Carbonates, limestone and lime
Follow limestone through thermal decomposition, lime manufacture and acid neutralisation, keeping reactants, products and observations distinct.
An original 0652 lesson covering the listed lime manufacture and carbonate decomposition content. Written practice is self-checked; it does not certify laboratory competence or prescribe real-world waste treatment.
Before you begin
- Recognise carbonates and chemical formulae
- Balance simple chemical equations
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which formula is calcium carbonate?
What you will learn
- Write the thermal decomposition equation for calcium carbonate
- Explain how limestone can neutralise acidic soil and industrial waste
- Connect carbonate reactions to carbon dioxide evidence
Heating limestone to make lime
Limestone is mainly calcium carbonate. Strong heating decomposes it into calcium oxide (quicklime) and carbon dioxide. This is a thermal decomposition reaction: one compound breaks down because of heat.
Word equation: calcium carbonate → calcium oxide + carbon dioxide. Symbol equation: CaCO₃(s) → CaO(s) + CO₂(g).
Neutralising acidic materials
Limestone can be added to acidic soil or acidic industrial waste because calcium carbonate reacts with acid. The products are a salt, water and carbon dioxide. In a model reaction with hydrochloric acid: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂.
The equation is a chemistry model, not a dosing instruction. Real treatment depends on measured acidity, the material being treated and local controls.
Recognise the gas
Carbon dioxide is produced when an acid reacts with a carbonate and when calcium carbonate decomposes. A standard school test is to bubble the gas through limewater: it turns milky. This observation supports the identification; it does not replace the balanced reaction equation.
Sources for this lesson
Pause and explain
Why can limestone reduce acidity?
Worked example
A student strongly heats 10.0 g of pure calcium carbonate. Name the solid product and write a balanced equation.
Show the worked solution
- Heating causes thermal decomposition.
- Calcium carbonate forms calcium oxide and carbon dioxide.
- Check that one calcium, one carbon and three oxygen atoms appear on each side.
Answer The solid is calcium oxide (CaO). CaCO₃(s) → CaO(s) + CO₂(g) is balanced: Ca 1, C 1 and O 3 on both sides.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Write the products of thermal decomposition of calcium carbonate and identify which product is lime.
Give me a hint
A metal carbonate heated strongly forms a metal oxide and carbon dioxide.
Compare my reasoning
- Start with CaCO₃(s).
- The oxide is CaO(s); the remaining carbon and oxygen form CO₂(g).
- Count atoms on both sides to check the equation.
CaCO₃(s) → CaO(s) + CO₂(g). Calcium oxide, CaO, is lime (quicklime). Each side has one Ca, one C and three O atoms.
Look for these in your work
- Includes both products
- Balances the equation
- Identifies CaO as lime
Use an equation to show how calcium carbonate can neutralise hydrochloric acid in acidic waste.
Give me a hint
A carbonate plus an acid forms a salt, water and carbon dioxide.
Compare my reasoning
- Name the salt from calcium ions and chloride ions.
- Write water and carbon dioxide as the other products.
- Balance hydrogen, chlorine and oxygen atoms.
CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂. The acid is consumed as the carbonate reacts; the equation is a classroom model, not an instruction for treating real waste.
Look for these in your work
- Uses calcium chloride as the salt
- Includes water and carbon dioxide
- Balances the equation
A soil sample is acidic. Explain why finely crushed limestone may help, and name one observation that could support carbon dioxide being formed in a separate school test.
Give me a hint
Think about what carbonate does to acid and how carbon dioxide is identified.
Compare my reasoning
- Calcium carbonate in limestone reacts with acidic material.
- The reaction forms a salt, water and carbon dioxide.
- Identify the gas using the standard limewater test.
Limestone can neutralise some acidity because calcium carbonate reacts with acid to form a salt, water and carbon dioxide. In a separate test, carbon dioxide turns limewater milky. Treatment amounts require proper analysis and control.
Look for these in your work
- Explains acid neutralisation
- Names carbon dioxide as a product
- Gives the limewater observation
Common mistakes
- Do not call calcium carbonate and calcium oxide the same substance.
- Do not omit carbon dioxide from the thermal decomposition equation.
- Do not treat a limewater observation as the reaction equation.
What can you explain now?
What two products form when calcium carbonate is heated strongly?
Compare with the explanation
Calcium oxide and carbon dioxide.
Thermal decomposition of limestone follows CaCO₃(s) → CaO(s) + CO₂(g).
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Make it stick
Recall the thermal decomposition equation and the three products of a carbonate–acid reaction.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.