Ionic Chemistry

Acid-Base Reactions

  • The acidity of a solution is the concentration of H (protons)
  • Acidity relates specifically to the concentration of H+ , H-
  • An acid is a substance which can lose one or more equivalents H+. and a base is a substance which can pick up H+
  • When an acid reacts with a base, H+ is transferred
  • Water can behave as an acid or a base (amphoteric)
  • Water can also ionize itself
  • As most acid/ base reactions take place in water, it is common to not include it in any equations.

Equilibrium – Acid Base Reactions

  • Equilibrium is relevant when talking about acidity
  • Many reactions can go backward as well as forward will remain stable- the system is said to be at equilibrium
  • After some time, the speed of the forwards reaction will be the same as the backwards reaction
  • The concentrations of the reactants and the products
  • Acids which only dissociate to a small extent are called weak acids

Strength and Concentration – Acid-Base Reactions

  • Strength and concentrations are different
  • Strength refers to the extent of dissociation
  • Concentration refers to the amount of the acid in solution
  • It is possible to have a concentrated solution of a weak acid or dilute solution of a strong acid.
  • Concentration is measured in mol dm-3
  • Acid strength could be measured by using Ka values but these are generally not convenient numbers

Acids in water

  • When an acid is added to water H will change
  • The acidity of a solution is conveniently expressed by pH
  • Pure water has a pH of 7
  • Acidic solutions will have greater H and pH < 7
  • Basic solutions will have smaller H and pH > 7

Bases – Acid- Base reactions

  • Bases can accept protons
  • As with the acids the strength of the base can be shown by the equilibrium constant
  • More commonly base strength is represented by pKa by considering the reaction of the conjugate acid 

Strong and weak bases

  • Strong bases include NaOH and KOH- these will be completely dissociated in water
  • Amines are examples of weak bases

Polyprotic Acids

  • Some acids can lose more than one proton and hence have more than one Ka value
  • Successive removals become more difficult as the molecule has to bear a greater and greater charge
  • It often forms the basis of buffer solutions

Buffer Solutions

  • Are specific recipes containing a weak acid and its conjugate base or a weak base and its conjugate acid
  • Buffers have the property of being able to oppose changes in pH despite the addition of acid/base
  • Important in maintaining pH in experimental set ups (either chemical or biological)
  • Studies involving proteins require buffered solutions to preserve their structures
  • Enzymes are often highly sensitive to changes in pH
  • Buffers can also help to preserve drugs in solutions for periods of time by preventing acidic/basic degradation.
  • Water has no buffering capacity
  • A buffered solution would be able to maintain its pH within a few hundredths of a pH unit after the addition of similar amounts of acid or base.

Buffer Solution in action

  • A common buffer system is the ethanoic acid/ sodium ethanoate solution
  • This equation is useful for buffer calculations but during its derivation some assumptions have been made
  • The biggest assumption is that the equilibrium concentrations are the same as the concentrations of the components which are mixed to make the buffer
  • To ensure that the effects of the assumptions are minimized, the concentrations of the components should exceed Ka by at least 100 times.

Buffer Capacity and Ranges

  • Buffers do not have limitless ability to resist change in pH
  • Addition of sufficient acid or base will exceed the capacity of the buffer and a significant change in pH will be observed.
  • This will happen before one of the buffer components is completely changed to the other
  • The more concentrated the buffer the greater its capacity
  • The most effective buffer will be one which has identical concentrations of acid/ conjugate base
  • The buffer will be effective            one unit either side of this point

Buffer Solution Ranges

  • The ethanoate buffer gave a pH of 4.74 with equal concentrations of acid and conjugate base so ethanoate buffers will be effective in the pH range 3.74 – 5.74
  • Buffer recipes can be found in books to ensure sufficient capacity, giving solutions of various pH

Other Ionic Reactions

  • Carbonates react with acids to form Carbon Dioxide gas
  • Sulfites react with acids to form sulfur dioxide gas
  • The above two reactions are overall reactions of the actual molecular events.
  • Sulfides react with acids to form hydrogen sulfide gas


  • To introduce the concept of receptors as drug targets
  • To introduce the concepts of agonists and antagonists
  • To consider the types of interaction which drugs may make with their targets
  • To consider the role of water in drug-receptor binding
  • To consider the roles of conformation and shape in receptor binding

Solutions and Molarity

  • The majority of ionic chemical reactions take place in aqueous solution
  • Molarity is the measurement of the concentration of a chemical in solution
  • The unit of molarity is the Molar (M)
  • In diluting a solution, the number of moles remains constant.

Redox Reactions

  • RedOx reactions are by far the most important type of reactions
  • RedOx reactions involve the transfer of electrons from one species to another
  • Oxidation is defined as the loss of electrons
  • Reduction is defined as the gain of electrons
  • Oxidation and reduction must occur simultaneously since the electrons lost in the Oxidation must go somewhere.
  • The Net Ionic Equation shows the reaction of iron metal with CU2 to produce iron and copper metal

Oxidizing and Reducing Agents

  • The species that is reduced itself and causes another species to be oxidized therefore known as the oxidizing agent
  • The species that are oxidized and causes another to be reduced is therefore known as the reducing agent

Oxidation Number

  • The concept of oxidation numbers is a simple way of keeping track of electrons in a reaction.
  • The oxidation number of an atom in a substance is the actual charge of the atom if it exists as a monatomic ion.

Rules for Assigning Oxidation Numbers

  • It is possible to predict the upper and lower limits of main group elements
  • The upper limit is equal to the group number
  • The lower limit is the group number -8
  • Oxygen will never have an ON = +6 and Flourine will never have an ON = +7
  • There are two ways to deal with RedOx Reactions (1) Treat them as any other reactions (2) We can write this reaction in terms of two half- reactions.
  • A half-reaction is one of the two parts of an oxidation-reduction reaction. One involves the loss of electrons and the other involves the gain of electrons (reduction)

Combination Reactions

  • A combination reaction is a reaction in which two substances, usually two elements, combine to form a third substance
  • A decomposition reaction is a reaction in which a single compound reacts to give two or more substances
  • A displacement reaction is a reaction in which an element reacts with compound, displacing an element from it.
  • A combustion reaction is a reaction in which a substance reacts with oxygen, usually with the rapid release of heat to produce a flame

Balancing RedOx Reactions

  • We can split the reaction into two half-cells before balancing
  • We will balance RedOx reactions using the Oxidation Number method


  • Assign ON to ALL elements in reaction
  • Identify the species that are oxidized/ reduced
  • Compute the number of e s lost in OX and gained RED draw lines between the two pairs including the number of e s lost/ gained
  • Multiply one or both reactions so that both numbers match, use these factors as balancing coefficients
  • Balance other species that were not involved in the electron exchange

Quantitative Analysis

  • Analytical chemistry deals with the determination of composition of materials that is the analysis of materials
  • Involves the determination of the amount of a substance or species present in a sample of material

Gravimetric analysis

  • Is a type of quantitative analysis in which the amount of a species in a material is determined by converting the species into a product that can be isolated and weighed.
  • Precipitation reactions are often used in gravimetric analysis
  • The precipitate from these reactions is then filtered, dried and weighed.


  • Most reactions are either precipitation reactions, acid-base reactions or oxidation-reduction reactions
  • Acid base reactions are non-proton reactions
  • Oxidation-reduction reactions involve a transfer of electrons from one species to another
  • Oxidation reduction reactions are the most important type of reactions
  • Oxidation reduction reactions usually fall into the following categories: combination reactions, decomposition reactions, displacement reactions and combustion reactions
  • Molarity is defined as the number of moles of solute per liter of solution. Knowing the molarity allows you to calculate the amount of solute in a given volume of solution
  • Quantitative             analysis involves the determination of the amount of a species in a material