Matter in Our Surroundings — Science STD 9 — Question

What is the valency of these elements and why?

Differentiate between physical and chemical change. Give one example of each. Give one example where both physical and chemical change is taking place.

Why are gases so easily compressible whereas it is almost impossible to compress a solid or a liquid?

On heating calcium carbonate gets converted into calcium oxide and carbon dioxide:
Is this a physical or a chemical change?

Calculate the mass of potassium sulphate required to prepare its 10% solution in 100g of water.

The teacher instructed three students ‘A’, ‘B’ and ‘C’ respectively to prepare a 50% (mass by volume) solution of sodium hydroxide (NaOH). ‘A’ dissolved 50g of NaOH in 100mL of water, ‘B’ dissolved 50g of NaOH in 100g of water while ‘C’ dissolved 50g of NaOH in water to make 100mL of solution. Which one of them has made the desired solution and why?

Why does a gas fill a vessel completely?

Which postulate of Dalton’s atomic theory can explain the law of conservation of mass?

You are given two liquids, one a solution and the other a compound. How will you distinguish the solution from the compound?

Is it possible to see atoms these days? Explain your answer.