Question

$25.3 \, g$ of sodium carbonate, $Na_2CO_3$ is dissolved in enough water to make $250 \, mL$ of solution. If sodium carbonate dissociates completely, molar concentration of sodium ion, $Na^+$ and carbonate ions,$CO^{2-}_3$ are respectively (Molar mass of $Na_2CO_3 = 106 \, g \, mol^{-1}$)

• A. 0.477 M and 0.477 M
• B. 0.955 M and 1.910 M
• C. 1.910 M and 0.955 M
• D. 1.90 M and 1.910 M

Answer 1

The Correct Option is C

Molarity = $\frac{25.3 \times 1000}{106 \times 250} = 0.955 \, M$
${ Na_2 CO_3 -> 2Na^+ + CO^{-2}_3}$
$= 2 \times 0.955 \, \, 0.955 \, M$
$= 1.910 \, M$

Answer 2

Ans: Molar concentration and molarity are interchangeable. It is the amount of solute in the given volume of solvent. The concentration of the solute in the solution can be expressed as molar concentration. It is the number of moles of solute per litre of solution (mol/L). The unit of molarity is called molar (M), it is the one mole of the solute that is per litre of the solution. 

The formula for the same is: C=n/V 

In this, C= molar concentration in mol//L (M)

n=Amount of solute in moles (mol) 

V=Volume of solution in litres (L) 

The molarity is used in the following: 

• Preparing solutions 
• Stoichiometric calculations 
• Titration and other analytical techniques
• Pharmacology