradually.




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