Question

To obtain a high enough ratio of moles water:moles anhydrous salt for your hydrated salt: Select one:

a. you should skip the step of heating the crucible before adding the hydrated salt

b. all of the water in the hydrate salt must be driven off

c. you must add water to the anhydrous salt

d. you must start with a sufficiently high mass of hydrated salt prior to heating

e. you should calculate the mass of water driven off from the crucible during the first heating step (before adding the hydrated salt)

Answer 1

Ans: b. all of the water in the hydrate salt must be driven off

Required mole ration = [No. of moles of water driven off ]/ [no. of moles of anhydrous salt remaining]

Option a is wrong because: If you skipped eating the crucible before adding the hydrated salt, in next heating the water molecules will gone.

Option c is wrong because: If you added water to the anhydrous salt, then you will get low ratio of moles water:moles anhydrous salt.

Option d is wrong because: high mass of hydrated salt prior to heating will not show change in the ratio.

Option e is wrong because: the mass of water driven off from the crucible during the first heating step will not be used in ration calculation.