Measurement of Matter — Flashcards
Maharashtra Board · Class 9 · Science
23 flashcards for Measurement of Matter (Maharashtra Board Class 9 Science) to test yourself on key terms and facts.
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State the Law of Conservation of Matter and who proposed it.
Answer
The Law of Conservation of Matter states that 'there is no rise or drop in the mass of matter during a chemical reaction.' It was proposed by French scientist Antoine Lavoisier in 1785. The total mass…
What is the Law of Constant Proportion? Give an example.
Answer
The Law of Constant Proportion states that 'the proportion by mass of constituent elements in different samples of a compound is fixed.' Proposed by J.L. Proust in 1794. Example: In water (H₂O), hydro…
Define atomic radius and state its unit.
Answer
Atomic radius is the distance between the nucleus of an atom and its outermost orbit. It determines the size of an atom. Unit: nanometre (nm), where 1 nm = 10⁻⁹ m. Atoms are extremely tiny, with hydro…
What is atomic mass number? How is atomic mass expressed today?
Answer
Atomic mass number is the total number of protons and neutrons in an atomic nucleus. Today, atomic mass is expressed in Unified Mass Unit (u), also called Dalton. 1u = 1.66053904 × 10⁻²⁷ kg. Carbon-12…
Define molecular mass and show how to calculate it for H₂O.
Answer
Molecular mass is the sum of atomic masses of all atoms in a molecule. For H₂O: H = 1u (2 atoms), O = 16u (1 atom). Molecular mass = (1 × 2) + (16 × 1) = 2 + 16 = 18u. Unit is Dalton (u).
What is a mole? Give the definition and formula.
Answer
A mole is the quantity of a substance whose mass in grams equals its molecular mass in Daltons. 1 mole = molecular mass in grams. Formula: Number of moles (n) = Mass of substance (g) / Molecular mass.
What is Avogadro's number? State its value and significance.
Answer
Avogadro's number (Nₐ) is the number of molecules in one mole of any substance. Value: 6.022 × 10²³. This means 1 mole of any substance contains 6.022 × 10²³ molecules. Named after Italian scientist A…
Calculate the number of molecules in 66g of CO₂. (Atomic masses: C=12, O=16)
Answer
Step 1: Molecular mass of CO₂ = 12 + (16×2) = 44u. Step 2: Number of moles = 66/44 = 1.5 mol. Step 3: Number of molecules = 1.5 × 6.022 × 10²³ = 9.033 × 10²³ molecules.
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