Thermal decomposition of calcium
carbonate
Dr. Rob Craig, Ph.D
• Adapted from:
• http://www.rsc.org/learn-
chemistry/wiki/...
Thermal decomposition of calcium
carbonate
• Calcium carbonate is strongly heated until it
undergoes thermal decomposition...
Bubbling carbon dioxide
• Thermal decomposition:
• CaCO3(s) → CaO(s) + CO2(g)
• The reaction is highly exothermic and the
...
Thermal decomposition of calcium
carbonate
What You need
• Calcium carbonate (Low hazard) Refer to
CLEAPSSR Hazcard 19B
• 1 Large (150 x 25 mm) test-tubes.
• 2 The c...
You need to prepare a tabulated results
sheet before you start your experiments.
Method Observations
Heat for 10 min
Add 2...
Procedure
• Set a lump of chalk (calcium carbonate) on a
gauze.
• If your gauze has a coated central circle, use the
edge ...
What do you see?
• Add about 10 cm3 more water to the solid. What
happens now?
• Filter half the mixture into the other bo...
Lets fill in chart. . . .
Method Observations
Heat for 10 min
Add 2-3 drops of water
Add 10 ml drops of water
Blow Bubbles...
Practical applications
• This set of experiments involves a variety of
important reactions and types of reactions,
with se...
Answers to questions
Why does the chalk crumble slightly on strong heating?
• Carbon dioxide/a gas is evolved; this forces...
Answers to questions
Why does the limewater turn cloudy? Write an
equation for the reaction which is occurring.
• Insolubl...
Answers to questions
• Reference
• This experiment has been reproduced from
Practical Chemistry:
• http://www.practicalche...
Differential thermal analysis
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This one thermal decomp CHM 02

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This experiment involves a comparison between the thermal stabilities of carbonates of reactive metals, such as sodium and potassium, and the carbonates of less reactive metals, such as lead and copper

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This one thermal decomp CHM 02

  1. 1. Thermal decomposition of calcium carbonate Dr. Rob Craig, Ph.D • Adapted from: • http://www.rsc.org/learn- chemistry/wiki/TeacherExpt:Thermal_decomp osition_of_calcium_carbonate
  2. 2. Thermal decomposition of calcium carbonate • Calcium carbonate is strongly heated until it undergoes thermal decomposition to form calcium oxide and carbon dioxide. • The calcium oxide (unslaked lime) is dissolved in water to form calcium hydroxide (limewater). • Bubbling carbon dioxide through this forms a milky suspension of calcium carbonate(S)
  3. 3. Bubbling carbon dioxide • Thermal decomposition: • CaCO3(s) → CaO(s) + CO2(g) • The reaction is highly exothermic and the small amount of water added is partly converted to steam in the process: CaO(s) + H2O(l) → Ca(OH)2(s) • Lastly • Ca(OH)2(s) + CO2(g) -> CaCO3(s) + H2O(l)
  4. 4. Thermal decomposition of calcium carbonate
  5. 5. What You need • Calcium carbonate (Low hazard) Refer to CLEAPSSR Hazcard 19B • 1 Large (150 x 25 mm) test-tubes. • 2 The calcium carbonate used should be in the form of pea-sized lumps of chalk. • 3 Blackboard chalk should not be used, as it is likely to be mostly calcium sulfate. • 4 Freshly purchased drinking straws should be used.
  6. 6. You need to prepare a tabulated results sheet before you start your experiments. Method Observations Heat for 10 min Add 2-3 drops of water Add 10 ml drops of water Blow Bubbles through solution Add Universal indicator
  7. 7. Procedure • Set a lump of chalk (calcium carbonate) on a gauze. • If your gauze has a coated central circle, use the edge where there is no coating. • Heat the chalk very strongly for 5 -10 minutes. Write down what you observe. Let the chalk cool and use tongs to move it into a boiling tube. Add 2 – 3 drops of water with a dropping pipette. Write down your observations.
  8. 8. What do you see? • Add about 10 cm3 more water to the solid. What happens now? • Filter half the mixture into the other boiling tube and, using a straw, gently blow a stream of bubbles through the filtrate. What do you see? • Test the remaining half of the mixture with Universal Indicator solution. • Write down what you observe.
  9. 9. Lets fill in chart. . . . Method Observations Heat for 10 min Add 2-3 drops of water Add 10 ml drops of water Blow Bubbles through solution Add Universal indicator
  10. 10. Practical applications • This set of experiments involves a variety of important reactions and types of reactions, with several references to industrial processes. • The roasting of limestone and the hydration ofthe quicklime formed has relevance in the manufacture of plaster and cement, and in the laboratory limewater is a common reagent for the testing of carbon dioxide.
  11. 11. Answers to questions Why does the chalk crumble slightly on strong heating? • Carbon dioxide/a gas is evolved; this forces its way out of the solid and breaks down its structure. What type of reaction is taking place during the heating process? Write an equation for the reaction. • Thermal decomposition; CaCO3(s) → CaO(s) + CO2(g) Why is steam evolved when drops of water are added? Write an equation for the reactionoccurring. • The reaction is highly exothermic and the small amount of water added is partly converted to steam in the process: CaO(s) + H2O(l) → Ca(OH)2(s)
  12. 12. Answers to questions Why does the limewater turn cloudy? Write an equation for the reaction which is occurring. • Insoluble calcium carbonate is being precipitated: Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l) What does the colour change occurring when limewater is added tell you about the pH of the solution? Explain why the pH would be expected to have this value. • The pH is about 11 - 14; soluble metal hydroxides are alkaline and therefore give high pH values
  13. 13. Answers to questions • Reference • This experiment has been reproduced from Practical Chemistry: • http://www.practicalchemistry.org/experimen ts/intermediate/materials/thermal- decompositionof- • calcium-carbonate,282,EX.html
  14. 14. Differential thermal analysis
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