Theory

Volumetric analysis is a quantitative chemical analysis technique used to determine the concentration of an unknown solution by measuring the volume of a solution of known concentration required to react completely with the unknown solution. In this experiment, the molarity of the given solution of H₂SO₄ will be determined by titrating it with a standard solution of NaOH. The reaction between NaOH and H₂SO₄ is a neutralization reaction, and the balanced chemical equation for this reaction is:

H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O

The volume of NaOH used in the titration is used to calculate the molarity of H₂SO₄.

Equipment and Apparatus Required

• Burette
• Pipette
• Conical flask
• Stirring rod
• Beaker
• Weighing balance

Chemicals Required

• H₂SO₄ solution
• NaOH solution (standard solution)
• Phenolphthalein indicator

Indicator

The phenolphthalein indicator is used to determine the endpoint of the titration. It changes from colorless to pink at a pH of around 8.2.

End Point Colors

The endpoint of the titration is indicated by the color change of the phenolphthalein indicator from colorless to pink.

Chemical Equations

The balanced chemical equation for the reaction between H₂SO₄ and NaOH is:

H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O

Procedure

1. Pipette 25 mL of the given solution of H₂SO₄ into a clean and dry conical flask.
2. Add a few drops of phenolphthalein indicator to the conical flask.
3. Add the standard solution of NaOH to the burette.
4. Record the initial burette reading.
5. Titrated the H₂SO₄ solution by slowly adding NaOH solution to the conical flask with constant stirring until the phenolphthalein indicator changes color from colorless to pink.
6. Record the final burette reading.
7. Repeat the titration two more times to obtain consistent results.

Observations with Supposed Calculation

Assuming the molarity of the NaOH solution is 0.1 M

Trial	Initial Burette Reading (mL)	Final Burette Reading (mL)	The volume of NaOH Used (mL)
1	0.0	22.1	22.1
2	0.0	22.3	22.3
3	0.0	22.2	22.2

The average volume of NaOH used in the titration is:

Average Volume = (22.1 mL + 22.3 mL + 22.2 mL)/3 = 22.2 mL

The balanced chemical equation for the reaction between H₂SO₄ and NaOH is:

H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O

From the equation, we know that 1 mole of H₂SO₄ reacts with 2 moles of NaOH.

So, the number of moles of NaOH used in the titration is:

Number of moles of NaOH = Molarity × Volume (in L) = 0.1 M × 22.2 mL / 1000 mL/L = 0.00222 moles

Since 1 mole of H₂SO₄ reacts with 2 moles of NaOH, the number of moles of H₂SO₄ present in the 25 mL of solution is:

Number of moles of H₂SO₄ = 0.00222 moles / 2 = 0.00111 moles

The volume of the given solution of H₂SO₄ used in the titration is 25 mL, which is equal to 0.025 L.

Therefore, the molarity of the given solution of H₂SO₄ is:

Molarity = Number of moles / Volume (in L) = 0.00111 moles / 0.025 L = 0.0444 M

Calculations

The molarity of the given solution of H₂SO₄ is 0.0444 M.

Precautions

• Make sure all the glassware and equipment used are clean and dry before starting the experiment.
• Handle the NaOH solution with care as it is corrosive.
• Add the indicator drop by drop and swirl the flask after each addition to avoid overshooting the end point.
• The burette readings should be taken at eye level, and the bottom of the meniscus should be aligned with the calibration mark.
• The titration should be repeated at least three times to ensure the accuracy and consistency of the results.
• Avoid using too much indicator as it can affect the accuracy of the titration.
• The volume of the H₂SO₄ solution should be accurately measured using a volumetric pipette or burette.
• Record all the observations carefully and accurately.