Question

If you mass 0.430 g of Co(NO3)2 6H2O and dissolve it in water, what further information would you need to calculate:_________.
a. the number of moles of Co(NO3)2 in the solution?
b. the molarity of the solution

Answer 1

Answer:

a. No information is required.

b. The volume of the solution.

Explanation:

Hello!

In this case, since hydrates are salts which have additional water in their structures, when making mole-mass calculations involving them, we need to consider the how many water molecules we find in the hydrate. In such a way, for 0.430 g of cobalt nitrate hexahydrate (six water molecules), we proceed as follows:

a. Since we have 0.430 g of hydrate, we may compute the moles of anhydrous cobalt nitrate by using the molar mass of the hydrate (291.04 g/mol) and then, by noticing that one mole hydrate has one mole of anhydrous, we are able to compute the moles of anhydrous cobalt nitrate as shown below:

$0.430gCo(NO_3)_26H_2O*\frac{1molCo(NO_3)_26H_2O}{291.04gCo(NO_3)_26H_2O} *\frac{1molCo(NO_3)_2}{1molCo(NO_3)_26H_2O}\\\\=1.48x10^{-3}mol Co(NO_3)_2$

It means no further information is required.

b. Since the molarity is defined by the division of the moles of solute over liters of solution (M=mol/V), we would need the volume of the solution to successfully compute it.

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