Chapter 22: Mixtures: Solutions, Colloidal Dispersions, and Suspensions Flashcards
What does the dispersed phase refer to?
to the particles scattered throughout the medium
What does the continuous phase refer to?
the medium in which particles are distributed
How are food mixtures classified?
classified by the size of particles distributed throughout the mixture
What are the 3 food mixtures? What size are the particles?
– Solutions: smallest particles
– Colloidal dispersions: particles larger than
those in solutions
– Suspensions: largest particles
What is a solution?
homogenous mixture of 2 or more substances
The dispersed phase is called what in a solution? The continuous phase?
- Dispersed: solute
- Continuous: solvent
Name 2 characteristics of the particles in a solution?
- Particles are small
- Have a high level of kinetic energy
Can solutions form gels?
No
Name the 3 types of solutions based on their states of matter and provide examples.
– solids in liquids (salt or sugar in water)
– liquids in liquids (flavorings and vinegars)
– gas in liquids (carbonated beverages)
What is solubility?
the amount of solute that will dissolve in a solvent
What does Le Chatelier’s principle state?
when the chemical equilibrium changes, the equilibrium shifts to counteract the change
What is solubility affected by?
temperature, particle size, concentration, pH, agitation, and vapor pressure
How does temperature affect solubility? Compare solids and gases.
- 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)
How does particle size affect solubility?
The smaller the solute’s particles are, the greater is the exposed surface area and the faster the solute will dissolve
What is concentration?
he measure of parts of one substance (solute) to the known volume of another (solvent)
What is a unsaturated solution? Saturated?
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
What is the saturation point?
When all water molecules have bonded to a solute, the solution is at the saturation point
What allows a solution to hold more solute?
Heat breaks bonds in the solute, allowing the solution to hold more solute
If a solution is heated then cooled, what forms?
Supersaturated solution
Ions with what charge are more soluble?
Singly charged ions tend to be more soluble than ions with 2 or more charges
Are smaller ions more soluble than larger ions?
Yes
Calcium carbonate dissolves in neutral water, but more quickly when what is added?
When an acid is added
What does agitation influence (2)?
- 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
What is vapour pressure? What is it important for?
– the pressure at which gases escape from and
dissolve into a liquid at the same rate
– important in maintaining gases in solution
Gas concentration in a liquid directly relates to what?
Pressure of the gas over the liquid
How does fizz in carbonated drinks occur?
because gas is added to liquid under pressure
How do you calculate mass percent?
(Mass of solute/Mass of solution) x 100 = mass percent
What drops and what rises when solutes are added to water? This change is greater as what increases?
- Freezing point drops
- Boiling point rises
- Change is greater as the mass percent of the solute increases
Solutes with what will produce solutions with even lower freezing points and higher boiling points?
Solutes containing ionic bonds
Name an example of the effects of solutes on the freezing point.
– 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
As the mass percent of a solute increases, what increases with it?
The solution’s vapour pressure
Vapour pressure is equalized by what? Molecules move in which direction? Give an example.
- 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
How are carbonated beverages made?
– 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
What are colloidal dispersions? What gives the mixture its unique characteristics?
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
Name the 3 types of colloidal dispersions. Give examples.
- Emulsions
- Foams
- Gels
- Jelly, mayonnaise, gelatin
What is the continuous phase in colloid dispersions? What is the dispersed phase?
- Continuous phase: medium that
holds the dispersed particles - Dispersed phase: particles
called colloids distributed throughout
How does the size of colloids compare to solutes?
Colloids are up to 1000 times larger than solutes
- Solute: up to 1 nm
- Colloids: 1nm and 1000 um
Do solute particles dissolve? Do colloids?
- Solutes dissolve
- Colloids do not dissolve, but can be dispersed
What happens when light rays pass through a colloidal dispersion?
they scatter and become visible, causing a phenomenon called the Tyndall effect
What happens when light rays pass through a solution? Why?
no change in the direction of the light ray is visible because solutes are too small to bend light
What keeps colloids dispersed? (2)
- 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)
Colloids of the same substance have the same what? This causes them to what?
- Same electrical charge
– This causes them to repel each other and water molecules to align around the colloid
In colloids, what happens if particles are denser in the continuous phase? What if they are less dense? Most colloids are what? What do they form?
- 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
What is an example of colloidal dispersion? What are the solutes, colloids, and what is in suspension?
– Lactose and mineral salts are solutes
– Proteins are colloids
– Fat is in suspension
Milk undergoes what to keep fat suspended? If untreated, what would happen?
- Homogenization
– If untreated, fat (cream) would rise to the top
What is an emulsion?
mixture of 2 immiscible liquids, where one is dispersed in droplet form in the other
What are temporary emulsions?
- unstable mixtures of a polar and a nonpolar liquid
– As the mixture stands, liquids will separate
What do permanent emulsions require? What is the chemical structure? Give an example.
- Emulsifier
- Polar and nonpolar end
- Lecithin found in egg yolks
Name examples of oil-in-water emulsions.
mayonnaise, salad dressings, and cake batters
Name examples of water-in-oil emulsions.
- Butter
- Margarine
What is thermal conductivity? What does it impact? Does water or oil have a greater thermal conductivity?
- ability to conduct heat energy
- impacts emulsions
- water is greater
Does an oil-in-water emulsion freeze faster than a water-in-oil emulsion? Why?
- oil-in-water emulsion will freeze faster than a water-in-oil emulsion
- water conducts heat energy faster than fat
When the emulsifier is a protein, what will destabilize emulsions?
High temperatures
Why are emulsions stable? What will destabilize it?
electrical attraction between water and the polar end of the emulsifier
- Running an electric current will destabilize it
How is ice cream an emulsion? What are the emulsifiers? What do they prevent?
water-based sugar solution that forms an emulsion with fat-based cream
- Gums pectins and lecithin are the emulsifiers that prevent crystallization
What are foams?
colloidal dispersions of gas or air bubbles in a liquid
Give examples of unstable and stable foams.
– Foam on root beer and soft drinks is an unstable foam
– Whipped cream and meringue are stable foams
Name the 4 conditions to keeping a foam stable.
– 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 does whipping cream develop the best foam? Why?
when it, the bowl, and beaters are well chilled because the viscosity of fat is greater when cool
When does egg white reach the fullest volume of foam?
when left at room temperature for a half hour before beating
When should sugar be added to produce the most stable foam?
after a foam begins to form but before it reaches the soft peak stage
What happens if you add sugar before a foam forms? After a foam completely forms?
– before a foam forms can delay foam formation
– after a foam completely forms will cause a coarse texture
In terms of acidity, when does whipping cream form the best foam?
when fresh because bacteria lower the pH with aging and change lactose to lactic acid
In terms of acidity, when do egg whites form the best foam? What is used to change the pH?
– 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
How does fat influence foam?
Fat reduces protein’s foaming ability to form a film around air bubbles (no egg yolk)
What is a suspension?
mixture of undissolved particles in a liquid
Why can suspensions be unstable? The continuous phase has to be what to keep the particles from floating or sinking? Are larger particles or smaller particles better?
– 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
Name examples of suspensions.
– fruit pieces in gelatin
– crushed berries in ice cream
– spices and herbs in Italian dressing
What are batters? Why do they result in a light, airy baked product?
are pourable mixtures with pieces suspended
throughout
- have air bubbles to provide leavening
Why can doughs be shaped rather than poured? What do they keep evenly suspended?
– have a higher proportion of flour so they can
be shaped rather than poured
– keep large particles evenly suspended
If you double the pressure over a gas-in-liquid solution, you can double what?
The amount of gas in solution
What has a higher freezing point and boiling point: 10% solution or 5% solution?
Higher freezing point: 10%
Higher boiling point: 10%
When a soft drink can is opened, the pressure above the solution _____
decreases
Do colloids have a notable impact on the boiling and freezing point of mixtures? Why?
Because colloids are larger, they can be dispersed in another substance, but won’t dissolve. No impact, unlike solutes
What is the dispersed phase in water-in-oil emulsions? Oil-in-water?
Water-in-oil: water
Oil-in-water: oil
How do you increase the stability of a batter?
- Decreasing the particle size
- Increasing the viscosity of the batter
