In this video we are going to have a look
at the pH scale and some other simple
indicators of acids and alkalis. In other
videos we have seen what makes something
acidic, neutral or alkaline. We can tell if
something is acidic, alkaline or neutral
by using an indicator. Indicators are
substances that show different colours
when they are in acidic or alkaline
conditions. Litmus paper is a simple
indicator that tells us whether
something is acid or alkali. Litmus is
red in acids and blue in alkalis.
Litmus paper is made from lichens
which have been used to die cloth for
hundreds of years. It can be used as a
liquid or paper. The paper is easier and
more reliable. It comes as red litmus
paper and blue litmus paper. Red litmus
paper changes colour from red to blue
under alkaline conditions but no change
under acidic conditions.
Blue litmus paper changes colour from blue to red under acidic conditions but no change under alkaline conditions.
So just remember that red litmus paper changes
colour for alkalis and blue litmus paper
changes colour for acids. However litmus
paper only tells us whether something is
acid or alkali, but it does not tell us
HOW acidic or alkaline a substance is. For
this, we have the pH scale and a
universal indicator. Universal indicator
is a mixture of different indicators or
dyes which has many different colour
changes and so shows us the pH value of
the solution. Again it can be used as a
liquid or paper. The pH scale runs from 0 to 14.
With 0 being extremely acidic, 7
being neutral and 14 being extremely alkaline.
Stomach acid is a strong acid
with pH of about 2. Acid rain has a pH
of about 5.5. Milk is neutral with a pH
of 7. Seawater is slightly alkaline.
Soapy water is a strong alkaline and
bleach is a really strong alkaline with a
pH of 13. Universal indicator is
so called due to it's ability to indicate
the entire pH spectrum. There are other
indicators that can be used that have
other colour changes, but these two are
the ones you need to know. We can also
get even more accurate measurements of
pH using a pH meter which will give us
readings to 0.01 of the pH. So from this
lesson you should now know that indicators can tell us whether something is acidic or
alkaline, and HOW acidic or alkaline it
is. Red litmus paper changes colour for
alkalis and blue litmus paper changes
colour for acids. And universal indicator can
give us more detail indicating where on
the 0 to 14 pH scale a solution is.
Acids are from 0 to 6, neutral is 7
and alkalis are 8 to 14.
