Acids, alkalis and titrations

Some acids you will never touch without full protective clothing and a spill plan; others you eat by the slice. The citric acid in an orange and the acid that demands gloves and goggles belong to the same chemical family — what changes is how much hydrogen ion they release and how concentrated the solution is. Alkalis have the same spread: the sodium hydroxide that clears blocked drains and the mild carbonate solutions in household products all sit on the same scale. This chapter gives you that scale, the tools to tell acids from alkalis in seconds, and the classic technique chemists use to make them react in exactly measured amounts: the titration.

Three questions organise the chapter. First, how do you tell an acid from an alkali? With indicators — the colour-switching dyes litmus, phenolphthalein and methyl-orange, and the full-range universal-indicator that estimates a pH value. Second, how acidic or alkaline is it, exactly? With the pH scale, which you will learn to read into five bands from strongly acidic to strongly alkaline. Third, what is really happening when they react? Acids are sources of hydrogen ions, alkalis are sources of hydroxide ions, and neutralisation is those two ions meeting to make water — one ionic equation that covers every acid–alkali reaction you will ever write at this level.

The chapter closes with a skill that belongs to chemistry alone in your specification: carrying out an acid–alkali titration with burette precision. Everything you learn here feeds forward — the reactions of acids continue in Chapter 17 (u2:c17) with salt preparations, and the calculation side of titrations is waiting in Chapter 6 (u1:c06).