Deck 20: The Main Group Elements

Question 1

In the reaction of trimethyl amine with trimethyl boron,

A) the product is [N(CH₃)₄⁺][B(CH₃)₂^-].
B) trimethyl boron is the Lewis base.
C) the product is (CH₃)₃N-B(CH₃)₃.
D) trimethyl amine is the Lewis acid.
E) no reaction occurs.

Answer 1

the product is (CH₃)₃N-B(CH₃)₃.

Question 2

Which of the following are Lewis acids?

A) I, II, and III
B) II, III, and IV
C) II, IV, and V
D) II and III
E) IV and V

Answer 2

II, IV, and V

Question 3

Which of the following are Lewis bases?

A) I, II, and III
B) I, III, and V
C) II, IV, and V
D) I and III
E) II and IV

Answer 3

I, III, and V

Question 4

What reactants likely lead to formation of the Lewis acid-base adduct shown below?

A) Pd²⁺ and Cl₂
B) Pd and Cl^-
C) Pd and SnCl₄
D) Pd²⁺ and Cl^-
E) PdCl₂ and Sn

Question 5

Which statements are true about the following reaction?
PF₅ + HF $\rarr$ H⁺ + PF₆^-
I. HF is a Brønsted acid and a Lewis acid.
II. PF₅ is the Lewis acid.
III. The F^- ion is the Lewis base.
IV. The orbital used in bonding is a dsp³ hybrid orbital.
V. PF₆^-is a Lewis acid.

A) I and V
B) II and III
C) I, III and IV
D) III and V
E) I and III

Question 6

Identify the Lewis acid and base in the reaction of trimethyl amine with trimethyl boron.

A) Base: trimethyl amine; acid trimethyl boron
B) Base: trimethyl boron; acid trimethyl amine
C) Neither acts as an acid nor a base.

Question 7

Which of the following groups of Lewis acids is in order of increasing hardness?

A) Cd²⁺, Zn²⁺, Ag⁺
B) Ag^+, Zn²⁺ Cd²⁺
C) Ag⁺, Cd²⁺, Zn²⁺
D) Cd²⁺, Ag⁺, Zn²⁺
E) Zn²⁺, Ag⁺, Cd²⁺

Question 8

Which of the following groups of Lewis bases is in order of decreasing hardness?

A) N(CH₃)₃, NH₃, P(CH₃)₃
B) NH₃, P(CH₃)₃, N(CH₃)₃
C) P(CH₃)₃, N(CH₃)₃, NH₃
D) NH₃, N(CH₃)₃, P(CH₃)₃
E) N(CH₃)₃, P(CH₃)₃, NH₃

Question 9

The reactions of Group 13 chlorides (BCl₃, AlCl₃, GaCl₃, InCl₃) with bases are predicted well by the HSAB principle. Which of the following is the predicted order of reactivity (completeness of adduct formation) of these compounds toward P(CH₂CH₃)₃?

A) AlCl₃ < InCl₃ < BCl₃ < GaCl₃
B) BCl₃< GaCl₃ < AlCl₃ < InCl₃
C) BCl₃ < AlCl₃ < GaCl₃ < InCl₃
D) AlCl₃ < BCl₃ < GaCl₃ < InCl₃
E) InCl₃ < GaCl₃ < AlCl₃ < BCl₃

Question 10

Identify the following as Lewis acids or bases and rank from hardest to softest: Al³⁺, Tl³⁺, Tl⁺.

A) bases Al³⁺, Tl³⁺, Tl⁺
B) acids Al³⁺, Tl³⁺, Tl⁺
C) acids Tl⁺, Tl³⁺, Al³⁺
D) bases Tl⁺, Tl³⁺, Al³⁺
E) acids Al³⁺, Tl⁺, Tl³⁺

Question 11

Identify the following as Lewis acids or bases and rank from hardest to softest: SbH₃, PH₃, PF₃.

A) bases SbH₃, PH₃, PF₃
B) acids PF₃, PH₃, SbH₃
C) acids SbH₃, PH₃, PF₃
D) bases PF₃, PH₃, SbH₃
E) acids PH₃, PF₃, SbH₃

Question 12

The substances below are main group compounds that follow the hard-soft acid-base principles quite reliably:
I. Al(CH₃)₃
II. MgCl₂
III. AlCl₃
IV. LiCl
V. LiCH₃
VI. Mg(CH₃)₂
Referring to these compounds, which of the (unbalanced) equations below is expected to proceed?

A) Al(CH₃)₃ + MgCl₂ $\rarr$ AlCl₃ + Mg(CH₃)₂
B) LiCl + Al(CH₃)₃ $\rarr$ LiCH₃ + AlCl₃
C) LiCH₃ + MgCl₂ $\rarr$ LiCl + Mg(CH₃)₂
D) Mg(CH₃)₂ + LiCl $\rarr$ LiCH₃ + MgCl₂

Question 13

Potassium is found in nature most often as a chloride salt, whereas copper and mercury more often occur as the sulphides. The best explanation for this observation is

A) potassium is softer than copper or mercury.
B) the coinage metals are smaller than potassium.
C) the coinage metals prefer the +2 oxidation state.
D) potassium is less electronegative than copper.
E) the coinage metal ions are softer than potassium.

Question 14

Are the chlorides of Pb, Pb(II) chloride and Pb(IV) chloride solids, liquids, or gases at room temperature?

A) PbCl₂: solid; PbCl₄: solid
B) PbCl₂: liquid; PbCl₄: liquid
C) PbCl₂: solid; PbCl₄: liquid
D) PbCl₂: liquid; PbCl₄: solid
E) PbCl₂: gas; PbCl₄: liquid

Question 15

What reasons are important for the use of Na₃AlF₆ in the production of aluminum?
I. The use of Na₃AlF₆ allows for electrolysis at lower temperature.
II. The fluoride will react with the electrodes.
III. The oxide ions combine with the fluoride ions.
IV. The fluoride is not readily oxidized.
V. The aluminum is more easily oxidized when bound to fluoride.

A) II and III
B) IV and V
C) I and V
D) I and IV
E) I, III, and V

Question 16

Why are heavy metals such as lead(II) and cadmium(II) toxic?

A) They can replace oxygen atoms in proteins.
B) They can bind to sulphur atoms on proteins.
C) They are hard Lewis acids.
D) They are insoluble in aqueous solution and will precipitate.
E) They form ionic compounds.

Question 17

Which of the following ionic species result when boric acid, H₃BO₃, is added to water:H₃O⁺, H₂BO₃^-, HBO₃^2-, BO₃^3-, B(OH)₄^-, OH^-?

A) H₃O⁺, H₂BO₃^-,
B) H₃O⁺, H₂BO₃^-, HBO₃^2-
C) H₃O⁺, H₂BO₃^-, HBO₃^2-, BO₃³
D) H₃O⁺, B(OH)₄^-
E) H₃O⁺, OH^-

Question 18

Which of the following boron halides has the most $\pi$ -bonding?

A) BI₃
B) BBr₃
C) BCl₃
D) BF₃
E) BF₄^-

Question 19

What is the product of the reaction of silicon-copper alloy with chlorobutane?

A)

B)

C)

D)

E) Cu metal

Question 20

Why is SiO₂ a solid and CO₂ a gas?

A) A Si atom is heavier than a C carbon.
B) Si has more electrons than C.
C) Intermolecular forces between SiO₂ molecules are stronger than those between CO₂ molecules.
D) It is preferable to form 4 Si - O single bonds rather than 2 Si - O double bonds.
E) SiO₂ forms ionic bonds.

Question 21

Silicon tetrachloride has Lewis acidic characteristics, whereas carbon tetrachloride does not. What orbital is used by SiCl₄ in forming adducts that gives SiCl₄ this property?

A) sp²
B) sp³
C) sp²d
D) sp³d
E) sp³d²

Question 22

Arsenic oxide (As₂O₃) is used as a standard in oxidation-reduction titrations because it is stable and reacts very predictably. Reaction with MnO₄^- in acidic solution gives aqueous arsenic (H₃AsO₄) and Mn²⁺. If the coefficient of MnO₄^-is 4 in the balanced chemical equation of reaction, the coefficient of H₃AsO₄ is

A) 2.
B) 4.
C) 5.
D) 8.
E) 10.

Question 23

Neutralization of 25 ml of 0.05 M H₃PO₄ requires what mass of solid sodium hydroxide, NaOH?

A) 0.05 g
B) 0.15 g
C) 0.02 g
D) 0.06 g
E) 2 g

Question 24

Which allotrope of carbon is the most thermodynamically stable?

A) diamond
B) fullerene
C) graphite
D) coke
E) carbon nanotube

Question 25

CFCs, chlorofluorocarbons, are being phased out of use as refrigerants because

A) they highly reactive producing numerous pollutants in our atmosphere.
B) they are toxic.
C) they may remain in the atmosphere for hundreds of years, but react in the upper atmosphere.
D) they are gases and hard to contain.
E) hydrochlorfluorocarbons are cheaper and more effective refrigerants.

Question 26

When SF₄ acts as a Lewis base, it donates an F^- ion and generates the SF₃⁺ ion. The structure of SF₃⁺ is

A) T-shaped.
B) trigonal planar.
C) trigonal pyramidal.
D) tetrahedral.
E) distorted trigonal bipyramidal.

Question 27

When SF4 acts as a Lewis acid, with trimethyl amine, it forms the adduct (CH₃)₃N-SF₄. The structure of sulphur in (CH₃)₃N-SF₄ is a(n)

A) distorted square planar.
B) tetrahedral.
C) octahedral.
D) square pyramidal.
E) trigonal bipyramidal.

Question 28

In the text, it is mentioned that sulphur compounds are poison for many catalysts. How, generally, would you expect that this is possible?

A) The sulphur coats the catalyst.
B) The sulphur reacts with the metal ions of the catalyst as a hard Lewis base.
C) The sulphur reacts with the other reactants.
D) The sulphur reacts with the metal ions of the catalyst as a soft Lewis base.
E) The sulphur changes the reaction products.

Question 29

Which polymer is fluoride found in?

A) CFC
B) Teflon
C) PVC
D) DDT
E) chlorofluorocarbons