3(iv)
Give one significant observation when:
(a) a solution of barium chloride is added to zinc sulphate solution.
(b) lead nitrate is heated in a test tube.
(c) chlorine gas is passed over moist starch iodide paper.
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(a) When barium chloride solution is added to a solution of Zinc sulphate, white ppt. of barium sulphate is obtained which is insoluble in dil. HCl or nitric acid.
ZnSO4 + BaCl2 ⟶ BaSO4 ↓ [white ppt.] + ZnCl2
(b) When lead nitrate is heated in a test tube, brown fumes of nitrogen dioxide (NO2) are evolved and a yellow residue of lead(II) oxide remains.
2Pb(NO3)2 $\xrightarrow{\Delta}$ 2PbO + 4NO2 + O2
(c) The moist starch-iodide paper turns blue-black because chlorine liberates iodine from iodide.
Cl2 + 2KI ⟶ 2KCl + I2