Qualitative Analysis - Result Question 75

####78. When 16.8g of white solid, X were heated, 4.4g of acid gas A, that turned lime water milky was driven off together with 1.8g of a gas B which condensed to a colourless liquid.

The solid that remained, Y, dissolved in water to give an alkaline solution, which with excess barium chloride solution gave a white precipitate Z. The precipitate effervesces with acid giving of carbon dioxide. Identify A,B and Y and write down the equation for the thermal decomposition of X.

(1984,4M)

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Solution:

  1. (X) is NaHCO3(M=84). The reactions involved are :

2NaHCO3Na2CO3(s)+CO2(g)+H2O(g) YYAB 168g106g44g18g 16.8g10.6g4.4g1.8g CO2+Ca(OH)2CaCO3+H2O

H2O(g) is condensed to liquid water.

Na2CO3+BaCl2BaCO3+2NaCl Y BaCO3+2HClBaCl2+H2O+CO2 Z



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