化學高手請進

Question

In the gravimetric determination of water of crystallization of hydrated Sodium sulphate (VI) , we cannot ensure all water of crystallization have been removed by observating the colour change because both the hydratedsalt and the anhydrous salt are white. How can we ensure all water of crystallization are removed in the heating process by an alternative method?

Answer 1

First of all, I think you can weigh the sample (hydrated salt) before heating.
After heating the sample for long time, i.e. 5 -10 minutes, then re-weigh the sample and record the mass.
Heat and weigh the sample repeatingly, if the weigh of the sample has no change after a long time. Then, I think it has been converted to a anhydrous salt.

Answer 2

Weigh a watch glass.
Then put some hydrated sodium sulphate(VI) to the watch glass. Weigh the watch glass with its content.
Put the watch glass with its content to a oven at 110°C overnight. Put the watch glass with its content in a desiccator for drying. After cool, weigh again.