Blue Litmus Paper 100 Strips/Vial
Blue litmus paper is a fast easy way to test for acidity; simply dip a strip into the solution in question and if it is acidic, it will turn red immediately; only $1.75.
Use pH4-5-10 test strips if you measuring weak acids or bases since litmus paper is not very accurate betwee pH5.5-8.5.
What Turns Blue Litmus Paper Red?
The pH litmus indicator chemical, 7-hydroxyphenoxazone, seen the image below, is extracted from lichens. It can be added to water or filter paper to make test strips. It changes from blue to red in the presence of acids such as lemon or orange juice, vinegar, urine or milk.
The image shows the blue litmus papers as they are available in both vial & pad; the strips are identical and turn from blue to red when dipped in an acid solution.