Equivalent Weight

Equivalent Weight

Equivalent weight is the Mass of on Equivalent.

That is the mass of a given substance which will combine with or displace a fixed quantity of another substance.

The use of equivalent weights in general chemistry has largely been superseded by the use of Molar Masses.

Uses

 Equivalent weight is a concept widely used in chemistry, particularly in the context of stoichiometry, redox reactions, and acid-base reactions. Here are some specific uses of equivalent weight :

 Equivalent weight is used in  the calculation of Normality.

01. Redox Reactions 

Equivalent weight is used to balance redox equations by ensuring that the number of equivalents of electrons transferred on both sides of the reaction is equal.

Determining Oxidation States: Equivalent weight helps in determining the oxidation state of elements involved in redox reactions.

02. Electrochemistry

Calculating Faraday’s Constant: Equivalent weight is used to calculate Faraday’s constant, which is essential in electrochemical calculations, such as determining the amount of substance deposited or consumed during electrolysis.

03. Quantitative Analysis

Titrations: Equivalent weight is used in acid-base titrations, where it helps in calculating the amount of acid or base reacted with a given volume of the titrant.

04. Molecular Weight Determination

Polyfunctional Compounds: Equivalent weight is helpful when dealing with polyfunctional compounds where multiple acidic or basic groups are present. It allows for a consistent comparison of reactivity.

05. Synthesis and Stoichiometry

Equivalent weight simplifies calculations involving reactant amounts in chemical reactions, providing a direct relationship between the amount of a substance and the moles of electrons involved.

06. Analytical Chemistry

Equivalent weight is used in gravimetric analysis methods, where the mass of a precipitate is used to determine the amount of substance present.

Formula

\[Equivalent Weight=\frac{Molecular\;Weight}{Valency}\]

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Calculation

1.)   Molar mass of NaOH = 23 g/mol (for Na) + 16 g/mol (for O) + 1 g/mol (for H)

=  40/1 

= 40 g/mol

2.)  Molar mass of HCl = 1 g/mol (for H) + 35.5 g/mol
(for Cl)

= 36.5/1

= 36.5 g/mol

3.)  Molar mass of H2SO4

= (2×1) g/mol (forH2) + 32 g/mol (for S) + (16×4) g/mol (for O4)

= 2 + 32 + 64

= 98/2

= 49 g/mol

4.)  Molar mass of KMnO4

= 39 g/mol (for K) + 55 g/mol (for Mn) + (16×4) g/mol (for O4)

= 158/1

= 158 g/ mol   

5.)   Molar mass of H2O2 

= (2×1) (for H2) + (16×2) (for O

= 2+32

= 34/2

= 17 g/mol

Example of Acids

No	Name of Acids	Formula	Basicity	Molecular Weight/Valency	Equivalent Weight
01	Hydrochloric Acid	HCL	1	35.5/1	35.5
02	Nitric Acid	HNO3	1	63/1	63
03	Sulphuric Acid	H2SO4	2	98/2	49
04	Acetic Acid	CH3COOH	1	60/1	60
05	Phosphoric Acid	H3PO4	3	98/3	32.66
06	Oxalic Acid	H2C2O7	2	90/2	45
07	Citric Acid	C6H8O7	3	192/3	64
08	Hydrofluoric Acid	HF	1	20/1	20
09	Carbonic Acid	H2CO3	2	62/2	31
10	Tartaric Acid	C4H6O6	2	145/2	75

Example Of Base

No	Name of Base	Formula	Acidity	Molecular Weight/Valency	Equivalent Weight
01	Sodium Hydroxide	NaOH	1	40/1	40
02	Potassium Hydroxide	KOH	1	56/1	56
03	Calcium Hydroxide	Ca(OH)2	2	74/2	37
04	Ammonium Hydroxide	NH4OH	1	35/1	35
05	Magnesium Hydroxide	Mg(OH)2	2	59/2	29
06	Lithium Hydroxide	LiOH	1	24/1	24
07	Sodium Bi Carbonate	NaHCO3	1	84/1	84
08	Potassium Carbonate	K2CO3	2	138/2	69
09	Sodium Phosphate	Na3PO4	4	164/4	41
10	Sodium Silicate	Na2SiO3	2	122/2	61