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Unit Eleven: Solutions. Solutions A solution is a homogeneous mixture of two or more substances ▫Homogeneous – uniform characteristics throughout ▫Heterogeneous.

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Presentation on theme: "Unit Eleven: Solutions. Solutions A solution is a homogeneous mixture of two or more substances ▫Homogeneous – uniform characteristics throughout ▫Heterogeneous."— Presentation transcript:

1 Unit Eleven: Solutions

2 Solutions A solution is a homogeneous mixture of two or more substances ▫Homogeneous – uniform characteristics throughout ▫Heterogeneous – different compositions; various throughout Solutions have at least two components ▫Solutes – the minority component ▫Solvents – the majority component ▫75% isopropyl solution – solute is water, solvent is isopropyl ▫3% H 2 O 2 – solute is H 2 O 2, solvent is water

3 Nine types of mixtures SoluteSolventExamples **GasGasAir **GasLiquidSoda GasSolidStyrofoam or marshmallows LiquidGasClouds **LiquidLiquidAlcohol in water LiquidSolidMercury on penny (amalgam) SolidGasSmoke **SolidLiquidSugar or salt in water (Liquid is usually solvent) **SolidSolidCoins, gemstones, alloys - ** means common type of solution -Amalgam: an alloy of mercury and another metal -Likes Dissolves Likes

4 Non-Solutions - Suspensions Suspensions ▫A mixture from which particles settle out upon standing ▫Particles are larger than in a solution ▫Suspended – temporarily out of school ▫Examples: Italian Dressing, muddy water, orange juice with pulp

5 Non-Solutions - Colloids Colloids ▫A permanent mixture whose particles are smaller than in a suspension and larger than in a solution ▫Particles will reflect light, cloudy appearance ▫Do not settle out and cannot be filtered ▫Milk, starch, dusty air, fog

6 NameParticle SizePermanenceExamples Solutiond < 1 nmPermanent Sugar-water, acids, bases, salt water Colloid1 nm < d < 100nmPermanentMilk, blood, mayonnaise Suspensiond > 100 nmSettles OutMud, clay, cement PropertySolutionsColloidsSuspensions Settling OutDo not settle Settle on standing FilteringUnchanged Separates when filtered Tyndall EffectDo not scatter lightScatters light Effect on Colligative Properties Does affectDoes not affect

7 Tyndall Effect Laser pointed through a solution, colloid, and suspension – what will happen?

8 Non-Electrolyte Aqueous solutions containing a solute that dissolves as molecules Do not conduct electricity CH 3 OH  CH 3 OH C 12 H 22 O 11  C 12 H 22 O 11

9 Electrolyte Aqueous solutions containing a solute that dissociates into ions Conducts electricity NaCl  Na 1+ + Cl 1- or Al 2 (SO 4 ) 3  2Al SO 4 2- Strong electrolytes have large portions of solute existing as ions Weak electrolytes have a fraction of the solute existing as ions

10 Solubility Solubility is the amount of compound (usually in grams) that will dissolve in a certain amount of liquid There are three types of solutions: ▫Unsaturated ▫Saturated ▫Supersaturated

11 Solubility Saturated Solutions ▫Hold the maximum amount of solute under the solution conditions ▫If additional solute is added to a saturated solution, it will not dissolve Unsaturated Solutions ▫Hold less than the maximum amount of solute under the solution conditions ▫If additional solute is added to an unsaturated solution, it will dissolve Supersaturated Solutions ▫Hold more than the normal maximum amount of solute ▫Any disturbance will precipitate the solute or make it come out of solution

12 Supersaturated Solution Example: Rock Candy

13 Solubility Curves 35 grams of NaCl per 100 grams at 25°C is a __ soln. 25 g of KNO 3 per 35 g of water at 50°C is a ___ soln. 45 g of KNO 3 per 100 g of water is cooled from 40°C to 0°C

14 Solubility Solubility depends on: ▫Identity of solute and solvent  Like dissolves like -> polar dissolves polar and nonpolar dissolves nonpolar ▫Temperature  For solids in liquids, solubility increases with increasing temperature  For gases in liquids, solubility decreases with increasing temperature

15 Solubility ▫Pressure  For solids in liquids, a change in pressure has very little effect on the solubility  For gases in liquids, higher pressure increases the solubility of the gas in the liquid  When a can of soda is opened, there is less pressure so the gas is less soluble

16 Worksheet One is due Friday (Tomorrow) Worksheet Two is due Monday ▫Skip Question 10 ▫Questions 3, 4, and 5 you cannot answer until Friday’s notes

17 Solubility Rate of solution – ▫How fast a substance dissolves and how quickly the substance goes into solution ▫Factors that increase the rate of solution for solids  Decrease particle size  Stirring  Increase temperature

18 Hydration versus Solvation Hydration ▫A solute is dissolved by water molecules attaching to ions and moving them into solution Solvation ▫Process of molecules of a solvent moving molecules or ions into solution

19 Concentrations Concentrations – the amount of solute in a solution ▫A dilute solution is one containing small amounts of solute relative to solvent ▫A concentrated solution is one containing large amounts of solute relative to solvent ▫Mass percent, molarity, and molality

20 Mass Percents Mass Percents – the number of grams of solute per 100 grams of solution Mass percent=(mass of solute)/(mass of solution)x100

21 Practice Problems Calculate the mass percent of NaCl in a solution containing 15.3 grams of NaCl and grams H 2 O. Calculate the mass percent of a solution containing 27.5 grams C 2 H 6 O and 175 mL of H 2 O A soft drink contains 11.5% sucrose by mass. What volume of soft drink solution, in mL, contains 85.2 grams of sucrose?

22 Molarity Molarity – the number of moles of solute per liter of solution A concentration of 6 M HCl contains 6 moles of HCl per 1 L of solution Molar solutions are prepared in a volumetric flask Molarity = M = moles of solute/liters of solution

23 Practice Problems Calculate the molarity of a sucrose solution made with 1.58 moles of solute diluted to a total volume of 5.0 L of solution. Calculate the molarity of a solution made by putting 15.5 grams of NaCl into a beaker and adding water to make 1.50 L of NaCl solution.

24 Practice problems 6.7 grams of NH 4 Cl is dissolved in enough water to make 803 mL of solution. What is the molarity of the solution. How many grams of NaOH are needed to make mL of a 1.00 M solution? What volume of a 1.0 M NaNO 3 solution can be prepared from grams of NaNO 3 ?

25 Solution Dilutions Most solutions are bought as stock solutions, however most labs need diluted solutions. We use M 1 V 1 =M 2 V 2

26 Practice Problems A laboratory procedure calls for 5.00 L of a 1.50 M KCl solution. How should you prepare this solution from a 12.0 M stock solution? To what volume should you dilute L of a 15 M NaOH solution to obtain a 1.0 M NaOH solution?

27 Practice Problems How much 6.0 M NaNO 3 solution should be used to make L of a 1.2 M NaNO 3 solution?

28 Solution Stoichiometry Tying it all together! How much M NaOH solution is required to completely neutralize L of M H 2 SO 4 solution? H 2 SO 4(aq) + 2 NaOH (aq) → Na 2 SO 4(aq) + 2 H 2 O (l)

29 Solution Stoichiometry How much M KI solution in liters is required to completely precipitate the lead in L of M Pb(NO 3 ) 2 ? 2 KI (aq) + Pb(NO 3 ) 2(aq) → PbI 2(s) + 2 KNO 3(aq)

30 Solution Stoichiometry How many milliliters of M Na 2 CO 3 are necessary to completely react with 27.2 mL of M HNO 3 according to the following reaction? 2HNO 3(aq) + Na 2 CO 3(aq) → H 2 O (l) + CO 2(g) + 2NaNO 3(aq)

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32 Molality Molality – is the number of moles of solute per kilograms of solvent A concentration of 6 m HCl contains 6 moles of HCl per 1 kg of solvent To make 1 liter of 1 m solution, one mole is added to enough water to make 1 L Which is more concentrated 1.0 m or 1.0 M? ▫1.0 M Molality = m = moles of solute/kg of solvent

33 Practice Problems What is the molality of the solution if 5.0 grams of KI are in grams of water? How many grams of calcium nitrate (Ca(NO 3 ) 2 ) must be added to 20.0 grams of water to make a 2.5 m solution?

34 Colligative Properties A property that depends on the number of solute particles and not the type of solute particles How much you have not what you have Two types ▫Freezing point depression ▫Boiling point elevation ▫These depend on quantity of solute not type of solute

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36 Colligative Properties Freezing point depression – difference in temperature between the freezing point of a solution and the freezing point of the pure solvent ▫Solute disrupts the formation of the orderly pattern thus requiring more energy  Solution freezes at a lower temperature than the pure solvent ▫Magnitude is proportional to the number of solute particles dissolved

37 ΔT f = K f m (# of particles) ΔT f = change in temperature K f = molal freezing point depression constant m = molality (# of particles) = how many particles of solute form in solution

38 Colligative Properties Boiling point elevation – difference in temperature between the boiling point of a solution and the boiling point of the pure solvent ▫Nonvolatile solute dissolved in the solvent disrupts the vapor pressure which increases the boiling point  Solution boil at a greater temperature than the pure solvent ▫Magnitude is proportional to the number of solute particles dissolved

39 ΔT b = K b m (# of particles) ΔT b = change in temperature K b = molal boiling point depression constant m = molality (# of particles) = how many particles of solute form in solution

40 Practice Problems What is the freezing point depression and the boiling point elevation of a pinch of salt (0.25 grams NaCl) in a 2.00 L aqueous solution? K f =1.86°C/m K b =0.512°C/m

41 Practice Problems What is the freezing point depression and boiling point elevation of a 0.40 m solution of sucrose in ethanol? K f =1.99°C/m K b =1.22°C/m F.p.=-114.6°C B.p.=78.4°C

42 Unit Eleven Test Tomorrow (Friday March 8 th ) Worksheet Five due Tomorrow Gizmo’s due Tomorrow Lab Report Revisions due Tuesday ▫Will have optional computer time on Monday


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