To study the properties of acids and bases HCl & NaOH by reaction with Litmus, Zn, NaHCO3 Video Lecture - Class 10

Properties of Acids and Bases
According to Arrhenius concept of acids and
bases, an acid is a substance which releases
one or more H+ ions in aqueous solution whereas
base is a substance which releases one or
more OH- ions in aqueous solution.
Many of the food items that we consume contain
acids and bases and their presence can be
identified with sour and bitter tastes.
Substances with a sour taste are often regarded
as acids.
Lemon juice, vinegar, grape fruit juice, etc.
are examples of acids.
Similarly substances with bitter taste and
soapy touch are regarded as bases.
Caustic soda, caustic potash, slaked lime,
etc., are examples of bases.
In this experiment, our aim is to study the
properties of acids and bases HCl and NaOH
by their reaction with litmus solution and
solid sodium carbonate.
Materials required:
Litmus solution blue and red, HCl, NaOH, dropper,
test tubes, sodium carbonate, boiling tube,
round bottom flask, phenolphthalein, lime
water, spatula, double bore cork, bent tube,
thistle funnel and stand with clamp,
Procedure:
To study the action of HCl and NaOH on litmus
solution, add a few drops of blue litmus solution
in one test tube and red litmus solution in
another test tube.
Place both the test tubes in a test tube stand
and add a few drops of HCl in each test tube.
You can see that the blue litmus solution
changes to red.
From this we can infer that HCl is an acid
having pH value below 7.
Similarly add a few drops of NaOH to red litmus
solution and blue litmus solution which is
taken separately in two other test tubes.
You can see that red litmus solution changes
to blue which indicates that NaOH is an alkali
having pH more than 7.
To study the action of HCl and NaOH on solid
sodium carbonate, first clamp the round bottom
flask to the stand and add a small quantity
of sodium carbonate and few drops of distilled
water into it.
Close the mouth of the flask with a double
bored cork and insert a thistle funnel and
a bent tube into the two different holes of
the rubber cork.
Now pour a small quantity of lime water into
the boiling tube and clamp it in another stand.
Then add HCl to the sodium carbonate solution
in the flask using the thistle funnel.
You can see that a gas evolves and passes
through the lime water and turns it milky.
Here due to the action of HCl on sodium carbonate,
carbon dioxide is formed which turns lime
water milky.
2HCl + Na2CO3 ? 2NaCl + CO2 +H2O
CO2 + Ca (OH) 2 ? CaCO3 +H2O
Now add a small amount of sodium carbonate
in a boiling tube and add NaOH solution into
it.
Then shake the boiling tube well.
Add a few drops of phenolphthalein into it.
We can observe that the colour of the solution
turns pink which indicates that both sodium
carbonate and NaOH do not react but form an
alkaline solution.
Precautions:
Add HCl to sodium carbonate only after making
the apparatus airtight, otherwise the gas
evolved in the reaction will get away through
the gap.
Handle the chemicals HCl and NaOH carefully
as they are harmful.