The aim is to find the accurate concentration of sulphuric acid H2SO4 using titration with anhydrous sodium carbonate Na2CO3

                              = the mass/(23 X 2) + 12 + (3 X 16)

this tells us the number of moles of sulphuric acid needed for the reaction

Number of moles of sulphuric acid = Number of moles of sodium carbonate.

• We will obtain the volume of sulphuric acid needed for the reaction from the experiment, which will be explained. Now we can find the concentration using the following formula:

                                                                           The number of moles

Concentration of sulphuric acid in moldm = ______________________

                                                                     The volume in dm

We can find the mass of sodium carbonate needed:

1 moldm in 250 cm gives us

1 X 250/100 = 0.25 X 106 = 26.5g

0.25 X molar mass = 0.25 X 106 = 26.5g

If we use 0.1 moldm:

1. X 26.5 = 2.65

APPARATUS:

• Volumetric flask
• 10 cm pipette
• 100 cm conical flask
• 50 cm burette
• distilled water
• sand
• methyl orange indicator
• a sample of sulphuric acid
• electronic scale

METHOD:

1. weigh 2.65 grams of anhydrous sodium carbonate.
2. Transfer the weighed sodium carbonate to a beaker and add 25 cm of distilled water to dissolve it completely and mix them.
3. After dissolving, transfer the solution to a 250 cm volumetric flask. Rinse the beaker thoroughly and transfer all the washes to the volumetric flask. Remember not to overshoot the graduation mark of the glass.
4. Make up the solution to the line on the neck by adding water.
5. Pipette 10 cm of sodium carbonate to a clean conical flask.
6. Add two drops of methyl orange indicator.
7. Fill up a 50 cm burette with sulphuric acid solution and add acid to the sodium carbonate in small volumes and swirl the flask after each addition.
8. Keep adding until you see the colour of sodium carbonate changes permanently.
9. Record the final burette reading and calculate the volume of H2SO4 you have used.
10. Your first attempt will be a rough titration, you will have gone beyond the end point and added more H2SO4 than is needed to react with all sodium carbonate in the flask. This gives an idea of what the end point is.
11. Repeat the process four times and record the volumes used. The four times should agree to within 0.1 cm.
12. When you get close to the end point add only one drop of acid and swirl at a time.
13. Record in a table looking like this:

Average titre =

From my preliminary experience, the method mentioned above provides precise and reliable results. The apparatus used in it are accurate. Here are the percentage errors of some of the apparatus:

• Volumetric flask: 0.08%
• Burette: 0.4%

  The method also avoids procedural errors such as:

• The solution in the volumetric flask needs mixing.
• The burette and the pipette should be washed out with the solutions being used.
• The apparatus should be clean.
• The end point of a titration can only be determined accurately if the acid from the burette is added drop by drop, with swirling, as the end point is reached.

Risk assessment:

• Lab coats should be worn during the experiment.
• Eye protection should be worn.
• Sulphuric acid causes severe burns. Solution equal to stronger than 1.5 M are corrosive. Solution equal to or stronger than 0.5 M but less than 1.5 M are irritant. If splashed in eyes, flood the eye with gently running tap water for 10 minutes. Seek medical attention.
• Technicians must be informed if any spillage or breakage occur.
• Hands must be washed after the experiment.

Hassan Elumairi