what is the difference between ph scale and universal indicator?
pH scale is a range of numbers given by working out -log[H+] for a given solution. It ranges from 14 to about -2. Universal indicator is a mixture of solutions that change colour depending on the value of the pH. Red indicates pH up to 2–4, orange from 3–6, green where pH=7, blue for 8–11 and purple for 11–14.