2.2.5Chemical Bonding, Application Of Chemical Reactions and Organic Chemistry
The Acid-Carbonate Reaction
5 min read 7 parts Lesson 18 of 54 1 quiz
Section 1 of 7The reaction
General equation
- General equation acid + metal carbonate → salt + water + carbon dioxide.
Ionic equation
- Ionic equation CO32–(aq) + 2H+(aq) → CO2(g) + H2O(l)
Observation
- Observation Fizzing (effervescence) is seen as carbon dioxide gas is given off.
- Saying 'carbon dioxide is formed' is a conclusion, not an observation.
Section 2 of 7Testing for carbon dioxide
1
Add dilute acid to the suspected carbonate in a test tube and watch for fizzing.
2
Fit a bung with a delivery tube straight away so none of the gas escapes.
3
Lead the delivery tube into a second test tube holding limewater, calcium hydroxide solution.
4
Observe the limewater: it turns milky (cloudy) if the gas is carbon dioxide.
Section 3 of 7Why limewater goes cloudy
1Gas bubbles in
- Gas bubbles in Carbon dioxide enters the limewater.
2Reaction
- Reaction CO2(g) + Ca(OH)2(aq) → CaCO3(s) + H2O(l)
3Insoluble product
- Insoluble product Calcium carbonate does not dissolve, so it forms as a fine white precipitate.
4Milky appearance
- Milky appearance The suspended solid makes the limewater turn milky.
Section 4 of 7Worked equations with named acids
| Reactants | Word equation | Symbol equation |
|---|---|---|
| Calcium carbonate and hydrochloric acid | calcium carbonate + hydrochloric acid → calcium chloride + water + carbon dioxide | CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g) |
| Sodium carbonate and nitric acid | sodium carbonate + nitric acid → sodium nitrate + water + carbon dioxide | Na2CO3(s) + 2HNO3(aq) → 2NaNO3(aq) + H2O(l) + CO2(g) |
| Copper(II) carbonate and sulfuric acid | copper(II) carbonate + sulfuric acid → copper(II) sulfate + water + carbon dioxide | CuCO3(s) + H2SO4(aq) → CuSO4(aq) + H2O(l) + CO2(g) |
Section 5 of 7Using the test
| Observation | Conclusion |
|---|---|
| Solid fizzes with dilute acid and the gas turns limewater milky | The solid is a carbonate, and the gas is carbon dioxide |
| No fizzing with acid | A carbonate is not present, or the acid is not reacting |
| Fizzing but limewater stays clear | The gas is not carbon dioxide, for example hydrogen from a metal |
Section 6 of 7Key terms
| Term | Meaning |
|---|---|
| Carbonate | A compound containing the carbonate ion, CO32–. |
| Effervescence | Fizzing caused by bubbles of gas escaping from a liquid. |
| Limewater | A solution of calcium hydroxide used to test for carbon dioxide. |
| Precipitate | An insoluble solid formed in a reaction between solutions or a gas and a solution. |
| Salt | A compound formed when the hydrogen in an acid is replaced by a metal ion or ammonium ion. |
| Neutralisation | A reaction in which an acid is cancelled out by a base or carbonate. |
Section 7 of 7Exam technique
1
Writing 'carbon dioxide' as the observation — the observation is fizzing and the limewater turning milky.
2
Saying limewater turns 'white' instead of milky or cloudy.
3
Forgetting to connect the delivery tube quickly, so the gas escapes before it reaches the limewater.
4
Giving the formula of the precipitate as CaCO — it is CaCO3.