Litmus paper is originally obtained from a natural dye and a kind of lichen. Lichen is a small plant that is formed from the symbiosis of fungus and algae together. Litmus paper is used to measure and identify acids and bases. Litmus paper has two colors, red and blue. Blue litmus paper is used for acidic environments and red litmus paper is used for game environments. Blue litmus paper turns red in acidic environment and red litmus paper turns blue in game environment. The neutral hub solution does not change the color of litmus paper.

Now we go to interesting experiments with litmus paper.

One of the interesting experiments using litmus paper is to detect the acidity or alkalinity of substances, which is for children to understand acidic and alkaline environments.

Three solutions of vinegar, lime and lemon juice can be used to show the acidic environment. For this purpose, we pour some of each in a separate bowl and then we use blue litmus paper to determine their acidity level. The higher the acidity of the solution, the redder the color of the paper. Soap and shampoo can be used as alkaline environments to show the game environment. Red litmus paper is used for this. In these environments, the bluer the paper is, the higher the pH is and the more playful it is.

Another experiment that can be done is using red cabbage. For this purpose, it is enough to boil red cabbage with a small amount of water on gas for 30 minutes. Then it was extracted and used as an identifier. If we dip litmus paper into the solution, we will see that it turns red. If I dip a white paper in cabbage liquid and put it in an acidic solution like lemon, we will see that it turns green. In this way, a new litmus paper can be made through red cabbage, which is considered as an indicator of acids.

Another interesting experiment is the use of litmus paper. To make this sheet, you can dip a white sheet from the previous experiment with red cabbage extract and let it dry. After the sheet dries, you can put any mark or writing on the sheet with a candle. Then spray an alkaline solution such as water and soap on the sheet. You will see the text appear on the sheet.

If you don’t have a candle at home, you can leave interesting shapes on the screen by spraying the lye solution on your hand.

So, in general, litmus paper is used to distinguish different substances, in terms of acidity or alkalinity.

Definition of pH

In chemistry, the scale used to measure the acidity or alkalinity of water-based solutions is pH. Ph is derived from the root of the potential of hydrogen. At room temperature, water is neither acidic nor basic and has a pH of about 7, which is called a neutral solution. The pH scale is logarithmic and shows the concentration of hydrogen ions in the solution. Lower pH means higher hydrogen ion concentration. The reason for this can be found in the pH formula and the lower concentration in the negative logarithm of base 10 (pay attention to the relationship below). Sometimes the activity value can be used instead of the concentration in the pH formula. At room temperature, pH less than 7 indicates acidic and pH higher than 7 indicates alkaline solution. The neutral state for pH (7 for room temperature) is highly dependent on temperature. If the temperature increases because the concentration of hydrogen in the solution increases, then the pH becomes less than 7.

Identification of acids and bases

One of the ways to detect acids or bases is identifiers. The main feature of the indicators is their color change against the acidity of the environment. In this way, by having the corresponding table (desired color against pH) that is available on the packages of the indicators, it is possible to recognize the range of pH. A colorimeter or spectrophotometer can be used to determine the desired color more accurately. General identifiers include a combination of several identifiers that identify a wide range of colors in different environments. Identifiers are made of moisture absorbent paper that carries various combinations of identifiers. One of the famous paper identifiers is litmus paper.

Another way to detect the acidity of the environment is to use digital pH meters. pH meter is an electrical device that can measure hydrogen ion concentration or its activity in aqueous basic solutions. The pH meter can measure the concentration of dissolved hydrogen by determining the potential difference between the reference electrode and the pH meter electrode.

Another way to detect acidic and alkaline environments is to use chemicals in solutions. The basis of the work of this group of chemicals is their color change against different environments. One of the most famous of these identifiers is methyl orange.