The pH scale measures the probability that a substance will give up a proton (or an H+ atom) and the probability that a substance will accept a proton. Many molecules, including dyes, will change structure by accepting protons from an acidic environment (an environment that readily releases protons) or releasing protons to an alkaline environment (an environment that readily accepts protons). Testing pH is an important part of many chemical and biological experiments. This test can be done by coating a sheet of paper with a dye that will change color in an acidic or alkaline environment.
Step
Method 1 of 2: Making pH Paper at Home Using Cabbage or Cabbage
Step 1. Cut some red cabbage
You'll need to cut about 1/4 of the head of red cabbage and put it in a blender. You must extract the chemical from the cabbage to coat the pH paper. These chemicals are called anthocyanins and can be found in plants such as cabbage, roses, and berries. Anthocyanins are purple under neutral conditions (pH 7.0), but change color in an acidic environment (pH 7.0).
- The same procedure can be used for berries, roses, or other plants that contain anthocyanins.
- This procedure does not apply to green cabbage. Green cabbage does not contain anthocyanins.
Step 2. Add boiling water to your cabbage
You can boil water on the stove or in the microwave. Whichever method you use, you will need 500 ml of water. Pour boiling water directly into the blender containing the cabbage. This will help remove the needed chemicals from the cabbage.
Step 3. Turn on the blender
You should blend the water and cabbage for best results. Let the blender run until the water is dark purple in color. This color change indicates that you have successfully removed the required chemicals (anthocyanins) from the cabbage and dissolved them in hot water. You should cool the contents of the blender for at least ten minutes before continuing.
Step 4. Pour the mixture through a sieve
You must remove the cabbage pieces from the indicator solution (colored water). Filter paper can replace the filter, but it may take longer. Once you have filtered the indicator solution, you can discard the cabbage pieces.
Step 5. Add isopropyl alcohol to your indicator solution
Adding about 50 ml of isopropyl alcohol will protect your solution from bacterial growth. Alcohol may change the color of your solution. If this is the case, add vinegar until the solution returns to a deep purple color.
Step 6. Pour the solution into a saucepan or bowl
You need a container that has a mouth wide enough to dip the paper into. You should choose a stain-resistant container as you will be pouring the dye into it. Ceramic and glass materials are good choices.
Step 7. Soak your paper in the indicator solution
Be sure to push the paper under the solution. You'll need to dip all the edges and sides of the paper. It is a good idea to wear gloves for this step.
Step 8. Let your paper dry on the towel
Look for a location that is free of acidic or alkaline vapors. The paper must dry completely before proceeding. Ideally, you leave it on overnight.
Step 9. Cut the paper into sheets
This allows you to test several different samples. You can cut the paper to any size you want, but generally, the paper is cut to the length and width of your index finger. This size allows you to dip the paper into the sample without dipping your finger in the sample.
Step 10. Use a sheet of paper to test the pH of different solutions
You can test household solutions such as orange juice, water, and milk. You can also mix a solution for testing, such as mixing water and baking soda. This will provide a variety of samples for testing.
Step 11. Store the sheet of paper in a cool and dry place
You should use an airtight container to store the sheets of paper until you use them. This will protect the paper from environmental contamination such as acidic or alkaline fumes. Leaving the paper in direct sunlight is also not ideal as this can cause bleaching over time.
Method 2 of 2: Making Litmus Paper at Home
Step 1. Look for dry litmus powder
Litmus is a compound derived from lichens, fungi that have a symbiotic relationship with algae and/or cyanobacteria that can carry out photosynthesis. You can buy litmus at an online or chemical supply store.
You can make your own litmus powder if you are a competent chemist. However, the process is quite complicated and involves adding compounds such as lemonade and potassium carbonate to mash the lichen and leave it for several weeks for the fermentation process
Step 2. Dissolve the litmus in the water
Be sure to stir the solution and heat it if the powder doesn't dissolve well. Litmus powder must dissolve completely in water. The final solution should be purplish-blue.
Step 3. Put your paper in the litmus solution
Wet all sides and edges of the paper with the solution. This will wet almost the entire surface of your test sheet and give the most accurate results. You don't need to let the paper "soak" as long as you are sure that all parts of the paper are wet.
Step 4. Let the paper dry
You should dry the paper in the open air, but make sure that the paper is not exposed to acidic or alkaline fumes. This vapor can contaminate sheets of paper and make them inaccurate. You should also store it in a dry, dark place to prevent contamination and bleaching.
Step 5. Use litmus paper to test for acidity
Blue litmus paper will turn red in an acidic environment. Keep in mind that litmus paper does not indicate the degree of acidity or whether a solution is basic or not. No change on the paper means the solution is basic or neutral and not acidic.
You can make red litmus paper (which will turn blue in an alkaline environment) by adding acid to the indicator solution before soaking your paper
Tips
- You can cut the paper into sheets before or after dipping it in the indicator solution. Just try not to cut the paper when it's wet.
- You can use the universal indicator to compare the readings on the sheet of paper you are making with the indicator for the same solution. This comparison will give you an idea of the accuracy of your reading.
- Only use distilled water.
- Use acid-free art paper.
Warning
- Store the prepared sheet of paper in a cool, dark, dry airtight container.
- Handle acid with extreme care and under the supervision of a responsible person such as a science teacher if you are doing a class project. Use proper protective equipment to handle any substance.
- Handle the test sheet only with dry hands.
