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Dilution and its Effects on Acids and Bases

Learn how the pH of an acid or base changes when diluted with water and understand the concept of serial dilution. Explore how diluting an acid or base affects its acidity or basicity.

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Dilution and its Effects on Acids and Bases

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  1. Unit 8: Solution Chemistry and Acids and Bases

  2. Lesson 87: Watered Down • Dilution

  3. ChemCatalyst • Imagine that a sample of drinking water has been contaminated with an acid. The pH is now 4.0. • What do you think would happen to the pH if you added more water to the sample? • Do you think you could ever get the pH back to 7? Explain why or why not.

  4. Key Question • How does dilution affect acids and bases?

  5. You will be able to: • complete a serial dilution of a solution • explain the effect of dilution on the acidity or basicity of a solution

  6. Discussion Notes • Adding water to an acid or a base dilutes the solution, making it less acidic or less basic. • An acid can never be turned into a base by diluting it with water, and a base can never be turned into an acid by diluting it with water.

  7. Discussion Notes (cont.) • Each time the H+ concentration is diluted tenfold, the pH number goes up 1 unit.

  8. Dilution • Preparation of a desired solution by adding water to a more concentrated solution. • Moles of solute remain the same, but volume and molarity change • M1V1 = M2V2

  9. Dilution • M1V1 = M2V2 • M1 = initial molarity • V1 = initial volume • M2 = final molarity • V2 = final volume • The units for V1 & V2 do not matter, as long as they are the same • M1 & M2 MUST be in Molarity

  10. Practice • Suppose we need to make 250.0 mL of a 0.10 M HCl solution from a 1.0 M HCl solution. How many mL of the concentrated solution do we need? • M1 = 1.0 M • V1 = ? • M2 = 0.10 M • V2 = 250.0 mL • M1V1= M2V2 • (1.0 M)(V1) = (0.10 M)(250.0 mL) • V2 = 25 mL

  11. Dilution Practice • What volume of 15.8M HNO3 is required to make 250 mL of a 6.0M solution? WORK: M1 V1 = M2 V2 (15.8M)V1 = (6.0M)(250mL) V1 = 95 mL of 15.8M HNO3 GIVEN: M1 = 15.8M V1 = ? M2 = 6.0M V2 = 250 mL

  12. Prepare for the Lab • Work in groups of four. • Wear safety goggles at all times. • Acids and bases are corrosive. Do not get any on skin or near eyes. • In case of a spill, rinse with large amounts of water.

  13. Wrap Up • How does dilution affect acids and bases? • Dilute solutions are less acidic and less basic than more concentrated solutions. • Dilution of an acid or a base results in a solution that is increasingly neutral. • It is not possible to go past a pH of 7 when diluting an acid or a base.

  14. Check-In • If you get lemon juice in your eye, you should flush the eye with lots of water. Why?

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