unit eleven: solutions. solutions a solution is a homogeneous mixture of two or more substances...
TRANSCRIPT
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Unit Eleven: Solutions
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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% H2O2 – solute is H2O2, solvent is water
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Nine types of mixturesSolute Solvent Examples
**Gas Gas Air
**Gas Liquid Soda
Gas Solid Styrofoam or marshmallows
Liquid Gas Clouds
**Liquid Liquid Alcohol in water
Liquid Solid Mercury on penny (amalgam)
Solid Gas Smoke
**Solid Liquid Sugar or salt in water (Liquid is usually solvent)
**Solid Solid Coins, gemstones, alloys- ** means common type of solution- Amalgam: an alloy of mercury and another metal- Likes Dissolves Likes
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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
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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
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Name Particle Size Permanence
Examples
Solution d < 1 nm Permanent Sugar-water, acids, bases, salt water
Colloid 1 nm < d < 100nm Permanent Milk, blood, mayonnaise
Suspension d > 100 nm Settles Out Mud, clay, cement
Property Solutions Colloids Suspensions
Settling Out Do not settle Do not settle Settle on standing
Filtering Unchanged Unchanged Separates when filtered
Tyndall Effect Do not scatter light Scatters light Scatters light
Effect on Colligative Properties
Does affect Does not affect Does not affect
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Tyndall Effect
Laser pointed through a solution, colloid, and suspension – what will happen?
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Non-Electrolyte
•Aqueous solutions containing a solute that dissolves as molecules
•Do not conduct electricity
•CH3OH CH3OH
•C12H22O11 C12H22O11
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Electrolyte• Aqueous solutions containing a solute that
dissociates into ions
• Conducts electricity
• NaCl Na1+ + Cl1- or Al2(SO4)3 2Al3+ + 3SO42-
• Strong electrolytes have large portions of solute existing as ions
• Weak electrolytes have a fraction of the solute existing as ions
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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
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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
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Supersaturated Solution
Example: Rock Candy
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Solubility Curves
•35 grams of NaCl per 100 grams at 25°C is a __ soln.
•25 g of KNO3 per 35 g of water at 50°C is a ___ soln.
•45 g of KNO3 per 100 g of water is cooled from 40°C to 0°C
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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
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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
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•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
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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
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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
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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
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Mass Percents
•Mass Percents – the number of grams of solute per 100 grams of solution
Mass percent=(mass of solute)/(mass of solution)x100
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Practice Problems• Calculate the mass percent of NaCl in a solution
containing 15.3 grams of NaCl and 155.0 grams H2O.
• Calculate the mass percent of a solution containing 27.5 grams C2H6O and 175 mL of H2O
• A soft drink contains 11.5% sucrose by mass. What volume of soft drink solution, in mL, contains 85.2 grams of sucrose?
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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 volumetricflask
• Molarity = M = moles of solute/liters of solution
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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.
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Practice problems• 6.7 grams of NH4Cl 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 500.0 mL of a 1.00 M solution?
• What volume of a 1.0 M NaNO3 solution can be prepared from 170.0 grams of NaNO3?
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Solution Dilutions
•Most solutions are bought as stock solutions, however most labs need diluted solutions.
•We use M1V1=M2V2
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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 0.100 L of a 15 M NaOH solution to obtain a 1.0 M NaOH solution?
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Practice Problems
•How much 6.0 M NaNO3 solution should be used to make 0.585 L of a 1.2 M NaNO3 solution?
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Solution Stoichiometry
•Tying it all together!
How much 0.125 M NaOH solution is required to completely neutralize 0.225 L of 0.175 M H2SO4 solution?
H2SO4(aq) + 2 NaOH(aq) → Na2SO4(aq) + 2 H2O(l)
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Solution Stoichiometry
•How much 0.115 M KI solution in liters is required to completely precipitate the lead in 0.104 L of 0.225 M Pb(NO3)2?
2 KI(aq) + Pb(NO3)2(aq) → PbI2(s) + 2 KNO3(aq)
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Solution Stoichiometry
•How many milliliters of 0.112 M Na2CO3 are necessary to completely react with 27.2 mL of 0.135 M HNO3 according to the following reaction?
2HNO3(aq)+ Na2CO3(aq) → H2O(l)+ CO2(g)+ 2NaNO3(aq)
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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
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Practice Problems
•What is the molality of the solution if 5.0 grams of KI are in 500.0 grams of water?
•How many grams of calcium nitrate (Ca(NO3)2) must be added to 20.0 grams of water to make a 2.5 m solution?
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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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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
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ΔTf = Kf • m • (# of particles)
•ΔTf = change in temperature
•Kf = molal freezing point depression constant
•m = molality
• (# of particles) = how many particles of solute form in solution
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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
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ΔTb = Kb • m • (# of particles)
•ΔTb = change in temperature
•Kb = molal boiling point depression constant
•m = molality
• (# of particles) = how many particles of solute form in solution
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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?
Kf=1.86°C/m Kb=0.512°C/m
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Practice Problems
•What is the freezing point depression and boiling point elevation of a 0.40 m solution of sucrose in ethanol?
Kf=1.99°C/m Kb=1.22°C/m
F.p.=-114.6°C B.p.=78.4°C
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•Unit Eleven Test Tomorrow (Friday March 8th)
•Worksheet Five due Tomorrow
•Gizmo’s due Tomorrow
•Lab Report Revisions due Tuesday▫Will have optional computer time on
Monday