13.4 Chapter summary

13.4 Chapter summary (ESBR7)

Presentation: 246T

• There are many different types of reactions that can take place. These include acid-base and redox reactions.

• The Arrhenius definition of acids and bases defines an acid as a substance that increases the concentration of hydronium ions (\(\text{H}_{3}\text{O}^{+}\)) in a solution. A base is a substance that increases the concentration of hydroxide ions (\(\text{OH}^{-}\)) in a solution. However this description only applies to substances that are in water.

• The Bronsted-Lowry model defines acids and bases in terms of their ability to donate or accept protons.

• A Bronsted-Lowry acid is a substance that gives away protons (hydrogen cations \(\text{H}^{+}\)), and is therefore called a proton donor.

• A Bronsted-Lowry base is a substance that takes up protons (hydrogen cations \(\text{H}^{+}\)), and is therefore called a proton acceptor.

• An amphoteric substance is one that can react as either an acid or base. Water (\(\text{H}_{2}\text{O}\)) is an example of an amphoteric substance.

• An amphiprotic is one that can react as either a proton donor (Bronsted-Lowry acid) or as a proton acceptor (Bronsted-Lowry base). \(\text{HCO}_{3}^{-}\) and \(\text{HSO}_{4}^{-}\) are examples of amphiprotic substances.

• A conjugate acid-base pair refers to two compounds in a reaction (one reactant and one product) that transform or change into the other through the loss or gain of a proton.

• The reaction between an acid and a base is a neutralisation reaction.

• Acids and bases are used in domestic uses (for example calcium carbonate on acidic soil) in biology (for example in antacids for stomach ulcers) and in industry (for example in absorbing harmful \(\text{SO}_{2}\) gas),.

• Indicators are chemical compounds that change colour depending on whether they are in an acid or in a base.

• When an acid reacts with a metal hydroxide a salt and water are formed. The salt is made up of a cation from the base and an anion from the acid. An example of a salt is potassium chloride \((\text{KCl})\), which is the product of the reaction between potassium hydroxide \((\text{KOH})\) and hydrochloric acid \((\text{HCl})\).

• When an acid reacts with a metal oxide a salt and water are formed. An example is the reaction between magnesium oxide \((\text{MgO})\) and hydrochloric acid \((\text{HCl})\).

• When an acid reacts with a metal carbonate a salt, water and carbon dioxide are formed. An example is the reaction between calcium carbonate \((\text{CaCO}_{3})\) and hydrochloric acid \((\text{HCl})\).

• Oxidation is the loss of electrons by a molecule, atom or ion.

• Reduction is the gain of electrons by a molecule, atom or ion.

• A redox reaction is one involving oxidation and reduction, where there is always a change in the oxidation numbers of the elements involved. Redox reactions involve the transfer of electrons from one compound to another.

• An oxidation number is the charge an atom would have if it was in a compound composed of ions.

• If the oxidation number of a species becomes more positive, the species has been oxidised and if the oxidation number of a species becomes more negative, the species has been reduced.

• A half reaction is either the oxidation or reduction reaction part of a redox reaction. In the two half-reactions for a redox reaction the number of electrons donated is exactly the same as the number of electrons accepted.

• An element that is oxidised is called a reducing agent, while an element that is reduced is called an oxidising agent.