1 What is purple litmus? Advantages of blue litmus compared to other PH indicators
Purple litmus or litmus paper – paper impregnated with an ethanol solution or water with a colorant is isolated from the roots of lichens Roccella and Dendrographa . This paper was originally purple in color and was used in chemistry experiments and pH measurements. After use, litmus paper will change to another color.
Fast results (usually used in experiments) are the biggest advantage of red litmus. Besides, litmus paper is also used to distinguish gases. Therefore, purple litmus is indispensable in current experiments or laboratories.
2 Classification of purple litmus
Purple litmus paper is divided into two main types: red litmus paper and blue litmus paper.
- Red litmus paper : Made by treating plain paper and a dye soaked in a dilute solution of sulfuric acid . Next, they are brought to dry by direct contact with the air.
- Blue litmus paper: When blue litmus paper is dipped in a solution, if the paper turns red, the solution is acidic , and if the paper does not change color, the solution is in equilibrium. Blue litmus is used to identify acids and vinegars.
Moreover, people also divide litmus paper into moist purple litmus and dry purple litmus . To know which type of litmus is moist and which is dry, we only need to put one of them in ammonia gas , if it is dry purple litmus it will not change color, if it turns blue, it is moist purple litmus.
How does purple litmus change color?
Purple litmus changes 3 colors depending on whether the solution is acidic , basic or neutral :
- Purple litmus turns red when litmus paper comes in contact with an acidic solution.
- Purple litmus turns blue when litmus paper comes in contact with a solution containing basicity.
- Blue litmus does not change color when the solution is neutral (acidity = basic).
4 Applications of purple litmus
Purple litmus has many applications in science as well as in life such as distinguishing chemicals, measuring pH or testing amniotic fluid,…
Used to distinguish chemical solutions
To identify whether a solution is basic or acidic, we only need a small piece of litmus paper that we can easily distinguish or recognize. Speak clearly:
- When purple litmus acts with acids (eg: HCL , H2SO4 ,…) red litmus will turn red.
- When blue litmus reacts with base (For example: NaOH , KOH ,…) litmus turns purple green Blue.
- When blue litmus is in equilibrium or neutral, it will not change color.
Measure pH with red litmus paper
That quick pH measurement is what litmus paper can do. However, the purple litmus pH measurement results are only approximate, not 100% accurate. To measure with the most accuracy we need to use a pH meter that will give us high accuracy.
In case of quick measurement we use purple litmus as follows: Tear a piece of litmus and dip it in water, then compare it with the accompanying color chart.
- If the pH index is from 1 to 7: the environment is acidic.
- From 7-14: basic environment.
- If litmus paper shows number 7: neutral medium.
In particular, purple litmus can test for amniotic fluid leakage of pregnant women in the final stage. From there, we know whether the fetal status inside the mother's womb is good or weak to make the most timely solutions.
5 Where to buy purple litmus?
Where is purple litmus sold or where quality is sold? These are questions many readers are wondering. On the market today, purple litmus is sold everywhere at a cheap price, but the quality is not sure. In particular, for those who study chemistry, buying substandard purple litmus will greatly affect the results.
You should choose reputable places such as pharmacies or scientific research centers to have the best quality and standard litmus paper!
Hope the above article will help you better understand purple litmus. Any questions, please leave a comment below to be answered!