Question

2.0 g of a mixture of Na2
CO3
and NaHCO3

was heated when its weight
reduced to 1.876 g. Determine the percentage composition of the mixture.

Answer 1

Answer:

The mixture is

53.2 % Na2CO3 and 46.8 % NaHCO3

Explanation:

When you heat a mixture of Na2CO3 and NaHCO3 only the NaHCO3 decomposes.

The equation for the decomposition is

2NaHCO3(s)→Na2CO3(s)+CO2(g)+H2O(g)

The loss in mass is caused by the loss of

H2O and CO2 (equivalent to the loss of H2CO3).

The loss in mass is

(220–182)g=38g

This corresponds to 38gH2CO3×1 mol H2CO3 62.02g H2CO3=0.613 mol H2CO3∴ Moles of NaHCO3=0.613mol H2CO3×

2 mol NaHCO31mol H2CO=1.225 mol NaHCO3 and Mass of NaHCO3=1.2225mol NaHC3×84.01 NaHCO31mol NaHCO3=102.9 g NaHCO3

The loss of mass after heating corresponds to

102.9 g of original NaHCO3

The rest of the original mixture must have been

Na2CO3 .

Mass of original Na2CO3=220g–102.9g=117.1 g% Na2CO3=117.1g220g×100%=53.2%NaHCO3=102.9g220g×100%=46.8%

Explanation:

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