Question: I was wondering how you can tell what kind of Intermolecular forces
are in a substance just by looking at the molecular formula?
Answer: No, you need to know its structure before you can tell what kind of
intermolecular forces are in a molecule. That way you can tell if it's polar or
whether it has any O-H, N-H, or F-H bonds.
So solid CO2 is held together by these London dispersion forces?
As I understand it, a temporary polarity in one molecule induces polaritiy in
neighbors and so forth. Now, in solid CO2, do all of the molecules
have some similar dipole moment because this seems like it would lead to an
overall dipole moment for the solid OR are the dipoles sort of continuously
switching around in direction?
It's the second one, with the dipoles switching around randomly. CO2
can't have a permanent dipole because the bond polarities cancel out in this
One of our lab questions was to use the van Hoff i factor in an equation to
determine the new freezing point of water and NaCl.
Delta T = 2 (1.00 m/kg)(1.86°C • kg/mol)
Delta T = 3.72°C
I thought it should have been less than the regular freezing point which is 0°C.
I didn't understand.
The equation that you are using is generic so that it will work with changes
in melting points OR changes in boiling points. Melting (freezing) points go
down in the presence of impurities and boiling points go up. What you are
calculating in either case is the CHANGE. You need to add or subtract from the
"normal" measurement in order to find the new value.
When talking about colligative properties, how do we know what molecules will
You should assume that soluble ionic compounds will ionize in water. Nonsoluble
ionics don't do anything, including dissolving. Strong acids and bases will separate.
Other covalent compounds will dissolve without separating.
Is the difference in an atom's size and ionization energy large enough between
rows that it can account for the big lead in melting points?
Melting points are usually related to intermolecular attractions rather than
size or ionization energy. Larger atoms with their larger number of electrons
have stronger London forces. The alkali metals break this trend and I cannot
provide a simple explanation for this strange behavior.
How many minutes will be required to deposit 1.00 g of Cr metal from an aqueous solution of CrO4- using a current of 6.00 amperes?
Thus, the answer is (b), 30.9 minutes.
Hey, I was wondering if you could give me some studying advice other than
sleeping and eating, both of which I will get plenty of. I was thinking of
doing the practice problems you assigned, and then working your example test
and quizzes up to the point that we have covered and then reviewing our quizzes
and notes. Do you think this will be sufficient? Any advice would be great, I
fear your test!
The approaches you are following are the ones I normally suggest. What I'll
ask you at this point is how many problems do you miss on the suggested problems
and what do you do when you miss a few? The solutions manual is now on
reserve--finally. When you miss a question, you should go back to the textbook
and read the relevant section to help clarify the concepts in your mind. And you
should come see me so that I can ask you leading questions to help you work on the
correct thought patterns.
If you've been doing the suggested problems and can handle the quizzes and an
essay question, you should be fine on the test. Don't get overly stressed,
because that can cause you to do stupid things on the test.
Hey, I was wondering if you could do problem 4 on your 4 quiz in 1998, I get
a big number, not sure if its right...
4. Ethene is converted to ethane by the reaction shown. If 1250. L of
ethene (C2H4) is reacted with 975 L of hydrogen (H2)
at 25.0 atm and 300 oC, what is the theoretical yield (in grams) of
C2H4 (g) + H2 (g)
First we use the ideal gas law to figure out how many moles of each gas we have.
Actually, we can look at the conditions and notice that both gases are at the
same conditions. That means there are more moles of ethene than of hydrogen, since
there is a larger volume. Thus, the hydrogen is the limiting reagent. So we'll be
lazy and not do the math for the ethene.
Solving the ideal gas equation for the number of moles of hydrogen,
V = 975 L
R = 0.08206
T = 573 K
n = 518 moles