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Solution Concentration

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  1. Solution Concentration

  2. Review • A solution is a homogeneous mixture. • The solvent is the major component of the solution. • The solute is the minor component and active ingredient. • A saturated solution holds the maximum amount of solute that is theoretically possible for a given temperature.

  3. How would you describe this picture?

  4. Solution Concentration • Is one glass of tea stronger than the other? • What’s true about the “stronger” glass of tea? • How much tea does it have in it compared to the other glass?

  5. Solution Concentration • Concentration – a ratio comparing the amount of solute to the amount of solution. • Many ways of expressing concentration: • % by weight (% w/w) • % by volume (% v/v) • parts per million (ppm) or parts per billion (ppb) for very low concentrations • molality (m) • Molarity (M)

  6. Concentrated vs. Dilute • The words “concentrated” and “dilute” are opposites. • EX: The dark tea is more concentrated than the light tea. • EX: The light tea is more dilute than the dark tea.

  7. = solute particles Dilute solution Concentrated solution Concentrated vs. Dilute

  8. Percent by Weight • % by weight (% w/w) • What is the % w/w of a solution if 3.00 grams of NaCl are dissolved in 17.00 g of water? • mass of solute = 3.00 g • mass of solution = 3.00 g + 17.00 g = 20.00 g • (3.00 g / 20.00 g) x 100% = 15.0% w/w

  9. Percent by Volume • % by volume (% v/v) • What is the % v/v of a solution if 20.0 mL of alcohol are dissolved in 50.0 mL of solution? • volume of solute = 20.0 mL • volume of solution = 50.0 mL • (20.0 mL / 50.0 mL) x 100% = 40.0%

  10. Molarity • Molarity (M) • UNITS: mol/L or Molar (M) • Example: 0.500 mol/L = 0.500 M

  11. Molarity • What is the Molar concentration of a sol’n if 20.0 grams of KNO3 (MM = 101.11 g/mol) is dissolved in enough water to make 800. mL? • Convert g of KNO3 to mol of KNO3 • Convert mL to L

  12. Molarity • What is the Molar concentration of a sol’n if 0.198 mol KNO3 is dissolved in enough water to make 0.800 L?

  13. Molarity • What is the Molar concentration of a sol’n if 10.5 grams of glucose (MM = 180.18 g/mol) is dissolved in enough water to make 20.0 mL of sol’n? • Convert g of glucose to mol of glucose. • Convert mL to L.

  14. Molarity • What is the Molar concentration of a sol’n if 0.0583 mol of glucose is dissolved in enough water to make 0.0200 L of sol’n?

  15. Calculating Grams • How many grams of KI (MM = 166.00 g/mol) are needed to prepare 25.0 mL of a 0.750 M solution? • Convert mL to L. • Solve for moles. • moles of KI = 0.750 M x 0.0250 L = 0.0188 mol KI

  16. Calculating Grams • How many grams of KI (MM = 166.00 g/mol) are needed to prepare 25.0 mL of a 0.750 M solution? • Convert 0.0188 mol KI to grams.

  17. Calculating Grams • How many grams of HNO3 (MM = 63.02 g/mol) are present in 50.0 mL of a 1.50 M sol’n? • Convert mL to L. • 50.0 mL = 0.0500 L • Solve for moles: • moles = (1.50 M)(0.0500 L) = 0.0750 mol HNO3 • Convert 0.0750 mol HNO3 to grams: • 0.0750 mol HNO3 = 4.73 g HNO3

  18. Dilution • Dilute (verb) - to add solvent to a solution. • Decreases sol'n concentration. • M1V1 = M2V2 • M1 = initial conc. • V1 = initial volume • M2 = final conc. • V2 = final volume • Assumes no solute is added.

  19. Stock Solution Impractically High Concentration Usable Solution Add H2O Dilution Question for Consideration: Why do you think chemical supply companies typically sell acids (and other solutions) in extremely high concentrations when it would be safer to ship more dilute solutions?

  20. Dilution • To what volume should 40.0 mL of 18 M H2SO4 be diluted if a concentration of 3.0 M is desired? • What do we want to know? • V2 • What do we already know? • M1 = 18 M • V1 = 40.0 mL • M2 = 3.0 M • (18 M)(40.0 mL) = (3.0 M)V2 • 720 M*mL = (3.0 M)V2 • V2 = 240 mL

  21. Dilution • You are asked to prepare 500. mL of 0.250 M HCl, starting with a 12.0 Molar stock sol'n. How much stock should you use? • What do we want to know? • V1 • What do we already know? • M1 = 12.0 M • M2 = 0.250 M • V2 = 500. mL • (12.0 M) V1 = (0.250 M)(500. mL)‏ • (12.0 M) V1 = 125 M*mL • V1 = 10.4 mL

  22. Dilution • To how much water should you add 20.0 mL of 5.00 M HNO3 to dilute it to 1.00 M? • What do we want to know? • How much water to add. (V2 - V1)‏ • What do we already know? • M1 = 5.00 M • V1 = 20.0 mL • M2 = 1.00 M • (5.00 M)(20.0 mL) = (1.00 M) V2 • 100. M*mL = (1.00 M) V2 • V2 = 100. mL • Water added = 100. mL - 20.0 mL = 80. mL