- On the right is the triclinic Bravais lattice. It has a
¹
b ¹ c and a ¹ b ¹
g ¹ 90°!
I've put atoms on the corners of the lattice. (You can't see the 8th one, hiding in the opposite
corner, but you know it's there.) Since there aren't any 90° angles, you might think that it
will be difficult calculating how many atoms are in this unit cell, but it isn't hard to
intuit it.
Tell me not only how many atoms there are in this unit cell but also explain your reasoning.
- At right is the unit cell of a molybdenum oxide. The structure is called "rutile" after its
parent crystal, and there are many examples of it in Nature.
Shown is a perspective and a top view. The greens are Mo and the reds are O (not to scale).
(The image is from the Naval Research Lab in Washington.)
- Since all the angles are 90°, to which crystal system does this belong?
- What is the empirical formula for this molybdenum oxide?
- How would the freezing point temperature of an ideal solution change if some of the
solute coprecipitated with the solvent? Why?
(Kf presumes
that only the solvent solidifies.)
- How would you create a cycle (a path) on the phase diagram that starts at
P1, T1)
and returns to that same point having passed through a boiling point
but not through
any condensation point? Use a sketch of a phase diagram in explaining your answer.
- Now that we've all apparently grown comfortable with bottled water that costs more
than gasoline, some (rich) imbecile has come up with the concept beverage based upon
oxygenated water as a health drink! Let's debunk this sucker with Henry's Law given that
KH = 958 atm / M for O2 at 37°C.
Assume we fill the standard 12 floz can (1 fluid ounce = 29.57353 ml) with water
at 37°C under the painfully high pressure of 2 atm of pure O2.
Calculate the number of moles of dissolved O2 in the can and compare it with the number of
moles of O2 in just one 4 L lung full of normal air at the same T.
- On the top of a high mountain, the air has only half the pressure at sea level. If
cooking speed varies linearly with (absolute) temperature
(it's really more complex),
by what fraction must we increase the
cooking time for a dish prepared in a double boiler on that mountain top (relative to
what it would be at sea level)? (DHvap of water
is about 44 kJ/mol.)
- I've just read my wife (the gourmet cook) that last question.
She didn't know that the water
boils cooler on mountain tops. So she insists that I make this question easy in compensation.
(Sorry, Doug.)
OK...we've concluded earlier that a tall tree can't suck water up from its roots any higher
than 33 feet, because that's one full atmosphere. "But the Sequoia trees," my wife points out,
"are 10 times higher than that." What if they used osmotic pressure to do the trick instead?
What would the concentration of moles of everything in their sap have to be? Assume 25°C.
"Gosh, it sounds hard," says my wife, "You're
sure it's easy?" Tell her, next time you see her, that it was a plug-in.
And, no, sap doesn't have to have that concentration; the tree uses capillarity too.
- Beef jerky (more properly, "jerked beef")
is dried and salted beyond all but the most indiscriminate palate.
But it's not treated that way to improve its taste but to act as a
bactericide. Beef jerky simply doesn't spoil,
but then those of us not inured to
it might be tempted to ask, "How would you know if it did?"
What is the mechanism of its preservation? How do the bacteria, always present,
become thwarted? What happens to these mean little, oversexed water sacks that our
chapters can tell us about?
- What's the molarity, [N], of 25% by weight aqueous ammonia if its density is 0.9106 g/cc.
Does the fact that NH3 is a weak base play any role here since we asked for [N]
instead of [NH3]?
- You're asked to develop a recommendation for an antifreeze solution of
ethylene glycol (C2H6O2) in water that will keep
a vehicle running at -50°F (Antartica).
How many kilograms of the
stuff would you have to dissolve in each kilogram of water to do the job?
Kf = 1.86 °C / m for water.
You try out your solution, and it freezes well higher than -50°F.
This sends you to the Handbook of Chemistry and Physics where you learn that the
freezing point of pure ethylene glycol is -17°C! What do
you then recommend for the -50°F engine?
(This must be for the mild season, since winter in Antartica reaches
-126°F!)