PPT 8.2 Properties of acids and bases: Acids and bases are essential concepts to understand in IB Chemistry – they play an important role in the understanding of many physical and chemical properties. This article will help you understand the properties of acids and bases, including pH levels and how acids and bases interact with other chemicals.
Acid-base reactions and neutralisation
An acid-base reaction is a chemical reaction between an acid and base, where the acid donates a proton (H+) to the base. The result of the neutralisation reaction is the formation of water molecules and either a salt or an ester compound. Understanding how to identify strong and weak acids and bases, as well as recognizing when neutralization will occur, are important concepts in IB Chemistry.
Neutralisation reactions with examples
Neutralisation reactions occur when an acid and a base react together to form a salt and water. For example, reacting hydrochloric acid with sodium hydroxide yields sodium chloride (NaCl) and water. In equations, this can be represented as ‘HCl + NaOH -> NaCl + H2O’. This reaction is often used to demonstrate that when strong acids and strong bases combine, they will cancel each other out to form water and a salt.
Neutralisation reactions and Heat energy
Neutralisation reactions are exothermic, meaning they release heat energy. This can be measured using a calorimeter, where the change in temperature of the reaction mixture is noted. The amount of heat energy released or absorbed (ΔH) can then be calculated from the change in temperature of the reaction system and the mass of the reactants. In an acid-base neutralisation reaction, this energy is released as the ions in each compound arrange themselves more favourably to form a salt molecule and water.
A key tool used to measure acidity and alkalinity is litmus paper. This can be dipped into the solution, changing colour depending on whether it is in an acidic or basic solution. However, more precise measurements are possible using indicators such as phenolphthalein. These indicators work by taking advantage of the fact that different substances change colour at different pHs. Phenolphthalein will stay pink in an acidic environment or turn clear in a basic one. By testing with multiple indicators, the precise pH of a given solution can be accurately determined.
Acid–base titrations are a very common way of measuring the concentration of an acidic or basic substance. This is done by adding a known volume, and therefore known concentration, of acid or base to the unknown solution until the pH does not change significantly anymore with added volume. The point at which no further change occurs in the pH is called the equivalence point. Knowing the volume and concentration of each molecule used in this process will allow you to calculate accurately calculate concentration of the original solution.
I hope that you have read PPT 8.2 Properties of acids and bases.
Read about the IB DP Chemistry IA here.