Concentration of a solution can be expressed in terms of molarity and molality
Molarity is the number of moles of solute in a liter of a solution.
Molarity (M) = Moles of solute/Volume(litres) of solution
Molality is the number of moles of solute in one kg of the solution
Molality (m) = Moles of solute/Mass (kg) of solution
Therefore if the volume or the mass of the solution is changed this would affect the concentration.
In addition, volume is a quantity which depends on temperature. However, mass is independent of temperature. Therefore any changes in temperature, can also bring about a change in the molarity of the solution.