Molarity Worksheet - Answer Key
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- What is molarity?
Molarity is one of the units used to describe the concentration of a solution.
- What are the units of molarity?
Molarity (M) = moles of solute
L of sol’n
- Calculate the molar concentration of all the ions in the following strong electrolytes.
- 75g of KCl dissolved in 250 mL of water.
- What is a dilution?
In a dilution the volume of a solution is increased but the moles of solute remains the same.
- What equation is useful in a dilution?
M1V1 = M2V2
M1 = Initial molarity M2 = Final molarity
V1 = Initial sol’n volume V2 = Final sol’n volume
*Caution – Only use this equation when a substance is NOT undergoing a reaction.
- How much water must be added to a 2.00M stock sol’n of NaOH to make 100.0 mL of a 0.100M NaOH sol’n?
We know that this is a dilution question because we are told that all we are doing is adding water to the solution. Adding water will increase the volume of solution, but not affect the moles of solute (NaOH) present in solution. This means that it is completely fine to use M1V1 = M2V2
(100.0 mL) (0.100 M) = (V2) (2.00M)
V2 =5.00 mL of stock solution needed
It is important to note that the question is asking for the amount of water required – we just solved for the amount of the concentrated stock solution we would need to dilute down.
Amount of water that must be added is
100.0 mL – 5.00 mL = 95.0 mL water