Experimental Foods Exam 1
Pure water freezes at
0 degrees Celsius
water changes structure from solid to a gas at?
540 Calories
how many calories are removed when water is changed to ice?
80
in colloidal dispersions, the __________________ phase extends throughout the system, surrounding all parts of the other phase
continuous phase
which is true about water activity?
converting free water to bound water decreases the Aw value
a supersaturated solution is?
important in the product of candies
colligative properties depend on the ___________ of solute particles in a given amount of solvent and not the nature of the solute
number
colligative properties depend on the _________ of solute particles in a given amount of solvent and ____________ of the solute
number; not the nature
which represent the physical properties and structures of water?
polar nature, hydrogen bonds
a sol is a kind of colloidal dispersion of
solid dispersed in liquid
what do colligative properties depend on?
the # of solute particles in a given amount of solvent
what is latent heat?
the amount of energy in calories per gram absorbed as a substance that undergoes a change in state
1 mole of a non-volatile ionizing solute will raise the boiling point of 1 liter of water by?
0.52 degrees C
what Aw range represents yeast and mold spoilage?
0.75-0.9
all foods have a water activity less than?
1
what is the specific heat of water?
1 cal/g/C
which results in the highest freezing point when added to 1 L of water?
1 g of sugar
which result in the highest boiling point when added to 1 L of water?
1 gram of salt 1 gram of sugar plus 0.5 gram of salt
what size particles must a solution have to be to be considered coarse?
1000 nm
the boiling point of water is ______ and its freezing point is ________
212 F, 32 F
all colloidal systems have _______ phases, known as the ______________
2; continuous phase and discontinuous phase
boiling point drops 1 degree F for every _______ foot increase
500
what are examples of bound water?
NaCl vitamin carbs emulsifiers
the way the positive and negative charges on a water molecule are concentrated is called?
a dipole
adsorption is when?
a dry food is placed in a wet environment
there is a cup of water, and you need to dissolve a substance in the water, which of these things could be used to create a solution?
a polar molecule
which one of these substances is classified as a "food dispersion"?
a solution, a suspension, an emulsion, and a colloid
which of the following statements is false?
a true solution contains more solute than the solvent can dissolve is considered unsaturated
which of the following i an unsaturated solution?
a true solution that contains less solute than the solvent can dissolve at a given temperature
one mole of which of the following will raise the boiling point of 1 L of water the most?
calcium chloride
what food product is made using the process of a supersaturated solution?
candies/fudge
which of the following is/are a colloidal dispersion?
casein gelatin protein albumen
starch granules in cold water is an example of a?
coarse suspension
in a true solution, dissolved sugar will?
decrease the vapor pressure
adding salt to water will _________ the freezing point and ____________ the boiling point
decrease; increase
in a true solution the dissolved/ionized susbtances will _______________ the vapor pressure of a solution, which will require ________ heat for the vapor pressure to overcome atmospheric pressure to reach the boiling point
decrease; more
adding solutes that dissolve or ionize ______________ the vapor pressure of the solution
decreases
as the percentage of water in a food is "bound", the water activity?
decreases
how do volatile solutes affect the boiling point of water?
decreases boiling point
the addition of solutes to water does what to the freezing point?
decreases the amount of time to freeze
how can you control Aw?
dehydration concentration addition of humectants freezing
____________ is when a wet food is placed in a dry environment
desorption
what are the two phases of a colloidal system?
discontinuous and continuous
what are true characteristics of water molecule?
easy form H bonds and ionic interactions with other/food molecules have a high specif heat
salad dressing is what type of colloidal dispersion?
emulsion
to change the state of water you must add or remove high amount of ?
energy
boiling point is when the pressure of the steam is __________ that of the atmosphere
equal to
which of the following are a type of colloidal dispersion?
foam and gels
which of the following is not an example of a colloidal dispersion? whipped cream foam yogurt fog marshmallow salad dressing
fog
freezing can be damaging to food systems due to?
formation of ice crystals (especially large crystals) concentration of soluble solids concentration of gasses (ie: oxygen) intermittent thawing (poor temperature control)
in which form of water is water activity measured?
free water
water activity can be measured from?
free water
all of the following states of water are below 100 degrees C except?
gas
a suspensoid (colloidal dispersion) is a mixture of?
gas in a solid
custard is an example of ____________, which is a colloidal dispersion
gel
what are two non-ionizing properties?
glucose, water
all of the following are examples of emulsions except? milk ice cream butter mayo
gravy
an example of sol would be
gravy
which of the following is an example of a sol?
gravy
what is a sol?
gravy starch
Aw is a value directly correlated with _____________ and chemical reactions
growth of microorganisms
Aw is a value directly correlated with
growth of microorganisms and chemical reactions
water that contains calcium and magnesium sulfates is referred to as?
hard water
When is heat released in heat of fusion?
heat is released when a liquid is transformed into a solid
heat energy absorbed in the conversion of water into steam is known as?
heat of vaporization
what is true about the structure of water?
hydrogen atoms are joined to the oxygen atom by two bonds that form an angle of almost 105 degrees water is a dipole
what type of interaction is surface tension?
hydrogen bonding
which of the following is true about water activity?
increase in moisture increases water activity
water activity lower than 0.9?
inhibit bacterial growth
what is true about latent heat?
it does not cause a rise in temperature
water activity is important in food service because?
it helps to predict shelf life
which of the following is true about vapor pressure?
it increases with increasing temperature
water is an unique substance because it has a high specific heat. What does this mean?
it takes more energy to heat water into steam compared to other substances
which is NOT a type of colloidal dispersion?
jello
gel colloidal dispersion is a ________, dispersed in a __________
liquid; solid
any food substance added to water will ________________ water activity, so all foods have a water activity ___________
lower; less than 1.0
which one of the following is an example of suspensoid?
marshmallow
which of the following is not a reason why freezing can be damaging to food systems?
melting and re-freezing
which of the following food products can one expect to have the lowest water activity?
milk powder
an example of a colloid is?
milk protein egg white protein gelatin protein pectin polysaccharide
water acts as a dispersing medium or solvent for all of these except? solubility mixtures hydration emulsion gels
mixtures
the relationship of water activity with __________ controls the shelf life of foods?
moisture
what occurs in a solution that has both water and salt dissolved in the water?
more energy is required for boiling point to be reached
in a water molecule oxygen has a partially ___________ charge, while the 2 hydrogens have partially _______ charge
negative; positive
which of the following statements are true regarding colloidal dispersions?
never truly dissolve in a solvent
colligative properties depend on the ___________ of solute particles in a given amount of solvent
number
colligative properties depend on the _______________ of solute particles in a given amount of solvent and ________________ of the solute
number/ not the nature
which of these examples demonstrates the activity of free water?
oranges and watermelon
the __________ concentrates the electrons of the oxygen atom away from the hydrogen atoms on a water molecule?
orientation
food dispersions are classified by their?
particle size
water contains intramolecular ________ bonds
polar covalent
the behavior of water molecules is strongly influenced by its?
polarity
the hydrogen atoms in water provide a ____________ content
positive
the 2 hydrogen atoms on water are partially ____________, while the one oxygen atom on water is partially __________________
positive; negative
addition of a substance to water will change the BP by?
raising the BP to 0.52 degrees C
in a true solution dissolved or ironized substances will _______ the vapor pressure of a solution, which means need ___________ heat for the vapor pressure to overcome atmospheric pressure and boil
reduce; more
which of the following foods do not contain a large amount of water?
rice
addition of these types of solutes will lower the freezing point by disrupting structure
salt and sugar
water activity and its relationship with moisture content help to predict?
shelf life
which one is the solid dispersed in a liquid?
sol
which colloidal dispersion is a solid dispersed in a liquid?
sol colloidal dispersion
what are examples of colloidal dispersions?
sol, gel, foam, suspensoid, emulsion
which of the following are types of colloidal dispersions?
sol, suspensoid, emulsion, gel
what is the colloidal dispersion of sol?
solid dispersed in a liquid
latent heat of fusion is temperature that remains constant as
solid turns to liquid
colloidal systems may be any combination of ______, -____, or __________ as longg as the particle size of one phase is within the dimensions of a colloidal
solid, liquid, gas
in a sol, the ___________ is the dispersed phase while the ___________ is the continuous phase
solid; liquid
which one is not the aspect for water acting as a dispersion medium or solvent?
sols
colligative properties depend on the number of __________ particles in a given amount of _____________ and not the nature of the ___________
solute; solvent; solute
________________ are homogeneous mixtures in which ____________ particles are small enough to dissolve within the _______________
solutions; solute; solvent
the plot of data for the resorption or desorption of water is called a
sorption isotherm
the difference between latent heat and specific heat is?
specific heat is the amount of heat needed to raise the temp. of water and latent heat is the amount of energy absorbed when water changes states
which of the following is not a colloidal dispersion?
starch mixture
which of the following is not a colligative property of water? static pressure mass fluidity boiling point/freezing point osmotic pressure
static pressure mass fluidity
what is not an example of a colloidal dispersion in a discontinuous phase?
sugar
what is an example of a true solution?
sugar dissolved in water
which is not a colligative property of water?
surface tension
marshmallow belongs to which colloidal dispersion type?
suspensoid colloidal dispersion
what is latent heat of fusion?
temperature remains constant as solid turns to liquid
triple point is the __________ and ____________ of the three phases are at equilibrium
temperature; pressure
what is the moisture sorption isotherm?
the relationship between moisture content and water activity at constant pressure and temperature it provides a record of water activity of a particular food it is an S-shaped curve when plotted on a graph
which of the following statements is completely true about dispersions?
the solvent in saturated solutions can dissolve increasing proportions of the solute as the temp. rises, which is known as a supersaturated solution
what is the triple point?
the temperature and pressure at which three phase (liquid, ice, and vapor) coexist at equilibrium
which is true of water activity?
the value is directly correlated to the growth of microorganisms and chemical reactions it is the amount of "free" water available the value decreases as the percentage of water in a food is "bound" changing from its "free" state all foods have a water activity less than 1
water activity is equal to the VP of a food divided by?
the vapor pressure of pure water
true solutions is the most stable because?
they are the smallest in particle size
what is the most stable type of dispersion?
true solution
which of the following dispersions has the smallest particle size and be characterized as the most stable of the three types of dispersions?
true solution
which type of dispersion contains the smallest particle size?
true solution
food dispersions are substances that are combined in several different ways. Combination of solvent and a solute can result in?
true solution and colloidal dispersion
what are the different types of dispersions?
true solution, colloidal dispersions, and course suspensions
which is the most stable of the three types of dispersions?
true solutions
which type of dispersion(s) is/are characterized as the most stable?
true solutions
which type of food dispersion is the most stable?
true solutions
combining a solvent and a solute results in either
true solutions colloidal dispersions coarse suspensions
dispersions are a combination between a solvent and a solute that can vary according to particle size. rank the types of dispersions according to particle size from smallest to largest
true solutions, colloidal dispersions, coarse suspensions
one gram of molecular weight of salt will have _______ as great as effect on the boiling point of a salt solution as will a gram of molecular weight of sugar
twice
___________________ influences the temperature at which boiling of a liquid occurs
vapor pressure
what are colligative properties to consider?
vapor pressure freezing point boiling point osmotic pressure
which are colligative properties of water?
vapor pressure (depression) boiling point (elevation) freezing point (depression) osmotic pressure (elevation)
what is an example of a colligative property?
vapor pressure and boiling point
what happens when a solute is added to solvent to form a solution?
vapor pressure decreases boiling point increases melting point decreases freezing point decreases
water activity of foods is measured by?
vapor pressure of food
these are all examples of colloidal dispersions except? proteins pectin starches gums vitamins
vitamins
which of the following is NOT a characteristic of water activity?
water activity represents the amount of water bound to salts, vitamins, carbohydrates and other solids in a food
which of the following is not true about water?
water is not a good solvent
freezing can be damaging to food systems for all of the following except? formation of ice crystals concentrations of soluble solids alters product macro nutrient content concentration of gases intermittent thawing
alters product macronutrient content
which of the following statements about colloidal dispersions is true?
an example of a colloid is a pectin
hydrogen bonds...
are relatively weak and they result in innumerable clusters of water molecules
what is not a part of colligative properties?
atmosphere pressure
boiling point is the temperature at which vapor pressure just exceeds
atmospheric pressure
the freezing point is not affected by?
atmospheric pressure
why is sodium chloride sprinkled on icy roads during the winter?
because the addition of sodium chloride lowers the freezing point of water making it more difficult for it to freeze
there is an inverse relationship between?
boiling point temperature and vapor pressure
how can water in foods stop being controlled?
by removing humectants
