Procedure

Preparation of Solutions:

Molybdate Solution:

Add 13.6 mL of concentrated sulphuric acid to 35 mL of water and allow the solution to cool. In a separate vessel, add 2.5 g of ammonium molybdate to 50 mL of water. Add the sulphuric acid solution to it and make up the volume.

Reducing Solution:

Dissolve 11.25 g sodium hydrogen phosphate in 30 mL water. Add 2.25 g sodium sulphate and 0.19 g 1-amino 2-naphthol 4-sulphonic acid and dilute the mixture to 75 mL with water. Stir the mixture thoroughly and filter.

Standard Solutions of Phosphate:

Dissolve 20 mg of potassium dihydrogen phosphate in 100 mL of water. The concentration of phosphate standard solution is 0.2 mg/mL.

Prepare 9 standard solutions containing:

• 0.5 mL molybdate solution
• 0.2 mL reducing solution
• x mL of phosphate stock solution
• y mL of distilled water

Where x + y = 9.3 mL and x = 2 - 0.2n, with n = 1, 2, ..., 9.

Also prepare a blank solution by mixing:

• 0.5 mL of molybdate solution
• 0.2 mL of reducing solution
• 9.3 mL of water

Set the wavelength to 635 nm and adjust the colorimeter reading to zero with the blank.
Place each standard solution of phosphate in turn in the cuvette and record the absorbance.

Dilute the soft drink sample 5 times. Mix:

• 1 mL of the diluted solution
• 0.5 mL molybdate solution
• 0.2 mL reducing solution
• 8.3 mL water

to prepare the test solution.

Measure the absorbance of the sample solution.
Plot a graph between absorbance and volume of phosphate in the standard solutions to obtain the calibration curve.
From the curve, determine the amount of phosphate in the test solution.

Calculation:

The amount of phosphate in the sample of soft drink is:
5 × 0.2 × V = 1 × V mg/mL

Where:

• 5 is the dilution factor
• 0.2 mg/mL is the amount of phosphate in the standard solution
• V is the volume of phosphate solution obtained from the graph

Procedure to View the Experiment Animation.

Instructions to run the Flash simulator on your system:

▶ Windows system
Step 1: Open Flash Player

Step 2: Copy the Flash content link by click the 📋 icon provided above.

Step 3: Click File → Open from the Flash Player menu.
Step 4: Paste the Flash content link in the Open window of the Flash Player and click the OK button.

▶ Linux system
Step 1: Install Wine on your Linux system.
For Ubuntu: sudo apt update
sudo apt install wine
For Fedora: sudo dnf install wine
Step 2: Open terminal and navigate to the folder where the Flash Player is downloaded.
Step 3: Open the Flash Player using wine flashplayer.exe

Step 4: Copy the Flash content link by click the 📋 icon provided above.
Step 5: Click File → Open from the Flash Player menu.
Step 6: Paste the Flash content link in the Open window of the Flash Player and click OK.