Hydrochloric acid (HCl) is a widely used reagent in chemistry and analytical laboratories. Here’s how to prepare and standardize molar (1.0 M) and normal (1.0 N) hydrochloric acid solutions.
Preparation of 1.0 M Hydrochloric Acid Solution:
A 1.0 M hydrochloric acid solution contains one mole of HCl in one liter of solution.
Materials Required:
– Concentrated hydrochloric acid (usually 37-38% HCl)
– Distilled water
– A glass stirring rod
– A glass or plastic container
– A 1.0 L volumetric flask
Procedure:
1. Use concentrated hydrochloric acid (usually 37-38% HCl) as the starting material. The concentrated HCl solution is already approximately 12 M.
2. Carefully measure out the required volume of the concentrated HCl solution. To prepare 1.0 L of 1.0 M HCl solution, you must dilute 83.33 mL of concentrated HCl solution with distilled water. Ensure accurate measurement, as concentrated HCl is highly corrosive.
3. Transfer the measured volume of concentrated HCl solution into a clean, dry glass or plastic container.
4. Add distilled water to the container while stirring with a glass rod. This dilution process will create a 1.0 M HCl solution.
5. Once the HCl is thoroughly mixed with the water, transfer the solution into a 1.0 L volumetric flask, rinsing the container with distilled water to ensure all the HCl is transferred.
6. Fill the volumetric flask with distilled water to the 1.0 L mark. The solution is now a 1.0 M hydrochloric acid solution.
Standardization of 1.0 M Hydrochloric Acid Solution to Prepare 1.0 N Solution:
To standardize the 1.0 M HCl solution and prepare a 1.0 N solution, you’ll need to determine its exact molar concentration.
Materials Required:
– Sodium carbonate (Na2CO3)
– Methyl orange indicator
– A burette
– A balance
– A 1.0 L volumetric flask
Procedure:
1. Weigh out a sample of sodium carbonate (Na2CO3) of known purity. Accurately weigh about 0.053 g of Na2CO3. The molar mass of Na2CO3 is 105.99 g/mol.
2. Dissolve the weighed Na2CO3 in distilled water and transfer it into a 1.0 L volumetric flask.
3. Add a few drops of methyl orange indicator to the Na2CO3 solution. Methyl orange will change color at the endpoint of the titration.
4. Prepare the burette with the 1.0 M HCl solution.
5. Titrate the Na2CO3 solution with the HCl solution until the color changes from pink to yellow or another noticeable endpoint color change.
6. Record the volume of HCl solution used for the titration. Use this volume to calculate the exact molar concentration of the HCl solution.
7. If the calculated molarity is close to 1.0 M, the solution can be considered a 1.0 N hydrochloric acid solution. If not, adjust the concentration and re-standardize if necessary.
