Solutions

1. Solutions

2. Solution = Solvent + Solute • Solvent: a substance that dissolves another substance • Or, the substance present in greater amount • Solute: a substance which is dissolved by another substance • Or, the substance present in lesser amount

3. Copper (II) Sulfate is dissolved in water to form a solution. Which substance is the solvent and which is the solute?

4. Water is sometimes called the “Universal Solvent” • It is the most common solvent in nature/biological systems • Why do you think water is such a good solvent? • Polarity • Hydrogen bonding

6. The positive end of water molecules are attracted to the negative part(s) of the solute • The negative end of water molecules are attracted to the positive part(s) of the solute • The attraction of water molecules to different parts of a solute is enough to break the solute apart

7. As each ion in the solute is drawn into solution, it is surrounded by water molecules • This process is called “solvation” • Solvation lessens the attraction of the solute ions to each other

8. If water is the universal solvent, then why does it not dissolve oil? • For a solution to form, the solvent and solute molecules must be attracted to each other • “Like Dissolves Like” • Polar solvents dissolve polar solutes • Nonpolar substances are attracted to other nonpolar substances, therefore nonpolar solvents will dissolve nonpolar solutes • Examples: I2, Hexane, Cooking Oils, Dichloromethane (CH2Cl2)

10. Problems • Identify the solute and solvent in solutions composed of the following: • 2.9g of NaCl and 200g H2O • 25.0mL of ethanol (a liquid) and 20.0mL H2O • 2.0g I2 and 20g Octane • Look at the pictures below. Explain why each substance will or will not dissolve in water.

11. Solubility • Solubility: the amount of solute that will dissolve in a specific solvent under given conditions • Polar solutes will be more soluble in polar solvents • Non-polar solutes will be more soluble in non-polar solvents • Amphiphilic solutes will be soluble in both polar and non-polar solvents • Have hydrophobic and hydrophilic regions • Example: Phospholipids

13. Solubility is expressed in g solute/100g solvent • Example: The solubility of Ethanol is 10g/100g H2O @ 23ºC • Unsaturated Solution: solution in which the solvent can dissolve more solute • Saturated Solution: solution in which the solvent cannot dissolve any more solute

14. When a solution is saturated, the rate of dissolution is the same as the rate of recrystallization/precipitation

15. Say we have a saturated sugar solution. How might we get even more sugar into the solution? • Heat it! • Solubilities of solids generally increase as the temperature increases

16. Supersaturated solution: an unstable solution which temporarily contains more dissolved solute than a normal saturated solution would at that specified temp

17. What about if you wanted to dissolve more oxygen in your water? Would you heat your water? • No! • The solubility of gases tend to decrease as the temperature is increased

19. So, how do you increase the solubility of gases in a liquid? • Decrease the temperature • Increase the pressure • Henry’s Law: the solubility of a gas in a liquid is directly proportional to the pressure of that gas above the liquid

20. Soluble and Insoluble Salts • How do you know that NaCl is soluble in water? • What about KBr? Is it soluble? • What about AgCl? • You can tell if a salt will be soluble or insoluble in water by looking up the cation and the anion on a solubility chart

22. Problems • Is the CO2,which is dissolved in soda, more or less soluble when you open the can? Why? • Which of the following is probably Ni(OH)2 in water? • Which is most likely Na2SO4 in water?

23. Problems Which of the following salts is soluble in water? Which is insoluble? • NaCl • KBr • AgCl

24. KBr NaCl AgCl

25. Problems Which of the following salts will be soluble in water? Which will be insoluble? • Ag2O • CdS • Fe(OH)2 • Na2SO4 • KCl

26. CdS Ag2O Fe(OH)2 Na2SO4 KCl

27. Concentrations • Concentration = amount solute/amount solution • There are various ways to express concentration • The most common way to express concentration is Molarity (M) • Molarity = moles solute/liters solution • Units: mol/L

28. Problems • You dissolve 5.66g KBr in enough H2O to make 27mL of solution. What is the molarity of your solution? • You dissolve 2.45 mg of CuSO4 in enough water to make 55.5 mL of solution, what is your concentration? • If you have 60.0 mL of a 0.988 M NaCl solution, how much NaCl did you start with?

29. Problems • Mass-volume percent (% m/v): mass of the solute divided by the volume of solution and multiplied by 100 • % m/v =(mass solute)/(volume solution) x 100 • Also defined as mass of solute per 100 ml of solution • Usually expressed in g/ml • You dissolve 5.66g KBr in enough H2O to make 27mL of solution. What is the mass/volume percent for the previous solution? • You dissolve 4.44 g NaCl in enough water to make 0.075 L of solution. What is the mass-volume percent? • You have a % m/v of 3.98 NaBr in 350 ml of solution. How much NaBr was used to make this solution?

30. Problems • Percent by Mass (%m/m): mass of solute in mass of solution multiplied by 100 • Mass % = mass solute/mass solution x 100 • Remember: mass solution=mass solute + mass solvent • Also defined as the number of grams of solute per 100g of solution • You make a solution by dissolving 7.55 g NaCl in 52.4g H2O. What is the mass % of solute in this solution? • You make a solution by dissolving 2.45 g KCl in 20.6mL of water. What is the mass % of solute in this solution? • You have a %m/m of 10.0% sucrose. If you used 25.0 g sucrose to make the solution, how much solvent (water) did you use?

31. Percent by volume (% v/v): volume of solute divided by volume of solution multiplied by 100 • VP = volume solute/volume solution x 100 • Units of volume must be the same for both solute and solvent Problems • You dissolve a 5 cm3 cube of sugar in 20mL of water. What is your volume percent of solute in this solution? • Your bottle of Jack Daniels says that the alcohol content is 14%. What does this mean?

32. More Problems • Your child has an ear infection and is given a suspension of 5.0 % (m/v) amoxicillin. How many grams of the antibiotic is she given in 10mL? • How many milliliters of a 4.0% (m/v) drug are needed if the patient is to receive 0.250g?

33. Dilutions • Dilution: the process by which more solvent is added to a solution in order to lower the concentration • C1V1 = C2V2 • C = Concentration • V = Volume

34. Problems • Joan has 50 mL of a 0.498 M glucose solution. She’d like to dilute this to a 0.250 M glucose solution. What will her final volume be? • A nurse wants to prepare a 1.0% (m/v) silver nitrate solution from 24 mL or a 3.0% stock solution of silver nitrate. How much water should be added to the 24 mL? • Mary has a 2.5 L bottle of a 0.989 M NaOH solution. She would like to make 525 mL of a 0.755 M NaOH solution. How will she do this?

35. Mixtures • Heterogeneous Mixture: a mixture in which the particles of each component remain separate and can be observed as individual substances • See distinct phases • See interface • Solute particle size above 200nm

37. Homogeneous Mixture: a mixture in which the composition is the same throughout • Only one phase present • Cannot see interface • Particle size less than 1nm • Often called “solutions”

39. Colloids • Mixtures with properties intermediate between heterogeneous and homogeneous mixtures • Particles tend to be small enough to pass through filters, but too large to pass through semipermeable membranes (1nm-200nm) • Particles are large enough to scatter light, producing a phenomenon called the Tyndall effect • Examples: Jell-O, Fog, Dust in air, Mayo

40. The Tyndall Effect • Named after the Irish scientist John Tyndall • Describes the light scattering effect cause by particles in a colloid • Can see the beam of light • Can see the particles in the colloid • Used to distinguish colloids from other types of mixtures

41. Suspensions • Heterogeneous mixtures which contain particles which are large enough to be trapped by filters and semipermeable membranes, but small enough to stay suspended for a while before settling out. • Examples: Muddy water, liquid medications, paint • Most things that direct you to shake or stir before using

42. Osmosis • The movement of water, through a semipermeable membrane, from regions of low solute concentration to regions of higher solute concentration • Spontaneous • The membrane must be permeable to the solvent, but not the solute

43. Movement of water to one side of the permeable membrane causes osmotic pressure • Osmotic Pressure is defined as the force per unit area that prevents water from passing through a membrane

44. In living systems, osmotic pressure is called turgor • Pressure of intracellular water and other contents press up against the cell membrane causing the cell to expand • Plant cells are prevented from rupturing by their cell walls • Allows plants to stand upright

45. What problems does osmosis present to aquatic and marine life?

46. Hypotonic solution: a situation in which the concentration of solute(s) is higher inside the membrane/cell than in the surrounding solution • Water flows into the cell by osmosis • Causes turgor and/or cell lysis • Hypertonic solution: a situation in which the concentration of solute(s) is lower inside the membrance/cell than in the surrounding solution • Water flows out of the cell by osmosis • Causes cell shrinkage called crenation

47. Isotonic solution: a situation in which the solute concentrations on the inside and outside of a membrane/cell are equal • There in no NET movement of water • Also called “Physiological Solutions”