Red litmus test 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 $2.65
You can make wider/longer strips using the 200x250mm-8x10" blue litmus paper sheets which can also be used for water leak detection.
If you need more than a simple qualitative (yes or no) answer that a liquid is acidic or alkaline, we supply universal pH indicator paper sheets that are 8x10" (200x250mm).
Use pH4-5-10 test strips if you are measuring weak acids or bases since litmus paper is not very accurate between pH5.5-8.5.
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. You can even build a physical model of 7-hydroxyphenoxazone.
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.
Test Strip Documentation
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