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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?

X and Y

Y and Z

Only Z

X and Z

Solution:

  1. Test tube X: Ethanoic acid does not react with sodium chloride. Hence, the flame is not extinguished.
  2. Test tube Y: CH3COOH + NaOH → CH3COONa + H2O
    Flame is not extinguished as there is no direct contact between water and flame.
  3. Test tube Z: 2CH3COOH + Na2CO3 → 2CH3COONa + CO2 + H2O
    Flame is extinguished due to the emission of CO2. Hence, on bringing test tube Z near a burning splinter, the flame is extinguished as CO2 does not support combustion.
    Option C is correct.