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Concentration of solutions

Concentration of solutions. Day 4. 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. Molarity. Molarity (M)= mol solute L solution.

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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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