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63 Cards in this Set
- Front
- Back
the unknown compound could have been
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glucose, sucrose, or glycerol
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learning objectives (4)
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calculate the molar mass of a dissolved compound using the experimentally observed freezing point depression
identify compounds based upon molar mass and physical properties add linear trend lines to plotted data graphically identify freezing points using linear extrapolation |
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experimental objectives (2)
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determining the mass of a substance by difference
measuring the freezing points of pure solvents and solutions |
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two cold-tolerant fish
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Atlantic Wolffish, Anarhichas lupus
rainbow smelt, Osmerus mordax |
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what bug species survive freezing in north america
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beetles, Cucujus clavipes
eggs of locusts, Locusta migratoria |
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what can survive being frozen solid
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terrestrial wood frog, Rana sylvatica
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in the _____, _______, a bio grad student, was researching how ______, a group of ____ species that live around ______, survived
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1960s
Arthur DeVries notothenioids fish Antarctica |
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how did the notothenioids survive
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they were expressing antifreeze proteins (AFPs)
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how to AFPs prevent the formation of big ice crystals in the cell
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they bind to small ice crystals, altering the structure of the crystal and prohibiting further growth
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are AFPs exclusive to notothenioids
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no, other fish and insect species also express AFPs
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how do cold-tolerant species lower the freezing point of water in their bodies
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they increase the concentration of dissolved solutes like sugars and glycerol in their tissues/blood plasma
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how does the terrestrial frog survive freezing
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it loses cellular water and converts glycogen to glucose within the cell
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freezing point depression is an example of a
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colligative property
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a physical property of solutions that depends on the number of dissolved particles in solution, but not the identity of the solute
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colligative property
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3 more colligative properties
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boiling point elevation, vapor pressure lowering, osmotic pressure
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for reasonable dilute solutions, colligative properties are entirely traceable to
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entropy
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second law of thermodynamics
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any spontaneous change occurs with an increase in the entropy of the universe
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a spontaneous change is a change that occurs with
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no outside intervention
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the universe is defined as
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the system and its surroundings
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deltaS_univ =
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deltaS_sys + deltaS_surr
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two related concepts associated with entropy function are
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disorder and probability
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freezing can only occur if deltaS_surr is
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positive and larger in magnitude than the negative deltaS_sys
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the universe tends to change in ways that have
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maximum probability
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solute molecules in a solution have the tendency to
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spread themselves evenly over the volume of the solution
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at the freezing point, the entropy gain of the surroundings is
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equal to the entropy loss of the solvent that freezes out
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transfer of heat (q) is always accompanied by
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an increase in entropy
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the lower the temp of the surroundings into which heat is released,
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the greater the entropy increase is
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deltaS_surr =
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q/T_surr
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the entropy change for the universe can be expressed as
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deltaS_sys + q/T_surr =deltaS_univ
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above the freezing point, entropy is
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less than zero
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at the freezing point, entropy is
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equal to -q/T_surr
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below the freezing point, entropy is
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greater than zero
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when the liquid A solute molecules start to freeze and the solute B becomes more concentrated, the entropy of B
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decreases
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when solid A freezes out of a solution containing some dissolved B, the entropy decrease is a bit _____ than when A freezes out from pure liquid A
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greater
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a lower temp is required for a solution because the entropy increase of the surroundings needs to
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balance the entropy decrease of the freezing of the liquid
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at the freezing point of a SOLUTION, the entropy change of the solution is equal to
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-q/T_surr
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the freezing point of the solution is ________ until all of the solvent is frozen
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further depressed
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deltaT_f =
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T_f pure solvent - T f solution
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the magnitude of deltaT_f is directly proportional to
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the concentration of the solute
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deltaT_f = (2nd equation)
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K_fm
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K_f
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the solvent-specific molar freezing depression constant
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m
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molality of the solution
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molal freezing point depression constant for water
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-1.8*C/m
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molality
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moles solute/kg solvent
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solutes that dissociate or ionize when dissolved in water
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electrolytes
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for ____, the number of moles of particles per formula unit in solution is greater than for _____
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electrolytes
nonelectrolytes |
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the effective molality of a dissolved sodium chloride solution is ______ the calculated molality
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twice
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the freezing point for a solution will decrease until the _______ for the solvent is reached
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saturation point
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a solution has reached its saturation point when
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the solvent cannot dissolve additional solute
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for a solution being frozen, once the saturation point is reached, additional freezing
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forces solute out of solution, maintaining a constant molality for the solution
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the temp at which the solution becomes saturated
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eutectic temperature
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what is it called when the temp of the solution is lower than the eutectic temp without further precipitating solute from solution
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a supersaturated solution
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supercooled solutions can be prepared by
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carefully lowering the temp of the solution without agitation
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when disturbed, supercooled solutions can
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suddenly precipitate their solutes, forming saturated solutions
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during the precipitation of solute from a supercooled solution,
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heat is evolved, raising the temp of the solution back to the eutectic temp
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what other chemical did we use
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sodium chloride
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was special chemical waste collection required
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no
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how do you find the freezing point on the graph
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add trendlines for cooling and freezing and it's where they intersect
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what are the series you use with the solution graph
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cooling 1, cooling 2, freezing
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what's the freezing point for the solution on the graph
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the intersection of cooling 2 and freezing
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where should excused absences be reported
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412 held
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eutectic temp is the
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lowest temp at which the solvent is still a liquid
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matts ta hours are
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1-2 wed
8-9 thurs 116 held |