Multiple choice

A 2.0 g mixture of Na2CO3 and NaHCO3 suffered a loss of 0.12 g on heating. The percentage of Na2CO3 in the mixture was

  1. 83.8%

  2. 16.1%

  3. 38.8%

  4. 61.2%
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A Correct answer
Explanation

Only NaHCO3 decomposes on heating: 2NaHCO3 -> Na2CO3 + H2O + CO2. The mass loss is due to H2O and CO2. Molar mass of 2NaHCO3 is 168 g/mol, and the loss is 62 g. Loss = 0.12g implies 0.12 * (168/62) = 0.325g of NaHCO3. Na2CO3 = 2.0 - 0.325 = 1.675g. Percentage = (1.675/2.0) * 100 = 83.75%.

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