Lesson Sequence: Day 4
Day 4: Molarity, lab 3.

Class discussion  Comparing the behavior of chemicals in solutions of water.

= Cs^{+} 
= Na^{+} 

= Cl^{} 
= Cl^{} 
Question: Will these 2 solutions conduct the same amount of current?
Rule (Students derive): To obtain the same behaviour of two salts in solution, they must have the same ratio of # of molecules to volume of water.
Definition: Molarity  a 1 molar (1M) solution of any chemical has a concentration in water of exactly 1 mole per liter of water.

Example: to obtain a 1M solution of NaCl
from periodic table,
MW of Na = 22.990 gm/mole

MW of Cl = 35.453 gm/mole

MW of NaCl = 58.443 gm/mole 
so, to make up a 1M solution of NaCl, dissolve 58.443 grams of salt in
1.0 liter of water. (This assumes the salt does not contribute significantly to the volume of the solution.)
 Example: to obtain a 1M solution of KCl,
from periodic table,
MW of K = 39.098 gm/mole

MW of Cl = 35.453 gm/mole

MW of KCl = 74.551 gm/mole 
so to make up a 1M solution of KCl, dissolve 74.551 grams of this salt in 1.0 liter of water.(This assumes the salt does not contribute significantly to the volume of the solution.)
Notice that for these two salts you would add different masses
of each salt to a liter of water. The # of molecules
per liter for each salt, however, would be identical.
What if you want to make up only 100 mL of 1M NaCl? How would this salt
solution be made up? (Have class solve)
Class problem, (finish for homework). Determine the molecular weight (MW) for each compound in the table and then the mass of salt you would add to each volume of water to make up salt solutions at the concentrations indicated at the top of each column of the
table.


1 M solution 
0.3 solution 
compound 
MW 
1 liter 
100 mL 
1 liter 
100 mL 
NaCl 





Nal 





NaF 





KCl 





CsCl 





CsBr 





MgCl_{2} 





CaCl_{2} 





SrCl_{2} 





BaCl_{2} 





 Do LAB 3
 Homework
 finish table
 finish writeup of LAB 3.
DAY 1
DAY 2
DAY 3
DAY 5
Teacher Info


