Red Litmus Paper 100 Strips/Vial
Red litmus paper turns blue when exposed to an alkaline solution; just dip a strip into the liquid & if it is basic, it will turn blue 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 Red Litmus Paper Blue?
The pH litmus dye chemical, 7-hydroxyphenoxazone, shown below, is extracted from lichens. You can make test solutions or paper by adding it to water or filter paper respectively. It changes from red to blue when exposed to alkaline materials (bases) such as sea water, baking soda, milk of magnesia, ammonia or oven cleaner.
The image shows the red litmus papers as they are available in both vial & pad; the strips are identical and turn from red to blue when dipped in an alkali (basic) solution.