Friday, May 11, 2007
Fri-Day 5
AP: here's the deal with question 1 from today's class. (1.) we didn't do anything wrong (other than feeling unsure and hesitating). (2.) Our answers were correct as solved by using the SRFC table into the ICE table, which we have ALWAYS done whenever a weak acid was titrated by a strong base or vice versa. (3.) You COULD have used Henderson-Hasselbalch as usual EXCEPT, in this ONE case/permutation of this question type, there is no significant advantage to using the equation because you would have to solve for the concentration of the acid, [HA], in the equation and STILL convert to moles by multiplying by the solution volume.
The bottom line: it is a good thing that we saw this (final) permutation of the titration question. With respect to acid-base equilibria,now we can say that we have seen it ALL.
Another important lesson, if you DO get stuck on ANY part II (or part I) question, just write out what you know and MOVE ON!!! If you have time (which you should have if you keep moving forward efficiently and confidently), you may think of the solution when you re-read and revisit the question with "fresh eyes".
We did a spec-20 problem and used Beer's Law (woot!). The AP has been obsessed with Beer's Law lately so, on Tuesday, we will see whether that streak continues.
Saturday at 10 AM, we'll meet again for a timed and proctored complete exam. This will be another good opportunity to simulate the real deal and to further confirm your score on this STANDARDIZED ( equivalent in content and scoring via scaling) exam.
Honors: we balanced some of the more difficult redox equations. In these equations, once the charge balancing is done, other reactants had to be balanced by mass. Generally, we balance elements other than O and H, and finish balance the O and then the H (usually by changing the coefficient of H2O. Practice more of these equations on the worksheets and text, this weekend. Also, if an element has a subscript in its formula, carry the element WITH its subscript into the oxidation and/or reduction half reaction.
We also discussed how to recognize easily whether a reaction is redox or not; the guaranteed redox reactions are
(1.) synthesis/combination and (2.) cationic or anionic single replacement.
Double replacement reactions are NOT redox reactions (you will see that the oxidation numbers do NOT change in these reactions). Decomposition reactions might or might not be redox depending on whether or not the compound decomposes completely into its elements or just into simpler compounds.
Regents: we balanced some of the more difficult redox equations. In these equations, once the charge balancing is done, other reactants had to be balanced by mass. Generally, we balance elements other than O and H, and finish balance the O and then the H (usually by changing the coefficient of H2O. Practice more of these equations on the worksheets and text, this weekend. Also, if an element has a subscript in its formula, carry the element WITH its subscript into the oxidation and/or reduction half reaction.
We also discussed how to recognize easily whether a reaction is redox or not; the guaranteed redox reactions are
(1.) synthesis/combination and (2.) cationic or anionic single replacement.
Double replacement reactions are NOT redox reactions (you will see that the oxidation numbers do NOT change in these reactions). Decomposition reactions might or might not be redox depending on whether or not the compound decomposes completely into its elements or just into simpler compounds.
The bottom line: it is a good thing that we saw this (final) permutation of the titration question. With respect to acid-base equilibria,now we can say that we have seen it ALL.
Another important lesson, if you DO get stuck on ANY part II (or part I) question, just write out what you know and MOVE ON!!! If you have time (which you should have if you keep moving forward efficiently and confidently), you may think of the solution when you re-read and revisit the question with "fresh eyes".
We did a spec-20 problem and used Beer's Law (woot!). The AP has been obsessed with Beer's Law lately so, on Tuesday, we will see whether that streak continues.
Saturday at 10 AM, we'll meet again for a timed and proctored complete exam. This will be another good opportunity to simulate the real deal and to further confirm your score on this STANDARDIZED ( equivalent in content and scoring via scaling) exam.
Honors: we balanced some of the more difficult redox equations. In these equations, once the charge balancing is done, other reactants had to be balanced by mass. Generally, we balance elements other than O and H, and finish balance the O and then the H (usually by changing the coefficient of H2O. Practice more of these equations on the worksheets and text, this weekend. Also, if an element has a subscript in its formula, carry the element WITH its subscript into the oxidation and/or reduction half reaction.
We also discussed how to recognize easily whether a reaction is redox or not; the guaranteed redox reactions are
(1.) synthesis/combination and (2.) cationic or anionic single replacement.
Double replacement reactions are NOT redox reactions (you will see that the oxidation numbers do NOT change in these reactions). Decomposition reactions might or might not be redox depending on whether or not the compound decomposes completely into its elements or just into simpler compounds.
Regents: we balanced some of the more difficult redox equations. In these equations, once the charge balancing is done, other reactants had to be balanced by mass. Generally, we balance elements other than O and H, and finish balance the O and then the H (usually by changing the coefficient of H2O. Practice more of these equations on the worksheets and text, this weekend. Also, if an element has a subscript in its formula, carry the element WITH its subscript into the oxidation and/or reduction half reaction.
We also discussed how to recognize easily whether a reaction is redox or not; the guaranteed redox reactions are
(1.) synthesis/combination and (2.) cationic or anionic single replacement.
Double replacement reactions are NOT redox reactions (you will see that the oxidation numbers do NOT change in these reactions). Decomposition reactions might or might not be redox depending on whether or not the compound decomposes completely into its elements or just into simpler compounds.
# posted by C @ 10:27 AM 
