Q. A student added a few pieces of zinc into dil.H₂SO₄ taken in a test tube. Suddenly, evolution of gas occurs. What gas is evolved?
Answer: Hydrogen gas
Q. Why do copper sulphate crystals change colour from blue to white on heating?
Answer: Due to lose of water of crystallization which can also be called as dehydration
Q. What happens when a small piece of iron is kept in copper sulphate solution?
Answer: Simple displacement reaction results in the Formation of a brown coating of copper on the surface of iron nail. The green colour of the solution is due to the displaced Fe²⁺ ions from the Iron nail
Q. While performing an experiment, a student adds sodium sulphate solution to a colourless solution. A white precipitate is immediately formed and is insoluble in dil. HCl. The colourless solution is …………………………… and the precipitate formed is……………………
Answer: Barium chloride reacts with sodium sulphate to form a white precipitate of barium sulphate[BaCl₂ and BaSO₄]
Q. When NaOH is added to zinc sulphate solution, a precipitate is formed which is soluble in excess of NaOH. The precipitate obtained is……………………. & the colour of the precipitate is……………….
Answer: A white gelatinous precipitate of zinc hydroxide is formed Zn(OH)₂ & white gelatinous
Q. On heating Pb(NO₃)₂, what is observed during the reaction?
Answer: Lead nitrate decomposes on strong heating with a crackling sound. It produces NO₂ (g), O₂ (g) and PbO (s)
Q. Take dilute sulphuric acid in a test tube and put a few zinc granules into the test tube. What will you observe?
Answer: Since Zn and dil H₂SO₄ react with each other liberating H₂ gas, the size of zinc granules keep on decreasing
Q. When magnesium combines with oxygen, it produces magnesium oxide that appears to be like:
Answer:int: Mg combines with O₂ to form a white ash of MgO
Q. 100 ml of a saturated copper sulphate solution was taken in a beaker. A small amount of iron filings was added to the beaker and left undisturbed overnight. The mixture was then filtered to obtain the residue. The residue was found to be what colour?
Answer: In this reaction copper particles are obtained which appears as reddish brown residue.
Q. When you place an iron nail in copper sulphate solution, the reddish brown coating formed on the nail is _______.
Answer: The reddish brown coating is a soft and dull coating of copper
Q. What is observed when dilute sulphuric acid is added to zinc granules?
Answer: Zn reacts with dil. H₂SO₄ to liberate H₂ gas and bubbles start coming from the surface of the Zinc granules.
Q. Why is magnesium ribbon held with a pair of tongs and not with bare hands, when it is burnt in air?
Answer: Magnesium metal is a good conductor of heat, so it gets very hot when it is held in the flame.