Anhydrous compounds are often used as a drying agent, or desiccant, because they

Question

Anhydrous compounds are often used as a drying agent, or desiccant, because they can easily absorb water, forming a hydrate. One important usage of anhydrous salts as a desiccant is between the two panes of a double paned window. The desiccant is placed in the frame and absorbs moisture so that there should not be any condensation or fogging up between the two panes of the window. However, the added desiccant will only be able to absorb a certain amount of water; once all of the desiccant is in the hydrated form, it will not be able to absorb more water. It also will not be easy to add more desiccant to the space between the window. Therefore, a good window desiccant will have a high capacity to absorb water per gram of the anhydrous desiccant. While working for Window World, you are part of a research team that needs to develop and implement a protocol for determining the capacity of desiccants, which can be expressed in terms of the mass of water that can be absorbed per gram of anhydrous salt. For each test you will be given an anhydrous salt and asked to determine how much water is present in the hydrate form. This project will be profitable only if you can find a material that has at least the absorption capacity of anhydrous calcium chloride (one of the most common desiccants) so you will need to be able to make that comparison. In lab, you practiced the best way to measure the amount of water in a hydrate sample by heating off the water. Will you be able to use the same method of measuring the water when starting with an anhydrous sample? Why or why not? How could you prepare a sample of your anhydrous desiccant to measure the amount of water present in the hydrate the same way you did in lab?

Explanation / Answer

Q1.

as the name implies, anhydrous means there is no water in the molecule, so you will NOT be able to use the same technique to detect water.

You could apply inverse theroy, i.e. "humidify/hydrate" the anhydrous material so you get a sample which is hydrated, and evenetually apply the same techniques as before. This way you can measure how much water is present in the molecule

Q2

First:

Measure anhydrous material, in the balance, get the correct amount of mass used

assume this material is "dry"

then,

in a closed container, use the anhydrous material as a dissecant, meaning that it will absorb water from the environment.

Then

get the dissecant, be carefull not to drop any material

weight it again,

the difference in mass should be the water/humidity absorbed by the anhydrous material

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