Australia's Science Forum

Good morning,
Year 12 Chemistry prac asks for Na 3Po4 sodium phospahte, am using Na2HPO4 sodium orthophosphate. Would any one know if you can purchase sodium phosphate or will it always be orthophosphate because as soon as you put it with water it will add the hydrogen anyway.

Taken from the CSIS page 232 Sodium Phosphate also known as Trisodium Phosphate or Trisodium Orthophosphate 7-12 so green. Slightly toxic if ingested: corrosive to all mucous membranes. Skin irritant since alkaline. Use eye and skin protection where splashes can occur.

I do hope this helps you little, Sodium Phosphate and Sodium Orthophosphate are the same.

Sodium Phosphate Monobasic NaH2PO4 M.W.=119.98 (Sodium Dihydrogen Orthophosphate)
Sodium phosphate dibasic Na2HPO4 M.W.=141.96 (di-Sodium Hydrogen Orthophosphate)
Sodium phosphate tribasic Na3PO4.12H2O M.W.=380.12 (tri-Sodium Orthophosphate)

I think there might be some difference. I have three different containers labelled as above. The names that I have listed in brackets are the actual names on the containers. The other names are in brackets on the bottles, stating whether they are monobasic, dibasic or tribasic. It's all very confusing. So if you have been asked for Na3PO4 which is tribasic then I don't know what will happen to the experiment if you give them the dibasic Na2HPO4.

If you specifically need a Na3PO4 solution you can easily prepare it from either the monobasic or dibasic phosphate and a relatively concentrated solution of NaOH.
For example... if you need a 0.1M solution of Na3PO4 you can dissolve 0.1mole of the NaH2PO4 (12.0g) or Na2HPO4 (14.2g) in 900ml of distilled water and add 2M NaOH until pH paper indicates a pH of 12, then dilute to a final volume of 1000mL.