What is an acid and what is an alkali?
Higher GCSE answer: The higher the concentration of hydrogen ions in an acidic solution, the lower the pH; and the higher the concentration of hydroxide ions in an alkaline solution, the higher the pH. 1. The higher the number of hydrogen ions in a certain volume, the higher their concentration. The higher the concentration, the more acidic the solution the lower the pH 2. The higher the number of hydroxide ions in a certain volume, the higher their concentration. The higher the concentration, the more alkali the solution the higher the pH. Neutral solutions – such as pure water, have a pH of 7 and contain low equal, concentrations of hydrogen and hydroxide ions
The answer to your question really depends upon the level of answer that you need. At a most basic level (excuse the chemistry pun!), acids taste sour and alkalis taste soapy. Or you could define them as having pH values below or above 7 respectively. Or you could talk about the release or acceptance of protons in solution. If you’d like to refine your question to the level you are at, I will amend the answer accordingly.
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