Question

How does molarity change with temperature?

Answer 1

According to Charle’s law when the pressure on a sample of a dry gas is held constant, the Kelvin temperature and volume will be in direct proportion i.e. volume and temperature follows direct relation. And in morality we deal with volume. As temperature changes volume also changes.

Complete step by step answer:
Molarity is a term used for expressing the concentration of a solution i.e. it is a unit of concentration. Molarity of a solution is defined as the number of moles of a solute dissolved per litre of the solution. It is represented as $'M'$ .
Formula Used:
$M = \dfrac{{No.\,of\,moles\,of\,solute}}{{Volume\,of\,solution\,in\,litres}}$
Step2:
$No.\,of\,moles = \dfrac{{Mass\,of\,solute}}{{Molar\,mass\,of\,solute}}$
Since no. of moles is given by mass of solute divided by its molar mass. And we know mass doesn’t change with temperature.
Step3: For a given solution, mass is independent of temperature, but the volume of a solution changes with temperature. So if we made a solution on a particular day let’s say at temperature $T = 298K$ the molarity of a solution is different but if we check the molarity of the same solution on another day at temperature $T = 305K$ we get different values. So basically the concentration of a solution changes with temperature.
Step4:
Temperature and volume follows direct relationship i.e.
$T \propto V$
Molarity follows inverse relation with volume of solution i.e.
$M \propto \dfrac{1}{V}$
Case 1: When temperature increases, volume also increases and consequently molarity of a solution decreases because molarity follows an inverse relation with both volume and temperature.
Case 2: When temperature decreases, volume also decreases and consequently molarity of a solution increases because molarity follows an inverse relation with both volume and temperature.

Note: The concentration of a solution is better expressed quantitatively. There are a number of terms which express concentration of a solution. But that term is used which doesn’t change with temperature or we can say those concentration terms are preferred in which concentration of a solution doesn’t change with change in any factor that’s why molality is preferred over molarity.