What are Indicators and Few Common Indicators? Video Lecture | Science Class 7 (Old NCERT)

while it is possible to quantitatively
measure the pH of a solution using a
device known as a pH meter there are
also ways to determine pH qualitatively
in this lesson we will learn about
indicators which help us indicate the pH
of a solution
an indicator changes color depending on
the pH of the solution analyzed because
of this they are also known as pH
indicators universal indicator is very
versatile as it can measure pH across
the entire scale from zero to 14 it is
not a single indicator but rather a
combination of various indicators if you
look at the color changes of universal
indicator according to the pH of a
solution you will find that it resembles
of rainbow if Universal indicator
solution turns deep red in a solution it
means that the solution is strongly
acidic with the pH of one to two if the
universal indicator solution turns green
it means that the solution is neutral
with the pH of seven if the universal
indicator solution turns dark blue or
purple it means that the solution is
strongly alkaline
indicator paper works in exactly the
same manner litmus is another indicator
commonly found absorbed onto paper as
litmus paper blue litmus paper turns red
under acidic conditions pH less than 7
red litmus paper turns blue under
alkaline conditions pH greater than 7
phenolphthalein is an indicator commonly
used to determine the end point of a
strong acid strong alkali or weak acid
strong alkali titration it goes from
colorless to fuchsia pink at a pH of 8.2
methyl orange is used to determine the
end point of either a strong acid strong
alkali or strong acid weak alkali
titration it is read at a pH lower than
3.1 and yellow at a pH higher than 4.4
in conclusion indicators are substances
that change color at a certain pH the
point at which an indicator changes
color is known as its endpoint which can
be at any pH common indicators that you
will encounter are universal indicator
litmus in the form of litmus paper
phenolphthalein and methyl orange