   Chapter 21, Problem 119IL

Chapter
Section
Textbook Problem

In 1937, R. Schwartz and M. Schmiesser prepared a yellow-orange bromine oxide (BrO2) by treating Br2 with ozone in a fluorocarbon solvent. Many years later, J. Pascal found that, on heating, this oxide decomposed to two other oxides, a less volatile golden yellow oxide (A) and a more volatile deep brown oxide (B). Oxide B was later identified as Br2O. To determine the formula for oxide A, a sample was treated with sodium iodide. The reaction liberated iodine, which was titrated to an equivalence point with 17.7 mL of 0.065 M sodium thiosulfate. I 2 (aq) + 2 S 2 O 3 2 − (aq)  →  2 I − (aq) + S 4 O 6 2 − (aq) Compound A was also treated with AgNO3, and 14.4 mL of 0.020 M AgNO3 was required to completely precipitate the bromine from the sample.(a) What is the formula of the unknown bromine oxide A?(b) Draw Lewis structures for A and Br2O. Speculate on their molecular geometry.

(a)

Interpretation Introduction

Interpretation: To predict the formula for unknown bromine oxide A in the given reaction.

Concept introduction: An oxide of bromine BrO2 is prepared by treating bromine with ozone. However, it was later observed that the heating of this oxide results in formation of two more oxides which can be identifed using reagents like sodium iodide and silver nitrate. The structure of these oxides can be either linear or bent.

Explanation

The oxide BrO2 is prepared by the reaction of bromine and oxygen. The reaction is,

3Br+2O33BrO2

Now, on heating BrO2, two more oxides A and B are formed. It is given that the oxide B has the formula Br2O.

The compound A on reaction with sodium iodide liberates iodine. Thus, bromine oxide is getting reduced in this reaction

(b)

Interpretation Introduction

Interpretation: To draw the Lewis structure for A  and Br2O. Molecular geometry of these compounds has to be speculated.

Concept introduction:

An oxide of bromine BrO2 is prepared by treating bromine with ozone. However, it was later observed that the heating of this oxide results in formation of two more oxides which can be identifed using reagents like sodium iodide and silver nitrate. The structure of these oxides can be either linear or bent.

Lewis structures are diagrams that represent the chemical bonding of covalently bonded molecules and coordination compounds.

It is also known as Lewis dot structures which represent the bonding between atoms of a molecule and the lone pairs of electrons that may exist in the molecule.

Molecular geometry is the shape of a molecule predicted by considering only bond pair of electrons

According to VSEPR theory, the geometry is predicted by the minimizing the repulsions between electron-pairs in the bonds and lone-pairs of electrons. The VSEPR theory is summarized in the given table as,

Electron-pairlone-pairElectron-pairgeometryMolecularshape20LinearLinear30TrigonalplanarTrigonalplanar21TrigonalplanarBent40TetrahedralTetrahedral31TetrahedralPyramidal22TetrahedralVshape50TrigonalbipyramidalTrigonalbipyramidal41TrigonalbipyramidalSeesaw32TrigonalbipyramidalTshape23TrigonalbipyramidalLinear60OctahedralOctahedral51OctahedralSquarepyramidal42OctahedralSquareplanar

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