Solutions

1. Solutions • Types of Aqueous Solutions • Solubility • Concentration • Colligative Properties of Solutions

2. Parts of a Solution A solution consists of two parts. Solute – the substance that is being dissolved. Solvent– the substance that is doing the dissolving.

3. Types of Solutions An aqueous solution is one in which water is the solvent. A tincture is one in which alcohol is the solvent. Identify the solute and solvent in each of the following: Salt water 0.5 M Lead(II) nitrate Solute: salt Solvent: water Solvent: water Solute: Lead(II) nitrate

4. Types of Aqueous Solutions There are several different ways in which aqueous solutions can be further classified. Solutions can be classified as acidic, basic, or neutral. Solutions can also be classified as electrolytic or nonelectrolytic.

5. Acidic, Basic and Neutral Solutions All solutions contain hydronium ions (H3O+)* and hydroxide ions (OH-). *The hydronium ion and the hydrogen ion (H+) are often used interchangeably. A solution is classified as acidic, basic or neutral by comparing the number of hydronium ions in solution with the number of hydroxide ions, by determining the pH of the solution, or by using indicators.

6. [H3O+] versus [OH-] Acidic Solutions: [H3O+] > [OH-] This means that the [H3O+] is greater than 10-7M. Basic Solutions: [H3O+] < [OH-] This means that the [OH-] is greater than 10-7 M. Neutral Solutions: [H3O+] = [OH-] This means that both the [H3O+] and the [OH-] are equal to 10-7 M?

7. The pH Scale The pH of a solution can be measured using a pH meter or by estimating it with an indicator. The pH scale ranges from 0-14. Acidic solution: pH < 7 Basic solution: pH > 7 Neutral solution: pH = 7

8. Indicators Indicators can also be used to classify solutions as acidic, basic or neutral. Indicators change color in acids and bases. One common indicator is litmus paper. Blue litmus paper turns red in acidic solutions. Red litmus paper turns blue in basic solutions.

9. Summary of Acidic, Basic, and Neutral Solutions Examples of Acids: HCl, HNO3, HF Examples of acidic solutions/mixtures: Gastric juice (1.0-3.0) Lemons (2.2-2.4) Soft Drinks (2.0-4.0) Bread (5.0-6.0) Examples of common bases: NaOH, NH3, Example of basic solutions/mixtures: Household Ammonia (11.0) Eggs (7.6-8.0) Hand soap (10) Baking soda (8.5) Example of neutral solutions/mixtures: Salt Water Sugar Water Pure Water Acidic Solution [H3O+] > [OH-] pH < 7 Basic Solution [H3O+]<[OH-] pH > 7 Neutral Solution [H3O+]=[OH-] pH = 7

10. Acidic, Basic & Neutral Solutions Which of the following substances is the most acidic? Most basic? Ammonia, pH = 11 Milk, pH = 6.6 Vinegar, pH = 2.2 Vinegar is the most acidic. Ammonia is the most basic.

11. Electrolytes An electrolyte is a substance that dissolves in water to produce a solution that conducts an electric current. Acids, bases, and salts (ionic compounds) are electrolytes. A conductivity tester can be used to determine if a solute is an electrolyte or nonelectrolyte.

12. Strong Electrolytes A strong electrolyte is a substance that completely ionizes in water. A strong electrolyte will cause the bulb of a conductivity tester to glow brightly. Soluble Ionic compounds, strong acids (HClO4, HClO3, HCl, HBr, HI, HNO3, H2SO4), and strong bases (LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2, and Ba(OH)2) are strong electrolytes.

13. Weak Electrolytes A weak electrolyte is a substance that only partially ionizes in water. A weak electrolyte will cause the bulb of a conductivity tester to glow dimly. Weak acids and bases are examples of weak electrolytes. An example of a weak electrolyte is acetic acid.

14. Nonelectrolytes A nonelectrolyte is a substance that dissolves in water to produce a solution that does not conduct an electric current. A nonelectrolyte will not cause the bulb of a conductivity tester to glow. Many molecular (covalent) compounds such as sugar are nonelectrolytes. They do not ionize in water.

15. Classify each of the following substances as an electrolyte or nonelectrolyte. Explain your answer. Electrolyte, it is an ionic compound. Lithium chloride Glucose, C6H12O6 Sulfuric Acid, H2SO4 Sodium hydroxide, NaOH Propanol, C3H7OH Nonelectrolyte, it is a covalent compound. Electrolyte, it is an acid. Electrolyte, it is a base. Nonelectrolyte, it is a covalent compound called an alcohol.

16. Solvation The water molecules collide with the surface of the solid solute There is an attraction between the solute and solvent molecules. Solvation is the process of dissolving an ionic solute. The solute particles are separated from the surface of the solid solute. The solvent molecules surround the solute particles. The steps occur continuously as each surface layer of solute molecules is dissolved, leaving the next layer exposed to the solvent.

17. Factors Affecting the Rate of Solution Formation Stirring (Agitation) or shaking the solution helps move the solute particles away from the solid solute faster. This brings more particles of the solute in contact with the solvent sooner causing the solute to dissolve at a faster rate.

18. Factors Affecting the Rate of Solution Formation Powdering the solid solute increases the amount of surface area. More solute particles are in contact with the solvent when the solid solute is ground into a fine powder.

19. Factors Affecting the Rate of Solution Formation If heat is applied to a solution, the molecules move faster and farther apart causing more collisions between the solute and solvent. This helps to separate the solute particles form one another and to disperse them among the solvent particles.

20. Solubility Solubility is a measure of how much of a solute can be dissolved in a given amount of solvent at a given temperature. The units for solubility are g/100 mL of H2O, g/100 g H2O or for a gas, g/L.

21. The Universal Solvent Water is known as the universal solvent because of its ability to dissolve so many substances. Water has the ability to dissolve so many substances because it is a polar molecule.

22. Predicting Solubility The solubility of one substance in another is in part predicted by the polarity of the molecules involved. Polar and ionic compounds are soluble in water. The charged ions or polar solute molecules are attracted to the polar ends of the water molecules, holding each other together in solution.

23. Predicting Solubility A nonpolar molecule has an even charge distribution and are not attracted to the polar water molecules. If a nonpolar substance such as oil is mixed with a polar solvent such as water, the nonpolar molecules slip from between the polar molecules as the polar molecules attract each other. This causes the formation of two distinct layers upon standing, as seen with an oil and vinegar salad dressing.

24. “Like Dissolves Like” The general rule is “Like Dissolves Like” Polar solvents, like water, can dissolve polar and ionic solutes. Nonpolar solvents can dissolve nonpolar solutes.

25. Classify each of the following as soluble or insoluble in water. Justify your answer. LiCl NH3 C6H6 Soluble, LiCl is an ionic compound. Soluble, NH3 is a polar covalent compound. Insoluble, C6H6 is a nonpolar covalent compound.

26. Factors Affecting Solubility Pressure For gases dissolved in liquids, an increase in pressure increases solubility and a decrease in pressure decreases solubility. Increasing and decreasing pressure has no effect on the solubility of solid and liquid solutes.

27. Henry’s Law Henry’s Law state that at a given temperature the solubility of a gas in a liquid is directly proportional to the pressure above the liquid.

28. If the solubility of a gas in water is 2.80 g/L at 2.5 atm of pressure, what is the solubility, in g per L at 1.0 atm of pressure? The temperature is held constant at 25°C.

29. Factors Affecting Solubility Temperature Generally, an increase in the temperature of a solution increases the solubility of solid solute in a liquid solvent. Decreasing the temperature of a solution increases the solubility of a gas in a liquid.

30. Reading Solubility Graphs A solubility graph indicates the amount of solute that will dissolve in 100 mL (100 g) of water.

31. Reading Solubility Graphs Use the solubility graph at the right to answer the following questions. What is the solubility of ammonium chloride at 80°C? 65 g NH4Cl/100 mL H2O Which is more soluble at 60°C, potassium nitrate or sodium nitrate? Sodium nitrate How many grams of sodium chloride will dissolve in 250 mL of water at 90°C? x = 100 g

32. Reading Solubility Graphs If you added 170 grams of potassium iodide to 100 mL of water at 20°C would all of the potassium iodide dissolve? Why or why not? It would not all dissolve. The solubility is only 145 g KI/100 mL water at that temperature. If not, how much potassium iodide would be left undissolved? 25 g

33. Saturated Solutions A saturated solution is a solution in which the dissolved substance is in equilibrium with the undissolved substance. A saturated solution contains the maximum amount of solute it can hold at a given temperature. If more solute is added, it will settle undissolved at the bottom of the solution. How many grams of potassium chlorate must be added to 100 mL of water to make a saturated solution at 60°C? ≈ 27 g

34. Unsaturated Solutions An unsaturated solution contains less solute than a saturated solution under the same conditions. If more solute is added, it will dissolve. If you dissolve less than _____ g of potassium iodide in 100 mL of water at 20°C, the solution will be unsaturated. 145

35. Supersatured Solutions A supersaturated solution contains more solute than a saturated solution under the same conditions. If a single crystal of solute is added to a supersaturated solution, the excess solute comes out of the solution and settles on the bottom. Crystallization may occur. http://www.edutube.org/en/video/sodium-acetate-sculptures-hot-ice Examples include rock candy, hand warmers

36. Supersatured Solutions How could a student make a supersaturated solution of sugar water in order to make rock candy? The student would make a saturated solution at a higher temperature and then allow it to cool.

37. Saturated, Unsaturated and Supersatured Solutions How could you experimentally determine if a solution is saturated, unsaturated, or supersaturated? Add more solute. If it dissolves, the original solution was unsaturated. If it crystallizes or causes more solute to come out of solution, it was supersaturated. If it sinks to the bottom, it was unsaturated.

38. Concentration of Solutions The concentration of a solution refers to the amount of solute dissolved in a given amount of solvent or solution. Concentrated Solution - contains a relatively large amount of solute in a solvent Dilute Solution – contains a relatively small amount of solute in a solvent

39. Concentration of Solutions The terms concentrated and dilute are unrelated to the degree to which a solution is saturated. Why? A saturated solution of a substance that is not very soluble might be very dilute.

40. Molarity Molarity (M) expresses concentration in terms of moles of solute per liter of solution

41. Molarity – Example Problems a. What is the molarity of a solution if 10.0 L of it contains 2.5 moles of solute?

42. Molarity – Example Problems b. How many moles of solute are in 0.50 L of 1.5 M solution? mol M L

43. Molarity – Example Problems c. A solution is prepared by dissolving 80.0 g of NaCl in enough water to give a total volume of 2.00 L. Calculate the molarity of the solution. First calculate the number of moles of NaCl.

44. How would you prepare 1.0 L of a 0.500 M solution of copper(II) Sulfate Pentahydrate?

45. Stoichiometry Problems Involving Molarity a. How many moles of copper are consumed when a long coil of the wire is immersed in 350 mL of 0.100 M silver nitrate solution? Cu(s) + 2AgNO3(aq) → Cu(NO3)2(aq) + 2Ag(s)

46. Stoichiometry Problems Involving Molarity b. In a car battery, lead(IV) oxide and sulfuric acid react to produce lead(II) sulfate and water. How many grams of lead(II) sulfate are produced when 2.5 mL of 6.0 M acid react with enough lead and lead(IV) oxide? Pb(s) + PbO2(s) +2H2SO4(aq) → 2PbSO4(s) + 2H2O(l)

47. Percent Solutions Solution concentrations can be expressed as a percent. Percent by volume Percent by mass Reminder: Solution = solute + solvent

48. Percent Solutions hydrogen peroxide rubbing alcohol What are some examples of solutions that are sold by percent concentration?

49. Percent Solutions – Example Problems a. What is the percent by mass of NaHCO3 in a solution containing 20 g NaHCO3 dissolved in 600 mL of H2O? The density of water is 1.0 g/mL. What is the mass of 600 mL of water? 600 g

50. Percent Solutions – Example Problems b. If you have 150.0 mL of a 30.% aqueous solution of ethanol, what volumes of ethanol and water are in the solution?