Question

How many water molecules are associated with 3.0 mol of $CoC{{l}_{2}}.6{{H}_{2}}O$?

Answer 1

Calculate the number of water molecules that are associated with 3 moles of the compound, then multiply it with Avogadro’s constant to find the number of water molecules.

Complete step-by-step answer: In order to answer the question, we need to know about moles and molar mass. Now, matter is made up of atoms, and as matter has mass, then the atoms should have an individual mass. Molar mass of an element or compound is the mass which houses $6\times {{10}^{23}}$ particles. For, example, the hydrogen molecule has a molar mass of 2 grams. This means 2 grams of hydrogen contains $6\times {{10}^{23}}$ atoms, and this number is also called the Avogadro’s number.
Number of moles of an element or a compound is the ratio of its given mass taken by the user, to its molar mass. More is the number of moles, more is the concentration of the substance.
Now, let us examine the compound. The compound is in a hydrated state and in every molecule of cobalt(III) chloride, 6 molecules of ${{H}_{2}}O$ are attached. However, in the question, we have been asked for 3 moles of the compound. So, if 1 mole contains 6 ${{H}_{2}}O$ atoms, then 3 moles of the compound will contain $6\times 3=18$ moles of water molecule.
As discussed above, we will have to find the number of water molecules by mole concept. As one mole of the water molecules will contain $6\times {{10}^{23}}$ number of atoms, so 18 moles of water molecules shall contain $6\times {{10}^{23}}\times 18=1.08\times {{10}^{25}}$ water molecules, which is the required answer for the question.

Note: It is to be noted that when a compound containing water molecules of hydration is heated up then the hydration molecules leave the compound as water vapour, thus, by decreasing the overall molar mass.