Question

What is the molar mass of calcium hydroxide?

Answer 1

Hint: Use the concept of Avogadro’s Law to find out the molar mass; the molar mass of the compound can be found out by adding up the individual molar masses of the elements.

Complete step-by-step answer: In order to answer the question, we need to know about molar mass as well as moles. Now, matter is made up of atoms, and for the fact that matter is made up of mass, then the atoms should have a mass of their own. 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 $2g\,mo{{l}^{-1}}$. 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( the mass manually taken by the experimenter), to its molar mass. More is the number of moles, more is the concentration of the substance. Now, let us come to the question.
In order to find out the molar mass of calcium hydroxide, we need to know the molar masses of its individual elements. The elements contained in calcium hydroxide are calcium, oxygen and hydrogen. Calcium hydroxide has the formula $Ca{{(OH)}_{2}}$, which means, it houses 1 calcium atom, 2 oxygen atoms and 2 hydrogen atoms. Calcium has molar mass of $40g\,mo{{l}^{-1}}$, oxygen atom has molar mass $16g\,mo{{l}^{-1}}$ and hydrogen atom has the molar mass of $1g\,mo{{l}^{-1}}$. So, the total molar mass of the compound will be:
\[\begin{align}
  & molar\,mass=40+(2\times 16)+(2\times 1) \\
 & \Rightarrow molar\,mass=40+28+2=74g\,mo{{l}^{-1}} \\
\end{align}\]
Hence, we obtain the molar mass of calcium hydroxide to be $74g\,mo{{l}^{-1}}$, which is the required answer for our question.

Note: It is to be noted that in case of a molecule, to find out the molar mass, the masses of individual elements are added up. For example, ${{H}_{2}}O$ molar mass is $(2\times 1)+16$ which comes out as 18 grams.