Lab Report: Standardization of HCl Solution

Aim

The aim of this experiment is to determine the concentration of a hydrochloric acid solution.

Introduction

Hydrochloric acid in laboratory grade is not pure enough to be used as a primary standard. Thus, it must be standardized with a primary standard solution after the hydrochloric acid solution is prepared to correctly determine its concentration.

In this activity, an unknown concentration solution of hydrochloric acid is standardized against a known concentration solution of sodium carbonate by using the titration method. A 'standard solution' is one with an accurate and stable concentration.

Here, the solution of sodium carbonate has been used as the standard solution. The reaction of hydrochloric acid and sodium carbonate is represented by the following equation:

2HCl + Na₂CO₃ → 2NaCl + H₂O + CO₂

Equipment

• Beaker (100ml)
• Volumetric flask (250ml)
• Conical flask (250ml)
• Pipette (25ml)
• Burette
• Retort Stand
• Sodium carbonate, Na₂CO₃
• Concentrated HCl
• Methyl orange indicator

Procedure

Part 1: Making a standard solution

1. Weigh 1.3g of anhydrous solid sodium carbonate accurately using a 100ml beaker.
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   Record the mass.

2. Transfer the sodium carbonate into a 250ml volumetric flask using a funnel.
3. Add distilled water into the volumetric flask until it's half full, close the flask with a stopper, and mix the solution by swirling it.
4. Add more distilled water cautiously until the water reaches the line at the neck of the volumetric flask. Close the flask with a stopper and mix it well.
5. This standard solution will be used to standardize the hydrochloric acid solution.

Part 2: Standardization of HCl acid solution

1. Rinse the burette with HCl solution and fill it with HCl solution.
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   Record the initial reading.

2. Transfer 25ml of sodium carbonate solution (Na₂CO₃) into three different 250ml conical flasks. Add 2-3 drops of methyl orange indicator to each conical flask.
3. Titrate the sodium carbonate (Na₂CO₃) in each flask slowly with the HCl solution in the burette until the indicator changes from yellow to pink. Record the burette reading at the end point of the titration.
4. Repeat the titration with the other two sodium carbonate (Na₂CO₃) solutions and record the results.
5. Average of the titre value = Average titre value of 1 = (23.20 + 23.00 + 23.00) / 3 = 23.06cm³

Results

Average of 3 titres: 23.06cm³

Data Analysis and Discussions

1. Concentration of standard solution (Sodium carbonate, Na₂CO₃) = mass / molar mass

Mass of Na₂CO₃ = 1.3g

Molar mass of Na₂CO₃ = 2(23.0) + 12 + 3(16) = 106

Concentration of Na₂CO₃ = 1.3g / 106g/mol = 0.01226 M

Volume = 0.27 dm³

C = n/V = 0.012 / 0.27 = 0.044 mol dm^-3

2. 2HCl + Na₂CO₃ → 2NaCl + H₂O + CO₂
3. Concentration of hydrochloric acid, HCl solution:

Number of moles of Na₂CO₃ = 0.012 moles

HCl : Na₂CO₃ = 2 : 1

(0.012/1) x 2 : 0.012

0.024 : 0.012

Therefore, the number of moles of HCl is 0.024.

Volume = 0.024 x 22.4 = 0.5376 dm³

Concentration = n/V = 0.024 / 0.5376 = 0.045 mol dm^-3

Errors and Sources of Uncertainty

1. Misreading the markings on the burette can lead to errors in reading and the results.

2. Concentration errors, which can affect the accuracy of the measurements, may occur if the solution is prepared incorrectly.

Experimental Design

1. Add another standard solution, such as a borax solution, for comparison to obtain more accurate results.
2. Use an additional indicator, like phenolphthalein, for comparison to determine the actual result.
3. Ensure safe handling of chemicals and solutions to prevent accidents. Always consult with a teacher before using any chemicals or acids. Wear safety glasses and gloves when working with corrosive and irritant substances like HCl.

Conclusion

In volumetric analysis, the titration method is essential and can assist in determining an unknown concentration. In this experiment, sodium carbonate served as the unknown concentration, and the concentration of hydrochloric acid was determined to be 0.045 mol dm^-3. The use of methyl orange as an indicator was suitable for this experiment as it changes color close to the reaction equivalence point. The results obtained are acceptable and fulfill the experiment's objective.