In indian pharmacopoeia they are preparing arsenic standard solution of 10 ppm by taking 330 mg of arsenic trioxide and made up the volume to 250 ml. Further took 1 ml of this solution and made up the volume up to 100 ml.As far as I know it’s a 5 ppm solution. If anyone have any idea how 330 mg of arsenic trioxide weight is converted to 10 ppm arsenic so plz share ur information.

Please note the following calculations & explanation -

The atomic weight of Arsenic is 74.92 (As)

Molecular weight of Arsenic trioxide is 197.84 (AS2O3)

Therefore,

197.84 mg = (2 X 74.92) = 149.84 mg 2As (2 Arsenic atoms)

Hence, 1 g mole of As2O3 = 2 As (2 Atoms of Arsenic)

Hence, 197.84 mg As2O3 = 149.84 mg Arsenic

Hence, 330 mg As2O3 = 249.84 mg Arsenic = 250 mg As

Hence, 330 mg As2O3 OR 250 mg Arsenic is present in 250 ml of solution.

Hence, 1 mg Arsenic (As) is present in 1 ml of the above solution.

This 1 ml is further diluted to 100 ml.

Hence, the diluted Arsenic solution has 1 mg Arsenic in 100 ml

Hence in 1000 ml diluted solution of Arsenic has 10 mg of Arsenic (As).

Hence this is a 10 ppm solution of Arsenic (As).

Please note the important formula is the number of mg (X mg) of solute dissolved in 1 liter of solution is (X) ppm solution.

Similarly, the number of mg (Y mg) of a substance present in 1 kg of material is (Y) ppm concentration.

Hope I have explained this in sufficient detail.

It was very helpful information that u shared thanku sir

You are always welcome.

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