Lecture 16.2- Concentration

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Section 16.2 lecture for Honors & Prep chemistry

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Lecture 16.2- Concentration

  1. 1. BELLWORK 1. Which factors determine how much a solute dissolves in a given solvent? 2. Which factors affect the rate of dissolution? 3. How is solubility measured? 4. Define saturated and unsaturated
  2. 2. When salts dissolve in water, positive and negative ions are separated and surrounded by polar water molecules.
  3. 3. Concentration measures how much solute is in a solution concentrated dilute High Low Concentration Concentration
  4. 4. Concentrated Chemists need to quantify concentration WE NEED NUMBERS!!!
  5. 5. Exactly how much solute is in the solution? What units could we use to quantify the amount of solute? Grams, moles, liters, teaspoons, number of ions Is the amount of solute enough info to measure the concentration? 1 gram of salt. In 10mL or in 10L? We must specify the amount of solvent as well
  6. 6. Concentration is the amount of solute the amount of solution Concentration can be measured in many units solute . total solution
  7. 7. Concentration can be measured in many units Grams/Liter Percent concentration by volume  %(v/v) Percent concentration by mass  %(w/w) Parts per million  ppm Molarity  M
  8. 8. Grams/Liter A solution with a concentration of 0.75g/L contains 0.75g of solute in every 1 liter How much solute is in 6.2L of the solution? 6.2 L x 0.75g/L = 4.65grams
  9. 9. Grams/Liter A solution has a concentration of 0.75g/L How much solute is in 250mL of the solution? 0.25L x 0.75g/L = 0.19grams How much solution contains 10g of solute? 10g x 1L = 13.33L 0.75g
  10. 10. Percent concentration by volume  %(v/v) %(v/v) = volume of solute x 100% volume of solution Hydrogen peroxide solutions are 3% H2O2 by volume. How much H2O2 is in a 500mL bottle? How much water? 500mL x 0.03 = 15mL 500ml solution – 15ml solute = 485ml solvent
  11. 11. Percent concentration by mass  %(w/w) %(w/w) = mass of solute x 100% mass of solution Determine the mass % of a NaCl solution if 58.5 grams of NaCl was dissolved in 50 ml of water (assume the density of water to be 1 g/ml)
  12. 12. Determine the mass % of a NaCl solution if 58.5 grams of NaCl was dissolved in 50 ml of water (assume the density of water to be 1 g/ml) 1. Convert ml of water to grams mass = 50 ml X 1 g/ml = 50 grams water 2. Determine total mass of solution Mass of solution = mass of solute + mass of solvent = 58.5 + 50 = 108.5 g 3. Apply the definition of mass percent mass % = 58.5/ 108.5 x 100%= 53.9% NaCl
  13. 13. Parts per million  ppm Parts per million or ppm is used for very dilute (weak) solutions. It is like percent, except it is permillion! ppm = grams solute x 106 grams of solution Do #6 from worksheet
  14. 14. And the one used most in chemistry Molarity  M Molarity = moles/liter 2M HCl contains 2 moles of HCl in every liter. How many moles are in 56mL of 2M HCl? .056L x 2moles/L = 0.112moles HCl
  15. 15. M = moles/Liter M x V = moles moles/liter x liters = moles
  16. 16. Making a solution of known concentration Do #9a
  17. 17. 16.2 Making Dilutions Dilution = Adding more solvent to a solution Molarity = Moles Doesn’t change Liter increases Dilution decreases concentration Making the solution MORE DILUTE!!
  18. 18. 16.2 Making Dilutions M1 and V1 are the molarity and volume of the initial solution M2 and V2 are the molarity and volume of the diluted solution.
  19. 19. How much 10M HCl is needed to make 200mL of a 0.5M solution? 10M x V1 = 0.5M x .2L add 0.01L or 10ml

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