Solutions

SolutionsSolutions

Nature of SolutionsNature of Solutions

A A solutionsolution is a homogeneous mixture of two or more is a homogeneous mixture of two or more substances in a single physical statesubstances in a single physical state

The substance that is dissolved is the The substance that is dissolved is the solutesolute. The . The substance that does the dissolving is the substance that does the dissolving is the solventsolvent..

Substances that dissolve in other substances are said Substances that dissolve in other substances are said to be to be soluble.soluble. If they don’t dissolve they are If they don’t dissolve they are insolubleinsoluble..

Types of SolutionsTypes of Solutions

Solid Solutions – involve at least one solid. Solid Solutions – involve at least one solid. The most common are solutions containing The most common are solutions containing two or more metals, called two or more metals, called alloysalloys Sterling silver, brass, bronzeSterling silver, brass, bronze

Gaseous Solutions – all mixtures of gasesGaseous Solutions – all mixtures of gases AirAir

Types of SolutionsTypes of Solutions

Liquid Solutions – involving at least one liquidLiquid Solutions – involving at least one liquid Antifreeze, vinegar, soft drinksAntifreeze, vinegar, soft drinks Liquids that mix in any amount are Liquids that mix in any amount are misciblemiscible. Liquids that . Liquids that

cannot mix in any proportions are cannot mix in any proportions are immiscible.immiscible.

Aqueous Solutions – solutions that have water as a Aqueous Solutions – solutions that have water as a solventsolvent Substances that dissolve in water to create electric current Substances that dissolve in water to create electric current

are called are called electrolyteselectrolytes

Concentration of SolutionsConcentration of Solutions

ConcentrationConcentration is the amount of solute in a is the amount of solute in a given amount of solvent or solutiongiven amount of solvent or solution

Molarity (M)Molarity (M) The molarity of a solution is equivalent to the The molarity of a solution is equivalent to the

moles of solute divided by the liters of solutionmoles of solute divided by the liters of solution


Molality (m)Molality (m) The molality of a solution is equivalent to the The molality of a solution is equivalent to the

number of moles of solute dissolved in each number of moles of solute dissolved in each kilogram of solventskilogram of solvents


Mole Fractions (X)Mole Fractions (X) The mole fraction is the number of moles of one The mole fraction is the number of moles of one

component (either solute or solvent) divided by the component (either solute or solvent) divided by the number of moles in solutionnumber of moles in solution

The sum of the mole fractions for the solute and The sum of the mole fractions for the solute and solvent must add up to 1solvent must add up to 1

SaturationSaturation

A solution is A solution is saturatedsaturated if it contains as much solute as if it contains as much solute as can possibly be dissolved under the existing can possibly be dissolved under the existing conditions of temperature and pressureconditions of temperature and pressure

A solution with less than the maximum amount of A solution with less than the maximum amount of solute than can be dissolved is solute than can be dissolved is unsaturatedunsaturated. If the . If the solution has a greater amount of solute than needed to solution has a greater amount of solute than needed to form a saturated solution it is form a saturated solution it is supersaturated.supersaturated.

How Solutions FormHow Solutions Form

Dissolving takes place at the surface of a solidDissolving takes place at the surface of a solid

The interaction between solute and solvent The interaction between solute and solvent molecules is called molecules is called solvationsolvation

When the solvent is water it is called When the solvent is water it is called hydrationhydration

SolubilitySolubility

SolubilitySolubility is the amount of a solute that will is the amount of a solute that will dissolve in a specific solvent under given dissolve in a specific solvent under given conditionsconditions

Factors Affecting SolubilityFactors Affecting Solubility

Nature of Solute and SolventNature of Solute and Solvent ““Like Dissolves Like” – polar solvents dissolve Like Dissolves Like” – polar solvents dissolve

polar solutes; nonpolar solvents dissolve nonpolar polar solutes; nonpolar solvents dissolve nonpolar solutes; ionic solutes are soluble in polar solventssolutes; ionic solutes are soluble in polar solvents

TemperatureTemperature In general, solubility increases as temperature In general, solubility increases as temperature

increasesincreases

Factors Affecting SolubilityFactors Affecting Solubility

Pressure (for gases)Pressure (for gases) The solubility of a gas in any solvent is increased The solubility of a gas in any solvent is increased

as the pressure of the gas over the solvent is as the pressure of the gas over the solvent is increasedincreased

Factors Affecting Dissolving RateFactors Affecting Dissolving Rate

Surface AreaSurface Area The greater the surface area (smaller pieces), the The greater the surface area (smaller pieces), the

faster the solute will dissolvefaster the solute will dissolve

StirringStirring Stirring increases the contact between the solvent Stirring increases the contact between the solvent

and the solute surfaceand the solute surface

Factors Affecting Dissolving RateFactors Affecting Dissolving Rate

TemperatureTemperature An increase in temperature increases the rate at An increase in temperature increases the rate at

which a solute dissolveswhich a solute dissolves

Colligative PropertiesColligative Properties

A property that depends on the concentration A property that depends on the concentration of solute particles but is independent of their of solute particles but is independent of their nature is a nature is a colligative propertycolligative property

There are four: There are four: vapor point reduction, boiling vapor point reduction, boiling point elevation, freezing point depression, and point elevation, freezing point depression, and osmotic pressureosmotic pressure


Vapor Pressure ReductionVapor Pressure Reduction When a nonvolatile solute (one that won’t vaporize When a nonvolatile solute (one that won’t vaporize

or sublime under existing conditions) is added to a or sublime under existing conditions) is added to a pure solvent, the solute molecules take up space at pure solvent, the solute molecules take up space at the surface of the liquidthe surface of the liquid

This prevents some solvent molecules from This prevents some solvent molecules from leaving the liquidleaving the liquid


However, there is no change in the rate at which However, there is no change in the rate at which molecules in the gas state return to the liquidmolecules in the gas state return to the liquid

This produces a shift – because more molecules leave This produces a shift – because more molecules leave the gas than enter it, the gas pressure is reduced the gas than enter it, the gas pressure is reduced ((vapor pressure reduction)vapor pressure reduction)

The magnitude by which the pressure is lowered is The magnitude by which the pressure is lowered is directly proportional to concentrationdirectly proportional to concentration


Boiling Point Elevation (Boiling Point Elevation (ΔΔTTbb = K = Kbbm)m) Boiling point is the temperature at which the vapor Boiling point is the temperature at which the vapor

pressure of a liquid is equal to the external pressure of a liquid is equal to the external pressure on its surfacepressure on its surface

Since the addition of a nonvolatile solute reduces Since the addition of a nonvolatile solute reduces the vapor pressure, a higher temperature is the vapor pressure, a higher temperature is required to make the substance boilrequired to make the substance boil


The amount by which the boiling point is The amount by which the boiling point is raised is the raised is the boiling point elevationboiling point elevation

The boiling point elevation is directly The boiling point elevation is directly proportional to molalityproportional to molality


Freezing Point Depression (Freezing Point Depression (ΔΔTTff = K = Kffm)m) The freezing point is the temperature at which the vapor The freezing point is the temperature at which the vapor

pressures of the solid and liquid phases are the samepressures of the solid and liquid phases are the same

If a nonvolatile solute is added, the vapor pressure of the If a nonvolatile solute is added, the vapor pressure of the solution is reduced in proportion to the mole fraction of the solution is reduced in proportion to the mole fraction of the solute – therefore the freezing point is loweredsolute – therefore the freezing point is lowered

Freezing point depression is directly proportional to Freezing point depression is directly proportional to molalitymolality


Osmotic Pressure (Osmotic Pressure (ππ)) The osmotic pressure is the pressure required to The osmotic pressure is the pressure required to

prevent osmosisprevent osmosis

When two solutions are at the same osmotic When two solutions are at the same osmotic pressure, they are pressure, they are isotonicisotonic


If a solution has a lower osmotic pressure than If a solution has a lower osmotic pressure than another, it is another, it is hypotonichypotonic Putting cells in a hypotonic solution causes them Putting cells in a hypotonic solution causes them

to burstto burst

If a solution has a higher osmotic pressure than If a solution has a higher osmotic pressure than another, it is another, it is hypertonichypertonic Putting cells in a hypertonic solution causes them Putting cells in a hypertonic solution causes them

to shrivelto shrivel

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