(a) List two gases which are monatomic (b) Mention one gas which forms: (i) dense white fumes with ammonia vapour (ii) yellow precipitate with ammoniacal si...

Assessment: WAEC SSCE - Chemistry - 1996 (Essay) Subject: Chemistry

Question 1 Report

(a) List two gases which are monatomic

(b) Mention one gas which forms:

(i) dense white fumes with ammonia vapour

(ii) yellow precipitate with ammoniacal silver trioxonitrate (V) solution.

Answer Details

(a) Two monatomic gases

Helium and neon (argon is also acceptable). The noble gases exist as single atoms, so they are monatomic.

(b) Gases

  • (i) Dense white fumes with ammonia vapour: hydrogen chloride (HCl). It combines with ammonia to form white fumes of ammonium chloride: NH3 + HCl → NH4Cl.
  • (ii) Yellow precipitate with ammoniacal silver trioxonitrate (V) solution: ethyne (C2H2). It reacts to form a precipitate of silver ethynide (silver acetylide).

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