Will sodium phosphate dibasic 0.5M in 500ml 5x(0.1M) form crystals at -4 degree celsius?

Question

I would like to know whether sodium phosphate dibasic NA2HPO4, 5 x 0.1M in 500ml water, prepared using 35.5g diluted in 500ml distilled water, will form crystals when stored at -4 degree celsius? I'm wondering why the one prepared by my senior forms crystals whereas mine don't. I've followed her instructions carefully. What seems to be the problem?

Answer 1

There are two possibilities. Assuming that you have waited as long as the senior, either you have done something different from what the senior did, or you have made a supersaturated solution.

Try dropping in a very small crystal of the salt into your solution at -4C. If you have made a supersaturated solution, material will start crystallising out. (This would explain what has happened, since sometimes supersaturated solutions form, and sometimes solute crystallises out under very similar conditions, depending on whether grains of dust, or rough spots on the vessel, are present.) Otherwise, you and your senior must have done something different, and you need to do some more detective work to find out what. No other explanations are possible.