May 19, 2024

# Hydrochloric acid: Preparation and standardization of molar and normal solutions

## Hydrochloric acid: Preparation and standardization of molar and normal solutions

Citation: Chaudhari, M. (2023). 0.1 N HCl preparation. Pharmacy Infoline. https://doi.org/10.5281/zenodo.10828329

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:

1. Add 8.3 mL of concentrated hydrochloric acid (37%) to a 1-liter volumetric flask.
3. Once the solution has cooled to room temperature, add more distilled water until the solution reaches the 1-liter mark on the flask.
4. Cap the flask and mix the solution thoroughly to ensure uniformity.

## Standardization of 0.1 M hydrochloric acid solution:

1. Weigh about 0.5 g of primary standard sodium carbonate (Na2CO3) using an analytical balance and transfer it to a clean, dry Erlenmeyer flask.
2. Add about 50 mL of distilled water to the flask and swirl gently to dissolve the sodium carbonate.
3. Add a few drops of methyl orange indicator to the solution.
4. Titrate the sodium carbonate solution with the 0.1 M hydrochloric acid solution until the solution turns from yellow to pink.
5. 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:

1. Weigh about 1.58 g of potassium hydrogen phthalate (KHP) using an analytical balance and transfer it to a clean, dry Erlenmeyer flask.
2. Add about 50 mL of distilled water to the flask and swirl gently to dissolve the KHP.
3. Add a few drops of phenolphthalein indicator to the solution.
4. Titrate the KHP solution with the 0.1 N hydrochloric acid solution until a pale pink color is observed.
5. 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

What equipment do I need to prepare 0.1 N HCl?

You will need a volumetric flask (typically 1 L), a graduated cylinder for measuring concentrated HCl, a pipette for accurate measurement of small volumes (optional, but recommended for better precision), and DI (deionized) water.

What concentration of commercial hydrochloric acid should I use?

Concentrated hydrochloric acid (HCl) is typically around 37% by weight. This is much stronger than the desired 0.1 N solution. You will need to dilute it with DI water.

How much concentrated HCl do I need to make 1 L of 0.1 N HCl?

You can use the following formula to calculate the volume of concentrated HCl needed:
`Volume of concentrated HCl (mL) = (Desired Normality x Desired Volume (L)) / (Concentration of commercial HCl as a decimal)`
For 0.1 N HCl in 1 L:
`Volume of concentrated HCl (mL) = (0.1 N x 1 L) / (37%) = 2.7 mL`

Do I add water to acid or acid to water?

Always add acid to water slowly and with stirring. Adding water to concentrated acid can be dangerous due to the exothermic reaction (heat generation) that can cause violent splattering.

What safety precautions should I take when preparing 0.1 N HCl?

Wear gloves, safety glasses or a face shield, and a lab coat.
Work in a well-ventilated fume hood.
Be aware of the proper disposal procedures for waste HCl according to your institution’s guidelines.

How can I check the accuracy of the prepared 0.1 N HCl solution?

This is typically done in a more advanced laboratory setting by performing a standardization process using a primary standard solution. However, for many routine applications, the dilution calculation is sufficient.

Can I store the prepared 0.1 N HCl solution?

Yes, you can store diluted HCl in a properly labeled container made of a suitable material (e.g., glass or polyethylene) in a cool, dry place. Over time, the concentration of HCl may slightly decrease due to evaporation. It’s recommended to label the bottle with the preparation date and expected shelf life.

Time needed: 15 minutes

How do I prepare the 0.1 N HCl solution?

1. Measure concentrated HCl

Measure 2.7 mL of concentrated HCl using a graduated cylinder (for less precise measurement) or a pipette (for higher precision).

Rinse the measuring device with a small amount of DI water and add the rinse water to the volumetric flask. Add approximately 500 mL of DI water to the volumetric flask.