Types of Chemical Reactions
and Solution Stoichiometry
I. Water, The Common Solvent
A. Water is a polar molecule where one end has a partial positive charge and the other end has a partial negative
charge.
B. Hydration is when the ions of a substance "fall apart" due to the attraction to water's partial charges.
C. "Like dissolves like" as seen when a polar molecule dissolves polar molecules and vice versa.
II. Aqueous Solutions: Strong and Weak Electrolytes
A. The substance dissolves in a solution is called a solute the other substance, such as water, is called the solvent.
Strong electrolytes conduct electricity efficiently while weak electrolytes do not.
B. Strong electrolytes dissolve completely into ions in water. These include strong salts, acids, and bases.
C. Weak electrolytes dissolve only slightly into ions in water. One example is acetic acid.
III. The Composition of Solutions
A. Molarity is moles of solvent per liter of solution. A standard solution is a solution whose molarity is accurately
known. Adding a known amount of grams in a flask and filling the flask with water to the liter mark makes a standard
solution
B. Stock solutions are concentrated forms of solutions. These solutions are diluted using water to produce a less-concentrated
version for experiments. A volumetric flask and a pipet are used to dilute concentrated solutions. The formula
to find the molarity of a solution after dilution is M1V1=M2V2.
IV. Types of Chemical Reactions
A. Precipitation Reactions: A reaction where two solutions are mixed and a solid forms out of the reaction. This
solid is called a precipitate. To predict what precipitate will form out of the reaction a solubility table is
used:
Soluble In Water | Insoluble In Water |
· NO3-- salts | · NaOH, KOH |
· Chloride, Bromide, and Iodide | · BaSO4, PbSO4, HgSO4, and CaSO4 |
· Sulfate Salts (SO4) | · Most (OH) salts\ |
· Li, K, Na, Cs, Rb, NH4 | · S2-, (CO3)2-, (CrO4)2-, (PO4)3- |
· Ag, Pb, Hg |
V. Balancing Oxidation-Reduction Reactions
A. Balancing reactions in an acidic solution involves several complicated steps. Before anything the reaction is
split up into two reactions where one substance is being reduced and the other is oxidized.
1. For each half reaction: (a) Balance all elements except Oxygen and Hydrogen. (b) Balance Oxygen using H2O. (c)
Balance Hydrogen using H+. (d) Balance the charge using electrons.
2. Multiply the half-reactions by an integer to equalize the number of electrons because they must cancel out.
3. Add the half reactions and cancel all species.
4. Check that the reaction has balance species and charge.
B. Balancing reactions in basic solutions is strikingly similar to balancing Acidic equations except for these
extra steps:
1. Balance the equation as if H+ ions were present.
2. To both sides of the obtained equation add a number of OH- ions to combine with the H+ to make water.
3. Cancel out water on both sides.
4. Check for balanced species and charges.
Vi. Simple Oxidation - Reduction Titrations
A. Same as the Acid-Base Titration except for Oxidation.