One of the most basic things a student must learn in any biology or chemistry class is how to use litmus paper, or litmus strips. Litmus strips are small rectangles of paper treated with chemicals that are used to test the acidity of liquid substances.
Learning how to use Litmus paper is a fairly simple task but the following article will help guide you further through the process.
Types of Litmus Paper
The first step in learning how to use litmus paper is figuring out what kind of Litmus paper you have. Litmus paper comes in three basic varieties, red, blue and purple or neutral.
When learning how to use litmus paper, there is no fancy way of determining what color litmus paper you have. Unless you are color-blind, just look at it and listen to whatever your eyes tell you.
Before figuring out how to use litmus paper you must first prepare the substance that you need to test. Keep in mind that litmus paper tests work only with liquids.
First put your liquid in a wide mouthed container of some sort, or obtain a pipette or dropper. Then apply the liquid to the litmus paper. To do this you may either dip one end of the litmus paper into the liquid, or place some on the paper using a pipette or dropper. Then observe the color change in the litmus paper to determine the substance’s acidity. Do not wait for the litmus paper to dry: this will give you an inaccurate result.
When learning how to use litmus paper the key thing to remember is to always associate the color red with acids (substances with a pH of less than 7) and the color blue with bases (substances with a pH of greater than 7). This applies regardless of the color litmus paper you are using.
If you are using blue litmus paper and the substance turns it red, then the substance is an acid. If the blue litmus paper doesn’t change color, you know that the substance is not an acid, but you need to use red litmus paper to determine if it is a base or neutral.
If you are using red litmus paper and the substance turns in blue than the substance is a base. If the red litmus paper doesn’t change color, you know that the substance is not a base, but you need to use the blue litmus paper to determine is an acid or neutral.
If the substance does not change the color of either red or blue litmus paper than it is a neutral substance.
If you are learning how to use litmus paper that is purple or neutral, the process is the same. The only difference to keep in mind when learning how to use litmus paper is that neutral litmus paper can turn red or blue so that you never need to use both colors of paper. When the paper turns red, it is an acid and when it turns blue, it is a base.
Now that you know how to use litmus paper you can determine if a substance is acidic or basic, however other methods will be required for more accurate quantitative measurements.
Note: When learning how to litmus paper always take proper safety procedures and never work without adult supervision.