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Unit 7: Solution Chemistry Chapter 13

Unit 7: Solution Chemistry Chapter 13. Chemistry CPA April 2014. Water: The “Universal Solvent”. Water is referred to as the “universal solvent” because it’s really good at dissolving a vast variety of substances. . Water is a Polar Molecule.

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Unit 7: Solution Chemistry Chapter 13

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  1. Unit 7: Solution ChemistryChapter 13 Chemistry CPA April 2014

  2. Water: The “Universal Solvent” • Water is referred to as the “universal solvent” because it’s really good at dissolving a vast variety of substances.

  3. Water is a Polar Molecule • Water is a polar molecule which means it has a “negative” end and a “positive” end • The “charged” ends of water help “dissociate” (pull apart) other molecules through attractive forces

  4. Hydrogen Bonding • Hydrogen bonding: helps water dissociate covalent compounds • When atoms of hydrogen are strongly attracted to electronegative atoms on another molecule (specifically oxygen, nitrogen, and fluorine) they make a connection to one another that acts as a bond.

  5. Solution Formation • A solution consists of a solute and a solvent • Solute: lesser amount of particles that gets dissolved • Solvent: greater amount of particles that “do” the dissolving. • Examples include: • Sugar and tea– sugar is the solute, water/tea the solvent • Medicine and your blood stream – medicine is the solute, blood is the solvent

  6. What affects the rate of a solution’s formation? • Solution formation is chemical term for “dissolving” • Stirring – aka “agitation” Stirring continually brings solutes into contact with solvent, speeding up solution formation. • Temperature Higher temperature means higher kinetic energy – particles move more quickly and collide with one another to speed up solution formation • Particle Size Smaller particle size = quicker solution formation

  7. Solubility – How does it work? • Dissolving all happens due to the kinetic energy of ALL particles involved in the solution. • Solvent particles are constantly “bumping into” solute particles, breaking their bonds, and ultimately separating the solute into smaller pieces. • Solubility – amount of solute that dissolves in a given quantity of a solvent at a specified temperature and pressure. Solubility is expressed in grams of solute per 100g of solvent.

  8. Concentration • Is the ratio of solute to solvent • If something is very concentrated, there is much more solute than solvent. • If something is very un-concentrated (i.e., “watered down” kool-aid), there is much more solvent than solute.

  9. Three expressions of solution concentration: • Saturated • Unsaturated • Supersaturated

  10. Saturated Solution • contains the maximum amount of solute for a given quantity of solvent at standard temperature and pressure.

  11. Unsaturated Contains less solute than a saturated solution at standard temperature and pressure.

  12. Supersaturated • Contains more solute than a solvent can theoretically hold. • You will have solid particles left over at the bottom of the container that won’t dissolve.

  13. How can you make a saturated solution unsaturated? Add more solvent; Add more water; dilute the solution

  14. How can you make a saturated solution supersaturated? • Add more solute

  15. Miscible vs. Immiscible • Miscible • two liquids that dissolve in each other in all proportions. • “Like dissolves Like” – polar and polar dissolve one another; nonpolar and nonpolar dissolve on another. • Example – ethanol and water, both polar molecules • Immiscible • liquids that are not soluble. • Polar and nonpolar substances repel one another and do not dissolve • Example – oil (nonpolar) and water (polar), oil (nonpolar) and vinegar (polar)

  16. Miscible vs. immiscible

  17. Solubility Curve • x-y graph showing solubility vs. temperature • Solubility is on the y-axis, expressed in grams/100g. of solvent • Temperature is on the x-axis, expressed in °C • On the curve = saturated solution. • Under the curve = unsaturated solution. • Above the curve – supersaturated solution.

  18. Solubility Curve Calculations • Solubility is grams of solute/100 g of solvent. Solubility = g. solute 100 g. of solvent What if a problem asked you to find how many grams of a solute you would need to dissolve into 200 g of solvent? 300 g of solvent?

  19. Solubility Curve 1. How many grams of KCl can be dissolved at 40°C?

  20. Solubility Curve 2. How many grams of KCl can be dissolved at 80°C?

  21. Solubility Curve 3. At 10°C, 20 grams of KCl is added to 100 grams of water. Is this solution saturated, unsaturated, supersaturated?

  22. Solubility Curve 4. At 10°C, 30 grams of KCl is added to 100 grams of water. Is this solution saturated, unsaturated, supersaturated?

  23. Solubility Curve 5. At 10°C, 50 grams of KCl is added to 100 grams of water. Is this solution saturated, unsaturated, supersaturated?

  24. Solubility Curve 6. Using your answer from #5, how many grams of KCl will settle to the bottom?

  25. Solubility Curve 7. At 10°C, how many grams of KCl are need to make a saturated solution in 200 grams of water?

  26. Solubility Curve 8. At 10°C, how many grams of KCl are need to make a saturated solution in 300 grams of water?

  27. What is the solubility of KNO3 at 20⁰C? • You dissolve 30 g of KCl in water at a temperature of 20⁰C. Is the solution unsaturated, saturated, or supersaturated? • Suppose you wanted to make a perfectly soluble solution of NaCl in 200 grams of water at 90⁰C. How many grams of NaCl would you need? • Which salt shows the least change in solubility from 0 ⁰C to 100 ⁰C? • Which salt shows the greatest change in solubility from 0 ⁰C to 100 ⁰C? • What general affect does increasing temperature have on the solubility of a substance?

  28. Concentration of Solutions • Used to describe the ratio of solute to solvent. • Three common ways to express concentration in chemistry: • Molarity – overall, molar mass-based concentration. Used on stock chemicals. • molality – can use just a scale! • % solution – used on household products; doesn’t use molar masses.

  29. Molarity • Defined as moles of solute per 1 liter of solution • *Note that the volume is the total volume that results, not the volume of the solvent alone. • The unit for molarity is M and is read as "molar."   (i.e. 3 M = three molar) • Equation: M = moles of solute_ Volume (Liters of solution)

  30. Solve for Molarity • What is the molarity of a 5.00 liter solution that was made with 10.0 moles of  KBr ?

  31. Solve for Volume What would be the volume of a 2.00 M solution made with 6.00 moles of LiF?

  32. Solve for Volume •                                 # of moles of soluteLiters of solution =   --------------------                                        Molarity • Given:  # of moles of solute = 6.00 moles           Molarity = 2.00 M (moles/L) • Liters of solution = 6.00 moles                               -----------                               2.00 moles/L • Answer = 3.00 L of solution

  33. Solve for molesIII. Basic molarity problems where the number of moles/grams of solute is the unknown. • How many moles of CaCl2 would be used in the making of 0.500 L of a 5.0M solution?

  34. # of moles of solute = Molarity x Liters of solution Given: Molarity = 5.0 M (moles/L)           Volume = 0.500 L # of moles of CaCl2 = 5.0 moles/L x 0.500 moles Answer = 2.5 moles of CaCl2

  35. IV. Given grams instead of moles Convert grams to moles •                      mass given# of moles = -----------------                    Molar mass

  36. Solve for Volume (and convert to moles) What is the volume of 3.0 M solution of NaCl made with 526 g of solute?

  37. Convert to moles Solution: First find the molar mass of NaCl. Na = 23.0 g x 1 = 23.0 gCl = 35.5 g x 1   = 35.5 g                                                 =58.5 g Convert to moles                      mass of sample# of moles = -----------------                      Molar mass                                    526 g# of moles of NaCl = ------------                                   58.5 g Answer:  # of moles of NaCl = 8.99 moles

  38. Example 2.  What is the volume of 3.0 M solution of NaCl made with 526g of solute? Finally, go back to your molarity formula to solve the problem:                               # of moles of soluteLiters of solution =   ------------------------------                                        Molarity Given:  # of moles of solute = 8.99 moles           Molarity of the solution = 3.0 M (moles/L)                                      8.99 moles# of Liters of solution = -------------                                     3.0 moles/L Final Answer = 3.0 L

  39. Solve for moles and then convert to grams • How many grams of CaCl2 would be used in the making 0.500 L of a 5.0M solution?

  40. Molarity by Dilution • Dilution is the process of decreasing the concentration of a stock solution by adding more solvent (usually water).

  41. Dilution Equation M1V1 = M2V2 Where: M1 is the Molarity of the stock solution V1 is the volume of the stock solution M2 is the Molarity of the diluted solution V2 is the volume of the diluted solution • The general purpose of the dilution equation is to find out the volume needed to dilute a stock solution to a desired (lower) concentration. • But - You will be given any three (3) of the four variables and be asked to solve for the missing one.

  42. Dilution Example #1 A stock solution of 1.00M of NaCl is available. How many milliliters are needed to make a 100.0 mL of 0.750M? • M1 = ______ M x _____ L = ______M x ______ L • V1 = ______ = ______ x ______ • M2 = _____ • V2 = ______

  43. Dilution Example #2 • Concentrated HCl is 12M. What volume is needed to make 2 L of a 1 M solution? • M1 = ______ M x _____ L = ______M x ______ L • V1 = ______ = ______ x ______ • M2 = _____ • V2 = ______

  44. Dilution Example #3 • Calculate the final concentration of a solution that was made by adding a 6 M/1L solution of NaOH to 2.5 L of water. • M1 = ______ M x _____ L = ______M x ______ L • V1 = ______ = ______ x ______ • M2 = _____ • V2 = ______

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