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Food Science > Chapter 22: Mixtures: Solutions, Colloidal Dispersions, and Suspensions > Flashcards

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

1
Q

What does the dispersed phase refer to?

A

to the particles scattered throughout the medium

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2
Q

What does the continuous phase refer to?

A

the medium in which particles are distributed

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3
Q

How are food mixtures classified?

A

classified by the size of particles distributed throughout the mixture

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4
Q

What are the 3 food mixtures? What size are the particles?

A

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

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5
Q

What is a solution?

A

homogenous mixture of 2 or more substances

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6
Q

The dispersed phase is called what in a solution? The continuous phase?

A
  • Dispersed: solute

- Continuous: solvent

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7
Q

Name 2 characteristics of the particles in a solution?

A
  • Particles are small

- Have a high level of kinetic energy

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8
Q

Can solutions form gels?

A

No

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9
Q

Name the 3 types of solutions based on their states of matter and provide examples.

A

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

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10
Q

What is solubility?

A

the amount of solute that will dissolve in a solvent

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11
Q

What does Le Chatelier’s principle state?

A

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

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12
Q

What is solubility affected by?

A

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

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13
Q

How does temperature affect solubility? Compare solids and gases.

A
  • 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)
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14
Q

How does particle size affect solubility?

A

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

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15
Q

What is concentration?

A

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

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16
Q

What is a unsaturated solution? Saturated?

A

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

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17
Q

What is the saturation point?

A

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

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18
Q

What allows a solution to hold more solute?

A

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

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19
Q

If a solution is heated then cooled, what forms?

A

Supersaturated solution

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20
Q

Ions with what charge are more soluble?

A

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

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21
Q

Are smaller ions more soluble than larger ions?

A

Yes

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22
Q

Calcium carbonate dissolves in neutral water, but more quickly when what is added?

A

When an acid is added

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23
Q

What does agitation influence (2)?

A
  • 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
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24
Q

What is vapour pressure? What is it important for?

A

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

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25
Q

Gas concentration in a liquid directly relates to what?

A

Pressure of the gas over the liquid

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26
Q

How does fizz in carbonated drinks occur?

A

because gas is added to liquid under pressure

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27
Q

How do you calculate mass percent?

A

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

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28
Q

What drops and what rises when solutes are added to water? This change is greater as what increases?

A
  • Freezing point drops
  • Boiling point rises
  • Change is greater as the mass percent of the solute increases
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29
Q

Solutes with what will produce solutions with even lower freezing points and higher boiling points?

A

Solutes containing ionic bonds

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30
Q

Name an example of the effects of solutes on the freezing point.

A

– 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

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31
Q

As the mass percent of a solute increases, what increases with it?

A

The solution’s vapour pressure

32
Q

Vapour pressure is equalized by what? Molecules move in which direction? Give an example.

A
  • 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
33
Q

How are carbonated beverages made?

A

– 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

34
Q

What are colloidal dispersions? What gives the mixture its unique characteristics?

A

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

35
Q

Name the 3 types of colloidal dispersions. Give examples.

A
  • Emulsions
  • Foams
  • Gels
  • Jelly, mayonnaise, gelatin
36
Q

What is the continuous phase in colloid dispersions? What is the dispersed phase?

A
  • Continuous phase: medium that
    holds the dispersed particles
  • Dispersed phase: particles
    called colloids distributed throughout
37
Q

How does the size of colloids compare to solutes?

A

Colloids are up to 1000 times larger than solutes

  • Solute: up to 1 nm
  • Colloids: 1nm and 1000 um
38
Q

Do solute particles dissolve? Do colloids?

A
  • Solutes dissolve

- Colloids do not dissolve, but can be dispersed

39
Q

What happens when light rays pass through a colloidal dispersion?

A

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

40
Q

What happens when light rays pass through a solution? Why?

A

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

41
Q

What keeps colloids dispersed? (2)

A
  • 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)
42
Q

Colloids of the same substance have the same what? This causes them to what?

A
  • Same electrical charge

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

43
Q

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?

A
  • 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
44
Q

What is an example of colloidal dispersion? What are the solutes, colloids, and what is in suspension?

A

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

45
Q

Milk undergoes what to keep fat suspended? If untreated, what would happen?

A
  • Homogenization

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

46
Q

What is an emulsion?

A

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

47
Q

What are temporary emulsions?

A
  • unstable mixtures of a polar and a nonpolar liquid

– As the mixture stands, liquids will separate

48
Q

What do permanent emulsions require? What is the chemical structure? Give an example.

A
  • Emulsifier
  • Polar and nonpolar end
  • Lecithin found in egg yolks
49
Q

Name examples of oil-in-water emulsions.

A

mayonnaise, salad dressings, and cake batters

50
Q

Name examples of water-in-oil emulsions.

A
  • Butter

- Margarine

51
Q

What is thermal conductivity? What does it impact? Does water or oil have a greater thermal conductivity?

A
  • ability to conduct heat energy
  • impacts emulsions
  • water is greater
52
Q

Does an oil-in-water emulsion freeze faster than a water-in-oil emulsion? Why?

A
  • oil-in-water emulsion will freeze faster than a water-in-oil emulsion
  • water conducts heat energy faster than fat
53
Q

When the emulsifier is a protein, what will destabilize emulsions?

A

High temperatures

54
Q

Why are emulsions stable? What will destabilize it?

A

electrical attraction between water and the polar end of the emulsifier
- Running an electric current will destabilize it

55
Q

How is ice cream an emulsion? What are the emulsifiers? What do they prevent?

A

water-based sugar solution that forms an emulsion with fat-based cream
- Gums pectins and lecithin are the emulsifiers that prevent crystallization

56
Q

What are foams?

A

colloidal dispersions of gas or air bubbles in a liquid

57
Q

Give examples of unstable and stable foams.

A

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

– Whipped cream and meringue are stable foams

58
Q

Name the 4 conditions to keeping a foam stable.

A

– 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

59
Q

When does whipping cream develop the best foam? Why?

A

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

60
Q

When does egg white reach the fullest volume of foam?

A

when left at room temperature for a half hour before beating

61
Q

When should sugar be added to produce the most stable foam?

A

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

62
Q

What happens if you add sugar before a foam forms? After a foam completely forms?

A

– before a foam forms can delay foam formation

– after a foam completely forms will cause a coarse texture

63
Q

In terms of acidity, when does whipping cream form the best foam?

A

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

64
Q

In terms of acidity, when do egg whites form the best foam? What is used to change the pH?

A

– 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

65
Q

How does fat influence foam?

A

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

66
Q

What is a suspension?

A

mixture of undissolved particles in a liquid

67
Q

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?

A

– 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

68
Q

Name examples of suspensions.

A

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

69
Q

What are batters? Why do they result in a light, airy baked product?

A

are pourable mixtures with pieces suspended
throughout
- have air bubbles to provide leavening

70
Q

Why can doughs be shaped rather than poured? What do they keep evenly suspended?

A

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

71
Q

If you double the pressure over a gas-in-liquid solution, you can double what?

A

The amount of gas in solution

72
Q

What has a higher freezing point and boiling point: 10% solution or 5% solution?

A

Higher freezing point: 10%

Higher boiling point: 10%

73
Q

When a soft drink can is opened, the pressure above the solution _____

A

decreases

74
Q

Do colloids have a notable impact on the boiling and freezing point of mixtures? Why?

A

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

75
Q

What is the dispersed phase in water-in-oil emulsions? Oil-in-water?

A

Water-in-oil: water

Oil-in-water: oil

76
Q

How do you increase the stability of a batter?

A
  • Decreasing the particle size

- Increasing the viscosity of the batter

Food Science (12 decks)

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