H 2 O WHAT PROPERTIES OF WATER MAKE IT ESSENTIAL TO LIFE OF EARTH? Good solvent High Surface tension Low vapor pressure High boiling point

Transcription

1 Unit 9: Solutions

2 H 2 O WHAT PROPERTIES OF WATER MAKE IT ESSENTIAL TO LIFE OF EARTH? Good solvent High Surface tension Low vapor pressure High boiling point

3 Water is a polar molecule. It experiences hydrogen bonding due to its polar nature.

4 After many hydrogen bonds are formed, you have a weak force holding all the water molecules to each other.

5 Hydrogen bonding is the reason water freezes into ice crystals of a certain repeating shape (hexagons) Volume increases.

6 Hydrogen bonding is what gives proteins and nucleic acids their three dimensional shape.

7 Hydrogen bonding also causes water to have. High Surface Tension (cohesion)

8 Surfactant Surface Tension can be decreased by adding a surfactant this type of substance interferes with hydrogen bonding. Surfactants are used in soaps, detergents, paints, adhesives, inks

9 Hydrogen bonds also cause water to have A high boiling point and a low vapor pressure.

10 Water is also attracted to other substances like glass. Water can be drawn up into a thin glass tube with no effort (capillary action) because of the attraction between the water and glass molecules.

11 Classification of Matter Matter anything composed of atoms Pure Substances Mixtures Elements Compounds Heterogeneous Mixtures Homogeneous Mixtures Two types of mixtures!

12 Heterogeneous Mixtures Two or more pure substances mixed unevenly (you can see the different components). Example: fruit salad, pizza, granite

13 Suspensions A suspension is a heterogeneous mixture that has large particles that will stay suspended as long as the mixture is in motion Once the motion stops, the particles will fall to the bottom or settle out Can be separated through filtering

14 Colloids Homogeneous mixtures where the medium sized particles are dispersed throughout but are not heavy enough to settle out. Appear cloudy and opaque Cannot be separated by filtering Can be separated by a centrifuge

15 How can light be used to tell the difference between colloids and solutions? Tyndall effect A beam of light passing through a solution, such as air, is not visible. Light passing through a colloid, such as fog, will be scattered by the larger particles and the light beam will be visible.

16 Homogeneous Mixtures Two or more pure substances mixed evenly. When you look at it, you can t see separate parts. Also called solutions (can be liquid, gas or solid solutions) Examples: salt water, soda, coffee,

17 Parts of a solution Solute the substance being dissolved. Solvent the substance that is doing the dissolving (usually present in a greater amount). The solute dissolves INTO THE solvent to form a solution. Solute Solvent

18 Miscible two substances that will mix and dissolve together in any proportion Immiscible two substances that are insoluble in one another. Water and oil are.

19 Factors that affect the rate of dissolution Temperature Dissolve faster at higher temp Agitation Dissolve faster when the mixture is shaken or stirred. Surface Area VS. Dissolve faster if you increase their surface area (broken up into smaller pieces)

20 Solubility in Water : The simple rule to remember is like dissolves like Water is a polar solvent and will dissolve polar molecules and substances that contain charged particles. Substances that dissolve in H 2 O are said to be soluble Ex: Sugar, ethanol (type of alcohol) which are polar, most ionic compounds Site of polarity can form H-bonding sucrose

21 When solid sodium chloride (NaCl) dissolves in water it breaks up into its individual ions.

22 Water is polar, the different ends are attracted to the charged ions. The positive and negative ions become surrounded by solventsolvation Cl - Na +

23 Electrolytic Solutions Ionic Compounds dissociate in aqueous solutions and create positive and negative ions in solution. Their ability to move nearly independently through the solution permits them to carry positive or negative electrical charges from one place to another. Hence the solution conducts an electrical current and are called electrolytes.

24 Electrolytic Solvation sugar Non- Electrolyte solute exists as molecules only acetic acid Weak Electrolyte solute exists as ions and molecules salt Strong Electrolyte solute exists as ions only

25 Electrolytic Solvation sugar Non- Electrolyte covalent compounds acetic acid Weak Electrolyte weak acids and bases salt Strong Electrolyte ionic compounds/ strong acids and bases

26 Which beakers contain an electrolytic solution: Solution 1 Solution 2 Solution 3 Solution 4 Solution 5 KCl Solution HNO 3 Solution Sugar Solution Acetic Solution Ammonia Solution

27 Substances that don t dissolve are called insoluble E.g. Petroleum (crude oil), which are non-polar So if you want to dissolve grease which is non-polar, you need to use a non-polar solvent. Petroleum in a non-polar organic molecule

28 How is solubility of a compound denoted in a chemical equation?, yields

29 How do we know if the products of a chemical reaction are (aq), a solution or (s), a suspension or a precipitate?

30 Double Replacement Reactions AB + CD AD + CB Which of the products produced will be soluble? potassium iodide + lead (II) nitrate barium nitrate + calcium carbonate

31 Saturation

32 MAXIMUM Amount of solute dissolved Saturation The point when no more solute can dissolve into a solvent at a given temperature ( a dynamic equilibrium exists between the solution and undissolved solute).

33 Unsaturated Solution An unsaturated solution is like a sponge that can hold more water. More solute can be dissolved at that temperature. I m still thirsty!

34 Supersaturated Solution A supersaturated solution is a solution that contains more of the solute than it can normally hold at a given temperature. Can be prepared by changing the conditions of a saturated solution (temperature, volume, or pressure).

35 Solubility UNSATURATED SOLUTION more solute dissolves SATURATED SOLUTION no more solute dissolves SUPERSATURATED SOLUTION becomes unstable, crystals form concentration

36 SOLVATION & SOLUBILITY CURVES

37 Solubility Solubility Curve shows the dependence of solubility on temperature

38 Solubility Curve Most solubility curves show the solubility of more than one solute. These graphs show comparisons. Which solute is most soluble at 100 C? KNO 3 is most soluble at 100 degrees.

39 Practice: What is the solubility of KBr at 80ºC? Which salt is the most soluble at 50ºC? At which temperature can you dissolve 160 g of KNO 3 in 100 g of water?

40 Unsaturated, Saturated, and Supersaturated solution Solutions that are below the line are always UNSATURATED SOLUTIONS. Solutions that are described by the line are always SATURATED SOLUTIONS. Solutions that are above the line are always SUPERSATURATED SOLUTIONS.

41 Practice: How many grams of sodium chloride can be dissolved in 100 g of water at 80ºC? If 40 g of potassium bromide is dissolved in 100 g of water at 80ºC, is the solution saturated, unsaturated, or supersaturated?

42 Solubility Curve What if we change the amount of water? In order to reach saturation, if we double the amount of water that is being used to prepare the solution, we would need to also double the solute. 20 g / 100g of water at 25 C 40 g / 200g of water at 25 C

43 Example: How many grams of KBr would be needed to saturate 50g of water at 90 C? It takes 100g of KBr to saturate 100g of water, so it would take 50g of KBr to saturate 50g of water.

44 What do you notice about the relationship between temperature and solubility of solids and gases in water? Generally, as temperature increases, the solubility of solids increase.

45 Solubility and Temperature As the temperature increases, the solubility of a gas decreases. Why?

46 Solubility of gases and temperature Increased temperature causes an increase in kinetic energy. The higher kinetic energy causes more motion in molecules which break intermolecular bonds and escape from solution. The solubility of gases decreases as the temperature increases. Ex: room temp soda tastes more flat than cold soda

47 Gas pressure and solubility Gases increase in solubility as pressure increases (Henry s law) The gas molecules are "forced" into the solution since this will best relieve the pressure

48 A solution is prepared with 10g of NaCl at 120 C. What type of solution is it? A. Unsaturated B. Saturated C. Supersaturated D. Heterogeneous Problems

49 Problems How many grams of KBr are needed to saturate 100g of water at 90 C? A. 80g B. 90g C. 100g D. 110g

50 Problems How many grams of KBr are needed to saturate 200g of water at 90 C? A. 160g B. 180g C. 200g D. 220g

51 CONCETRATIONS & DILUTIONS

52 These statements are vague so lets get more specific.. Concentration Measure of how much solute is dissolved in solution, or strength of solution. Concentrated: A solution with a relatively high concentration of solute strong coffee Dilute: very little solute in the solution weak coffee

53 Concentration Molarity(M) is used by chemist to describe concentrations. It s a measure of how many moles of solute are present for each liter of solution. A 9M solutions is more concentrated than a 3M solutions. molarity (M) moles L of of solute solution

54 Suppose you have 2.00 moles of sugar and you mix it with enough water to make 1.00 liter of solutionwhat is the molarity of the solution? 2M or two molar

55 Practice Find the molarity of a solution containing 75 g of MgCl 2 in 250 ml of water. Given: Mass = 75g Volume = 250 ml Unknown: M=? M mol L

56 Practice How many grams of NaCl are required to make a 1.54M solution using L of water? Given: Molarity= 1.54 M Volume = 0.500L Unknown: mass=? M mol L

57 Other ways to express Molality (m) concentration Concentration calculated by dividing the moles of solute by the kilograms of solvent (usually water) used to dissolve. m=mols solute/kg solvent Suppose you dissolve 18.2 grams of sucrose (C 12 H 22 O 11 ) into 200. grams of water. What is the molality of the solution?

58 Other ways to express Mole fraction (X) concentration X= moles of component/total moles of all components You mix 1.7 moles of sodium chloride with 6.7 moles of water. What is the mole fraction of the sodium chloride?

59 Other ways to express Percent (%) mass concentration % mass = grams of component/total mass of mixture 16 grams of NaBr are mixed with 32 grams of water. What is the % mass of sodium bromide?

60 Dilution Preparation of a desired solution by adding water to a concentrate. Moles of solute remain the same. M V M V

61 What volume of 15.8M HNO 3 is required to make 250 ml of a 6.0M solution?

62 Practice How much 0.05 M HCl solution can be made by diluting 250 ml of 10 M HCl? How much water would I need to add to 500 ml of a 2.4 M KCl solution to make a 1.0 M solution?