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Normality – Definition, Formula, Equations and Solved Examples

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  • Last Updated : 15 Sep, 2022
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In physical chemistry, one of the important terms used is the normality formula. The normality formula is used to measure the concentration of a solution like molarity and molality. Normality is a measure of the number of grams equivalent to solute present given volume of the solution. Redox reactions, precipitation reactions, and acid-base chemical reactions all often make use of normality. It depends on the temperature and the chemical reaction being observed. The term “equivalent concentration” describes how reactive a solution is. This is frequently used in redox reactions and acid-base reactions.

What is Normality?

The concentration of the given solution during the specific chemical process is determined by normality. In other words, normality can be defined as the number of grams of solute equivalents present in each liter of solution. 

Normality formula

 

Normality is generally used in acid-base chemistry, to determine the concentrations. In precipitation, reactions calculate the number of ions that are expected to precipitate in a given reaction. And in redox reactions, determine how many electrons a reducing or oxidizing chemical can donate or take.

  • Normality is represented by the letter “N.” 
  • The gram/liter is the SI unit. Other units used for normality are eq L-1 or meq L-1.
  • Normality is also called by the name equivalent concentration.

Normality Formula

The concentration of the given solution is determined using the Normality Formula:

Normality (N) = Number of Gram Equivalents / Volume of the Solution (in liters)

Here, the number of gram equivalents are defined as:

Number of Gram Equivalents = Weight of Solute (in gm) / Equivalent Weight of Solute

Hence,

Normality (N) = Weight of Solute (in gm) / (Equivalent Weight of Solute × Volume of the Solution (in liters))

Steps to Calculate Normality

In order to calculate normality, students might use a few strategies,

  • The first part of advice for students is to collect information on the equivalent weight of the reacting substance or solute. To learn about molecular weight and valence, consult your textbook or reference books.
  • The number of gram equivalents of solute is calculated in the second stage.
  • Remember to determine the volume in liters.
  • Finally, the formula is used to calculate normality, with the values replaced.

Normality Equations 

  • The normality equation, which can be used to estimate the volume of a solution needed to make a solution of different normality, is as follows,

Initial Normality (N1) × Initial Volume (V1) = Final Normality (N2) × Final Volume (V2)

  • If four distinct solutions with the same normality and volume are combined, the resultant normality is;

NR = (NaVa + NbVb + NcVc + NdVd) / (Va+Vb+Vc+Vd)

  • When four solutions (na, nb, nc, nd) with varied solute molarity, volume, and H+ ions are mixed, the resultant normality is given by,

NR = (naMaVa + nbMbVb + ncMcVc + ndMdVd) / (Va+Vb+Vc+Vd)

Relation between Normality and Molarity

Two significant and usually utilized terms in chemistry are normality and molarity. They are employed to denote a substance’s quantitative measurement. It is a chemical unit of concentration, similar to normality. The number of moles of solute per liter of solution is known as molarity. It also goes by the name “molar concentration.” Molarity, such as dissociation or equilibrium constants, is frequently utilized in the determination of pH.

Normality (N) = Molarity × Molar mass / Equivalent mass

Normality (N) = Molarity × Basicity = Molarity × Acidity

Differences Between Normality and Molarity

Normality

Molarity

Normality is the number of grams equivalent per liter of solution.Molarity is the number of moles per liter of solution.
Normality is also termed equivalent concentration.Molarity is also known as molar concentration.
The units of normality are N or eq L-1.The unit of molarity is M or Moles L-1.

Uses of Normality

  • It is used in acid-base chemistry to determine concentrations. For example, the presence of compound ions such as hydronium ions (H3O+) or hydroxide ions (OH) in a solution is clearly the result of normality.
  • The number of chemical ions that are likely to precipitate in a particular reaction is determined in precipitation reactions using normality. In both acid-base and precipitation chemical reactions, 1/feq is an integer number.
  • To determine how many electrons a reducing or oxidizing chemical may accept or donate, it is used in redox processes. A fraction could be represented as 1/feq in redox reactions.

Read More:

Solved Examples on Normality

Example 1: Calculate the normality of a 310 mL NaOH solution made by dissolving 0.4 gram of NaOH.

Solution:

The formula to calculate the normality is,

Normality (N) = Number of gram equivalents / Volume of the solution in liters

Number of gram equivalents = weight of solute / Equivalent weight of solute

Equivalent weight of solute = 23+16+1 = 40

Since,

Normality (N) = weight of solute / Volume of the solution in liters × Equivalent weight of solute

N = (4/40) × (1000/310)

= 0.1 × 3.2258

= 0.3225 N

Example 2: When 19.0 ml of the citric acid solution is titrated with 30.09 mL of 0.1811 N KOH, what is the citric acid concentration?

Solution:

According to the normality equation:

Na × Va = Nb × Vb

Therefore,

Na × 19.0 = 0.1811 × 30.09  

Na = (0.1811 × 30.09) / 19.0 

= 5.4492 / 19.0

= 0.2868 N

Example 3: When 0.321 g sodium carbonate is mixed in a 250 mL solution, determine its normality.

Solution:

The chemical formula of Sodium carbonate is Na2CO3

Therefore, by the normality formula:

N = Na2CO3 × (1 mol/105.99 g) × (2 eq/1 mol)

N = 0.1886/0.2500

= 0.07544 N

Example 4: When the concentration of H3PO4 is 2.2 M, calculate and discover the normality.

H3AsO4 + 2NaOH → Na2HAsO4 + 2H2O

Solution:

Only two of the H+ ions of H3AsO4 react with NaOH to generate the product, according to the described reaction. As a result, there are two equivalents of the two ions. The above formula will be used to find the normality.

N = Molarity × Number of equivalents 

Therefore, 

N = 2.2 × 2

= 4.4

Example 5: What is the normality of the following 1 L aqueous solution with 55 gram NaOH dissolved in it?

Answer:

Given that, 

Equivalent weight of solute = 40g

Since, Number of gram equivalents = weight of solute / Equivalent weight of solute

Number of gram equivalents = 55/40

= 1.375 eq

Normality (N) = Number of gram equivalents / Volume of the solution in liters

Therefore,

N = 1.375/1

= 1.375 eq/L

FAQs on Normality 

Question 1: What is the difference between Molarity and Normality?

Answer:

The number of moles of solute per liter of solution is known as morality, whereas the number of grams equivalent of solute per liter of solution is known as normality.
In addition, whereas Molarity is a measurement of the moles in respect to the total volume of the solution, Normality is a measurement of the gram equivalent in relation to the total volume of the solution.

Question 2: What is Gram equivalent?

Answer:

The gram equivalent is defined by the amount or the mass of the substances that is utilized to displaces a fixed amount of another substance.

Question 3: What is the formula for Molarity?

Answer:

The formula to calculate the molarity, M is

Molarity, M = Number of moles of Solute / Volume of Solution in Liters.

Question 4: What is the relation between normality and molarity?

Answer:

The relation between molarity and normality is given by,

Normality (N) = Molarity × Molar mass / Equivalent mass

Question 5: Write any two uses of Normality.

Answer:

Uses of Normality,

  • In precipitation reactions, normality is used to determine how many ions are expected to precipitate.
  • It determines how many electrons a reducing or oxidizing substance can contribute or absorb in redox processes.

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