 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. Indicators are substances that show different colors when they are in acidic or alkaline conditions. Litmus paper is a simple indicator that tells us whether something is acid or alkaline. This is red in acids and blue in alkalis. Litmus paper is made from lichens, which have been used to dye 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 litmus paper and blue litmus paper. Red litmus paper changes color from red to blue under alkaline conditions, but no change under acidic conditions. Blue litmus paper changes color from blue to red under acidic conditions, but no change under alkaline conditions. So just remember that red litmus paper changes color for alkalis and blue litmus paper changes color for acids. However, litmus paper only tells us whether something is acid or alkaline, 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 dyes which has many different color changes and so shows us the pH value of the solution. Again, it can be used as a liquid or a 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. Soapy 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 color 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 alkali and how acidic or alkali it is. Red litmus paper changes color for alkalis and blue litmus paper changes color for acids. And universal indicator can give us more detail indicating where on the 0 to 14 pH scale a solution is. So from 0 to 6 neutral is 7 and alkalis are 8 to 14.