Question

Does molarity increase or decrease with temperature?

Answer 1

Molarity is one of the methods to determine the concentration of unknown sample solutions.
Molarity of solution is defined as total number of moles of solute dissolved per litre of the solution.
A solution which contains one-gram mole concentration of solute present in one litre of the solution is known as one molar solution.

Complete answer:
Molarity of solution is expressed as-
$M = \dfrac{m}{{{V_{\left( L \right)}}}}$
Where $M$is the molarity of the solution
$m$ Is number of moles of solute present in the solution
$V$ Total volume of the solution in litres.
Liquid which is used in the form of solution has a tendency to alter its volume depending upon temperature.
As we know, intermolecular attraction between the liquid particles is smaller than solid particles, so when we change the temperature of liquid its particles either come closer or move apart.
When particles come closer, this will result in an increase in density.
Similarly, on raising the liquid temperature particles of liquid move apart and density of liquid decreases.
Density of any liquid is calculated by formula
$D = \dfrac{M}{V}$
Where $D$ is density
$M$ is Mass of substance
$V$ Is the volume of solution
From the above formula we observe that density of any liquid is inversely proportional to its volume.
So, on raising the temperature as the density of liquid decreases its volume increases.
Similarly, on lowering the temperature as the density of liquid increases its volume increases.
When particles come closer, this will result in an increase in density. This is termed as liquid contraction which is usually seen when the temperature of liquid decreases.
Which means that as the density of liquid changes with change in temperature its volume also changes.
From the formula of molarity, we already observe that molarity of solution is inversely proportional to volume of solution.
Therefore, when temperature increases, volume of liquid increases which results in decrease in molarity.
In a similar way when temperature decreases, volume of liquid decreases which results in increase in molarity.
Hence, we conclude that molarity is a temperature dependent property.

Note:
Do not confuse the term molality which is also used to express the concentration of solute in moles present Kg of solvent.
Molality is an independent property to temperature because it does not depend on volume of solution.