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Purple litmus is a familiar name in chemistry, used to measure pH or apply in other experiments. So what is purple litmus? How to change color? What is the application of purple litmus? Find out with lassho.edu.vn in the article below!
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 and a pigment extracted from the roots of lichens Roccella and Dendrographa. This type of 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) is the biggest advantage of red litmus. Besides, litmus paper is also used to distinguish gases. Therefore, purple litmus is indispensable in experiments or in laboratories today.
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 is wet litmus and which is dry, we only need to put one of them in ammonia gas if it is dry purple litmus will not change color, if the litmus paper turns blue, it is moist purple litmus.
How does purple litmus change color?
Blue 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 basic solution.
- Blue litmus does not change color when the solution is neutral (acidity = basic).
Applications of purple litmus
Purple litmus has many applications in science as well as life such as distinguishing chemicals, measuring pH or testing amniotic fluid, …
Used to distinguish chemical solutions
To identify if 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 reacts with acids (eg: HCL, H2SO4, …) the blue litmus will turn red.
- When blue litmus reacts with bases (eg, NaOH, KOH, …), blue litmus turns blue.
- When 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, 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.
For 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 the amniotic fluid of pregnant women in the last stage. From there, we know whether the fetal status inside the mother’s womb is good or weak to make the most timely solutions.
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 studying 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!
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