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Concentration of solutions

This guide provides an overview of solution concentration, specifically focusing on molarity as a measure of solute strength in a solvent. It covers key definitions, volume conversion factors, and practical examples demonstrating how to calculate molarity and perform dilution. Learn how to determine molarity from moles and grams of solute and how to dilute concentrated stock solutions effectively. This resource is ideal for chemistry students looking to grasp essential concepts related to solutions and their concentrations.

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Concentration of solutions

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  1. Concentration of solutions Day 4

  2. Concentration • A measurement of the amount of solute in a given amount of solvent or solution (unit of measurement = molarity) • Kind of like the “strength” of the solution

  3. Molarity Molarity (M)= molsolute L solution

  4. Volume conversion factors • 1 cm3 = 1 mL • 1 dm3 = 1 L

  5. Dilute • A dilute solution is a solution in which there is more solvent than solute. • For example, to dilute some solution, you could add excess water to it.

  6. Example #1: • If we put 0.500 mol of sodium hydroxide into 1.00 L of solution, what is the molarity of the solution?

  7. Molarity= mol solute/L sol’n 0.50 mol NaOH M= 2.00 L = 0.25 M NaOH

  8. Example #2: • What is the molarity if we have 80.0 g NaOH in 1.00 L of solution?

  9. 80.0 g NaOH 1 mol NaOH =2.00 mol Molarity= mol solute/L sol’n 40.0 g NaOH = 2.00 M NaOH 2.00 mol NaOH M= 1.00 L

  10. Example #3: • How many moles of KOH are in 0.50 L of 0.10 M KOH?

  11. Molarity= mol solute cross multiply! 1 L sol’n (0.50 L) mol KOH= (0.10 M KOH) = 0.05 mol KOH

  12. Example #4 • How many grams of KOH are in 2.75 L of 0.25 M KOH?

  13. Molarity = moles cross multiply! L Moles = Molarity * L = 0.25 mol/L * 2.75L = 0.69 moles KOH 0.69 mol KOH 56.097 g KOH = 38.7 g KOH 1 mole KOH (39)

  14. Molarity - Dilution Some chemicals are sold as pre-prepared concentrated solutions (stock solutions). To be used, stock solutions usually must be diluted.

  15. Always Add Acid

  16. Molarity – Dilution Calculations Stock (original) Dilute (new solution) M1V1 = M2V2 • M1 – Molarity of stock solution • V1 – Volume of stock solution (L or mL) • MD – Molarity of dilute solution • VD – Volume of dilute solution (L or mL)

  17. *In dilution calculations, the units for volume must be the same.

  18. 2.) Molarity - Dilution • Example #1: How much 12.0 M HCl is required to make 2.50 L of a 0.500 M solution? • Ms * Vs = MD * VD

  19. MS VS = MD VD or M1 V1= M2 V2 MS = 12.0 M HCl MD= 0.500 M HCl VS = ?? VD = 2.50 L (0.500 M HCl) (2.50 L) VS = (12.0 M HCl) = 0.104 L HCl

  20. 2.) Molarity - Dilution • Example #2: What volume of a 1.50 M solution can be made using 0.0250 L of 18.0 M H2SO4 ? • MS VS = MD VD

  21. MS VS = MD VD MS = 18.0 M H2SO4 MD= 1.50 M H2SO4 VS = .0250 L VD = ???? (.0250 L) (18.0 M H2SO4) VD= (1.50 M H2SO4) = 0.300 L H2SO4

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