Sir Thomas Graham

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LECTURE 39

• Sir Thomas Graham

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Thomas Graham

• 1.diffusion of gases (Graham's law)
• 2.the absorption of gases by charcoal
• 3.solubility of gases
• 4.colloids and emulsions
• 5.phosphorus compounds including phosphine and
  inorganic phosphates
• 6.the aurora borealis

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Thomas Graham

• Graham's lectures were boring as far as his
  students were concerned. He is reported to have
  been awful at teaching elementary classes - he
  couldn't keep discipline, and he was hopeless at
  explaining his subject to an audience.
• Where he did excel, however, was in practical
  laboratory work. Graham was a brilliant
  experimentalist, who had the ability to inspire
  his students to do excellent research.

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Studied diffusion as a method of separating large
molecules from similar compounds, led to the
technique of dialysis. Graham's method is still
inuse in hospitals today, for purifying the
blood of patients with kidney failure.
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Dialysis Machine
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Homework435 442
Do problems 7- 12 on page 442
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Collect homework and handout
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Last time we discussed the combination of the
various gas laws into the ideal gas law

• It is not called ideal because it is perfect. It
  is called ideal because these equations only work
  in a perfect world with ideal gases

Pv nRT
But they do work
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What is the pressure in atmospheres exerted by a
.500 mole sample of nitrogen gas in a 10 L
container at 298K ?

• Remember to check units
• R .0821. Atm L /mole K.

Pv nRT
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What pressure, in atm is exerted by 0.325 mole
of hydrogen gas in a 4.08 L container at 35 C

• R .0821. Atm L /mole K.

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What mass of chlorine gas Cl2 in grams. is
contained in a 10 liter Tank at 27oC and 3.50
atm of pressure? 

• Remember to check units
• R .0821. Atm L /mole K.

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What is the volume of 71 grams of chlorine gas
Cl2 at 0 oC and 1 atm of pressure? 
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Stoichiometery and the ideal gas law

• At 1 atm of pressure and 27 oC, .5 liters of
  Hydrogen gas combine with excess oxygen gas to
  produce water and carbon dioxide gas. How many
  grams of water is produced

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You need to supply oxygen to your astronauts for
3 days!!!

• Remembering that potassium chlorate decomposes
  into potassium chloride and oxygen gas (2KCl03?
  2KCl 3O2) If you need to create 400 liters of
  oxygen gas at 1 atm and 27 oC, how many grams
  of KClO3 do you need to have on board to decompose

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What about when you want to study a condition
where you change the number of moles

• Set up the all inclusive ideal gas law as a
  before and after

SUPER EQUATION
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If n and T go unchanged then you get
Here you are comparing the initial condition to a
final condition
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By setting up the equations back to back then you
can find a final condition
Before and After
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Oxygen gas (O2, which is the molecular structure
when oxygen occurs in nature - remember it is
diatomic), is a product of the decomposition
reaction of potassium chlorate (KClO). 2 KClO
(s)? 2 KCl (s) O2 (g)When this reaction is
complete, 125 mL of oxygen gas are collected at
26C and 0.944 atm.Calculate the volume of the
gas at 14C and the same pressure.
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If a balloon has 200 ml at 55 Coand 1 atmWhat
is the new volume if the temperature is -211 Co
at the same pressure
http//www.academic.rccd.cc.ca.us/freitas/Chem2A/
Homeworks/Worksheets/Practice20Ideal20Gas20Law
20Problems.pdf
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We have talked about how chemicals have

• Specific mass
• Charge
• Exert pressure
• Tendency to clump
• Propensity to react
• Big dog vs small dog

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What determines how fast these vapors move
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We have even said that chemicals have a
particular aerodynamics
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Understand some terms

• Diffusion the spread of one substance through
  space, or though a second substance (such as the
  atmosphere)
• Effusion The rate of escape of a gas through a
  tiny pore or pinhole in its container

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The ability for a molecule or atom to move
through an area is called diffusion

• Show food coloring

We are not talking about mechanical mixing caused
by a independent force like turbulence.
Movement by virtue of inherent Kinetic energy
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Diffusion is the act of one substance traveling
through another substance.
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the gas particle travels through the maze of air
molecules at different speeds
the gas particle travels through the maze of air
molecules at different speeds
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ALL MOLECULES MOVE AND IF THEY ARE ALL THE SAME
TEMPERATUER WHICH MOVE FASTER

• THE SMALL OR THE LARGE?

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Which is faster
Which takes more energy to move?
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This ability or lack of ability for a molecule to
move through the maze of another molecule or
molecules is explained mathematically by looking
at the square root of the weight..
GRAHAMS LAW OF DIFFUSION
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Thomas Graham studied effusion in detail. He
found that at constanttemperature and pressure,
the rate of effusion of a gas is inversely
proportionalto the square root of the gass
molar mass, M.
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We can compare the speed of two gases
experimentally and mathematically
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A tube
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Two cotton balls that when they combine produce a
precipitate NH4Cl
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The fumes from the cotton balls react when they
hit but where will they meet???
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The smaller atom NH4 moved faster
But how much faster?
Football field and big girlfriend story
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Graham figured that the rate of movement equaled
the square of the molar masses
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Mathematically we see this by stacking Grahams
law
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How else are atoms slowed down and held back
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Membranes have a kind of restrictor grid that
prevents the movement
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Your bodies have that same kind of restrictor

• Lungs Skin
• Brain Nerves
• Intestines Eyes
• Kidneys Blood vessels