Normality
Sep 23, 2022, 16:45 IST
Normality
in chemistry is one of the terms used to measure the concentration of a solution. It is abbreviated "N" and is sometimes referred to as the equivalent concentration of the solution. It is mainly used as a measurement of reactive substances in solution and during titration reactions or especially in situations involving acid-base chemistry.
By standard definition, normality is described as the number of gram or molar equivalents of solute present in one liter of solution. When we say equivalent, it is the number of moles of reactive units in the compound.
-
Normality =
Number of gram equivalents per volume of solution in liters
-
Number of gram equivalents =
weight of solute / Equivalent weight of solute
-
N =
Weight of Solute (gram) × [Equivalent weight × Volume (L)]
-
N =
Molarity × Molar mass × [Equivalent mass]
-1
-
N =
Molarity × Basicity = Molarity × Acidity
There are specific tips that students can follow when calculating normality.
-
The first tip for students to follow is to gather information about the equivalent mass of the reactant or solute. Look in your textbook or reference books to learn about molecular weight and valency.
-
The second step involves calculating the no. of gram equivalent of solute.
-
Students always remember that volume is calculated in liters.
-
Finally, normality is calculated using a formula and substituting the values.
The process of addition gradually of a solution for a concentration and volume with another solution of unknown concentration until the reaction proceeds towards its neutralization is known as Titration. To calculate the normality of the acid and base titration:
N
1
V
1
= N
2
V
2
Where,
-
N
1
= Normality of the Acidic solution
-
V
1
= Volume of the Acidic solution
-
N
2
= Normality of the basic solution
-
V
3
= Volume of the basic solution
For calculating the normality equation, let us understand the mixtures of Normality.
Let’s consider two ideal solutions having normalities as N
a
and N
b
, and the Volume as V
a
and V
b
as mentioned below:
Where,
N
a
= Normality of the acidic solution,
V
a
= Volume of the acidic solution,
N
b
= Normality of the basic solution, and
V
b
= Volume of the basic solution.
By adding these two solutions, we get a mixture whose Volume is V
a
+ V
b
, and the Normality considers N.
Thus, we got the Normality Formula for the mixture:
N = (N
a
V
a
+ N
b
V
b
) / (V
a
+ V
b
)
Let’s check the given three Cases below:
Case 1 -
The concentration of the acidic solution is greater than the concentration of the basic solution (release of H+ ions > OH- ions)
Therefore, N
a
V
a
> N
b
V
b
Case 2 -
The concentration of the basic solution is less than the acidic solution.
So, N
a
V
a
< N
b
V
b
(release of OH
-
ions > H
+
ions)
Case 3 -
When concentration is the same, then Na Va = Nb Vb is the equation of Normality.
In this given case, OH
-
ions and H
+
ions are not released.
Therefore, the number of gram equivalent of H+ ions is equal to the number of gram equivalent of OH- ions. This type of solution is neutral, and such a process is called neutralization.
There are four types of Normality.
Seminormal - The solutions whose normality is ½ or N/2.
Binormal - The solutions having normality as 2 or 2 N.
Decinormal - Normality is 1/10 or N/10.
CentiNormal - Normality is 1/100 or N/100.
|
Normality
|
Molarity
|
|
It is known as equivalent concentration.
|
It is known as molar concentration.
|
|
It is known as the number of gram equivalent per litre of solution.
|
It is known as the number of moles per litre of solution.
|
|
It is used in measuring the gram equivalent in relation to the total volume of the solution.
|
It is used in measuring the ratio between the number of moles in the total volume of the solution.
|
|
The units of normality are N or eq L
-1
.
|
The unit of molarity is M or Moles L
-1
|
Normality and Molarity are two essential and commonly used terms in chemistry. They are used to denote a quantitative measurement of a substance. But what does Molarity have in relation to normality? We will understand the relationship between the two mentioned below.
Like normality, in chemistry, the unit is concentration. The no. of moles of solute per liter of solution is known as Molarity. It is also called molar concentration. Molarity is generally used in calculating pH, i.e., dissociation or equilibrium constants, etc.
The formula of molarity is given as:
Molarity (M) = No. of moles of solute per volume of the solution in litres.
Now, when we talk about relationships, normality contains molarity. While molarity is the first step in calculating the total volume or concentration of solutions, normality is used for more advanced calculations, especially when determining the one-to-one relationship between acids and bases:
Normality = [Molarity × Molar mass] × [Equivalent mass]
-1
However, in this case, we have to find the basicity as well. Students can count the number of H
+
ions present in the acid molecule, which it can donate. The following formula can be used to find the normality of bases:
Normality = Molarity × Basicity
Acidity can be determined by counting the number of OH
-1
ions that a base molecule can donate. To calculate the normality for acids, we can make use of the following formula:
Normality = Molarity × Acidity
We can also convert molarity to normality by applying the following equation.
N = M × number of equivalents
When determining concentrations in acid-base chemistry. For example, normality is used to indicate the concentrations of hydronium ions (H
3
O
+
) or hydroxide ions (OH
–
) in a solution.
Normality is used in precipitation reactions to measure the number of ions likely to precipitate in a specific reaction.
It is used in redox reactions to determine the number of electrons that a reducing or oxidizing agent can donate or accept.
All chemists use normality in acid-base chemistry to avoid molar ratios in calculations or to get more accurate results. Although normality is commonly used in precipitation and redox reactions, it has some limitations. These limitations are as follows:
-
It is not the correct unit of concentration in situations other than those listed above. It is an obscure measure, and molarity or molality is better unit option.
-
Normality needs a defined equivalence factor.
-
It is not a particular value for a specific chemical solution. The value can vary significantly depending on the chemical reaction. For further clarification, one solution may contain different normalities for different reactions.
Q1. In the given reaction, calculate and find the normality when it is 1.0 M H
3
PO
4
H
3
AsO
4
+ 2NaOH → Na
2
HAsO
4
+ 2H
2
O
Ans.
If we see at the given reaction, we can quickly identify that only 2 of the H+ ions of H3AsO4 react with NaOH to form the product. So, the two ions are 2 equivalents. To find the normality, we will apply the formula.
N = Molarity (M) × number of equivalents
N = 1.0 × 2 (replacing the values)
Therefore, the normality of the solution = 2.0.
Q2. What is the normality of the following?
0.0521M H
3
PO
4
0.1381M NaOH
Ans.
N = 0.0521 mol/L × (3 eq/1mol) = 0.156 eq/L = 0.156 N
N = 0.1381 mol/L × (1 eq/1mol) = 0.1381 eq/L = 0.1381 N
Q3. What will be the concentration of citric acid be if 24.00 ml of the citric acid solution is titrated with 29.12 mL of 0.1718N KOH?
Ans.
N
a
× V
a
= N
b
× V
b
Na × (24.00 mL) = (0.1718N) (29.12 mL)
Therefore, the concentration of citric acid = 0.208 N.
Q1. What does normality depend on?
Ans.
Normality totally depends upon the volume of the solution. Thus, it will vary with temperature changes.
Q2. What is the SI unit of normality?
Ans.
The units of normality are N or eq L
-1
. The unit of Molarity is M or Moles L
-1
.
Q3. Does normality change with volume?
Ans.
Normality and Molarity depend upon volume, so they change with dilution, while molality doesn't change with volume change.
Q4. How do you calculate normality from mass?
Ans.
Multiply the normality by the mass equivalent and the volume of the solution (in L) to calculate the dissolved compound's mass (in grams).
