Difference Between pH Paper and Litmus Paper

Main Difference – pH Paper vs Litmus Paper

pH is a scale used to measure the acidity or basicity of a solution. pH can be defined as the logarithmic value of inverse of proton (H⁺) concentration. A higher pH value indicates the presence of acidic species and a lower pH value indicates the presence of basic species. There are several methods to determine the pH of a solution. Titrations can be used to quantitatively measure the proton concentration. With that, the pH value can be calculated. If not, we can use pH papers or Litmus papers to determine the pH of a solution. The main difference between pH Paper and litmus paper is that pH Paper can give the pH value of the solution whereas litmus paper can determine whether a solution is acidic or basic.

Key Areas Covered

1. What is pH Paper
      – Definition, Properties, Applications
2. What is Litmus Paper
      – Definition, Properties, Applications
3. What is the difference between pH Paper and Litmus Paper
      – Comparison of Key Differences

Key Terms: Acidic, Acidity, Basic, Basicity, Litmus Paper, pH, pH Paper

What is pH Paper

pH paper is an indicator that can be used to determine the pH value of a solution. pH papers are made as strips and are saturated with pH indicators. Therefore, in the presence of an acid or a base, the pH papers can change their color according to the pH of that solution. Normally, pH papers are immersed in solutions to see the color change or a drop of the solution can be placed on the pH strip. When the color change occurs, the color is compared with the reference scale. With this, one can determine the pH of a particular solution.

Figure 01: A pH paper roll

The above image shows a typical pH paper roll. The paper strip is yellow colored and it can change in to different colors in the presence of solutions that range from pH 1 to 14. The color change occurs from red to blue. The red color is given by highly acidic solutions and blue color is given by highly basic solutions. But if the color is changed to a light green, then the color should be compared with the reference scale. According to the reference given, a green color indicates a basic solution. But if there is no color change, then the solution is neutral and the pH is 7.  

As the pH paper is saturated with a pH indicator, the color change is given immediately. When a piece of pH paper is dipped in a solution, the chemical species in the paper react with the hydronium ions (or else OH^– ions) resulting in a change of the color of that pH indicator present in the pH paper.

What is Litmus Paper

A litmus paper is an indicator that is used to determine the acidity or the basicity of a solution. The paper used to make the litmus paper is free of contaminants that can cause color changes due to the pH of the solution. The primary raw material that is used in production of litmus is Lichen. Infusion of Lichen cause the litmus paper to become pH active.

Litmus papers are available in both red and blue colors. When a drop of basic solution is put on to the red Litmus, it changes the color to blue. If a drop of a base is put onto blue Litmus, it will not make a color change.

If a drop of acid is put onto a red litmus paper, the color would not be changed. But if a drop of acid is put onto a blue litmus, the color would change from blue to red. However, litmus papers cannot give an exact number for the pH value of a solution. It can just indicate whether the solution is acidic or basic.

Figure 02: Red and Blue Litmus Papers

Sometimes, the color of the litmus paper can change when it is kept outside. This is because the acidic or basic species present in the atmosphere can cause color changes in the litmus paper. Most litmus papers have been made to give the color change in the range of 4.5 to 8.3. That means, only solutions with a pH below 4.5 and above 8.3 will give the color change.

Difference Between pH Paper and Litmus Paper

Definition

pH Paper: pH paper is an indicator that can be used to determine the pH value of a solution.

Litmus Paper: A litmus paper is an indicator that is used to determine the acidity or the basicity of a solution.

Value

pH Paper: pH papers can give the exact pH value of a solution.

Litmus Paper: Litmus papers cannot give a value for the pH of a solution.

Precision

pH Paper: pH papers give more precise results.

Litmus Paper: Litmus papers give a less precise indication.

Color

pH Paper: pH papers can give a range of colors in the presence of solutions with different pH values.

Litmus Paper: Litmus papers can give only two colors.

Conclusion

The choice of a better pH indicator in chemical experiments is very important. Sometimes, we may need a pH indicator that can give the exact pH value of a solution. But sometimes, it is not necessary to know the pH values, only the acidity or the basicity of a solution needs to be known. pH paper and Litmus paper are useful pH indicators. However, pH paper can give the pH value of the solution whereas litmus paper can only determine whether a solution is acidic or basic. This is the main difference between pH paper and litmus paper.

References:

1.”How is PH Paper Made?” Sciencing. N.p., n.d. Web. Available here. 17 July 2017. 
2.”Litmus Paper.” How Products Are Made. N.p., n.d. Web. Available here. 17 July 2017.

Image Courtesy:

1.”Paper indicador” By Ariadna.creus – Own work (CC BY-SA 4.0) via Commons Wikimedia
2.”Red and blue litmus papers” By Kanesskong – Own work (CC BY-SA 4.0) via Commons Wikimedia