Difference Between Litmus Paper and pH Paper

Litmus Paper vs pH Paper
 

Litmus Paper

Litmus paper is an indicator, which can be used to determine acidic and basic solutions. Normally this comes as a paper stripe. Mixture of water-soluble dyes extracted from lichens like Roccella tinctoria are absorbed into filter paper stripes to make litmus paper. In this mixture, there are about 10- 15 types of dyes. There are two types of litmus papers as blue and red. Red litmus paper is used to test basic solutions. Red litmus papers turn blue when encountered with a basic solution. Whereas blue litmus papers turn red when encounter with an acidic solution. The neutral litmus papers are purple in color. The color change of litmus papers is taking place over pH range 4.5-8.3 at 25 °C. Therefore, one of the disadvantages of litmus papers is that they cannot be used to determine the pH value. The strength of the acidity or the basicity also cannot be determined using litmus papers, on the other hand, the readings are instantaneous, and easy to take. Litmus papers can be used by anyone without any expertise knowledge. They only have to know which color is relevant to acidic and basic pH value.

pH Paper

pH is a scale, which can be used to measure the acidity or basicity in a solution. The scale has numbers from 1 to 14. pH 7 is considered as a neutral value. Pure water is said to be having pH 7. In the pH scale, from 1-6 acids are represented. Acids can be categorized into two, based on their ability to dissociate and produce protons. Strong acids like HCl, HNO₃ are ionized completely in a solution, to give protons. Weak acids like CH₃COOH partially dissociate and give fewer amounts of protons. An acid with pH 1 is said to be very strong, and as the pH value increases, acidity is decreased. The pH values more than 7 indicate basicity. As the basicity increases, pH value will also increase and strong bases will have pH value 14.

pH papers are indicators which are easy to use. They are common in every chemical laboratory. They come in various types as rolls, stripes, etc. Though pH meter is the best equipment to measure the pH value accurately, pH papers are the best alternative when quick and approximate measurements are needed. With the pH paper, a color chart is provided. When the pH paper in the solution, where pH should be determined, the paper will show a certain color. This color change is relevant to the pH of the solution. Sometimes the colors are not so contrasting, so it is bit difficult to determine the pH range. Therefore, one disadvantage of pH papers is determining the value. Other disadvantage is that pH papers provide a pH range, so the exact pH value of the solution cannot be determined. However, there are lots of advantageous of pH papers too. They give fast reading, easy to use (does not need expert knowledge), portable, inexpensive, and reading are accurate for the most part.