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Unit 1 – Section C Solubility of Solids in Water.

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1 Unit 1 – Section C Solubility of Solids in Water

2 HW Read & take notes on sections C.1 - C.3

3 Could something dissolved in the water in the Snake River have caused the fish kill? C.1 Solubility of Solids in Water

4 Let’s dissolve potassium nitrate in water… KNO 3 is the solute & H 2 O is the solvent C.1 Solubility of Solids in Water (continued)

5 The KNO 3 will dissolve to the point at which the H 2 O can hold no more. At this point the solvent is said to be saturated. C.1 Solubility of Solids in Water (continued)

6 The maximum quantity of a substance that will dissolve in a certain quantity at a specific temperature is called its solubility. C.1 Solubility of Solids in Water (continued)

7 The solubility of most substances will change depending on the temperature the graphic representation of this relationship is called the solute’s solubility curve. C.1 Solubility of Solids in Water (What effects this ?)

8 Below the curves the area represents an unsaturated solution. There it contains less than it potentially can. C.1 Solubility of Solids in Water (Continued)

9 This type of solution is called a supersaturated solution. C.1 Solubility of Solids in Water (Continued) Consider a 100mL solution containing 80g of KNO 3 at 60°C, you reduce the temperature to 40°C. What do you think would happen? If all the solute stays in solution...

10 1. a.Mass in ______ g of KNO 3 that will dissolve in 100 g of H 2 O at 60°C? b. Mass in ______ g of KCl that will dissolve in 100 g of H 2 O at 60°C? C.2 Solubility & Solubility Curves (Practice)

11 2. a.25 g of KNO 3 + ____ g will be saturated in 100 g of H 2 O at 30°C? C.2 Solubility & Solubility Curves (Practice)

12 2. b. 45 g KNO 3 = 25 g KNO mL H 2 O X mL H 2 O C.2 Solubility & Solubility Curves (Practice) Solve for X... X = 55 mL of H 2 O

13 3. a.150 g of KNO 3 minus ____ g which will stay in solution in 100 g of H 2 O at 55°C? Means _____ g will precipitate out. C.2 Solubility & Solubility Curves (Practice)

14 3. b. 70 g KNO 3 = 150 g KNO mL H 2 O X mL H 2 O C.2 Solubility & Solubility Curves (Practice) Solve for X... X = 214 mL of H 2 O at 55°C

15 C.3 Constructing a solubility curve

16 HW Read & take notes on C.4 & C.5

17 We are interested in finding out how the atoms of the solute and solvent interact? C.4 Dissolving Ionic Compounds While an entire H 2 O molecule is electrically neutral, (the charge of the cation and anion balance) the electrons are not evenly distributed. This uneven distribution makes it a polar molecule.

18 Polar H 2 O molecules are attracted to other polar molecules. C.4 Dissolving Ionic Compounds (Continued) This gives H 2 O the ability to dissolve a great many substances.

19 H 2 O molecules are attracted to ions located on the surface of an ionic substance. C.4 Dissolving Ionic Compounds (Continued) H 2 O’s negative (oxygen) is attracted to the crystals cation.

20 Dissolving involves competition between 3 types of attraction: C.4 Dissolving Ionic Compounds (Continued) 1.Between solute and solvent 2. “ solvent particles themselves. 3.And between particles within the solute crystals.

21 H 2 O is highly polar. C.4 Dissolving Ionic Compounds (Continued) Therefore H 2 O is extremely effective at dissolving charged or ionic substances.

22 We dissolve 40 g of KCl in 100 g of H2O at 50°C. Then cool the temperature to 25°C. a)What changes do you predict? C.5 The Dissolving Process At 50°C? At 40°C? At 25°C? Unsaturated Supersaturated

23 You may change the concentration of a solution by: C.5 The Dissolving Process (Continued) Decreasing the volume of H 2 O, make the remaining solvent more concentrated. (by evaporation) Increasing the volume of H 2 O, make the remaining solvent less concentrated. (adding solvent)

24 Decreasing the volume of H 2 O, make the remaining solvent more concentrated. (by evaporation) C.5 The Dissolving Process (Continued) We dissolve 40 g of KCl in 100 g of H 2 O at 35°C. We allow ¼ of the water to evaporate, what will happen? 40 g KCl = X g KCl 100 mL H 2 O 75 mL H 2 O X = the amount of KCl that the 75 g of H 2 O can hold in solution X = 30 g of KCl can be held in solution.

25 C.5 The Quizzing Process HW – Pre-review sections C.6 & C.7 pgs and (Especially) problem out section C.7

26 Saturated & unsaturated does not adequately describe the properties of a solution. So we use the term concentration, which refers to how much solute is dissolved in a specific quantity of solution. C.6 Solution Concentrations

27 Another way to describe concentration, is with percent value. C.6 Solution Concentrations (Continued) Example: 5 g of NaCl dissolved in 95 g of H 2 O = 5% NaCl solution (by mass) THINK 5 g 5 g + 95 g Parts per 100

28 For smaller concentrations C.6 Solution Concentrations (Continued) Parts per million (ppm) Parts per billion (ppb) Example: Maximum nitrates allowed in our drinking water is 10 ppm Easier to write than %

29 Problem: What is the concentration of a 1% NaCl-H 2 O solution expressed in ppm? C.6 Solution Concentrations (Continued) 1% of 1,000,000 = 1,000,000 X ,000ppm

30 C.7 Describing Solution Concentrations 1) 1 tsp of sucrose is dissolved in 1 C of H 2 O. a)Solute ? b)Solvent?

31 C.7 Describing Solution Concentrations (continued) 2) Concentration of sucrose expressed as % by mass? a) 17 g of sucrose dissolved in 183 g of H 2 O? b) 30 g of sucrose dissolved in 300 g of H 2 O?

32 C.7 Describing Solution Concentrations (continued) 3) Concentration expressed as ppm? i g of Fe(III) dissolved in 500 g of H 2 O? ii g of Ca dissolved in 850 g of H 2 O?

33 C.7 Describing Solution Concentrations (continued) 4) 45 g of KCl in 100 g of H 2 O at 60°C? a.Concentration of the solution? b. After adding 155g of H 2 O?

34 C.7 Describing Solution Concentrations (continued) 5) A saturated solution of KNO 3 at 25°C?

35 HW Read & take notes on C.8 & C.9. Remember to make certain you understand the sections and bring me questions if you do not.

36 C.8 Inappropriate Heavy-metal ion concentrations Many metal ions, Fe(II)  (Fe +2 ), K +, Ca 2+ and Mg 2+ are necessary for good health. We get most of what we need from food and in some instances the H 2 O we drink.

37 C.8 Inappropriate Heavy-metal ion concentrations (Continued) Not all metal ions are beneficial, some called heavy-metal ions are harmful to humans. They have greater atomic masses than the essential metallic elements. Of greatest concern to us is Pb 2+ and Hg 2+ Because : Widely dispersed in the environment Bind to proteins in biological systems

38 C.8 Inappropriate Heavy-metal ion concentrations (Continued) The heavy-metal ions do not get excreted by living organisms ( They stay in our bodies ), so they get concentrated upwards in the food chain.

39 C.8 Inappropriate Heavy-metal ion concentrations (Continued) In low concentrations heavy-metals are hard to detect and even more difficult to remove. ( We need to eliminate production & use of these elements ), this practice is called green chemistry.

40 C.8 Heavy-metal ion Pb 2+ Many industrial uses: Until 1970s, Pb(C 2 H 5 ) 4 (tetraethyl lead) was added to gasoline. Before 1978 Pb paint was used in houses.

41 C.8 Heavy-metal ion Hg 2+ Uses include: In 18 th & 19 th centuries, Hg(NO 3 ) 2 (mercury (II) nitrate) was used in hat making. Prolonged exposure lead to mercury poisoning (“mad as a hatter”). Thermometers, medical and weather. Antiseptics, fungicides and pesticides.

42 C.9 Inappropriate pH Levels The pH scale is an easy way to measure and report the acidic, basic, or chemically neutral character of a solution. Range 0 – 14 pH < 7.0 = acid pH > 7.0 = basic

43 C.9 Inappropriate pH Levels (continued) Basic solutions (those with pH greater than 7.0) are called alkaline. Example: NaOH, sodium hydroxide – active ingredient in oven and drain cleaners.

44 C.9 Inappropriate pH Levels (continued) A change of 1 pH unit equals a tenfold (10x) difference in acidity or alkalinity. Example: lemon juice at pH 2 is 10x more acidic than soda at a pH of 3.

45 C.9 Inappropriate pH Levels (continued) Most acids are made up of molecules that easily give up one or more H + ions. Example: the acid in vinegar – acetic HC 2 H 3 O 2

46 C.9 Inappropriate pH Levels (continued) Most bases are made up of molecules that include OH - ions. Example: the active ingredients in milk of magnesia Mg(OH) 2

47 C.9 Inappropriate pH Levels (continued) Neither acids nor bases ? We call these neutral. Example: H 2 O, NaCl and C 12 H 22 O 11

48 HW Notes & Pre-read C.10 & C.12 (Please note we are passing over C.11)

49 C.10 Inappropriate Molecular Substance Concentrations Some substances such as (sugar) C 12 H 22 O 11 and (ethanol) C 2 H 6 OH, dissolve in H 2 O but not as ions – they are called molecular substances. They are non-crystalline.

50 C.10 Inappropriate Molecular Substance Concentrations (continued) What determines the solubility of a molecular substances in H 2 O? In large part it is determined by the distribution of electrical charges.

51 C.10 Inappropriate Molecular Substance Concentrations (continued) The ability of an atom to attract shared electrons when bonding within a compound is known as the element’s electronegativity. In molecular substances the differences may not be large enough for ions to form, but the electrons may be unevenly distributed.

52 C.11 Solvents

53 C.12 Inappropriate dissolved O 2 levels? In most instances solubility increases with temperature, is the same true for gases? What is the solubility of O 2 in 20°C water? In 40°C water?

54 C.12 Inappropriate dissolved O 2 levels? (continued) Dissolved gases have an additional factor which must be taken into account, atmospheric pressure.

55 C.12 Inappropriate dissolved O 2 levels? (continued) Gas solubility is directly related to the pressure on that gaseous substance on the liquid.

56 C.12 Inappropriate dissolved O 2 levels? (continued) For sodas CO 2 is forced into solution under high- pressure.

57 C.13 Temperature, Dissolved Oxygen, and Life As we have learned the temperature of H 2 O affects how much O 2 it can hold in solution. Different living organisms have different O 2 needs.

58 C.13 Temperature, Dissolved Oxygen, and Life (continued) How does changing water temperatures affect fish internally? Remember fish are cold-blooded 1.Body temperature rises. 2.Metabolism increases 3.Fish eat more, swim more & require more O 2

59 C.13 Temperature, Dissolved Oxygen, and Life (continued) Additionally there are both lower limits and upper limits to the amount of dissolved O 2 a fish can tolerate.

60 C.14 Determining the Cause of the Fish Kill Let’s examine the data

61 HW On pg 82 Questions 2-4 & 8-10

62 1. Mass in ______ g of KCl that will dissolve in 100 g of H 2 O at 70°C? Q.2 pg 82

63 3. a. 2 g sucrose = x g sucrose 1 mL H 2 O 100 mL H 2 O b. 2 g sucrose = x g sucrose 1 mL H 2 O 355 mL H 2 O c. 2 g sucrose = x g sucrose 1 mL H 2 O 946 mL H 2 O Q.3 pg 82 Solve for X...

64 Q.8 & 9 pg g 35 g g #8 X 100% = #9 55 g x g X 100% = 20% Solve for X...

65 Q 10 pg mg/L which is equal to g/L g g g X 100% = % Pb concentration Finally1,000,000 times equals ppm of Pb


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