Acids and Bases

• Neutral substances have a pH value close to 7.
• An acid is a substance that, when dissolved in water, increases the concentration of hydrogen ions.
• ▪A base is a substance that, when dissolved in water, increases the concentration of hydroxide ions.
• In Bronsted-Lowry, an acid is a proton donor.
• In Bronsted-Lowry, a base is a proton acceptor
• Amphiprotic substances can donate or accept a proton.
• The term conjugate means “joined together as a pair.”
• In every acid–base reaction, equilibrium favors transfer of the proton from the stronger acid to the stronger base to form the weaker acid and the weaker base.
• Amphoteric substances can act as either acids or bases.
• This special equilibrium constant is referred to as the ion product constant for water, Kw .
• pH is a method of reporting hydrogen ion concentration.
• ▪ Indicators, including litmus paper, are used for less accurate measurements
• pH meters are used for accurate measurement of pH; electrodes indicate small changes in voltage to detect pH.
• Bromthymol blue ranges from yellow to blue.
• Strong acids completely dissociate to ions. Weak acids partially dissociate to ions.
• Polyprotic acids have more than one acidic proton.
• ▪ It is always easier to remove the first proton than any successive proton.
• Like weak acids, weak bases have an equilibrium constant called the base dissociation constant.
• Lewis acids are electron pair acceptors.
• Lewis bases are electron pair donors.
• Buffer solutions are solutions of a weak conjugate acid-base pair.
• Buffers are particularly resistant to pH changes, even when strong acid or base is added.
• In electrochemical reactions, electrons are transferred from one species to another.
• Metals tend to lose electrons and are oxidized, non metals tend to gain electrons and are reduced.
• Loss of Electrons is Oxidation and that species is a Reducing Agent.
• Gain of Electrons is Reduction and that species is an Oxidising Agent.
• In order to keep track of what loses electrons and what gains them, we assign oxidation numbers.
• Elements in their elemental form have an ON of 0
• The oxidation number of a monatomic ion is its charge.
• Oxygen has an oxidation number of negative 2, except in the peroxide ion in which it has an oxidation number of negative 1.
• Hydrogen is +1 except in metal hydrides when it is negative 1
• Fluorine always has an oxidation number of negative 1.
• The other halogens have an oxidation number of negative 1 when they are negative; they can have positive oxidation numbers, however, most notably in oxyanions
• The sum of the oxidation numbers in a polyatomic ion is the charge on the ion.
• The sum of the oxidation numbers in a neutral compound is 0
• Law of conservation of mass: the amount of each element present at the beginning of the reaction must be present at the end.
• Conservation of charge: electrons are not lost in a chemical reaction.
• Half-reactions are a convenient way of separating oxidation and reduction reactions.
• The Leclanché dry cell is a type of primary (nonrechargeable) battery commonly used in household applications.
• It consists of a zinc anode, a manganese dioxide cathode, and a carbon rod surrounded by a mixture of ammonium chloride and zinc chloride as the electrolyte.