[spec] add notes for rest of chapter 9

diff --git a/chem/water.md b/chem/water.md
index 34beb005a14d29d2e51b190dd353314d1628ac96..f8600a64e2dccf37833eb039ebc7f4d2883549d2 100644 (file)
--- a/chem/water.md
+++ b/chem/water.md
@@ -79,6 +79,8 @@
 - special concentration unit in mol / L (abbbreviation M)
 $$c={n \over v}$$
 
+$$c_1v_2=c_2v_2=n\quad\leftarrow(\operatorname{constant})$$
+
 | Quantity               | Symbol  | Unit          |
 | ---------------------- | ------- | ------------- |
 | molar mass             | $M$     | g / mol       |
@@ -87,8 +89,10 @@ $$c={n \over v}$$
 
 ## Precipitation reactions
 Ions in solution combine to form a new compound.
+Occurs when concentration exceeds solubility.
 Precipitation reactions happen when water cannot dissociate ionic lattice structure.
 Precipitate (product):
+
 - generally insoluble in water
 - forms as solid particles that settle
 - forms from compounds insoluble in water