How to use a litmus paper to test for an acid and a base

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Read script on how to use a litmus paper in water & Acid

Prepare a sample

Pour an aqueous sample (or dissolve a sample in water) into a glass or beaker. The litmus test does not work if the sample is not aqueous. Nearly everything is acid or alkaline except pure water, which is neutral, so it has a pH value of 7 on the scale.

Dip litmus paper into sample

Hold one end of a piece of red litmus paper, dip it into the sample and then remove it. There is no need to leave it in the sample for any length of time because any color change is immediate. Repeat this step with a piece of blue litmus paper. Again, there is no need to leave the paper in the sample for any length of time.

Analyze the result

Analyze how each paper reacts to the sample. If the liquid is alkaline, the red paper turns blue, and the blue paper does not change. If it is acidic, the red paper does not change, and the blue paper turns red. If it is neutral, neither the red paper nor the blue paper change.

Using Litmus paper with Gas

Dampen the litmus paper

Wet a red piece of litmus paper and a blue piece of litmus paper with water. Use the correct safety precautions for the gas you are testing.

Expose litmus paper to Gas

Under a fume hood, open the container of gas and allow some of it to come in contact with both pieces of paper. Place the papers in contact with the gas. Litmus papers react to gasses the same way they react to liquids, except gas reacts more evenly across the entire surface of the paper.

Analyze the result

Analyze how each paper reacts to the sample. If the gas is alkaline, the red paper turns blue, and the blue paper does not change. If the sample is acidic, the red paper does not change, and the blue paper turns red. If it is neutral, neither the red paper nor the blue paper change.