In this video, we're going to have a look at the pH scale and some other simple indicators of acids and alkalis. In other videos, we have seen what makes something acidic, neutral or alkaline. We can tell if something is acidic, alkaline or neutral by using an indicator. Lipsis are substances that show different colours when they are acidic or alkaline conditions. Lipsis paper is a simple indicator that tells us whether something is acid or alkaline. Lipsis is red in acids and blue in alkalis. Lipsis paper is made from lichens which have been used to die cloth for hundreds of years. It can be used as a liquid or paper. The paper is easier and more reliable. It comes as red lipis paper and blue lipis paper. Red lipis paper changes colour from red to blue under alkaline conditions but no change under acidic conditions. Blue lipis paper changes colour from blue to red under acidic conditions but no change under alkaline conditions. So just remember that red lipis paper changes colour for alkalis and blue lipis paper changes colour for acids. However, lipis paper only tells us whether something is acid or alkalite but it does not tell us how acidic or alkaline a substance is. For this we have the pH scale and a universal indicator. Universal indicator is a mixture of different indicators or dies which has many different colour changes and so shows us the pH value of the solution. Again it can be used as a liquid or paper. The pH runs from 0 to 14 with 0 being extremely acidic, 7 being neutral and 14 being extremely alkaline. Stomach acid is a strong acid with pH of about 2. Acid rain has a pH of about 5.5. Milk is neutral with a pH of 7. Sea water is a slightly alkaline. Soapy water is a strong alkaline and bleach is a really strong alkaline with a pH of 13. Universal indicator is so called due to its ability to indicate the entire pH spectrum. There are other indicators that can be used that have other colour changes but these two are the ones you need to know. We can also get even more accurate measurements of pH using a pH meter which will give us readings to 0.01 of the pH. So from this lesson you should now know indicators can tell us whether something is acidic or alkalite and how acidic or alkalite it is. Red litmus paper changes colour for alkaline and blue litmus paper changes colour for acids. And Universal indicator can give us more detail indicating where on the 0 to 14 pH scale a solution is. Acids are from 0 to 6, neutral is 7 and alkalites are 8 to 14.