Transcript Determining Transition Temperatures of Hydrates

Kam Ganesan
Sandy Hu
Lowell Kwan
Kristie Lau
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Introduction of Transition Temperature
Procedure
 Seeding
 Supercooling
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Observations
Conclusion of Data
Sources of Experimental Error
Discussion
Transition Temperature (II)
(1) solid
another phase = evolution/absorption of heat
 this temperature = transition temperature
 Hydrates
 Seeding & Supercooling
 Crystallization
 Applications
(2) Superconductivity
loss of electrical resistance
 this temperature = transition temperature
 Zero resistance
- Type I
- Type II
 Quantum effect
 Meissner effect
 Applications
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Compounds with water
in formula
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Does not indicate a
wet substance
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In the formula:
 X · YH2O
▪ X is the compound
▪ Y indicates the molecules
of water
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Chemical Formula:
 Na2S2O35H2O
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also sodium hyposulfite
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Molar mass = 179 gmol-1
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colourless crystalline compound
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variety of uses
 photographic processing
 antidote to cyanide poisoning
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slightly toxic and harmful to skin
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Retort stand
Test tube clamp
Ring clamp
Wire gauze
Bunsen burner
Flint lighter
Beaker tongs
Thermometer
Boiling tube
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20 g of Sodium
Thiosulphate Pentahydrate
Scoopula
1 L beaker
Safety Goggles
Computer (with software)
150 mL of water
Temperature probe
Electronic Scale
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Set up retort stand
with all necessary
equipment
Measurement and
add all substances
Attach and set up
temperature probe
to the computer and
prepare LoggerPro
program
Above: Setup of experiment.
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20mL Sodium Thiosulphate
Pentahydrate
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temperature , until hydrate
evaporates
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air jacket
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cooled to ~40 °C (i.e. supercool)
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seed crystal added
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temperature
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crystallization occurs
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temperature stabilizes
Above: Setup of experiment.
Above: Sodium thiosulphate in
crystallized form
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Lowering temperature
below freezing point
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Supercooled substance
will crystallize rapidly
when seed crystal is
added
Above: Melted sodium
thiosulphate pentahydrate
cooling in the air jacket.
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one crystal of a substance is added to solution of
substance solution
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acts as basis for the intermolecular interactions to
form upon
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Expedites crystallization
Tim e (s)
18
00
17
00
16
00
15
00
14
00
13
00
12
00
11
00
10
00
90
0
80
0
70
0
60
0
50
0
40
0
30
0
20
0
10
0
0
Temperature (˚C)
Tem perature of Sodium Thiosulpahte Pentahydrate
80
70
60
50
40
30
20
10
0
Temperature of Sodium Thiosulphate Pentahydrate (311s - 1781s, 30 Second Intervals)
80
70
60
40
30
20
10
Time (s)
17
51
16
91
16
31
15
71
15
11
14
51
13
91
13
31
12
71
12
11
11
51
10
91
10
31
97
1
91
1
85
1
79
1
73
1
67
1
61
1
55
1
49
1
43
1
37
1
0
31
1
Temperature (˚C)
50
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Seeding at super cooled state
causing evolution of heat
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rapid crystallization
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transition temperature
approximately 47.6˚C
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close to the theoretical
transitional temperature,
approx. 48˚C
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fairly accurate results
 99.17% accuracy
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Contamination
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Capabilities of LoggerPro
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Time Lapse of 5 seconds lost
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Judging change of state
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Condensation
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Discussion
 Transition Temperatures
 Endothermic Versus Exothermic
 Practical Uses and Application
 Modifications to the Experiment
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Transition Temperature (II)
 Transition Temperature of Glass
 Superconductivity
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change from one solid phase to another
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found to be when temperature stays constant
after crystal added
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It is therefore when 2 states exist in equilibrium in
a substance
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Endothermic: absorbs heat
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Exothermic: releases heat
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Compound was heated until it changes state, then
it is cooled
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Crystal is then added to supercooled liquid
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Was our experiment ENDO or EXO (If wrong, try
again)?
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Sodium thiosulphate crystal acts as a seed crystal
speeding up crystallization process
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Compound releases heat (EXOthermic) when crystal is
added
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Temperature of compound rapidly rises
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Seed crystal allows intermolecular forces to react and
collide (increase speed of recrystallization)
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Temperature changes include
steady fall as liquid cools
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Once crystal is added to
supercooled liquid, temperature
rapidly rises as crystallization takes
place
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Water bath
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Use of temperature
probes and LoggerPro
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Super cooling
 Air jacket
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Seeding and
Crystallization
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Better computer
software
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Ensuring uniformity in
heating substance
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Determination of liquid
state
Above: The thermometer
probe, stirring rod and
substance are crammed in a
small space.
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Temperature at which
amorphous solid
becomes brittle when
cooled and malleable
when heated
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Transitions
temperatures apply to
polymers or glass
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Kinetic energy
Zero
Resistance
Superconductivity
Meissner Effect
Quantum
Effects
Applications
Type I
Type II
Magnetic
Levitation
SUPERCONDUCTORS
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Varying physical properties:
 Heat capacity
 Critical temperature
 Critical field
 Critical current density
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Properties that stay the same:
 All superconductors have exactly ZERO resistance
NORMAL
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Electric resistant
Current is a “fluid of electrons”
moving across heavy ionic lattice
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Electrons constantly collide with
ions in lattice
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During collision, energy carried
by the current is absorbed by the
lattice and converted to heat →
vibrational kinetic energy of
lattice ions
SUPER
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Zero resistance
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Electronic fluid cannot be resolved
in individual electrons
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Instead, it consists of electrons
known as Cooper Pairs:
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attractive force between electrons
from the exchange of phonons
 Due to QM, the energy spectrum of
this Copper pair fluid has an energy
gap (limited energy ΔE that must be
supplied in order to excite the fluid)
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If ΔE is larger than thermal energy
of lattice fluid will not be scattered
by the lattice
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occurs when temperature T is
lowered below critical
temperature Tc (value of
critical temperature varies for
different materials)
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Usually 20 K to less than 1 K
(kelvins)
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Behavior of heat capacity (cv,
blue) and resistivity (ρ, green)
at the superconducting phase
transition
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If the voltage = zero, the resistance is
zero (sample is in superconducting
state).
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The simplest method to measure
electrical resistance of a sample is:
 Place in electrical circuit in series with
current source I
 Measure resulting voltage V
 The resistance is given by Ohm’s law:
The Meissner effect breaks down when the applied
magnetic field is too large.
 Superconductors can be divided into two classes
according to how this breakdown occurs:
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o TYPE 1: soft
o TYPE 2: hard
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Consists of superconducting metals and metalloids.
Characterized as the "soft" superconductors.
Require the coldest temperatures to become
superconductive.
Obtains intermediate state.
They exhibit sharp transition to a superconducting state.
Has "perfect" diamagnetism (ability to repel a magnetic
field completely).
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Lead (Pb)
Mercury (Hg)
Tin (Sn)
Aluminium (Al)
Zinc (Zn)
Beryllium (Be)
Platinum (Pt)
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BCS Theory is used to explain this phenomenon
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It states: When sufficiently cooled, electrons form "Cooper
Pairs" enabling them to flow unimpeded by molecular
obstacles such as vibrating nuclei.
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Consists of metallic compounds and alloys.
Characterized as “hard" superconductors
Difference from Type 1: transition from a
normal to a superconducting state is gradual
across a region of "mixed state" behavior.
Mixed state: do not change suddenly from
having resistance to having none (has a
range of temperatures where there is a
mixed state).
Not perfect diamagnets; they allow some
penetration of a magnetic field.

(Sn5In)Ba4Ca2Cu10Oy

HgBa2Ca2Cu3O8

Tl2Ba2CaCu2O6
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Sn2Ba2(Tm0.5Ca0.5)Cu3O8+

Pb3Sr4Ca2Cu5O15+
Pb3Sr4Ca2Cu5O15 [left]
Sn2Ba2(Ca0.5Tm0.5)Cu3Ox [right]
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When a superconductor is
placed in a weak external
magnetic field H, it
penetrates the super
conductor a very small
distance λ, called the
London penetration depth
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This decays exponentially to
0 within the bulk of the
material
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The Meissner Effect is the expulsion of a magnetic field
from a superconductor
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The Meissner effect was explained by the brothers Fritz and
Heinz London, who showed that the electromagnetic free
energy in a superconductor is minimized provided:
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H = magnetic field
Λ= London penetration depth
Magnetic Levitation
When temperature of superconductor in
a weak magnetic field is cooled below
the transition temperature…
A magnet levitating above a superconductor,
cooled by liquid nitrogen.
Surface currents arise generating a magnetic field which yields a 0 net
magnetic field within the superconductor.
 These currents do not decay in time, implying 0 electrical resistance.
 Called persistent currents, they only flow within a depth equal to the
penetration depth.
 For most superconductors, the penetration depth is on the order of
100 nm.
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Superconductivity: a quantum
phenomenon, thus several
quantum effects arise.
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1961: flux
quantization discovered - the
fact that the magnetic flux
through a superconducting ring
is an integer multiple of a flux
quantum.
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The Cooper pairs (coupled
electrons) of a superconductor
can tunnel through a thin
insulating layer between two
superconductors.
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Superconducting
magnets
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Maglev Trains
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MRI Imagers
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Power Transmission
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Electric Motors