Chemblog!

DIHYDROGEN MONOXIDE, OH MY!

AP: we looked at all permutations of sparingly soluble salts in equilibrium with a SATURATED solution of their respective ions. We showed that, given the Ksp of any of these salts, you can calculate (1) the molar solubility of the salt: "the number of moles of the salt that DISSOLVES per liter of solution FORMED" and (2) the MOLARITY of each of the ions in solution.
REMEMBER, though we use the same letter, s, the molar solubility of the salt does NOT mean the same thing as the MOLARITY of the dissolved ions. Of course, if you know the salt, you can get the molarity of the dissolved ions from the molar solubility of the salt simply by multiplying the molar solubility of the salt by the COEFFICIENT of the
dissolved ion in the balanced solution equilibrium equation.
We then went on to compare the solubilities of the SAME TYPES of salts and showed that you CANNOT readily/easily/by simple inspection of the Ksp's compare the solubilities of salts that have DIFFERENT empirical formula ratios.
We then briefly spoke about the heart of the unit, which involves Le Chatelier and the common ion effect. In most of these problems, we will do a TWO-STEP SOLUTION. We will do regular stoichiometry (COEFFICIENTS are KEY!) in a SRFC table; then, we will do an equilibrium calculation using the Ksp and an ICE table. This will seem long at first but these problems are shorter yet they require more thought than buffer problems. Check out the tutorials that are on our website.

In the "5 steps to a 5" book, we did the stoichiometry unit. Gauge your comfort level at approximating and NOT using a calculator on the timed part I questions. You must work accurately (first) and quickly (second) on the AP exam.

Honors: we finished Dalton's Law as applied to collecting a gas over water. When you see that situation, LOOK FOR the temperature and the Table of Vapor Pressure of Water values. Then ,apply Dalton's Law knowing that some of the total pressure is due to the pressure of the water vapor.
We then just began talking about Graham's Law as it relates to the kinetic energy, velocity, and rate of effusion of lighter vs. heavier molecules. Check out the formulas in the notes and tutorials and we will finish out the gas unit on Monday.

Regents: we explained and labelled the FIVE parts of a heating curve of a given substance showing the changes (or lack thereof) in kinetic and potential energy that occur for each part of the "curve".
We did quantitative energy calculations for each part. The parts that involve a change in temperature/average kinetic energy call for the formula "q = mcdT", which is heat added (in Joules) equals MC delta T ( that old skool rapper emcee Delta Tee!)
For the parts of the curve that have no temperature change due to the change in phase/potential energy only, we simply use q = mdH, which is heat added = mass times the heat of fusion (melting) or the heat of vaporization (boiling); all of the relevant values are in the Reference Table as are the formulas!
We will cool down with a cooling curve on Monday. There IS a test on Tuesday on the Gas Law unit as well as on the heating/cooling curves.
I will put up the text answers this weekend. STUDY STUDY STUDY. The end of the quarter is nigh.

Happy St. Patrick's Day!!!