NaCl is stable in the temperature range between 200 o C and 850 o C, but in that
ID: 873932 • Letter: N
Question
NaCl is stable in the temperature range between 200 oC and 850 oC, but in that range, NaHCO3 decomposes by the reaction:
2 NaHCO3 (s) ? Na2CO3 (s) + H2O (g) + CO2 (g)
If a mixture of the two is heated to temperatures in the above range, the gaseous products will escape and the residue will contain the original NaCl and an amount of solid Na2CO3. The Na2CO3 is related stoichiometrically to the amount of NaHCO3 which has decomposed. If the reaction has proceeded to completion (no remaining NaHCO3), the moles, and therefore the weight of NaHCO3 originally in the sample, are able to be determined.
We heat the sample several times, weighing the residue after each heating.
We use the following criterion to establish that the reaction is complete:
the weight of the residue changes in weight by less that 5.0 mg (plus or minus) in two successive heatings.
The following data were collected in such a determination:
What was the weight of NaHCO3 in the original sample?
What was the percent of NaHCO3 in the original sample?
DATA VALUE (g) Weight of empty crucible 15.6593 Initial weight of crucible + sample 17.5687 Weight of crucible + residue after 1st heating 17.1965 Weight of crucible + residue after 2nd heating 17.1857 Weight of crucible + residue after 3rd heating 17.1798 Weight of crucible + residue after 4th heating 17.1770Explanation / Answer
Solution:
We write balanced reaction.
2 NaHCO3 (s) ---> Na2CO3 (s) + H2O (g) + CO2 (g)
We have to calculate original mass of NaHCO3.
To calculate mass, moles are required and moles are calculated by using reaction stoichiometry.
We use given data to get moles
We calculate original sample
Mass of sample = wt of (crucible + sample )
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