Question

How many moles are in $98.3g$ of aluminium hydroxide, $Al(OH{)}_3$ ?

Answer 1

Hint: In order to determine the number of moles we have to use the relation that number of moles is equal to the ratio of given mass and molar mass of the compound.

Complete step by step answer:
The molar mass of aluminium hydroxide $(Al(OH{)}_3)$ is:
Molar mass = $27+3(16+1)\Rightarrow 27+51\Rightarrow 78$
Molar mass is defined as the mass of a substance in one mole quantity. That means one mole of aluminium hydroxide weighs $78g$ .
One mole = $78g$
So, the number of moles present in $98.3g$ of aluminium hydroxide is:
$$\begin{gathered} \Rightarrow {\displaystyle \frac{1\times 98.3}{78}}mole \\ \Rightarrow 1.26mole \end{gathered}$$
Hence, $1.26moles$ are present in $98.3g$ of aluminium hydroxide.

Additional information:
Mathematically, molar mass of a chemical compound is defined as the ratio of the given mass of compound and the molar mass of compound this ratio is measured in moles. The molar mass of a substance is considered as its bulk property. It is an average of many instances of the compound, which often vary in mass due to the presence of isotopes. Generally, the molar mass is determined from the standard atomic weights and that’s why it is thus a terrestrial average and a function of the relative abundance of the isotopes of the constituent atoms on Earth. The molar mass is appropriate for converting between the mass of a substance and the amount of a substance for bulk quantities.

Note:
There is an Avogadro constant. Avogadro law states that one mole of any constituent particles or entities contains $6.022\times {10}^{23}$ number of particles. These entities could be ions, atoms, molecules and so on. This law was given by Avogadro and this quantity is known as Avogadro constant. Avogadro constant is represented by $N_A$ .