Atoms and molecules and chemical reactions — Flashcards
Telangana Board · Class 9 · Physical Science
20 flashcards for Atoms and molecules and chemical reactions (Telangana Board Class 9 Physical Science) to test yourself on key terms and facts.
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A piece of iron weighs 100g before rusting. After rusting, will it weigh more, less, or the same? Explain why.
Answer
It will weigh MORE than 100g. During rusting, iron reacts with oxygen from air to form iron oxide (rust). The oxygen atoms add to the iron's mass, increasing the total weight. This follows the law of …
Why does burning magnesium produce such a bright white light?
Answer
When magnesium burns, it combines with oxygen to form magnesium oxide (2Mg + O₂ → 2MgO). This is a highly exothermic reaction that releases enormous energy as heat and light. The intense white light i…
What happens when you heat calcium carbonate (limestone) strongly? Write the chemical equation.
Answer
Calcium carbonate decomposes into calcium oxide (quicklime) and carbon dioxide gas. CaCO₃(s) → CaO(s) + CO₂(g). This is thermal decomposition. The CO₂ gas can extinguish a burning match stick brought …
Calculate the molecular mass of sulfuric acid (H₂SO₄). Given: H=1u, S=32u, O=16u
Answer
Molecular mass = 2(H) + 1(S) + 4(O) = 2(1) + 32 + 4(16) = 2 + 32 + 64 = 98u. Therefore, the molecular mass of H₂SO₄ is 98 unified mass units.
What is one mole of a substance? Why is this unit important in chemistry?
Answer
One mole is the amount of substance containing 6.022×10²³ particles (Avogadro's number). It's important because it allows us to count atoms and molecules by weighing them. For example, 1 mole of carbo…
Why do iron nails turn brown when dipped in copper sulfate solution?
Answer
Iron is more reactive than copper, so it displaces copper from copper sulfate solution. The reaction is: Fe + CuSO₄ → FeSO₄ + Cu. The brown coating is metallic copper deposited on the iron nail. This …
How do you write the chemical formula for aluminum oxide using the criss-cross method?
Answer
1. Write symbols: Al O 2. Write valencies: Al³⁺ O²⁻ 3. Criss-cross valencies: Al₂O₃ 4. The formula is Al₂O₃ (aluminum has valency 3, oxygen has valency 2, so we need 2 Al atoms and 3 O atoms to balanc…
What is the difference between atomic mass and molar mass? Give an example.
Answer
Atomic mass is expressed in 'u' (unified mass units) while molar mass is in grams. They are numerically equal. Example: Carbon atomic mass = 12u, Carbon molar mass = 12g. 12u refers to one atom, 12g r…
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