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CAIE A-Level Chemistry 3.5.2 Predicting Shapes and Bond Angles

Practise transferring VSEPR reasoning from known examples to analogous molecules and ions.

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

Exam points

  • draw the central atom’s valence-shell electron arrangement before assigning a molecular shape
  • use electron-domain geometry and remove lone-pair positions when naming the shape
  • adjust ideal bond angles for lone-pair or multiple-bond repulsion and give a justified range when appropriate

3.5.2—The shapes of, and bond angles in, molecules question 1

[Maximum number: 1]

Nitrogen and phosphorus are elements in Group 15 of the Periodic Table.

A common test for nitrates is the reaction with NaOH and Al . Equation 1 shows the reaction.

 equation 13NO3−+8Al+5OH−+18H2O→3NH3+8[Al(OH)4]−\text { equation } 1 \quad 3 \mathrm{NO}_{3}^{-}+8 \mathrm{Al}+5 \mathrm{OH}^{-}+18 \mathrm{H}_{2} \mathrm{O} \rightarrow 3 \mathrm{NH}_{3}+8\left[\mathrm{Al}(\mathrm{OH})_{4}\right]^{-}

Suggest the shape of the [Al(OH)4]−\left[\mathrm{Al}(\mathrm{OH})_{4}\right]^{-}ion.

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