Equivalent weight of Element:
V atoms of hydrogen can combine with 1 atom of that element.
V×1.008 parts by wt. of hydrogen can combine with 1 atom of that element.
1.008 parts by wt. of hydrogen can combine with A parts by wt. of that element.
E parts by wt. of hydrogen can combine with A/V parts by wt. of that element.
Equivalent weight of Acid:-
Equivalent weight of acid is defined as the number of parts by weight of that acid which contains one replaceable hydrogen, for example:-
In HCl
36.5 parts by wt. of HCl contains one replaceable hydrogen
So, equivalent weight of HCl is 36.5.
Similarly in H2SO4.
98 parts by wt. of H2SO4 contains 2 replaceable hydrogen.
98/2 parts by wt. of H2SO4 contains 1 replaceable hydrogen.
ie, Equivalent wt. of H2SO4 = 49
Basicity is the number of replaceable of hydrogen present in a molecule of an acid.
Depending on the number of replaceable hydrogen present in a molecule, acids are classified as monobasic acid, dibasic acid, tribasic acid etc.
|
Monobasic Acid
|
Replaceable
Hydrogen |
|
Hydrochloric Acid – HCl
Nitric Acid – HNO3
Acetic Acid – CH3COOH
|
1
1
1
|
|
Dibasic Acid
|
Replaceable
Hydrogen |
|
Sulphuric Acid – H2SO4
Oxalic Acid – COOH
|COOH
|
2
2
|
|
Tribasic Acid
|
Replaceable
Hydrogen |
|
Phosphoric Acid – H3PO4
|
3
|
Equivalent Weight of Base:
molecule of a base for oxides. It is twice the number of oxygen.
Equivalent Weight of Salt:
Equivalent weight of salt is the ratio of molecular weight of salt with total positive charges present on cations.
Determination of Equivalent Weight of Metal:
a] Oxide Formation Method:
In this method a small piece of pure metal is weighed exactly. This metal piece is converted into its oxide directly or indirectly. After this, this metal oxide is also weighed then weight of oxygen consumed during the formation of oxide is calculated. Finally equivalent weight of metal is calculated as:-
Observation and Calculation:
Weight of crucible = w1 gm
Weight of oxygen = (w3-w2) gm
= E
ii] Hydrogen Displacement Method
This method is applicable for only those metals which can displace hydrogen from dilute acid. In this method a small piece of pure metal is weighed correctly and allowed to react with dilute acid. The volume of hydrogen gas is collected. This volume is converted into STP by using combined gas equation. After this weight of evolved hydrogen is calculated finally.
Observation and Calculation:
Weight of metal piece = W1 gm
Volume of hydrogen displaced = V1
Pressure of hydrogen (P1) = p-f
Here, p is moist hydrogen pressure,
f is aqueous tension,
Temperature = T1
At STP,
Pressure (P2) = 760mmHg
Temperature (T2) = 273K
Volume (V2) = ?
