Monday, February 05, 2007
Monday, Day 3
AP: we did a couple of heterogeneous equilibrium problems involving solids and gases. We learned that the AMOUNT of solids or liquids in no way shape or form affects the equilibrium concentrations or partial pressure of any gaseous reactants or products. Also, since ICE tables only contain CONCENTRATIONS, just cross out the entire column involving any solid or liquid.
HOWEVER, from the changes in concentrations of any aq or gaseous reactant or product and the COEFFICIENTS from the balanced equation, you can calculate the loss or gain in MOLES of any solid or liquid reactant or product.
Tomorrow, we will EXPLAIN, DRAW, and, complete Le Chatelier's Principle at the PARTICLE level in terms of stresses and EFFECTIVE COLLISIONS PER SECOND.
Then, we begin our new unit: Acids and Bases!
Honors: we did some of the more difficult % composition to empirical formula problems; these problems have empirical formulas that take an extra step to decipher. For example, if after dividing the number of moles of atoms of each element in your compound by the lower (est) number of moles of one of the elements, you then get a NON-integer ratio, you must do one more step. So, if you get, for example, C 1.00 H 2.666 , then change the numbers to fractions to see what number is in the denominator of the fraction...i.e. C 1 H 8/3 (because 2.666 = 2 and 2/3 = 8/3) ; so, multiply both subscripts by 3 in order to eliminate the fraction and you get C3H8, which is the correct empirical formula!
We then learned about the SCALING FACTOR which is the ratio of the gram-molecular mass (of the molecule) to the EMPIRICAL formula mass that you calculated from the percent composition. Once you get the scaling factor, multiply the subscripts of the empirical formula by the scaling factor, which will net you the actual molecular formula.
Regents: we reviewed the concept of moles and the atomic mass scale; then we got much more practical and calculated the molar masses of atomic, molecular, and ionic substances. These masses are called gram-atomic mass, gram-molecular mass, and gram-formula mass, respectively. Just set up a table to keep track of each element and the number of moles of each in a given compound and you will be able to methodically calculate the molar mass of any substance.
Tomorrow, I will post worksheets regarding these calculations. Bring your Orange Review Books to class this week; we will be doing problems from that book during class.
HOWEVER, from the changes in concentrations of any aq or gaseous reactant or product and the COEFFICIENTS from the balanced equation, you can calculate the loss or gain in MOLES of any solid or liquid reactant or product.
Tomorrow, we will EXPLAIN, DRAW, and, complete Le Chatelier's Principle at the PARTICLE level in terms of stresses and EFFECTIVE COLLISIONS PER SECOND.
Then, we begin our new unit: Acids and Bases!
Honors: we did some of the more difficult % composition to empirical formula problems; these problems have empirical formulas that take an extra step to decipher. For example, if after dividing the number of moles of atoms of each element in your compound by the lower (est) number of moles of one of the elements, you then get a NON-integer ratio, you must do one more step. So, if you get, for example, C 1.00 H 2.666 , then change the numbers to fractions to see what number is in the denominator of the fraction...i.e. C 1 H 8/3 (because 2.666 = 2 and 2/3 = 8/3) ; so, multiply both subscripts by 3 in order to eliminate the fraction and you get C3H8, which is the correct empirical formula!
We then learned about the SCALING FACTOR which is the ratio of the gram-molecular mass (of the molecule) to the EMPIRICAL formula mass that you calculated from the percent composition. Once you get the scaling factor, multiply the subscripts of the empirical formula by the scaling factor, which will net you the actual molecular formula.
Regents: we reviewed the concept of moles and the atomic mass scale; then we got much more practical and calculated the molar masses of atomic, molecular, and ionic substances. These masses are called gram-atomic mass, gram-molecular mass, and gram-formula mass, respectively. Just set up a table to keep track of each element and the number of moles of each in a given compound and you will be able to methodically calculate the molar mass of any substance.
Tomorrow, I will post worksheets regarding these calculations. Bring your Orange Review Books to class this week; we will be doing problems from that book during class.
# posted by C @ 2:51 PM 
