Chapter 22: Mixtures: Solutions, Colloidal Dispersions, and Suspensions

to the particles scattered throughout the medium

the medium in which particles are distributed

classified by the size of particles distributed throughout the mixture

– Solutions: smallest particles
– Colloidal dispersions: particles larger than
those in solutions
– Suspensions: largest particles

homogenous mixture of 2 or more substances

• Dispersed: solute

- Continuous: solvent

• Particles are small

- Have a high level of kinetic energy

No

– solids in liquids (salt or sugar in water)
– liquids in liquids (flavorings and vinegars)
– gas in liquids (carbonated beverages)

the amount of solute that will dissolve in a solvent

when the chemical equilibrium changes, the equilibrium shifts to counteract the change

temperature, particle size, concentration, pH, agitation, and vapor pressure

• Solids: amount of solute that a solvent will hold increases with temp (ex: candy production)

• Gases: amount of gaseous solute that a solvent holds DECREASES as temp increases (ex: soft drinks lose their carbonation faster at room temp)

The smaller the solute’s particles are, the greater is the exposed surface area and the faster the solute will dissolve

he measure of parts of one substance (solute) to the known volume of another (solvent)

Unsaturated: solution that can dissolve more solvent at a given temperature
Saturated: holding all the solute that will dissolve in a solvent at any given temperature

When all water molecules have bonded to a solute, the solution is at the saturation point

Heat breaks bonds in the solute, allowing the solution to hold more solute

Supersaturated solution

Singly charged ions tend to be more soluble than ions with 2 or more charges

Yes

When an acid is added

• Agitation or stirring speeds the dissolving rate until the saturation point is reached

• Agitation also adds a small amount of energy that slightly raises the temperature

– the pressure at which gases escape from and
dissolve into a liquid at the same rate
– important in maintaining gases in solution

Pressure of the gas over the liquid

because gas is added to liquid under pressure

(Mass of solute/Mass of solution) x 100 = mass percent

• Freezing point drops

• Boiling point rises

• Change is greater as the mass percent of the solute increases

Solutes containing ionic bonds

– Sugar and milk solids (solutes) cause the ice cream solution to have a lower freezing point
– Surrounding the ice cream solution in a metal can is ice that melts when salt is added
– The saltwater solution has a lower freezing point than does the ice cream mixture (salt + ice = endothermic, absorbs heat energy)
– Heat energy is transferred from the ice cream
mixture to the saltwater solution
– As the ice cream mixture loses heat energy, its temperature drops, allowing it to freeze

The solution's vapour pressure

• either absorbing water or allowing solutes to escape

• in the direction with the least resistance

• Soft drinks fizz after opening the container until vapor pressure is reached

– water is treated to yield consistent quality
– sweeteners, flavorings, coloring agents, acids, and carbon dioxide are the solutes
– carbohydrate gums or pectins give diet drinks the mouthfeel of sweetened drinks
– acids act as flavor enhancers and preservatives
– sodium benzoate is usually added as a preservative

• Soft drinks sold at restaurants and refreshment stands are made with a concentrated syrup added to water

mixtures in which microscopic particles of one substance are evenly distributed in another

• The particles, which are not dissolved, give the mixture its unique characteristics

• Emulsions

• Foams

• Gels

• Jelly, mayonnaise, gelatin

• Continuous phase: medium that
  holds the dispersed particles

• Dispersed phase: particles
  called colloids distributed throughout

Colloids are up to 1000 times larger than solutes

• Solute: up to 1 nm

• Colloids: 1nm and 1000 um

• Solutes dissolve

| - Colloids do not dissolve, but can be dispersed

they scatter and become visible, causing a phenomenon called the Tyndall effect

no change in the direction of the light ray is visible because solutes are too small to bend light

• The motion of the molecules in the continuous phase causes collisions that keep the colloids dispersed

• The electrical charge of colloids (like charges repel and water will form a cushion around colloids, preventing them from separating)

• Same electrical charge

| – This causes them to repel each other and water molecules to align around the colloid

• More dense: sink as a mixture sits

• Less dense: rise to the top of the mixture (fat at the top of gravy)

• Most are starches and proteins, which form colloid dispersions when the molecular structure changes

– Lactose and mineral salts are solutes
– Proteins are colloids
– Fat is in suspension

• Homogenization

| – If untreated, fat (cream) would rise to the top

mixture of 2 immiscible liquids, where one is dispersed in droplet form in the other

• unstable mixtures of a polar and a nonpolar liquid

| – As the mixture stands, liquids will separate

• Emulsifier

• Polar and nonpolar end

• Lecithin found in egg yolks

mayonnaise, salad dressings, and cake batters

• Butter

| - Margarine

• ability to conduct heat energy

• impacts emulsions

• water is greater

• oil-in-water emulsion will freeze faster than a water-in-oil emulsion

• water conducts heat energy faster than fat

High temperatures

electrical attraction between water and the polar end of the emulsifier

• Running an electric current will destabilize it

water-based sugar solution that forms an emulsion with fat-based cream

• Gums pectins and lecithin are the emulsifiers that prevent crystallization

colloidal dispersions of gas or air bubbles in a liquid

– Foam on root beer and soft drinks is an unstable foam

| – Whipped cream and meringue are stable foams

– The liquid must be viscous enough to trap and
hold air
– A stabilizer must be present that stretches and forms a thin film around bubbles
– The surface tension of the film should be less than that of water
– The liquid must have a low vapor pressure

when it, the bowl, and beaters are well chilled because the viscosity of fat is greater when cool

when left at room temperature for a half hour before beating

after a foam begins to form but before it reaches the soft peak stage

– before a foam forms can delay foam formation

| – after a foam completely forms will cause a coarse texture

when fresh because bacteria lower the pH with aging and change lactose to lactic acid

– eggs are fresher and have a lower pH, between 7.0 and 8.0

| – cream of tartar is used to further lower pH to 4.6 and 4.8

Fat reduces protein’s foaming ability to form a film around air bubbles (no egg yolk)

mixture of undissolved particles in a liquid

– unstable due to the size of the dispersed particles
– The continuous phase must be viscous enough to keep the particles from floating or sinking
– The larger the particles, the more viscous the continuous phase must be to maintain stability

– fruit pieces in gelatin
– crushed berries in ice cream
– spices and herbs in Italian dressing

are pourable mixtures with pieces suspended
throughout

• have air bubbles to provide leavening

– have a higher proportion of flour so they can
be shaped rather than poured
– keep large particles evenly suspended

The amount of gas in solution

Higher freezing point: 10%

| Higher boiling point: 10%

decreases

Because colloids are larger, they can be dispersed in another substance, but won't dissolve. No impact, unlike solutes

Water-in-oil: water

| Oil-in-water: oil

• Decreasing the particle size

| - Increasing the viscosity of the batter