PrayogX › Chemistry › The p-Block Elements (Group 17)

Identify X, Y and Z - chlorine, nitrogen trichloride and chlorine trifluoride: structure and uses

Three unknowns hidden in a chain of reactions. Press start and the lab does the rest: MnO2 and concentrated HCl give a greenish-yellow gas that a colour chart and an atom balance identify as Cl2; Cl2 in excess turns NH3 into NCl3 one H at a time; Cl2 and excess F2 at 573 K give ClF3. Each product is built in 3D, its shape worked out by VSEPR, and every option is tested claim - evidence - verdict before the answer is revealed. No prediction stage - input, run, watch, result.

Sub-topics covered

• Preparation of chlorine: MnO2 + conc. HCl
• Reaction of chlorine with ammonia - excess Cl2 gives NCl3, excess NH3 gives N2 and NH4Cl
• Interhalogen compounds: Cl2 + 3F2 -> 2ClF3 at 573 K
• VSEPR shapes: trigonal pyramidal NCl3, T-shaped ClF3
• Lewis basicity and the -I effect of substituents
• Uses of chlorine and of ClF3

What it teaches

• X is the greenish-yellow gas from MnO2 + 4HCl -> MnCl2 + Cl2 + 2H2O; atom balance leaves exactly two Cl atoms for X, so X = Cl2
• Chlorine is used for sterilising drinking water - (A) true
• With Cl2 in excess every N-H of NH3 is replaced: NH3 + 3Cl2 -> NCl3 + 3HCl, so Y = NCl3
• NCl3 has 3 bond pairs and 1 lone pair on N: tetrahedral electron geometry, trigonal pyramidal molecule - not planar, (B) false
• Cl (3.16) is more electronegative than N (3.04) and H (2.20) is less; the chlorines withdraw density from N, so NCl3 is a weaker Lewis base than NH3 - (D) false
• Cl2 + 3F2 -> 2ClF3 at 573 K with F2 in excess, so Z = ClF3: 3 bond pairs + 2 lone pairs, T-shaped
• ClF3 fluorinates uranium to UF6 (U + 3ClF3 -> UF6 + 3ClF), the volatile compound used in the enrichment of 235U - (C) true

Simulation ID

• ADV-2026-P1-CHE-Q06 · revision 1

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