Acids, Bases and Salts · Lesson 3 of 12
How Do Metal Carbonates And Metal Hydrogencarbonates React With Acids?
“Carbonates meet acids, bubbles happen, and lime water gets suspiciously milky.”
• Describe how metal carbonates and metal hydrogencarbonates react with acids. • Identify carbon dioxide using lime water. • Explain why lime water turns milky. • Explain what happens when excess carbon dioxide is passed through lime water. • Write balanced equations for carbonate and hydrogencarbonate reactions.
When an acid is added to a metal carbonate or a metal hydrogencarbonate, brisk bubbling occurs. The gas released is carbon dioxide. This reaction provides one of the most useful patterns for recognising carbonates.
Sodium Carbonate And Hydrochloric Acid
Sodium carbonate reacts with hydrochloric acid to form sodium chloride, water and carbon dioxide. The formation of carbon dioxide is seen as effervescence.
Sodium Hydrogencarbonate And Hydrochloric Acid
Testing Carbon Dioxide With Lime Water
The gas produced can be passed through lime water, which is calcium hydroxide solution. Carbon dioxide reacts with calcium hydroxide and forms insoluble calcium carbonate. The fine solid particles make the solution appear milky.
A Precipitate is an insoluble solid formed during a reaction in solution.
Passing Excess Carbon Dioxide Through Lime Water
If carbon dioxide is passed for longer, the milkiness disappears. The calcium carbonate reacts further with carbon dioxide and water to form soluble calcium hydrogencarbonate.
Limestone, Chalk And Marble
Limestone, chalk and marble are different natural forms of calcium carbonate. Their appearance and physical form differ, but they share the same important chemical compound, calcium carbonate.
Problem
Balance CaCO₃ + HCl → CaCl₂ + H₂O + CO₂.
- 1.Calcium is already balanced with one atom on each side.
- 2.The product CaCl₂ contains two chlorine atoms.
- 3.Place a coefficient of two before HCl.
- 4.The left side now contains two hydrogen atoms, which match one H₂O molecule.
- 5.Carbon is one on both sides.
- 6.Oxygen is three in CaCO₃ and three in H₂O plus CO₂.
- 7.The balanced equation is CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂.
Quiz
Why does lime water initially turn milky when carbon dioxide is passed through it?
Which gas is released when a metal carbonate reacts with an acid?
What causes the milkiness when carbon dioxide is passed through lime water?
Why does the milkiness disappear when excess carbon dioxide is passed through lime water?
Practice Problems
- Write and balance the reaction between sodium carbonate and hydrochloric acid.
- Write the reaction between sodium hydrogencarbonate and hydrochloric acid.
- Explain how lime water can be used to identify carbon dioxide gas.
- Explain why the milkiness of lime water disappears when excess carbon dioxide is passed through it.
- Balance CaCO₃ + HCl → CaCl₂ + H₂O + CO₂ and verify the number of atoms on both sides.
Key Takeaways
• Metal carbonates react with acids to form salt, carbon dioxide and water. • Metal hydrogencarbonates react with acids to form salt, carbon dioxide and water. • Carbon dioxide turns lime water milky because insoluble calcium carbonate forms. • Excess carbon dioxide converts calcium carbonate into soluble calcium hydrogencarbonate. • Limestone, chalk and marble are different forms of calcium carbonate.