Acids, Alkalis and Titrations

Definition of Acids and Alkalis

An acid is a substance that can donate a hydrogen ion (H+) or accept a lone pair of electrons.
Examples of acids include hydrochloric acid (HCl), sulfuric acid (H2SO4) and nitric acid (HNO3).
An alkali is a base that can dissolve in water. They produce hydroxide ions (OH-) in solution.
Examples of alkalis include sodium hydroxide (NaOH), potassium hydroxide (KOH), and calcium hydroxide (Ca(OH)2).

pH Scale and Indicators

The pH scale measures how acidic or basic a substance is. The scale ranges from 0 to 14.
A pH of 7 is neutral, values less than 7 are acidic and values greater than 7 are alkaline.
An indicator is a substance that changes colour depending on the pH of the solution.
Common indicators include litmus paper (blue in alkaline, red in acidic), phenolphthalein (pink in alkaline, colourless in acidic) and universal indicator which gives a range of colours for different pH values.

Strong and Weak Acids and Alkalis

Strong acids and alkalis fully ionise in solution. In other words, all the acid/alkali particles dissociate to form ions.
Weak acids and alkalis only partially ionise, meaning not all the particles dissociate.
The strength of an acid or alkali doesn’t influence its concentration. Concentration refers to how much of an acid or alkali is present in a certain volume of solution.

Titrations

A titration is a process in lab chemistry that determines the concentration of an unknown solution (usually an acid or alkali).
It involves slowly adding a solution of known concentration (the titrant) to the unknown solution until the reaction between them is just complete, indicated by a colour change from an indicator.
Burette, which is used to add the titrant, allows for precise measurement of the volume that causes the colour change, thus allowing the concentration to be calculated.

Neutralisation Reactions

Neutralisation is a chemical reaction between an acid and a base (alkali), producing a salt and water.
For example, hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH) to produce sodium chloride (NaCl) and water (H2O).
In a neutralisation reaction, the H+ ions from the acid react with the OH- ions from the alkali to form water (H2O).

Understanding these concepts is essential in predicting and understanding the outcome of reactions involving acids and bases, as well as safely and effectively carrying out titration procedures in the lab.