What happens to a salt during thermal decomposition?
A salt breaks down into simpler substances when heated. The products depend on the anion present in the salt.
What is the general equation for the thermal decomposition of carbonates?
Metal Carbonate → Metal Oxide + Carbon Dioxide
Write the chemical equation for the decomposition of calcium carbonate.
CaCO₃(s) → CaO(s) + CO₂(g)
Which gas is released when metal carbonates decompose?
Carbon dioxide (CO₂).
How can carbon dioxide gas be identified?
By bubbling it through limewater, which turns cloudy due to the formation of calcium carbonate.
Which carbonates do not decompose under normal heating conditions?
Sodium carbonate (Na₂CO₃) and potassium carbonate (K₂CO₃).
What is the general equation for the thermal decomposition of nitrates?
Metal Nitrate → Metal Oxide + Nitrogen Dioxide + Oxygen
What colour is nitrogen dioxide gas?
Reddish-brown.
How can oxygen gas be identified?
By using a glowing splint, which relights in the presence of oxygen.
Write the balanced chemical equation for the decomposition of lead(II) nitrate.
2Pb(NO₃)₂(s) → 2PbO(s) + 4NO₂(g) + O₂(g)
What are the products when copper(II) nitrate is heated?
Copper(II) oxide (CuO), nitrogen dioxide (NO₂), and oxygen (O₂).
What type of gas is produced when some metal sulfates decompose?
Sulfur trioxide (SO₃).
Write the balanced chemical equation for the decomposition of copper(II) sulfate.
CuSO₄(s) → CuO(s) + SO₃(g)
What gas is produced when iron(II) sulfate decomposes?
Sulfur dioxide (SO₂) and sulfur trioxide (SO₃).
How can chloride ions be identified in a salt sample?
By adding silver nitrate, which forms a white precipitate of silver chloride.
Write the chemical equation for the reaction between chloride ions and silver nitrate.
Ag⁺(aq) + Cl⁻(aq) → AgCl(s)
What test can be used to identify sulfate ions in a solution?
The addition of barium chloride, which forms a white precipitate of barium sulfate.
What is the purpose of qualitative analysis in chemistry?
To identify the presence of specific ions in a salt through chemical tests.
What happens to a glowing splint in the presence of oxygen?
It relights.
What colour change occurs when copper(II) carbonate decomposes?
It changes from green to black as copper(II) oxide forms.
Explanation Questions
Why do metal carbonates decompose when heated?
Heat provides energy to break the bonds in the carbonate compound, leading to the formation of a metal oxide and carbon dioxide.
Why do some metal carbonates, like sodium carbonate, not decompose when heated?
Sodium and potassium carbonates are thermally stable, meaning they require much higher temperatures to decompose than what is achievable in a laboratory.
Why does nitrogen dioxide turn blue litmus paper red?
Nitrogen dioxide is acidic and dissolves in water to form nitric acid, which lowers the pH and turns blue litmus paper red.
Why is thermal decomposition of nitrates more complex than that of carbonates?
Nitrates contain polyatomic ions that break down into multiple products, including a metal oxide, nitrogen dioxide, and oxygen gas.
Why does limewater turn cloudy when carbon dioxide is bubbled through it?
Carbon dioxide reacts with calcium hydroxide in limewater to form insoluble calcium carbonate, which appears as a white precipitate.
Why does heating lead(II) nitrate produce brown fumes?
The brown fumes are nitrogen dioxide gas (NO₂), which is released during the decomposition of lead(II) nitrate.
Why do some metal sulfates release sulfur trioxide when heated?
The sulfate ion decomposes, releasing sulfur trioxide gas, which can further react to form sulfuric acid in the atmosphere.
Why does the residue from heated copper(II) carbonate appear black?
The green copper(II) carbonate decomposes into black copper(II) oxide.
How does the decomposition of nitrates contribute to fire hazards?
The oxygen gas released supports combustion, increasing fire risks.
Why is thermal decomposition useful in industry?
It allows extraction of useful materials, such as quicklime from limestone.