ChemistryChapter 18: Qualitative Analysis
Carbon Dioxide
In the lab, CO2 is made from HCl + marble chips (CaCO3) -> CaCl2 + CO2 + H2O.
Learning objectives
- State the main idea of carbon dioxide in clear words.
- Explain why carbon dioxide is useful in chemistry.
- Apply the correct method, observation, equation, or comparison.
- Avoid the common mistakes and write a complete exam answer.
Definition
In the lab, CO2 is made from HCl + marble chips (CaCO3) -> CaCl2 + CO2 + H2O. Limewater is aqueous Ca(OH)2. The gas turns limewater milky because solid CaCO3 forms. That test distinguishes CO2 from O2, which does not milk limewater.
Important terms
- HCl
- In the lab, CO2 is made from HCl + marble chips (CaCO3) -> CaCl2 + CO2 + H2O.
- marble chips
- In the lab, CO2 is made from HCl + marble chips (CaCO3) -> CaCl2 + CO2 + H2O.
- CaCO3
- In the lab, CO2 is made from HCl + marble chips (CaCO3) -> CaCl2 + CO2 + H2O.
- CaCl2 + CO2 + H2O
- In the lab, CO2 is made from HCl + marble chips (CaCO3) -> CaCl2 + CO2 + H2O.
- Limewater
- In the lab, CO2 is made from HCl + marble chips (CaCO3) -> CaCl2 + CO2 + H2O.
- Ca(OH)2
- In the lab, CO2 is made from HCl + marble chips (CaCO3) -> CaCl2 + CO2 + H2O.
Overview
Making the gas, then proving it:
Lab Preparation
Marble chips are mainly CaCO3. Dilute HCl attacks the carbonate and CO2 bubbles off. The other products are CaCl2 in solution and water. Collect the gas by downward delivery (it is denser than air) or over water if the question allows.
Examples HCl + CaCO3 in a flask · Bubbles of CO2 · CaCl2 left in solution
Limewater Test
Bubble the gas through limewater (aqueous Ca(OH)2). A white milkiness is CaCO3. Oxygen relights a glowing splint but leaves limewater clear, so the two gases are not confused if you use the right test.
Examples Limewater turns milky · O2: limewater stays clear · If you keep bubbling, milk may clear later
WHAT — Core idea
In the lab, CO2 is made from HCl + marble chips (CaCO3) -> CaCl2 + CO2 + H2O. Limewater is aqueous Ca(OH)2. The gas turns limewater milky because solid CaCO3 forms. That test distinguishes CO2 from O2, which does not milk limewater.
WHY — Why it matters
Equation to remember: CaCO3 + 2HCl -> CaCl2 + CO2 + H2O. The milkiness reaction is Ca(OH)2 + CO2 -> CaCO3 + H2O.
HOW — Method, evidence, or comparison
1. 1. LAB PREPARATION: Marble chips are mainly CaCO3. Dilute HCl attacks the carbonate and CO2 bubbles off. The other products are CaCl2 in solution and water. Collect the gas by downward delivery (it is denser than air) or over water if the question allows. 2. 2. LIMEWATER TEST: Bubble the gas through limewater (aqueous Ca(OH)2). A white milkiness is CaCO3. Oxygen relights a glowing splint but leaves limewater clear, so the two gases are not confused if you use the right test.
HOW — Answer in an exam
Milky limewater is the CO2 test. A glowing splint is the oxygen test. Do not swap them in an answer.
Explanation
Equation to remember: CaCO3 + 2HCl -> CaCl2 + CO2 + H2O. The milkiness reaction is Ca(OH)2 + CO2 -> CaCO3 + H2O.
In simple words
Milky limewater is the CO2 test. A glowing splint is the oxygen test. Do not swap them in an answer.
Key points
- HCl
- marble chips
- CaCO3
- CaCl2 + CO2 + H2O
Exam preparation
Exam Focus
Quick revision
Revision Zone
Review the key facts, formulas and checks before you move on.Carbon Dioxide
Sticky Notes · Quick Revision
WHAT
- In the lab, CO2 is made from HCl + marble chips (CaCO3) -> CaCl2 + CO2 + H2O.
Key Points
- HCl
- marble chips
- CaCO3
- CaCl2 + CO2 + H2O
- Limewater
HOW
- Marble chips are mainly CaCO3.
- Bubble the gas through limewater (aqueous Ca(OH)2).
Example
- HCl + CaCO3 in a flask
- Bubbles of CO2
- CaCl2 left in solution
Common Mistake
- Carbon dioxide turns limewater milky; oxygen relights a glowing splint.
Exam Tip
- Milky limewater is the CO2 test.
- A glowing splint is the oxygen test.
60-second revision
- In the lab, CO2 is made from HCl + marble chips (CaCO3) -> CaCl2 + CO2 + H2O.
- Limewater is aqueous Ca(OH)2.
- Marble chips are mainly CaCO3.
- Bubble the gas through limewater (aqueous Ca(OH)2).
- Milky limewater is the CO2 test.
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