Short Answer Questions: Nature of Matter: Elements, Compounds, and Mixtures | Science Curiosity Class 8 - New NCERT PDF Download

Ques 1. Suggest separation technique(s) one would need to employ to separate the mixture: Common salt, water and sand
Ans: Sedimentation, decantation, filtration and evaporation
Sedimentation is the process where solid particles settle at the bottom of a liquid. This is followed by decantation, which involves carefully pouring off the liquid, leaving the solid behind. Next, filtration is used to separate solids from liquids using a filter paper. Finally, evaporation removes the liquid, leaving behind any dissolved solids.

• Sedimentation: Particles settle at the bottom.
• Decantation: Pouring off the liquid.
• Filtration: Using filter paper to separate solids.
• Evaporation: Removing liquid to leave solids.

Ques  2. The 'sea-water' can be classified as a homogeneous as well as a heterogeneous mixture. Comment.
Ans: Sea-water can be classified as both a homogeneous and a heterogeneous mixture due to the following reasons:

• It is considered homogeneous because it contains dissolved salts, creating a uniform solution.
• It is also seen as heterogeneous because it includes various insoluble components, such as sand, microbes, and shells.

Ques  3. What would you observe when

(a) an aqueous sugar solution is heated to dryness.
Ans: When an aqueous solution of sugar is heated to dryness:

• The water evaporates, leaving sugar behind in the container.
• If heated further, the sugar may become charred.

(b) a mixture of iron filings and sulphur powder is heated strongly.
Ans: When a mixture of iron filings and sulphur powder is heated strongly, a chemical reaction occurs, resulting in the formation of ferrous sulphide.

Ques  4. Classify the following as physical or chemical properties

(c) Metallic sodium is soft enough to be cut with a knife.
Ans: Metallic sodium is soft enough to be cut with a knife. This characteristic demonstrates the softness of sodium, which is a physical property.

Ques  5. Name the process associated with the following

(e) Settling of sand when a mixture of sand and water is left undisturbed for some time.
Ans: When mixture of sand and water is left undisturbed, the sand settle at the bottom of water, thus this is the process of sedimentation.

Ques  6. An element is sonorous and highly ductile. Under which category would you classify this element? What other characteristics do you expect the element to possess?
Ans: Since the element is sonorous and ductile, it can be classified as a metal. Other expected characteristics of metals include:

• Good conductivity of heat and electricity
• Lustrous appearance
• Malleability (can be shaped into thin sheets)