Chemistry
Distinguish between the following as directed:
(a) Sodium sulphite solution and sodium sulphate solution. [using dilute H2SO4]
(b) Lead salt solution and zinc salt solution. [using NH4OH solution in excess]
Practical Chemistry
ICSE 2022
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Answer
(a) On adding dilute sulphuric acid to sodium sulphite solution and warming, a colourless gas with suffocating smell of burning sulphur is evolved. The evolved gas turns lime water milky and changes the colour of acidified K2Cr2O7 solution from orange to green suggesting that it is SO2.
Na2SO3 + H2SO4 (dil.) ⟶ Na2SO4 + H2O + SO2↑
Sodium sulphate does not react with dilute sulphuric acid as an acid does not react with its own salt due to the presence of same anion.
(b) A lead salt gives a chalky white ppt. on reaction with ammonium hydroxide that is insoluble in excess of ammonium hydroxide. For example:
Pb(NO3)2 + 2NH4OH ⟶ 2NH4NO3 + Pb(OH)2 ↓
On the other hand, zinc salt forms a white gelatinous ppt. which dissolves when excess of ammonium hydroxide is added. Hence, the two can be distinguished.
ZnSO4 + 2NH4OH ⟶ (NH4)2SO4 + Zn(OH)2 ↓
Zn(OH)2 + (NH4)2SO4 + 2NH4OH ⟶ [Zn(NH3)4]SO4 + 4H2O
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Study the diagram, which shows the Brown Ring Test and answer the questions given below:
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(a) Which ion is determined by Brown Ring Test?
(b) Why is freshly prepared iron[II] sulphate used in the test?
(c) Name the substance Z.
Identify the acid in each case:
(a) The acid formed when sulphur reacts with concentrated nitric acid.
(b) An acid, which on adding to lead nitrate solution produces a white precipitate which is soluble on heating.
(c) The acid formed when potassium nitrate reacts with a least volatile acid.
Give one word for the following statements:
(a) The compounds of various metals found in nature with earthly impurities.
(b) A homogeneous mixture of two or more metals or a metal and a non-metal in specific ratios.
Give the IUPAC name for the following:
