Question

What is the mass of 0.20 mole of $ C_2H_5OH $ (ethanol)?

Answer 1

Hint : In order to solve the question, we need to understand the concept and formula of Mole. Mole is defined as exactly $ 6.022 \times {10^{23}} $ particles (Atoms, molecules or ions).This number is called Avogadro number. Mole is a S.I unit for measurement of quantity of substance. Also we need to know the molar weight of Ethanol.

Complete Step By Step Answer:
Given-Number of moles=0.20 moles
We know that mass of hydrogen=1g/mole, Mass of carbon=12g/mole, Mass of oxygen=16g/mole
Molar mass of Ethanol $ ({C_2}{H_5}OH) $ $ = (12 \times 2) + (1 \times 5) + (16 \times 1) + (1 \times 1) = 46g/mole $
The formula of moles (n) =given mass/Molar mass
Therefore given mass=number of moles*molar mass
Given mass will be $ = 0.20 \times 46 = 9.2g $
Additional Information: Apart from the above formula we can calculate number of moles in various ways-
1. Number of moles=Atomic Mass/ molecular mass/formula mass of ionic compounds.
Example-1 mole of Carbon=12g
2. At S.T.P (Standard temperature pressure) i.e. at a temperature of 0 °C and 1 atm pressure or at N.T.P(Normal temperature pressure) i.e. at a temperature of 25 °C and a pressure of 1 atm ,1 mole=22.4 litre of that gas.
Example-At S.T.P 1 mole of oxygen=22.4 litre of oxygen.
3. It is also given by the formula $ n = N/{N_A} $ where n is the number of moles , $ N $ is the number of molecules of particles and $ {N_A} $ is the Avogadro number.

Note :
This concept of calculating mass of any solution or liquid using the number of moles provided or calculating the number of moles is highly beneficial in chemistry laboratories and for all practical purposes. It is very important in the study of Stoichiometry like calculating the strength of solution, Molarity, molarity etc.