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Question 28

Potassium hydrogencarbonate (KHCO3\text{KHCO}_3KHCO3​) decomposes on heating.

Three possible equations for the decomposition are:

  • Equation 1: 2KHCO3(s)→K2O(s)+2CO2(g)+H2O(g)2\text{KHCO}_3(\text{s}) \rightarrow \text{K}_2\text{O}(\text{s}) + 2\text{CO}_2(\text{g}) + \text{H}_2\text{O}(\text{g})2KHCO3​(s)→K2​O(s)+2CO2​(g)+H2​O(g)
  • Equation 2: KHCO3(s)→KOH(s)+CO2(g)\text{KHCO}_3(\text{s}) \rightarrow \text{KOH}(\text{s}) + \text{CO}_2(\text{g})KHCO3​(s)→KOH(s)+CO2​(g)
  • Equation 3: 2KHCO3(s)→K2CO3(s)+CO2(g)+H2O(g)2\text{KHCO}_3(\text{s}) \rightarrow \text{K}_2\text{CO}_3(\text{s}) + \text{CO}_2(\text{g}) + \text{H}_2\text{O}(\text{g})2KHCO3​(s)→K2​CO3​(s)+CO2​(g)+H2​O(g)

When 25.00 g25.00\text{ g}25.00 g of potassium hydrogencarbonate is heated until it is fully decomposed, 17.25 g17.25\text{ g}17.25 g of solid is formed.

a.

Complete the table by calculating the amount, in moles, of each solid. Give your answers to 3 significant figures.

SolidMrM_{\text{r}}Mr​ of solidMass of solid in gAmount of solid in mol
KHCO3\text{KHCO}_3KHCO3​10025.00
K2O\text{K}_2\text{O}K2​O9417.25
KOH\text{KOH}KOH5617.25
K2CO3\text{K}_2\text{CO}_3K2​CO3​13817.25
[4]
b.

Use the information in the table to explain which equation, 1, 2 or 3, represents the decomposition of potassium hydrogencarbonate.

[3]

Chemical formulae, equations and calculations Questions

  1. IGCSE
  2. /Chemistry
  3. /Chemical formulae, equations and calculations