14. Elements, Compounds and Mixtures​

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Chapter 14 – Elements, Compounds & Mixtures (Class 7, Maharashtra Board)

Chapter 14: Elements, Compounds & Mixtures

Class 7 • Maharashtra Board (General Science) Questions Red • Answers Green Comic Sans • Big fonts • Clean line spacing • Mobile friendly

1) 20 Important Words & Meanings (Meanings in simple Hindi only)

Matterकोई भी चीज़ जो जगह घेरे और द्रव्यमान रखे।
Substance (Pure)जिसमें केवल एक ही प्रकार का घटक हो।
Elementजो एक ही प्रकार के परमाणुओं से बना हो।
Compoundदो या अधिक तत्व मिलकर बना नया पदार्थ।
Mixtureदो या अधिक पदार्थों का भौतिक मेल, अनुपात निश्चित नहीं।
Atomतत्व का सबसे छोटा कण।
Moleculeपरमाणुओं का समूह जो स्वतंत्र रूप से रहता है।
Metalचमकीला, तापन/विधुत का अच्छा सुचालक, पीटकर पतला-खींचकर तार बनता।
Non-metalधातुओं जैसे गुण नहीं; अक्सर भंगुर, सुचालक नहीं।
Metalloidधातु व अधातु दोनों के कुछ गुण जिनमें हों।
Alloyधातुओं (या धातु+अधातु) का मिश्रधातु; गुण सुधारे हुए।
Solutionघोल—घुला हुआ समान मिश्रण (समान रूप से मिला)।
Soluteजो घुलता है (जैसे चीनी)।
Solventजिसमें घुलाया जाता है (जैसे पानी)।
Distillationउबालकर वाष्प बना फिर ठंडाकर शुद्ध द्रव पाना।
Separating Funnelदो न मिलने वाले तरल अलग करने की विधि।
Centrifugationतेज़ घुमाव से ठोस कण नीचे अलग करना।
Chromatographyघोल में मिले सूक्ष्म घटक अलग दिखाना/पहचानना।
Sublimationठोस का सीधे वाष्प बनना (जैसे कपूर)।
Immiscible Liquidsजो आपस में न मिलें (जैसे तेल-पानी)।

2) Important Notes (Quick Revision)

  • Matter has mass and volume; exists as solids, liquids, gases.
  • Pure substance has only one kind of particle; mixture has two or more; proportion in a mixture is not fixed; no new substance forms on mixing.
  • Element: molecules/atoms of only one kind (e.g., H, O, Fe). Compound: atoms of different elements combined in a fixed ratio (e.g., water $\mathrm{H_2O}$).
  • Properties of a compound are different from those of its elements (H burns, O supports burning, but $\mathrm{H_2O}$ extinguishes fire).
  • Metals (lustrous, malleable, ductile, conductors), non-metals (generally dull, brittle, insulators), metalloids (Si, As) show mixed properties.
  • Alloys (brass, steel, 22-carat gold) improve strength, hardness, corrosion resistance.
  • Symbols (H, O, Na, Cl…) and formulae (NaCl, $\mathrm{H_2SO_4}$) are short scientific notations.
  • Separation of mixtures: picking, sieving, winnowing, filtration, evaporation, distillation, separating funnel (immiscible liquids), magnetic separation, centrifugation (cream from milk), chromatography (ink colours).
  • Distillation: boil → vapour → cool to liquid; separates solvent from solute and purifies liquids.
  • Separating funnel: uses density difference of immiscible liquids (e.g., water below, kerosene above).

3) 20 Important One-Word/Line Questions (Answers 1–2 lines)

  1. Define matter.
    Anything that has mass and occupies space.
  2. What is a pure substance?
    Material made of only one kind of particle.
  3. What is an element?
    Substance of only one type of atom.
  4. What is a compound?
    Substance formed by chemical combination of elements in a fixed ratio.
  5. What is a mixture?
    Physical combination of substances; variable composition.
  6. Give one example of element, compound, mixture.
    Fe; $\mathrm{H_2O}$; air/bhel.
  7. Smallest particle of an element?
    Atom.
  8. Smallest particle of a compound?
    Molecule.
  9. State of oxygen in air?
    Gas; exists as molecules $\mathrm{O_2}$.
  10. Is CO$_2$ an element?
    No, it’s a compound of C and O.
  11. Two properties of metals.
    Conduct heat/electricity; malleable/ductile; lustrous.
  12. What is an alloy?
    Mixture of metals (or metal + non-metal) with improved properties.
  13. Define solution.
    Homogeneous mixture of solute in solvent.
  14. What does distillation separate?
    Solvent from solution / different liquids by boiling points.
  15. Purpose of separating funnel?
    Separate immiscible liquids (e.g., oil and water).
  16. Use of centrifugation at home?
    Separating cream from milk; spin-drying clothes.
  17. Chromatography is used for?
    Separating/identifying small amounts of components in a mixture (e.g., ink colours).
  18. Symbol of sodium and potassium.
    Na and K.
  19. Write formula of water and methane.
    $\mathrm{H_2O}$ and $\mathrm{CH_4}$.
  20. Why is 22-carat gold used for jewellery?
    It’s an alloy—harder/stronger than pure gold.

4) 20 Very Short Answer Questions (1–2 lines)

  1. Give two properties common to all matter.
    Has mass and occupies space (volume).
  2. Is steel an element or alloy?
    Alloy (iron + carbon and others).
  3. State if milk is pure substance or mixture.
    Mixture/colloid.
  4. Define metalloid with one example.
    Shows mixed properties; e.g., silicon (Si).
  5. Write symbol of chlorine and calcium.
    Cl and Ca.
  6. Name the gas supporting combustion.
    Oxygen ($\mathrm{O_2}$).
  7. Water extinguishes fire—element or compound property?
    Compound property (different from H and O).
  8. What is solute in salt solution?
    Salt (NaCl).
  9. What is solvent in salt solution?
    Water ($\mathrm{H_2O}$).
  10. Why is air called a mixture?
    Variable composition; components keep their properties.
  11. Which method separates sand from salt?
    Dissolve–filter–evaporate.
  12. Which method separates kerosene from water?
    Separating funnel.
  13. Which method purifies drinking water in labs?
    Distillation (to get distilled water).
  14. Why does cream collect in centrifugation?
    Heavier/lighter parts separate under high rotational force.
  15. What moves up in paper chromatography?
    Solvent (by capillary action) carrying soluble components.
  16. Is brass an element?
    No, it’s an alloy (Cu + Zn).
  17. Name one non-metal that is liquid at room temperature.
    Bromine (Br$_2$).
  18. Write formula of glucose.
    $\mathrm{C_6H_{12}O_6}$.
  19. Name the element with symbol W.
    Tungsten (Wolfram).
  20. Why are alloys made?
    To improve hardness, strength, corrosion resistance, etc.

5) 20 Short Answer Questions (about 2–3 lines)

  1. Differentiate briefly: element vs compound.
    Element has one type of atom; compound has atoms of different elements chemically combined in fixed ratio.
  2. State two features of mixtures.
    Variable composition and components retain their properties; can be separated by physical methods.
  3. Why are properties of water different from H and O?
    Chemical combination forms new molecules $\mathrm{H_2O}$ with new properties.
  4. Classify: air, brass, sodium chloride.
    Air—mixture; brass—alloy (mixture); NaCl—compound.
  5. Explain principle of separating funnel.
    Immiscible liquids form layers by density; the denser liquid drains first via stopcock.
  6. State the steps to separate sand + salt.
    Add water → filter (sand remains) → evaporate filtrate to get salt.
  7. How does distillation purify water?
    Boils impure water → vapour → condensation gives pure distilled water; solutes remain behind.
  8. What does chromatography depend on?
    Different solubilities in the moving solvent and different attraction to stationary paper.
  9. Give two uses of centrifugation.
    Cream separation; separating blood components; lab precipitate collection.
  10. List three properties of metals.
    Lustre, malleability/ductility, good thermal/electrical conductivity.
  11. What is an alloy? Give two examples.
    Mixture of metals; examples: steel (Fe+C), brass (Cu+Zn).
  12. Why pure gold is not used for all jewellery?
    Very soft; alloying (22-carat) gives strength and durability.
  13. Write symbols: sodium, potassium, iron, copper.
    Na, K, Fe, Cu.
  14. Write formulae: water, methane, sodium chloride.
    $\mathrm{H_2O}$, $\mathrm{CH_4}$, NaCl.
  15. How to separate ink colours?
    Paper chromatography; solvent lifts components to different heights.
  16. Why is air called a homogeneous mixture?
    Gases are uniformly mixed; composition fairly uniform in small regions.
  17. Name three laboratory separation methods.
    Filtration, distillation, chromatography (also centrifugation, sublimation).
  18. Which gas in air is most abundant?
    Nitrogen ($\mathrm{N_2}$).
  19. Why doesn’t salt settle in salt solution?
    It dissolves to ions; forms a true solution—particles too small to settle.
  20. Is coal a pure substance?
    No, it’s mainly carbon with other substances—a complex mixture.

6) Textbook Exercise – Perfect Answers (Chapter 14)

Q1) Who are my companions? (Match the pairs)
  • 1. Stainless steel → Alloy (e)
  • 2. Silver → Metal (f)
  • 3. Bhajani mixture for milling → Mixture (c)
  • 4. Salt → Compound (b)
  • 5. Coal → Non-metal (a) (coal is largely carbon, a non-metal; practically a complex mixture)
  • 6. Hydrogen → Element (d)
Q2) Write the names of elements for: Zn, Cd, Xe, Br, Ti, Cu, Fe, Si, Ir, Pt.
Zinc, Cadmium, Xenon, Bromine, Titanium, Copper, Iron, Silicon, Iridium, Platinum.
Q3) Molecular formulae: Hydrochloric acid, Sulphuric acid, Sodium chloride, Glucose, Methane.
Hydrochloric acid: $\mathrm{HCl}$ • Sulphuric acid: $\mathrm{H_2SO_4}$ • Sodium chloride: NaCl • Glucose: $\mathrm{C_6H_{12}O_6}$ • Methane: $\mathrm{CH_4}$.
Q4) Give scientific reasons.
  1. Buttermilk is churned to get butter: Centrifugation effect—agitation causes fat globules (less dense) to separate from the liquid (whey).
  2. In chromatography, ingredients rise to limited heights: Each component has its own solubility in the mobile solvent and attraction to paper; balance of these keeps them at characteristic heights.
  3. Wet cloth wrapped around water container in summer: Evaporation of water from the cloth absorbs heat (latent heat), cooling the container and water.
Q5) Explain the difference.
(a) Metals(a) Non-metals
Lustrous, malleable/ductile, conduct heat/electricity.Generally dull, brittle (if solid), poor conductors.
Examples: Cu, Fe, Al.Examples: S, P, O.

(b) Mixtures(b) Compounds
Variable composition; components keep properties; separated physically.Fixed ratio; new properties; separated chemically.
Example: air, brass.Example: $\mathrm{H_2O}$, NaCl.

(c) Atoms(c) Molecules
Smallest unit of an element.Two or more atoms bonded; can be element ($\mathrm{O_2}$) or compound ($\mathrm{H_2O}$).

(d) Distillation(d) Separating Funnel
Boil–condense; separates solvent/volatile components; miscible liquids by b.p.Separates immiscible liquids by density (layering) using a stopcock.
Example: obtain distilled water from salt solution.Example: separate kerosene from water.
Q6) Answer in your own words.

(a) Simple separation of mixtures: Handpicking (stones from pulses), sieving (flour), winnowing (husks), magnetic separation (iron filings), filtration (sand–water), evaporation (salt from brine), crystallization, sublimation (camphor), centrifugation (cream), chromatography (ink).

(b) Daily-use examples: Elements/Metals—Fe pans, Cu wires, Al foils; Non-metals—O$_2$ breathing, C (pencil); Compounds—NaCl, sugar $\mathrm{C_{12}H_{22}O_{11}}$, baking soda $\mathrm{NaHCO_3}$; Mixtures—air, milk, soil, tea.

(c) Uses of centrifugation: Cream separation; lab separation of precipitates; blood component separation; spin-drying clothes.

(d) Where/why: distillation vs separating funnel: Distillation—purify/potable water, separate alcohol–water (different b.p.). Separating funnel—separate immiscible liquids (oil–water) in labs/industry due to density differences.

(e) Precautions: Distillation—use boiling chips, secure joints, do not distil to dryness, cool condenser properly. Separating funnel—allow layers to settle, remove stopper before opening stopcock, collect lower layer slowly, wear eye protection.

✅ Quick check: Compound ≠ Mixture — compounds have fixed ratios (e.g., water $\mathrm{H_2O}$), mixtures don’t (e.g., air).

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