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Calculating Dilution of Solutions

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  • 0:05 Dilution of Solutions
  • 1:38 Example
  • 2:38 Making a Solution
  • 3:30 Lesson Summary
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Lesson Transcript
Instructor: Amy Meyers

Amy holds a Master of Science. She has taught science at the high school and college levels.

Learn what a solution is and how to properly dilute a new solution from a stock solution. Learn the dilution equation that combines molarity, the volume of stock solution and desired solution to determine how much stock solution is needed for the new solution.

Dilution of Solutions

Whether it's in your house, your office, or a scientist's lab, storage space is often hard to come by and very precious. Just like you and the cleaning supplies that are probably hidden under your kitchen sink, making the cupboard overflow, scientists often have cupboards overflowing with chemicals. Just like you, they find it easier to keep liquids in a concentrated form, called a stock solution, because it takes up less room. Then, scientists dilute the solutions to the needed concentration at the time of use. Knowing how to dilute a solution is an important concept to learn.

To review a bit, you know what a solution is. It is a homogeneous mixture that isn't chemically combined.

Since a solution isn't chemically combined, there can be different amounts of solute dissolved in the solvent. Remember that the solute is the substance dissolved in the liquid. The solvent is the liquid the solute was dissolved in. Because of that, we have to specify how much of each substance - solute and solvent - is in the solution. We usually do this with the term molarity, which is the number of moles of solute per liter of solution.

The equation to use when diluting a stock solution
Stock Solution Dilution Equation

To dilute a stock solution, the following dilution equation is used: M1 V1 = M2 V2

M1 and V1 are the molarity and volume of the concentrated stock solution, and M2 and V2 are the molarity and volume of the diluted solution you want to make.

Example

Pretend you are doing a lab experiment that requires 3 L of a 0.5 M solution of HCl. Your stock solution is 10 M. How much stock solution do you need to add to water to make the needed solution?

M1 = 10 M
V1 = ? (It is the unknown.)
M2 = 0.5 M
V2 = 3 L

Set up your equation:
M1 V1 = M2 V2

Rearrange the equation to solve for V1:
V1 = M2 V2 / M1

Fill in your known values and solve:
V1 = (0.5 M)(3 L) / 10 M
V1 = 0.15 L

So, you need to add 0.15 L of stock solution to water to make 3 L of diluted solution.

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