Question

A student adds a few drops of ethanoic acid to test tubes X, Y and Z containing aqueous solutions of sodium chloride, sodium hydroxide and sodium carbonate respectively. If he now brings a burning splinter near the mouth of the test tubes immediately after adding the ethanoic acid in each one of them, in which of the test tube or test tubes the flame gets extinguished?
A) X and Y
B) Y and Z
C) X and Z
D) Only Z

Answer 1

Hint: Usually there are three things which keeps a flame burning that are Oxygen, fuel and heat
To extinguished a flame we need to get rid of any one of these
Fire extinguishers generally consist of carbon-di-oxide or nitrogen which are known to be suppressors of fire.
We will use the same fact to get the result of the above test by finding which out of the following compounds sodium chloride, sodium hydroxide and sodium carbonate on reaction with ethanoic acid either produce carbon-di-oxide or Nitrogen gas.

Complete step by step answer:
 In the given question ethanoic acid is first added to test tube X which contains solution of sodium chloride as we all know that sodium chloride is a salt while ethanoic acid is an acid hence there will be no reaction between them hence there cannot be evolution of neither carbon-di-oxide nor nitrogen
So test tube X cannot extinguish the flame when a burning splinter is brought near its mouth

Next the splinter is brought near test tube Y which has sodium hydroxide and some drops of ethanoic acid
As we all know sodium hydroxide is a base while ethanoic acid is an acid and they both will react to form a salt and water as follow
$C{H_3}COOH + NaOH \to C{H_3}COONa + {H_2}O$
Here also there is evolution of neither carbon-dioxide nor nitrogen
So test tube Y also cannot extinguish the flame when a burning splinter is brought near its mouth
Finally the splinter is brought near to Test tube Z which contains sodium carbonate and some drops of ethanoic acid
As we all know that sodium carbonate is a metal carbonate
And metal carbonate on reaction with an acid (which is ethanoic acid here) forms salt, water and carbon-di-oxide as follow
$2C{H_3}COOH + N{a_2}C{O_3} \to C{H_3}COONa + {H_2}O + C{O_2}$

Here since there is evolution therefore the flame will get extinguished and thus the option ‘D’ is the correct solution for this question.

Note:
Carbon-di-oxide $\left( {C{O_2}} \right)$ is stable compound of carbon which already has two oxygen atom thus it cannot further be oxidized making it neither combustible nor a supporter of combustion
Which is the biggest reason for its application in fire extinguishers