Hydrochloric acid: Preparation and standardization of molar and normal solutions
Hydrochloric acid (HCl) is a strong acid commonly used in the preparation and standardization of molar and normal solutions. Here is a general procedure for the preparation and standardization of a 0.1 M hydrochloric acid solution and a 0.1 N hydrochloric acid solution:
Preparation of 0.1 M hydrochloric acid solution:
- Add 8.3 mL of concentrated hydrochloric acid (37%) to a 1-liter volumetric flask.
- Add about 800 mL of distilled water to the flask and swirl gently to mix.
- Once the solution has cooled to room temperature, add more distilled water until the solution reaches the 1-liter mark on the flask.
- Cap the flask and mix the solution thoroughly to ensure uniformity.
Standardization of 0.1 M hydrochloric acid solution:
- Weigh about 0.5 g of primary standard sodium carbonate (Na2CO3) using an analytical balance and transfer it to a clean, dry Erlenmeyer flask.
- Add about 50 mL of distilled water to the flask and swirl gently to dissolve the sodium carbonate.
- Add a few drops of methyl orange indicator to the solution.
- Titrate the sodium carbonate solution with the 0.1 M hydrochloric acid solution until the solution turns from yellow to pink.
- Record the volume of the hydrochloric acid solution used for the titration.
Calculation:
The molar mass of Na2CO3 is 105.99 g/mol. The equation for the reaction between Na2CO3 and HCl is:
2Na2CO3 + 2HCl → 2NaCl + CO2 + H2O
From the balanced equation, we know that 2 moles of Na2CO3 react with 2 moles of HCl. Therefore, the number of moles of HCl can be calculated from the volume of hydrochloric acid solution used in the titration and the molarity of the solution.
The weight of Na2CO3 used in the titration can also be used to calculate the molarity of the hydrochloric acid solution.
Standardization of 0.1 N hydrochloric acid solution:
- Weigh about 1.58 g of potassium hydrogen phthalate (KHP) using an analytical balance and transfer it to a clean, dry Erlenmeyer flask.
- Add about 50 mL of distilled water to the flask and swirl gently to dissolve the KHP.
- Add a few drops of phenolphthalein indicator to the solution.
- Titrate the KHP solution with the 0.1 N hydrochloric acid solution until a pale pink color is observed.
- Record the volume of the hydrochloric acid solution used for the titration.
Calculation:
The molar mass of KHP is 204.22 g/mol. The equation for the reaction between KHP and HCl is:
KHP + HCl → KCl + H2O + CO2
From the balanced equation, we know that 1 mole of KHP reacts with 1 mole of HCl. Therefore, the number of moles of HCl can be calculated from the volume of hydrochloric acid solution used in the titration and the normality of the solution.
The weight of KHP used in the titration can also be used to calculate the normality of the hydrochloric acid solution.
Note: It is important to perform the calculations carefully and accurately, as any errors in the preparation or standardization of the solutions can affect the accuracy and reliability of the results. It is also important to handle hydrochloric acid with care
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