LinkExchange Member

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

Describing Reactions in Solution: The molecular equation only shows the reactants and the products without any knowledge of the charges. The complete ionic equation shows all ions in the equation. After eliminating all spectator ions in the equation the net ionic equation if formed. This equation shows the two ions that react to form a precipitate. The stoichiometry of precipitation involve one of the ions being a limiting reactant.
B. Acid-Base Reactions are about the same as precipitation reactions except that they usually involve H+ and OH- ions in the net ionic equation. Titration is using a known reaction between a substance with known mass that is titrated into a solution that contains a substance to find its volume or mass.
C. Oxidation-Reduction Reactions involve reactions where one substance gains electrons while the other loses electrons. The substance that gains electrons is reduced and is called the oxidizing agent and the substance that loses electrons is oxidized and is called the reducing agent. Reactions can be analyzed to find the substances that are oxidized and reduced by looking at the oxidation levels of substance before and after the reaction. Oxidation levels of substance can be found using the following rules:
1. Elements (in their natural form) have an oxidation state of 0.
2. The oxidation of a monatomic ion is the same as the charge. For example Na is +1 and Cl is -1.
3. Oxygen (O) is always assigned a state of -2 unless it is Peroxide compounds such as H2O2 where it is -1.
4. In covalent compounds with nonmetals Hydrogen has a state of +1.
5. Fluorine is always assigned -1.
6. The sum of the oxidation states in a neutral molecule must equal zero (0). The sum of the oxidation states in a ion must equal its charge, ex: +1.

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.