Acid-base and Redox Reactions

Two of the main types of chemical reactions are acid-base reactions, and redox reactions. Both of these involve the transfer of fundamental particles from one substance to the other. A knowledge of what each type of reaction involves is important to the understanding of many other aspects of chemistry. The other main type of chemical reaction is ion exchange, which is the type of reaction involved in the standard tests for the anions.

In acid-base reactions, protons are transferred from the acid to the base.

In redox reactions, electrons are transferred from the oxidising agent to the reducing agent.

Definitions

The important definitions of acid-base. and of redox chemistry that should be known are listed below. Many of them involve “pairs” of definitions, that are opposites of each other, e.g., a brønsted acid is a proton donor while a brønsted base is a proton acceptor.

For the Leaving Certificate, the main areas to be covered are:
(i) How to label the various substances in an acid-base equation
(ii) The tests for the various anions, e.g., sulfate, chloride, carbonate, etc.
(iii) How to calculate a pH value (this is part of Equilibria)
(iv) How to calculate oxidation numbers
(v) How to balance redox equations.


How to label the various substances in an equation

The Brønsted acid and base are the reactants (i.e., those written on the left-hand side of the equation); the conjugate substances are the products (i.e., those on the right-hand side). The Brønsted acid is the substance which loses the proton in the course of the reaction (and is converted to the conjugate base). The Brønsted base is the substance which gains the proton (and is converted to the conjugate acid).


Important Acid Reactions

Acid + base —> salt + water
Acid + carbonate —> salt + water + CO2


Oxidation Numbers

It is important to know the rules for calculating oxidation numbers and how oxidation numbers are used to balance redox equations. The rules will be found in any of the standard Leaving Certificate chemistry textbooks.

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