Atoms and Molecules
Karnataka Board · Class 9 · Science
Flashcards for Atoms and Molecules — Karnataka Board Class 9 Science. Quick Q&A cards covering key concepts, definitions, and formulas.
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A student mixes 5.3 g sodium carbonate with 6 g acetic acid and gets 2.2 g CO₂, 0.9 g water, and 8.2 g sodium acetate. Does this follow the law of conservation of mass?
Answer
Yes! Total mass of reactants = 5.3 + 6 = 11.3 g. Total mass of products = 2.2 + 0.9 + 8.2 = 11.3 g. Since mass before = mass after, this confirms the law of conservation of mass - matter cannot be cre…
If 3 g of hydrogen needs 24 g of oxygen to form water (H:O = 1:8 ratio), how much oxygen is needed for 6 g of hydrogen?
Answer
Using the law of constant proportions, hydrogen and oxygen combine in a fixed 1:8 ratio. For 6 g hydrogen: 6 × 8 = 48 g of oxygen needed. This demonstrates that elements always combine in definite pro…
Why can't we see atoms with our naked eyes even though everything around us is made of atoms?
Answer
Atoms are incredibly small (radius ~10⁻¹⁰ m). Millions of atoms stacked together would barely equal the thickness of paper. They're smaller than the wavelength of visible light, so our eyes cannot det…
What happens when you heat copper sulphate solution with sodium carbonate solution in a closed flask?
Answer
A chemical reaction occurs: CuSO₄ + Na₂CO₃ → CuCO₃ + Na₂SO₄. Blue copper sulphate changes to greenish copper carbonate precipitate. The flask is closed to prevent gas escape, ensuring total mass remai…
How do you write the chemical formula for calcium chloride using valency method?
Answer
Step 1: Write symbols Ca and Cl. Step 2: Write valencies Ca²⁺ and Cl⁻. Step 3: Cross-multiply valencies. Step 4: Ca needs 2 Cl atoms to balance charges. Formula: CaCl₂. The 2+ charge of Ca is balanced…
Why does water always contain hydrogen and oxygen in 1:8 ratio by mass regardless of its source?
Answer
This follows the Law of Constant Proportions (Law of Definite Proportions). Water molecules always have the formula H₂O - 2 hydrogen atoms (2×1=2u) and 1 oxygen atom (16u), giving a constant 2:16 = 1:…
What is an atomic mass unit (u) and why is carbon-12 used as the standard?
Answer
1 atomic mass unit (u) = 1/12th the mass of one carbon-12 atom. Carbon-12 is chosen because: (1) it's stable, (2) it gives most elements whole number atomic masses, (3) carbon forms many compounds, ma…
Calculate the molecular mass of sulfuric acid (H₂SO₄).
Answer
Molecular mass = Sum of atomic masses of all atoms. H₂SO₄ contains: 2 H atoms (2×1=2u), 1 S atom (32u), 4 O atoms (4×16=64u). Total = 2+32+64 = 98u. This means one molecule of sulfuric acid is 98 time…
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Sources & Official References
- Karnataka SSLC — kseeb.kar.nic.in
- Dept of Pre-University Education, Karnataka
- National Education Policy 2020 — education.gov.in
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