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## Chemistry library

### Course: Chemistry library>Unit 11

Lesson 3: Mixtures and solutions

# Dilution

AP.Chem:
SPQ‑3 (EU)
,
SPQ‑3.A (LO)
,
SPQ‑3.A.2 (EK)
A common method of making a solution of a given concentration involves taking a more concentration solution and adding water until the desired concentration is reached. This process is known as dilution. We can relate the concentrations and volumes before and after a dilution using the following equation: MV₁ = MV₂ where M₁ and V₁ represent the molarity and volume of the initial concentrated solution and M₂ and V₂ represent the molarity and volume of the final diluted solution. Created by Sal Khan.

## Want to join the conversation?

• can you just multiply the 500 mls by the .125 molars and get the same answer?
• Yes, that's essentially what Sal did. A more simplified way of solving this is by using the dilution formula: (M1)(V1) = (M2)(V2), where M's are molarities and V's are volumes. 1 means the initial state and 2 mean the final state.

So for this problem here where we want 500 mL of a 0.125 M solution of sodium sulfate and start with 1.00 M solution of sodium sulfate, we want to know how much volume of the 1.00 M solution we need to add. So M1 = 1.00 M, M2 = 0.125M, V2= 500 mL, V1= is unknown and what we solve for. So V1 = (0.125 M)(500 mL)/(1.00M) = 62.5 mL. So that's what Sal's doing essentially and what you suggested to do, both are just following the dilution formula.

Hope that helps.
• How can you know when to use the M1*V1=M2*V2 formula?
• Well whenever you are trying to create a more dilute solution you would use that formula. A more dilute solution meaning a solution with a lower concentration than the original. You use this quite often in chemistry when you want to work with a solution with a specific concentration.

Another use for the dilution formula is that it allows you to know how much acid/base to add to an analyte when doing acid/base titrations using strong acids and strong bases.

Hope that helps.
• Why is 500 mL = 0.500L, I thought that 500 has 1 significant figure and 0.500 has 3? Shouldn't it be 0.5L?
• Are molarity and moles the same thing? Do they have the same unit?
(1 vote)
• Molarity and moles are measuring different things and hence have different units.

A mole is the unit for the amount of substance, or how much of something there is. It is defined as an Avogadro's number of particles, or 6.02214076 x 10^(23) particles. In the same way that a dozen of something is 12 particles. So a dozen eggs is 12 eggs, a dozen people is 12 people, a dozen atoms is 12 atoms. A mole of eggs is 6.02214076 x 10^(23) eggs and a mole of atoms is 6.02214076 x 10^(23) atoms. We use such a large number in chemistry because atoms are so small that having even a small amount of atoms like a gram could already be a mole of atoms. So it's more convenient to use moles of atoms instead of saying 6.02214076 x 10^(23) atoms each time we do a calculation.

Molarity is a unit of concentration, with units of moles of solute/ liters of solvent. Concentration being how much of a substance is in a given volume. A solvent being a liquid into which something is dissolved into, which is referred to as the solute. Together a solute and a solvent are called a solution. So if you have a glass of salt water, you have a solution of water where the water is the solvent and the salt is the solute. If you have a lot of salt in the water then it is a concentrated solution which we would express with a large molarity. And a small amount of salt in the water is an unconcentrated solution with a small molarity.

Hope that helps.