0:10 → 0:18
While it is possible to quantitatively measure the pH of a solution using a device known as a pH meter,
0:18 → 0:23
there are also ways to determine pH qualitatively.
0:23 → 0:30
In this lesson, we will learn about indicators which help us indicate the pH of a solution.
0:30 → 0:36
An indicator changes color depending on the pH of the solution analyzed.
0:36 → 0:41
Because of this, they're also known as pH indicators.
0:41 → 0:50
Universal indicator is very versatile, as it can measure pH across the entire scale from 0 to 14.
0:50 → 0:55
It is not a single indicator, but rather a combination of various indicators.
0:55 → 1:05
If you look at the color changes of universal indicator according to the pH of a solution, you will find that it resembles a rainbow.
1:05 → 1:16
If universal indicator solution turns deep red in a solution, it means that the solution is strongly acidic, with a pH of 1-2.
1:16 → 1:24
If the universal indicator solution turns green, it means that the solution is neutral with a pH of 7.
1:24 → 1:32
If the universal indicator solution turns dark blue or purple, it means that the solution is strongly alkaline.
1:38 → 1:43
Universal indicator paper works in exactly the same manner.
1:43 → 1:51
Litmus is another indicator commonly found absorbed onto paper as litmus paper.
1:51 → 1:57
Blue litmus paper turns red under acidic conditions, pH less than 7.
1:57 → 2:04
Red litmus paper turns blue under alkaline conditions, pH greater than 7.
2:04 → 2:15
Phenolphtalein is an indicator commonly used to determine the end point of a strong acid, strong alkali or weak acid-strong alkali-titration.
2:15 → 2:22
It goes from colorless to fuchsia pink at a pH of 8.2.
2:22 → 2:32
Methyl orange is used to determine the endpoint of either a strong acid, strong alkali or strong acid-weak alkali-titration.
2:33 → 2:40
It is red at a pH lower than 3.1 and yellow at a pH higher than 4.4.
2:40 → 2:47
In conclusion, indicators are substances that change color at a certain pH.
2:47 → 2:54
The point at which an indicator changes color is known as it's endpoint, which can be at any pH.
2:54 → 3:05
Common indicators that you will encounter are universal indicator, litmus in the form of litmus paper, phenolphthalein and methyl orange.