Caption

Mineral water with universal indicator added. Universal indicator changes colour depending on whether it has been added to an acid or an alkali. Mineral water is neutral, neither acidic nor alkaline. In such a solution, universal indicator has a yellow-green colour. In acidic solutions universal indicator turns a colour between red (strong acid) and pale orange (weak acid). In alkaline solutions, it turns between green (weak alkali) and purple (strong alkali).