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II. Concentration

Ch. 13 & 14 - Solutions. II. Concentration. What is different between the glasses of Kool-aid?. Solution concentration can be described generally. Dilute - reduced in strength, weak, watered down. Concentrated – stronger, pure. Has less water.

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II. Concentration

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  1. Ch. 13 & 14 - Solutions II. Concentration

  2. What is different between the glasses of Kool-aid?

  3. Solution concentration can be described generally • Dilute - reduced in strength, weak, watered down. • Concentrated – stronger, pure. Has less water.

  4. What is the problem with just using dilute and concentrated as descriptions of the solution concentration?

  5. Concentrated Dilute Solution A Solution B Solution C Is solution B dilute or concentrated? • The terms dilute and concentrated are relative. • Scientists need a more precise way of referring to the concentration of a solution.

  6. Solution concentration can be described specifically • Do you remember the “mole” from Stoichiometry? • What is a mole? • How might you use it to describe the concentration of a solution?

  7. A. Concentration • The amount of solute in a solution. • Describing Concentration • % by mass - medicated creams • % by volume - rubbing alcohol • ppm, ppb - water contaminants • molarity - used by chemists • molality - used by chemists

  8. Molarity The ratio of the moles of solute to the volume of solution in liters. Moles of solute Molarity (M) = Volume in Liters of Solution

  9. How to read Molarity • 6.0 M NaCl • Read: “6 molar solution of NaCl” • Can be abbreviated 6M solution • You must be careful to label the molarity with a capital M so that it is not confused with m for molality.

  10. How to make a 6M NaCl solution using molarity (a) Add 6 moles NaCl to the volumetric flask. How would you measure that? 6 molesNaCl 58.443 g NaCl 1 mole NaCl = 351 g NaCl

  11. How to make a 6M NaCl solution using molarity (b) Add distilled or deionized H2O to dissolve and mix the NaCl (c) Fill the flask with dH2O until you reach the 1000mL line.

  12. Types of Calculations with Molarity: 1. Finding concentration of a solution.2. Finding the mass of solute needed.3. Finding the volume of solution made.

  13. Finding Concentration • Antifreeze is a solution of ethylene glycol, C2H6O2 in water. If 4.50 L of antifreeze contains 27.5 g of ethylene glycol, what is the concentration of the solution? 27.5 g C2H6O2 1 mol C2H6O2 4.5 L 62.08 g C2H6O2 = 0.0984 mol/L or 0.0984 M C2H6O2

  14. Finding Mass • What mass of sodium carbonate, Na2CO3, is present in 50 ml of a 0.750M solution? Conversion Factor 1 L 50 ml 105.99 g Na2CO3 0.750 mol 1000 mL 1 mol Na2CO3 1 L = 3.97 g Na2CO3

  15. Finding Volume Conversion Factor • What volume of 1.50 mol/L HCl solution contains 10.0 g of hydrogen chloride? 10.0 g HCl 1 L 1 mol HCl 36.46 g HCl 1.50 mol = 0.183 L or 183 mL

  16. Practice Problems

  17. Practice Problems 1. A 0.750 L aqueous solution contains 90.0 g of ethanol, C2H5OH. Calculate the molar concentration of the solution in mol/L.

  18. Practice Problem 2. What mass of NaCl are dissolved in 152 mL of a solution if the concentration of the solution is 0.364 M?

  19. Practice Problem 3. What mass of dextrose, C6H12O6 is dissolved in 325 mL of 0.258 M solution?

  20. Practice Problem 4. A mass of 98 g of sulfuric acid, H2SO4, is dissolved in water to prepare a 0.500 M solution. What is the volume of the solution?

  21. Practice Problem 5. A solution of sodium carbonate, Na2CO3, contains 53.0 g of solute in 215 mL of solution. What is its molarity?

  22. Practice Problem 6. What is the molarity of a solution of HNO3 that contains 12.6 g of solute in 5.00 L of solution?

  23. mass of solvent only 1 kg water = 1 L water B. Molality

  24. B. Molality • Find the molality of a solution containing 75 g of MgCl2 in 250 mL of water. 75 g MgCl2 1 mol MgCl2 95.21 g MgCl2 0.25 kg water = 3.2m MgCl2

  25. B. Molality • How many grams of NaCl are req’d to make a 1.54m solution using 0.500 kg of water? 0.500 kg water 1.54 mol NaCl 1 kg water 58.44 g NaCl 1 mol NaCl = 45.0 g NaCl

  26. Practice Problem What is the molality of a solution made from 2.4 moles of NaCl and 0.80 kg of water?

  27. Practice Problem What is the molality of a solution made from 63 g of HNO3 in 0.50 kg of water?

  28. Practice Problem How much water is needed to make a 0.50 m solution from 3.2 g of NaCl?

  29. Practice Problems What mass of CH3OH is needed to add to 1.20 kg of water to make a 3.00 m solution?

  30. C. Dilution • Preparation of a desired solution by adding water to a concentrate. • Moles of solute remain the same.

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

  32. Dilution Practice Water is added to 200. mL of a 2.0 M solution of CaCl2 to increase the volume of the solution to 400. mL. What is the new concentration?

  33. Dilution Practice To what volume must 1.0 L of a 6.0 M solution of HCl be diluted in order to prepare a 0.2 M solution?

  34. 500 mL of 1.54M NaCl 500 mLwater 500 mL volumetric flask 500 mL mark 45.0 gNaCl D. Preparing Solutions • 1.54m NaCl in 0.500 kg of water • mass 45.0 g of NaCl • add water until total volume is 500 mL • mass 45.0 g of NaCl • add 0.500 kg of water

  35. 95 mL of15.8M HNO3 250 mL mark water for safety D. Preparing Solutions • 250 mL of 6.0M HNO3by dilution • measure 95 mL of 15.8M HNO3 • combine with water until total volume is 250 mL • Safety: “Do as you oughtta, add the acid to the watta!”

  36. Turn in one paper per team. Complete the following steps: A) Show the necessary calculations. B) Write out directions for preparing the solution. C) Prepare the solution. For each of the following solutions: 1) 100.0 mL of 0.50M NaCl 2) 0.25m NaCl in 100.0 mL of water 3) 100.0 mL of 3.0M HCl from 12.1M concentrate. Solution Preparation Lab

  37. 500.O ml of 0.50 M NaCl • Remember: 0.50 M = 0.50 mole/1 Liter • Convert 0.50 moles to grams of NaCl • 0.50 mole NaCl = 29.23 grams but this is in 1 liter • Figure out how much you need for 0.1 L • Set up a proportion. 29.23g = x 1 L 0.5 L • X = 14.62 g, measure this amount on a balance and add to a volumetric flask. • Then fill with distilled water to the 500 ml mark.

  38. 0.25 mNaCl in 100 ml of water • Remember: 0.25 m = 0.25 moles/1kg of water • Convert 0.25 moles to grams. • 0.25 moles = 14.61 grams – this is in 1 kg of water. • Figure out how much you need for 0.100 kg of water. • 1kg = 1L • Set up a proportion. 14.61 g = x 1 kg 0.100 kg • X = 1.461 g, measure this amount on a balance and add to a flask. • Then measure out 100 ml of water in a graduated cylinder. Add this volume of water to the flask containing the NaCl.

  39. How do you make a 100.0 mL solution with a concentration of 3.0 M HCl from 12.1M concentrate • This is a dilution problem because you have 2 different concentrations. • Solve for the first volume: (12.1)(V1) = (3.0)(0.100) • V1 = 0.025 L or 25 mL • Measure out 25 mL of HCl in a graduated cylinder • In a 100 mL volumetric flask, add about 50 mL of water then slowly pour the 25 mL of HCl into the flask. Then add the remaining volume of water to the 100 ml mark.

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