Does the molarity change with the volume? For example we did an experiment in lab with one trial containing 0.1 M KI at 100 mL and another with 50mL. So does the molarity (M) change with volume change?
No and yes. The answer to your question is no, the molarity is the same whether the volume is 50 mL, 25 mL, 100 mL or 1 L. However, since the volume of a liquid changes with temperature, the molarity DOES change as the temperature (and volume) changes. The point is that if we make up a solution that is supposed to be 1 M and it is in a 1 L volumetric flask and the temperature of the room is 35 C, the flask is calibrated to hold 1 L at 20 C (not 35 C); therefore, the solution will NOT be 1 M.
The molarity (M) is defined as the number of moles of solute dissolved in one liter (L) of solution. It is expressed in moles per liter (mol/L) or moles per cubic decimeter (mol/dm³). In this case, you mentioned that you conducted an experiment with one trial containing 0.1 M KI in 100 mL and another with 50 mL.
To determine whether the molarity changes with a volume change, we need to apply the equation:
Molarity (M) = moles of solute (mol) / volume of solution (L)
In both trials, the moles of solute (KI) will remain the same since the chemical substance being dissolved does not change. However, the volume of the solution will differ, which is why we need to calculate the molarity for both cases.
Trial 1:
Molarity = moles of solute / volume of solution
Given: Molarity = 0.1 M, Volume = 100 mL = 0.1 L
To calculate the moles of solute, multiply the molarity by the volume in liters.
moles of solute = 0.1 M * 0.1 L = 0.01 mol
Trial 2:
Given: Molarity = 0.1 M, Volume = 50 mL = 0.05 L
Calculate the moles of solute the same way:
moles of solute = 0.1 M * 0.05 L = 0.005 mol
From these calculations, it is evident that the moles of solute remain the same, regardless of the volume of the solution. Therefore, the molarity remains the same as well. In this case, both trials have a molarity of 0.1 M, indicating the same concentration of KI despite the difference in volume.