Question

Determine the number of atoms in a mole of ${\text{Ca}}{\left( {{\text{OH}}} \right)_{\text{2}}}$.
A. $30\, \times \,6.02 \times {10^{23}}$ atoms
B. $5 \times \,6.02 \times {10^{23}}$ atoms
C. $6\, \times \,6.02 \times {10^{23}}$ atoms
D. None of these

Answer 1

Hint: According to the Avogadro, one mole of any substance has $\,6.02 \times {10^{23}}$ atoms, ions or molecules. This number $\,6.02 \times {10^{23}}$ is known as Avogadro number.

Complete step by step answer:
First, determine the number of atoms in one mole of calcium hydroxide and then multiply the number of atoms with the Avogadro number to determine the total number of atoms in a mole.
${\text{Ca}}{\left( {{\text{OH}}} \right)_{\text{2}}}$ is a compound. A compound is a substance made up of two or more different types of elements.
${\text{Ca}}{\left( {{\text{OH}}} \right)_{\text{2}}}$ is made up of three types of elements. Calcium, hydrogen and oxygen.
So, each molecule of ${\text{Ca}}{\left( {{\text{OH}}} \right)_{\text{2}}}$ has a total of five atoms, one of calcium, two of oxygen and two of hydrogen.
Each atom of ${\text{Ca}}{\left( {{\text{OH}}} \right)_{\text{2}}}$ has$\,6.02 \times {10^{23}}$atoms per mole.
So, the element of ${\text{Ca}}{\left( {{\text{OH}}} \right)_{\text{2}}}$ will have,
 $\,6.02 \times {10^{23}}$atoms per mole.
Therefore, a mole of ${\text{Ca}}{\left( {{\text{OH}}} \right)_{\text{2}}}$ has $\,5 \times 6.02 \times {10^{23}}$ atoms.
Therefore the option (B) is correct.

Additional information: In the same manner, the number of ions can also be determined. As the given ${\text{Ca}}{\left( {{\text{OH}}} \right)_{\text{2}}}$ has three types of ions, one calcium and two hydroxide ions.
${\text{Ca}}{\left( {{\text{OH}}} \right)_{\text{2}}}\, \to {\text{C}}{{\text{a}}^{{\text{2 + }}}}{\text{ + }}\,{\text{2}}\,{\text{O}}{{\text{H}}^{\text{ - }}}$
So, the total number of ions will be $3\, \times \,6.02 \times {10^{23}}$ ions.

Note:
The number of atoms present in $12\,{\text{g}}$ of carbon-12 is known as one mole. The total number of atoms is the sum of all the atoms of a compound. The subscript after the bracket represents the numbers of atoms that are present within the bracket. The superscript represents the charge of an ion not the number of that ion.