Experiment 17

Objective

To determine the concentration of hydrochloric acid (HCl) using a standard solution of sodium carbonate (Na₂CO₃).

Introduction

Sodium carbonate acts as a weak, di-acidic base, while hydrochloric acid is a strong monoprotic acid. Methyl orange is used as the indicator in this acid-base titration because it changes color at the endpoint.

The reaction proceeds as follows:

Na2​CO3​+2HCl→2NaCl+CO2​+H2​O

Using the formula for molarity (M₁V₁ = M₂V₂):

●      V₁ = Volume of HCl = 10 mL

●      M₁ = Concentration of HCl (unknown)

●      V₂ = Volume of Na₂CO₃ = 10 mL

●      M₂ = Concentration of Na₂CO₃ = 0.1 M

Calculation:

10 x M1 = 10 x 0.1

 = 0.1 M of HCI

Materials

Chemicals

●      Sodium carbonate (Na₂CO₃)

●      Hydrochloric acid (HCl)

●      Distilled water

●      Methyl orange (indicator)

Apparatus

●      250 mL flask

●      Funnel

●      Pipette

●      Burette

Reagent Preparation

●      Dissolve 2.65 g of sodium carbonate in 100 mL of distilled water to prepare a 0.2 M solution.

●      Dilute HCl to a concentration of 0.1 M.

Procedure

1.    Preparation of Flask

●      Wash the 250 mL flask thoroughly and dry it in an oven.

2.    Setting Up Sodium Carbonate Solution

●      Measure 10 mL of 0.1 M sodium carbonate solution into the flask using a pipette.

3.    Adding the Indicator

●      Add 1–2 drops of methyl orange to the sodium carbonate solution. The solution will appear yellow.

4.    Titration Process

●      Using a burette, add HCl solution dropwise to the flask containing sodium carbonate and methyl orange.

●      Continue adding HCl until the solution changes color to pink, indicating the endpoint.

5.    Observation and Replication

●      Record the volume of HCl required to reach the endpoint.

●      Repeat the titration 1–2 times for accuracy.

Observations

●      The color changes to pink at the endpoint.

●      Approximately 10 mL of 0.1 M HCl is required to neutralize the sodium carbonate solution, confirming the HCl strength is 0.1 M.

Questions

1.    What is an acid-base reaction?

2.    What is an indicator?

3.    Which indicator is used for a weak base and strong acid titration?

4.    What is methyl orange?