Substances dissolve in water in different ways:
Once dissolved, substances can be electrolytes or nonelectrolytes:
Strong acids and ionic compounds are strong electrolytes, weak acids and weak bases are weak electrolytes. All other compounds are nonelectrolytes.
Memorize that all nitrates (NO3), acetates (C2H3O2), ammonium salts (NH4), and Group 1A metals are soluble.
Molecular equation — lists the reactants and products without indicating the ionic nature of the compounds.
Complete ionic equation — all strong electrolytes (strong acids, strong bases, and soluble ionic salts) are dissociated into their ions.
Net ionic equation — only lists ions that form the form the product, not spectator ions that are present on both sides.
When writing net ionic equations for double replacement reactions, dissociate all strong electrolytes (strong acids, ionic compounds) and cross out anything that remains unchanged from the reactants to the products. Precipitates do not dissociate into ions.
These strong acids are strong electrolytes, and therefore dissociate completely in water.
All other acids are weak acids, and do not dissociate completely in water.
All Group 1A and Group 2A (from calcium down) are strong bases.
Strong bases break down into OH- in water, e.g. NaOH → Na+ + OH-.
Metal oxides can also be considered bases, because they can combine with water to form a base, e.g. CaO + H2O → Ca(OH)2.
These are a sub-class of double-replacement reactions.
Reactions between an acid and a base are called neutralization reactions. When a base is a metal hydroxide, water and a salt (an ionic compound) are produced.
When a strong acid reacts with a strong base, both are able to dissociate. Therefore, the net ionic equation is always
H+ (aq) + OH- (aq) → H2O (l).
When a weak acid reacts with a strong base the net ionic equation will include nondissociated molecules. This is because the weak acid cannot be broken down into its ions, because it does not completely dissociate in water.
Single replacement reactions occur when one element replaces another in a compound.
Only elements higher on the activity series can replace elements that are lower on it. You will be provided with the activity series list if needed.
The loss of electrons is called oxidation, while the gain of electrons is called reduction (because its charge is reduced). One cannot occur without the other, and these reactions are often called redox reactions.
To determine if a redox reaction has occurred, we assign an oxidation number to each substance. Oxidation numbers are the imaginary charges the atoms would have if they were ions.
How to determine oxidation numbers:
After assigning oxidation numbers, one can look at the oxidation numbers of elements in the reactants and products: