Litmus paper is one type of natural indicator which is made by litmus dye with cellulose used to determine acid and base. It helps to indicate the presence of acidic or basic solution for various experiment. This paper is used as an acid-base indicator. It is generally prepared by wood cellulose paper and litmus dye. Litmus chemical dye is purple type color which is extracted lichen plants.
This paper strip is generally placed in a liquid for determining the pH. The used of this strip of paper, which is red color at any pH level less than 4.5 and blue color at any pH upper than 8.3, allows to inspect whether a solution is acidic or basic type in nature.
The blue litmus paper doesn’t change its own color when it is treated in alkaline solutions. The red litmus paper doesn’t change its own color when it is treated in acidic solution. Neutral litmus paper contains purple color and becomes red color under the acidic conditions and in blue color under alkaline conditions.
This paper doesn’t identify the values of pH in solution.
History of Litmus Paper
This paper was invented Arnaldus de Villa Nova for the first time around 1300 AD who was Spanish physician. This paper is generally blue color dye molecule that mostly found in the area of Netherlands.
It is also prepared from Roccella Montagnei and Dedographa Leucophoea species. This paper can be prepared from 10 to 15 different types of dyes nowadays.
Litmus Paper Colors
A weak diprotic acid is found in red litmus paper. It changes color and turns into blue color when keeps in a base solution.
A conjugate base is generally found in blue litmus paper. It changes color and turns into red when keeps in a acid solution.
Litmus Paper Experiment
This paper helps to indicate acidity or alkalinity to the user because it contains red or blue color. We must dip this paper into the experimental solution or use a pipette or dropper dropping a small amount of the solution over the paper.
Blue type of this paper helps to indicate an acid that has a pH level of around 4.5 to 5.5 or lower than that. On the other hand, red type of this paper changes in the color over the paper when the pH of solution greater than 8.
pH Scale for Litmus Paper
pH expresses the concentration of hydrogen ion into the solution. The ranges of pH scale from 0 to 14 and equates to the negative logarithm of the concentration of hydrogen ion in a solution.
The pure water shows pH level is 7 because it is neutral. The solutions which have pH less than 7 are acidic. The solutions which have pH more than 7 are basic type in nature.
Advantages
It is a cheaper and ecofriendly process to identify the acidic or basic nature of solution.
This paper is available and biodegradable in nature.
We can identify the solution characteristic very quickly by this paper.
Purple type of this Paper is a neutral type litmus paper and turns into red when the solution contains pH value ranges below 4.5. It turns into blue when the solution contains pH value ranges above 8.5 pH value.
Blue type of this paper turns into red when the solution contains pH value ranges below 4.5. It does not change when the solution contains pH value ranges above 8.5 pH value.
Red type of this paper turns into blue when the solution contains pH value ranges above 8.5. It does not change when the solution contains pH value ranges below 4.3 pH value.
Limitations
It is not a reliable indicator because it is unable to show a numerical pH value.
This paper changes it color for various reasons rather than acid-base reaction.
This paper cannot work properly at higher temperature.
Use of Litmus Paper
This natural type indicator is used to identify the acidity or basicity of a solution. Wet litmus paper is used to detect the nature of gases. It is used chemistry laboratory for distinguish acid and base solution.
Frequently Asked Questions (FAQ’s)
What is litmus paper?
It is a natural indicator produced from natural dye with cellulose used to determine acid and base character in a solution.
How is litmus paper used to identify a chemical?
Litmus paper is red color at any pH level less than 4.5 and blue color at any pH upper than 8.3, allows to inspect whether a solution is acidic or basic.
What is the difference between litmus paper and pH paper?
Litmus paper is used very much for identifying the basic or acidic characteristics of solution. pH paper is used to estimate the values of pH range in solution.
