Question

Approximately how many moles of potassium permanganate, $KMn{{O}_{4}}$, are present in 40g of this compound? (Atomic weights: K=39; Mn=55; O=16)
(A) 1 mole
(B) 0.5 mole
(C) 0.25 mole
(D) 0.1 mole

Answer 1

Hint: Moles is the amount of substance present in any compound. Molar mass can be calculated by the sum of individual masses of the atom present in the compound. Moles of a compound or atom can be found using weight, molecular weight etc.

Complete step by step solution:
The mole (symbol- mol) is the unit of measurement for the amount of substance in the International System of Units (SI).
The formula of moles to be used is:
\[mole=\dfrac{weight}{\text{molecular weight}}\]
Molecular weight of $KMn{{O}_{4}}$ is $[39+65+(16x4)] =$ $158grams$.
158g of $KMn{{O}_{4}}$ contains 55grams of Potassium (atomic weight of potassium is 55grams)
Therefore, 40g of $KMn{{O}_{4}}$ contains $\dfrac{55}{158}\times 40$, which is equal to 14 grams of potassium.
55 grams of potassium equal to 1 mole of potassium, therefore, 1gram of potassium equals $\dfrac{1}{55}$mole of potassium.
Thus, 14grams of potassium equals $\dfrac{1}{55}\times 14$mole of potassium, which is equal to 0.25 mole of potassium.

Therefore, the correct answer is the (C) option.

Note: A mole of a substance or a mole of particles is defined as exactly \[6.02214076\times {{10}^{23}}~\] particles, which may be atoms, molecules, ions, or electrons. In short, for particles 1 mol = \[6.02214076\times {{10}^{23}}~\]. The molar mass of a substance is the mass of 1 mole of that substance, in multiples of the gram. The amount of substance is the number of moles in the sample.