Question Answers For All Chapters – General Science Class 7
Elements, Compounds and Mixtures
1. Who are my companions?
| Group A | Group B | Answer |
|---|---|---|
| 1. Stainless steel | (a) Non-metal | (e) Alloy |
| 2. Silver | (b) Compound | (f) Metal |
| 3. Bhajani mixture for milling | (c) Mixture | (c) Mixture |
| 4. Salt | (d) Element | (b) Compound |
| 5. Coal | (e) Alloy | (a) Non-metal |
| 6. Hydrogen | (f) Metal | (d) Element |
2. Write the names of elements from the following symbols:
✔ Zn – Zinc
✔ Cd – Cadmium
✔ Xe – Xenon
✔ Br – Bromine
✔ Ti – Titanium
✔ Cu – Copper
✔ Fe – Iron
✔ Si – Silicon
✔ Ir – Iridium
✔ Pt – Platinum
3. What are the molecular formulae of the following compounds?
✔ Hydrochloric Acid → HCl
✔ Sulphuric Acid → H₂SO₄
✔ Sodium Chloride (Salt) → NaCl
✔ Glucose → C₆H₁₂O₆
✔ Methane → CH₄
4. Give Scientific Reasons
(a) Buttermilk is churned to get butter.
→ Churning separates the lighter butter fat from buttermilk using the process of centrifugation.
(b) In chromatography, the ingredients of a mixture rise up to a limited height when water rises up to the upper end of the paper.
→ Different substances in a mixture move at different speeds, so they separate at different heights on the chromatography paper.
(c) A wet cloth is wrapped around a water storage container in summer.
→ When water evaporates from the wet cloth, it absorbs heat from the container, cooling the water inside.
5. Explain the Differences
(a) Metals and Non-Metals
| Metals | Non-Metals |
|---|---|
| Good conductors of heat and electricity. | Poor conductors of heat and electricity. |
| Shiny and malleable (can be shaped). | Dull and brittle (breaks easily). |
| Example: Iron, Copper, Gold. | Example: Oxygen, Sulfur, Carbon. |
(b) Mixtures and Compounds
| Mixtures | Compounds |
|---|---|
| Substances are physically combined. | Elements are chemically combined. |
| Can be easily separated. | Cannot be separated by physical means. |
| Example: Air, Sand + Water. | Example: Water (H₂O), Salt (NaCl). |
(c) Atoms and Molecules
| Atoms | Molecules |
|---|---|
| Smallest unit of an element. | Formed when two or more atoms combine. |
| Example: Hydrogen (H), Oxygen (O). | Example: Oxygen molecule (O₂), Water (H₂O). |
(d) Separation by Distillation and by Separating Funnel
| Distillation | Separating Funnel |
|---|---|
| Used to separate liquids with different boiling points. | Used to separate two liquids that do not mix (immiscible liquids). |
| Example: Purification of water. | Example: Separating oil and water. |
6. Write answers to the following questions in your own words.
(a) How are the components of mixtures separated by simple methods?
→ Mixtures can be separated by filtration (removing solids from liquids), evaporation (removing water from salt), distillation (separating liquids), and chromatography (separating colors in ink).
(b) Which elements (metals and non-metals), compounds, and mixtures do we use in our day-to-day life?
→ Metals: Iron (Fe) in utensils, Copper (Cu) in wires.
→ Non-Metals: Oxygen (O) for breathing, Carbon (C) in coal.
→ Compounds: Water (H₂O), Table salt (NaCl).
→ Mixtures: Air, Milk, Sugar solution.
(c) In everyday life, where and for what purpose do we use centrifugation?
→ Centrifugation is used to separate heavier and lighter components in a mixture.
Examples:
✔ Separating cream from milk in dairy.
✔ Separating blood components in laboratories.
(d) Where are the methods of separation by distillation and by separating funnel used? Why?
→ Distillation is used to purify water or separate alcohol from water because it works by boiling and condensing.
→ Separating Funnel is used to separate oil and water because oil floats on water and does not mix with it.
(e) Which precaution will you take while using the methods of distillation and separation by separating funnel?
✔ Distillation: Ensure proper heating and cooling systems are in place to prevent accidents.
✔ Separating Funnel: Allow the liquids to settle properly before separating to get a clear division between layers.
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