Determination of Molarity in Chemical Reactions: A Comprehensive Guide

Molarity is a crucial concept in chemistry that helps us understand the concentration of solutions. In this article, we will demonstrate a detailed approach using titrations and dilution to determine the molarity of different solutions. We will focus on the specific scenario involving the interaction between sodium hydroxide (NaOH) and hydrochloric acid (HCl) as well as the subsequent dilution and titration with sulfuric acid (H2SO4).

Introduction to Molarity

Molarity (M) is the number of moles of solute dissolved per liter of solution. It is a widely used unit in chemical reactions and titrations to express solution concentration. Mathematically, Molarity (M) is calculated as:

M n / V

where n is the number of moles of the solute and V is the volume of the solution in liters.

Titrating NaOH with HCl

In a titration involving 40 ml of a NaOH solution and 20 ml of 1/20 molar (0.05M) HCl, the first step is to determine the molarity of the NaOH solution.

Calculation of Molarity of NaOH

The reaction between NaOH and HCl can be represented as:

NaOH HCl → NaCl H2O

From the given data:

40 ml of NaOH reacts with 20 ml of 1/20 molar HCl

Using the molarity equation:

M1 × V1 M2 × V2

40 × M 20 × 0.05

M 0.025 M

Restating the Combined Solution and Dilution

When the combined solution of 40 ml (0.025 M) NaOH and 20 ml (0.05 M) HCl is diluted to 200 ml, the resulting solution can be analyzed for its molarity.

Calculation of Resultant Molarity

The molarity of the combined solution is given by:

M1 (40 × 0.025 20 × 0.05) / 60

M1 (1 1) / 60

M1 2 / 60 0.01 M

Titrating the Resultant Solution with H2SO4

The resultant 200 ml (0.01 M) solution is then titrated with sulfuric acid (H2SO4), and it is observed that 25 ml of this solution exactly requires 50 ml of H2SO4 solution to reach the endpoint.

Calculation of Molarity of H2SO4

Using the balanced equation for the reaction between NaOH and H2SO4:

2NaOH H2SO4 → Na2SO4 2H2O

2 0.01 M 25 1 M2 50

M2 0.005 M

Step-by-Step Explanation

1. **Initial Calculation of NaOH Molarity**:

M1 × V1 M2 × V2

40 × M 20 × 0.05

M 0.025 M

2. **Calculation of Resultant Molarity**:

M1 (40 × 0.025 20 × 0.05) / 60

M1 (1 1) / 60

M1 2 / 60 0.01 M

3. **Calculation of Molarity of H2SO4**:

2 0.01 M 25 1 M2 50

M2 0.005 M

Therefore, the molarity of the H2SO4 solution is 0.005 M.

Conclusion

Understanding molarity is essential for accurate experimental measurements in chemistry. This article has demonstrated the step-by-step process of determining the molarity of different solutions through titrations and dilutions. By applying basic chemical equations and the molarity formula, we can accurately determine the concentrations of solutions involved in complex chemical reactions.

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Keywords: Molarity, Chemical Equations, Dilution, Acid-Base Reaction