Edward Wen

Solutions

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Solution• Homogeneous mixtures

composition may vary from one sample to anotherappears to be one substance, though contains multiple materials

• most Homogeneous materials are actually Solutions

Gas state: common airLiquid: Gasoline (dozens of compounds), Soda water (sugar or asparatame, CO2, citric acid, fructose)Solid: Alloy such as brass

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Solutions: Solute + Solvent

• Solute: the dissolved substance. Sugar in Sodaseems to “disappear”“takes on the state” of the solvent

• Solvent: the substance solute dissolves in. Water in Soda

does not appear to change state

• Aqueous solutions: solutions in which the solvent is water.

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Common Types of Solution

Solution PhaseSolute Phase

Solvent Phase Example

Gaseous solutions gas gas air (mostly N2 & O2)

Liquid solutionsgas

liquidsolid

liquidliquidliquid

soda (CO2 in H2O)vodka (C2H5OH in H2O)seawater (NaCl in H2O)

Solid solutions solid solid brass (Zn in Cu)

•Alloys: solutions that contain Metal solutes and a Metal solvent, such as Nickel (5 cents of 1$), Brass, Stainless steel

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How Soluble? Solubility• Soluble: when one substance (solute) dissolves

in another (solvent) HomogeneousSalt and Sugar are soluble in water: Saline and SodaAcetic acid (HC2H3O2) in water: VinegarOxygen gas in Nitrogen gas: Air

• Insoluble: when one substance does not dissolve in another Heterogeneous

Oil is insoluble in water: Italian salad dressing

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Will It Dissolve?Chemist’s Rule of Thumb –

Like Dissolves Like• a chemical will dissolve in a

solvent if it has a similar structureto the solvent

• when the solvent and solute structures are similar, the solvent molecules will attract the solute particles at least as well as the solute particles to each other

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Classifying Solvents

Solvent ClassStructural

FeatureWater, H2O polar O-H

Ethyl Alcohol, C2H5OH polar O-H

Acetone, C3H6O polar C=O

Toluene, C7H8 nonpolar C-C & C-H

Hexane, C6H14 nonpolar C-C & C-H

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Solubility in Water, A Polar Solvent?• Ionic compound (Yes): Ions are attracted to polar

Water. Salt NaCl dissolve in water

• Polar molecules (Yes): attracted to polar solventstable Sugar, Alcohol, glucose

• Nonpolar molecules are NOT attracted to Waterβ-carotene, (C40H56), is not water soluble; it dissolves in fatty (nonpolar) tissues

Those molecules with both polar and nonpolar structures: depends on structural features in the molecule

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Salt Dissolved in Water

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Solubility• Definition: the maximum amount of solute that

can be dissolved in a given amount of solvent• Usually a limit to the solubility of one substance

in anotherExceptions: gases are always soluble in each othertwo liquids that are mutually soluble are said to be miscible

alcohol and water are miscibleoil and water are immiscible

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Descriptions of Solubility• Saturated solutions have the maximum amount of

solute that will dissolve in that solvent at that temperature

• Unsaturated solutions can dissolve more solute• Supersaturated solutions are holding more solute

than they should be able to at that temperatureunstable

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Solubility of Solid Depends on Temperature

Higher temp higher solubility of solid in liquid

Lower temp higher solubility of gas in liquid

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Solubility of Gases Decreases at higher Temperature

Observation 1: Warm soda pop fizzes more than cold soda pop Cause: Solubility of CO2 in water decreases as temperature increases.

Observation 2: When water is heated up, gas bubbles appear even before boiling occurs.Cause: Solubility of air in water decreases as temperature increases.

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Solubility of Gas depends on PressureHenry’s Law: • higher pressure = higher solubility• CO2 is dissolved under Pressure into

bottled/canned soda

Under which conditions does oxygen gas have the best solubility?

A. high temperature and high partial pressure (PO2)

B. high temperature and low partial pressureC. low temperature and low partial pressureD. low temperature and high partial pressure

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Solution Concentration Descriptions

• Diluted solutions have low solute concentrations

• Concentrated solutions have high solute concentrations

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Concentrations – Quantitative Descriptions of Solutions

• Solutions have variable composition. Salt vs. Water in Seawater

• To describe a solution accurately, you need to describe the components and their relative amounts

• Concentration = amount of solute in a given amount of solution

Seawater: Salt concentration 3.4%Dead Sea: Salt concentration 30%Vinegar: Acetic acid concentration 5%

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Weight/Volume Percent (w/v)%

• mass of solute (gram) in every 100 mL of solution

Vinegar is 5% (w/v) solution of acetic acid by mass, then there are 5 grams of acetic acid in every 100 mL of vinegar

Mass of Solute, g(w/v)% 100%Volume of Solution, mL

= ×

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InformationGiven: 0.35 g phenol. 25

mL solutionFind: (w/v)%

Example:Chloraseptic sore throat spray contains 0.35 g of phenol in 25 mL of solution. Find the weight/volume percent concentration of phenol.

0.35 g phenol(w/v)% 100% 1.4% (w/v) phenol25 mL solution

= × =

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Volume/Volume Percent (v/v)%

• Volume of solute (mL) in every 100 mL of solution

Common rubbing alcohol is 50~91% (v/v) solution of isopropanol (or 2-propanol) in every 100 mL of solution.

Volume of Solute, mL(v/v)% 100%Volume of Solution, mL

= ×

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InformationGiven: 101 mL ethanol,

750 mL solution (wine)Find: (v/v)%

Example:A 750-mL bottle of wine contains 101 mL of ethanol. Find the volume/volume percent concentration of ethanol.

101 mL ethanol(v/v)% 100% 13.5% (v/v) ethanol750 mL solution

= × =

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Mass Percent (%)• mass of solute (gram) in every 100

gram of solutionif a solution is 0.9% by mass, then there are 0.9 grams of solute in every 100 grams of solution

• Mass of solution = Mass of solute + Mass of solvent

SolutionofMassSolvent ofMassSolute of Mass

%100g Solution, of Mass

g Solute, of Mass Percent Mass

=+

×=

23

%.

%

100nsol' g 5220OHC g 7.52Percent Mass

100solution masssolute mass Percent Mass

62 ×=

×=

= 13.5802%

InformationGiven: 27.5 g C2H6O; 175 g H2OFind: % by massEq’n:

Example:Calculate the mass percent of a solution containing 27.5 g of ethanol (C2H6O) and 175 g of H2O

%100nSol' g

Solute g % Mass ×=

= 13.6%

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Parts per million (ppm) concentration

• mass of solute (gram) in every 1,000,000 gram of solution

• Orvolume of solute (mL) in every 1,000,000 milliliter of solution

6Mass of Solute, gppm 10Mass of Solution, g

= ×

6Volume of Solute, mLppm 10Volume of Solution, mL

= ×

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Using Concentrations asConversion Factors

• concentrations show the relationship between the amount of solute and the amount of solvent

12% by mass sugar(aq) means 12 g sugar ≡ 100 g solution

• The concentration can then be used to convert the amount of solute into the amount of solution, or visa versa

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InformationGiven: 85.2 g C12H22O11Find: mL sol’nCF: 11.5 g C12H22O11 ≡ 100 mL

sol’nSM: g sucrose → g sol’n → mL sol’n

Example:A soft drink contains 11.5% (w/v) sucrose (C12H22O11). What volume of soft drink in milliliters contains 85.2 g of sucrose?

741 mL

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InformationGiven: 500. mL rubbing alcoholFind: mL sol’nCF: 85 g isopropanol≡ 100 mL

rubbing alcohol

Example:Rubbing alcohol contains 85% (v/v) isopropanol. What volume of isopropanol is contained in 500. mL rubbing alcohol?

4.3 x 102 mL

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Molarity Concentration

• Definition: Moles of solute per 1 liter of solution• Purpose: describing how many molecules of solute

in each liter of solution• Unit: mole/L, abbreviated as “M”.• If a sugar solution concentration is 2.0 M , 1 liter of

solution contains 2.0 moles of sugar, 2 liters = 4.0 moles sugar, 0.5 liters = 1.0 mole sugar

molarity = moles of soluteliters of solution

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Why Molarity?Many reagents used in chemistry, even many biology

labs, are in the form of solution. Molarity concentration of solution is particularly

important and useful because

• Easy to prepare a solution to a given molarity• Easy to use: To obtain given amount (mole) of

reagent, just calculate the volume of solution to be used:

Volume (L) = mole ÷ molarity

Example:

Calculating Molarity

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InformationGiven: 250 mL solution; 15.5 g NaCl

NaCl;

Example:Calculate the molarity of a solution made from 15.5 g of NaCl in 250 mL solution.

solutionliterssolute moles Molarity =

1.06 M NaCl

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Calculations involving Molarity

Molarity = mole ÷ Volume (L)

• Solve for mole: Mole = Molarity × Volume (L)

• Solve for volume of solution in liters: Volume (L) = mole ÷ molarity

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10.9 L solution

InformationGiven: 1.24 mol NaOHFind: L solutionCF: 0.114 mol = 1 LSM: mol → L

Example:How many liters of a 0.114 M NaOH solution contains 1.24 mol of NaOH?

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4 24 2

4 2

0.2334 mol (NH SNH S s )1 L11.25 mL ( )1000 mL 1 L

0.002626 mol

olution

N( H S)

× ×

=

InformationGiven: 0.2334 M (NH4)2S solution

V = 11.25 mL Find: g (NH4)2SCF: 0.2334 mol = 1 L

Find mole first!

Example:How many grams of (NH4)2S are in 11.25mL 0.2334 M (NH4)2S solution?

4 24 2

4 2

68.15 g NH S( )0.002626 mol ( )1 mol

0.1790 g

NH S

N( H S)

×

=

• When mixing more solvent into a solution, the volume of final solution is greater than the original solution

• The mole of solute remains the same before and after mixing more solvent

• The final concentration of solution is lower than in the beginning.

Dilution

Making a Solution by DilutionFor dilution, mole solute = M1 x V1 = M2 x V2

Example: A student added 1.00 L water to 2.00 L 1.00 M HCl.

The final volume became 3.00 L.

mole HCl before mixing = M1 x V1 = 2.00 mole= mole HCl after mixing more water.Final molarity of solution = 0.667 M.

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Example—What Volume of 12.0 M KCl Is Needed to Make 5.00 L of 1.50 M KCl Solution?

Given:Initial solution Final solution

Concentration 12.0 M 1.50 MVolume ? L 5.00 L

0.625 L

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Example—Determine the Concentration of the Solution after dilution

• A solution made by diluting 125 mL of 0.80 M HCl to 500 mL.

M2 = 0.20 M

Boiling Point Elevation: Reduced evaporation in solution

A liquid solution containing a nonvolatile solute has higherboiling point than the pure solvent

Freezing point Depression

A water-antifreeze mixture has a higher boiling point and lower freezing point than pure water. This will reduce the chance of engine coolant being frozen or being evaporated too quickly.

A liquid solution containing a nonvolatile solute has lowerfreezing point than the pure solvent.

Osmosis

Higher concentration of solution has stronger tendency to uptake solvent

The liquid level in the tube rises until equilibrium is reached.

Osmosis

Semi-permeable membrane separating (a) pure water and a salt-water solution, and (b) a dilute salt-water solution.

Osmotic Pressure and Reverse Osmosis (RO)

Osmotic pressure is the amount of pressure needed to prevent the solution in the tube from rising as a result of the process of osmosis. RO: When the added pressure exceeds the osmotic pressure, pure water leaves the concentrated solution.

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Red blood cell in NaCl solutions

(a) Hyptonic solution. In pure water.

(b) Crenation in concentrated sodium chloride solution.

(c) Cells neither swell nor shrink in physiological saline solution.

Copyright David M. Phillips/Visuals Unlimited

Dialysis

Through the semipermeable membrane, there is a net movement of ions and small molecules from a region of higher concentration to a region of lower concentration.Larger molecules such as protein remains inside the membrane.

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Dialysis in Real World