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Q & A: evaporation of water from hydrates

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Most recent answer: 08/27/2011
Q:
At what temperature bound water in the materials can be evaporated means can 105 degree celcius temperature evaporate the bound water present in the material in the complex form like Lactose Monohydrate?
- vipin (age 32)
Ahmedabad, Gujrat, India
A:
The answer is a bit complex. There's no sharp temperature below which water stays in a hydrate and above which it evaporates. There's an equilibrium between some water vapor and water in the hydrate. So whether water will evaporate faster than it rejoins the hydrate depends not only on the temperature but also on the amount of water vapor in the atmosphere.  The higher the temperature, the higher the pressure of the water vapor in equilibrium with the hydrate. The equilibrium vapor pressure as a function of temperature will be different for each hydrate.

The water bound in the hydrate is presumably more stable than it would be as pure water. Otherwise it would leave the hydrate and form pure water. My guess (I haven't looked up the numbers for lactose monohydrate) is that at 105C, your hydrate will hold on to most of its water unless the air is especially dry.

Mike W.

(published on 08/27/2011)

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