By definition, transition metals are elements that have, or readily form ions with, which feature?
Partially filled d orbitals
✓
Completely filled p orbitals
A single s valence electron
Partially filled p orbitals
Correct Answer
Partially filled d orbitals
Transition metals are defined by having, or easily forming, partially filled d orbitals, which explains their variable oxidation states, color and magnetism. Completely filled p orbitals describe noble gases, not transition metals. A single s valence electron describes the alkali metals. Partially filled p orbitals belong to main group elements in the p block.
Category: Transition Metal Properties
Question 2
A transition metal oxide in which the metal has a very high oxidation state, such as Mn2O7, is best described as which?
Ionic and basic
Covalent and acidic
✓
Ionic and amphoteric
Metallic and neutral
Correct Answer
Covalent and acidic
As the oxidation state of a transition metal rises, its oxides become more covalent and more acidic; Mn2O7, with manganese at +7, is an acidic oxide. Ionic and basic describes oxides with the metal in a low oxidation state. Ionic and amphoteric fits oxides with intermediate oxidation states. Metallic and neutral does not describe transition metal oxides.
Category: Transition Metal Properties
Question 3
In a blast furnace, which substance reduces iron oxides to molten iron?
Carbon dioxide
Calcium silicate
Carbon monoxide
✓
Sulfur dioxide
Correct Answer
Carbon monoxide
Coke reacts with oxygen and carbon dioxide in the furnace to form carbon monoxide, which removes oxygen from iron oxides and leaves iron metal. Carbon dioxide is a product of that reduction, not the reducing agent. Calcium silicate is the slag that carries away impurities. Sulfur dioxide is released when sulfide ores are roasted.
Category: Metal Production
Question 4
Blister copper from a smelter is cast into anodes. Which process then refines it into very pure copper?
Distillation
Liquation
Roasting
Electrolysis
✓
Correct Answer
Electrolysis
Impure copper anodes are oxidized in an electrolytic cell and pure copper is deposited at the cathode, a method called electrolytic refining. Distillation is used for metals with low boiling points such as zinc and mercury. Liquation separates a low-melting metal such as tin from its impurities. Roasting heats a sulfide ore in air before smelting and does not purify the finished metal.
Category: Metal Production
Question 5
Ethylenediamine (en) is a bidentate ligand. What is the coordination number of cobalt in [Co(en)3]3+?
6
✓
3
9
12
Correct Answer
6
Each ethylenediamine bonds through two nitrogen atoms, so three en ligands supply 3 x 2 = 6 donor atoms, giving a coordination number of 6. An answer of 3 counts ligands instead of donor atoms. An answer of 9 assumes three donor atoms per ligand. An answer of 12 assumes four donor atoms per ligand instead of the two nitrogens that en actually uses.
Category: Complex Structure
Question 6
What is the oxidation state of iron in the complex ion [Fe(CN)6]3-? Each cyanide ligand carries a 1- charge.
-3
+3
✓
+6
-6
Correct Answer
+3
The charges must add to the ion's charge: x + 6(-1) = -3, so x = +3. An answer of -3 simply copies the overall charge of the ion. An answer of +6 counts the six ligands but ignores the overall charge. An answer of -6 is the total charge of the ligands, not the metal.
Category: Naming Complexes
Question 7
Which geometry does a complex with coordination number 2, such as [Ag(NH3)2]+, have?
Bent
Trigonal planar
Linear
✓
Tetrahedral
Correct Answer
Linear
With two donor atoms on opposite sides of the metal, complexes such as [Ag(NH3)2]+ are linear, with a 180 degree bond angle. Bent geometry arises in molecules like water with lone pairs on the central atom, not in these complexes. Trigonal planar needs three groups around the center. Tetrahedral is one of the common geometries for coordination number 4.
Category: Complex Structure
Question 8
Ligands bond to a metal ion by donating a pair of electrons. In acid-base terms, a ligand acts as which?
Lewis acid
Proton donor
Free radical
Lewis base
✓
Correct Answer
Lewis base
A ligand donates an electron pair to the metal, which makes the ligand a Lewis base and the metal ion a Lewis acid. Lewis acid describes the metal, the electron-pair acceptor. Proton donor describes a Bronsted-Lowry acid, which is not how a ligand bonds. Free radical refers to a species with an unpaired electron, not an electron-pair donor.
Category: Complex Structure
Question 9
EDTA can wrap around a metal ion and bond to it through six donor atoms at once. How is EDTA classified?
Hexadentate
✓
Bidentate
Tetradentate
Monodentate
Correct Answer
Hexadentate
A ligand that binds through six donor atoms is hexadentate; EDTA forms very stable chelates and is used to remove metal ions such as lead from the body. Bidentate ligands, such as ethylenediamine, bind through two atoms. Tetradentate ligands, such as heme, bind through four. Monodentate ligands, such as ammonia, bind through only one atom.
Category: Complex Structure
Question 10
The complex anion [Fe(CN)6]4- is named hexacyano followed by which name for the metal?
Iron(II)
Ferrate(II)
✓
Ferrate(III)
Iron(III)
Correct Answer
Ferrate(II)
When a complex is an anion, the metal name takes the -ate ending, and iron uses its Latin root to become ferrate; the oxidation state is x + 6(-1) = -4, so x = +2. Iron(II) would be correct only if the complex were neutral or a cation. Ferrate(III) has the right ending but the wrong oxidation state. Iron(III) has both the wrong ending and the wrong oxidation state.
Category: Naming Complexes
Question 11
[Co(NH3)5Br]SO4 and [Co(NH3)5SO4]Br differ only in which anion is bonded to the metal and which is outside the coordination sphere. What kind of isomers are they?
Linkage isomers
Geometric isomers
Ionization isomers
✓
Optical isomers
Correct Answer
Ionization isomers
Ionization isomers exchange an anion inside the coordination sphere with the counterion outside it, so they release different ions in solution. Linkage isomers keep the same ligands but bond one of them through a different atom. Geometric isomers have the same ligands arranged differently in space, as in cis and trans forms. Optical isomers are nonsuperimposable mirror images.
Category: Isomerism
Question 12
A nitrite ligand can bond to cobalt through its nitrogen atom or through one of its oxygen atoms. Two complexes that differ only in this way are which kind of isomers?
Ionization isomers
Geometric isomers
Optical isomers
Linkage isomers
✓
Correct Answer
Linkage isomers
Linkage isomers contain the same ligands, but an ambidentate ligand such as NO2- or SCN- is attached through a different donor atom. Ionization isomers swap an inner-sphere anion with an outer counterion. Geometric isomers differ in the spatial arrangement of ligands, such as cis versus trans. Optical isomers are mirror images that cannot be superimposed.
Category: Isomerism
Question 13
Cisplatin, [Pt(NH3)2Cl2], is an anticancer drug. Which geometry does it have around platinum?
Square planar
✓
Tetrahedral
Octahedral
Trigonal bipyramidal
Correct Answer
Square planar
Cisplatin is a square planar platinum(II) complex with its two chloride ligands next to each other, which is why it has a cis isomer at all. Tetrahedral complexes cannot have cis and trans isomers because all four positions are adjacent. Octahedral geometry requires six donor atoms. Trigonal bipyramidal geometry requires five.
Category: Isomerism
Question 14
Two complexes are nonsuperimposable mirror images of each other, like a left and right hand. What are they called?
Linkage isomers
Enantiomers
✓
Ionization isomers
Cis-trans isomers
Correct Answer
Enantiomers
Enantiomers, or optical isomers, are mirror images that cannot be superimposed; examples include the two forms of [Co(en)3]3+. Linkage isomers differ in which atom of a ligand bonds to the metal. Ionization isomers differ in which anion is inside the coordination sphere. Cis-trans isomers are geometric isomers that are not mirror images of each other.
Category: Isomerism
Question 15
In an octahedral crystal field, which pair of d orbitals is raised highest in energy?
The dxy and dxz orbitals
The dxz and dyz orbitals
The dz2 and dx2-y2 orbitals
✓
The dxy and dx2-y2 orbitals
Correct Answer
The dz2 and dx2-y2 orbitals
The dz2 and dx2-y2 orbitals point directly at the six ligands along the axes, so they are repelled most and form the higher eg set. The dxy, dxz and dyz orbitals point between the axes and form the lower t2g set, so the dxy and dxz orbitals and the dxz and dyz orbitals are both lower-energy pairs. The dxy and dx2-y2 orbitals mix one orbital from each set.
Category: Crystal Field Theory
Question 16
Which of these ligands produces the largest crystal field splitting?
H2O
Cl-
F-
CN-
✓
Correct Answer
CN-
In the spectrochemical series, cyanide is a strong-field ligand and causes a large splitting energy, which often gives low-spin complexes. H2O is an intermediate ligand that splits the d orbitals less than cyanide. Cl- is a weak-field ligand near the low end of the series. F- is also a weak-field ligand, only slightly stronger than Cl-.
Category: Crystal Field Theory
Question 17
Water is a weak-field ligand, so in [Fe(H2O)6]2+ the six d electrons of Fe2+ occupy all five d orbitals singly before any pairing occurs. How many unpaired electrons does this ion have?
4
✓
2
6
Correct Answer
4
Five electrons occupy the five d orbitals singly and the sixth must pair, leaving 4 unpaired electrons, so the ion is paramagnetic. An answer of 0 describes the low-spin arrangement found with a strong-field ligand like cyanide. An answer of 2 does not match either a high-spin or a low-spin d6 ion. An answer of 6 ignores the fact that there are only five d orbitals.
Category: Color and Magnetism
Question 18
Compared with a complex of the same metal ion with weak-field ligands, a complex with strong-field ligands absorbs light of which kind?
Longer wavelength, lower energy
Shorter wavelength, higher energy
✓
Longer wavelength, higher energy
Shorter wavelength, lower energy
Correct Answer
Shorter wavelength, higher energy
Strong-field ligands create a larger splitting, so the absorbed photon must have more energy and therefore a shorter wavelength; such complexes often look yellow, orange or red. Longer wavelength, lower energy describes absorption by weak-field complexes. Longer wavelength, higher energy is impossible because photon energy decreases as wavelength increases. Shorter wavelength, lower energy is impossible for the same reason.
Category: Color and Magnetism
Question 19
Which ion forms complexes that are colorless because its d subshell is completely filled?
Cu2+
Fe3+
Zn2+
✓
Cr3+
Correct Answer
Zn2+
Zn2+ has a d10 configuration, so no electron can be promoted from the lower d set to the higher one and no visible light is absorbed. Cu2+ is d9 and has a vacancy in the upper set, so its complexes are colored. Fe3+ is d5 and forms colored complexes. Cr3+ is d3 and is well known for green and violet complexes.
Category: Color and Magnetism
Question 20
The splitting in a tetrahedral field is only about four-ninths of the octahedral value for the same metal and ligands. As a result, tetrahedral complexes are usually which?
Low spin
Diamagnetic
Colorless
High spin
✓
Correct Answer
High spin
Because the tetrahedral splitting is small, it is almost always less than the pairing energy, so electrons spread out singly and the complexes are high spin. Low spin requires a splitting larger than the pairing energy. Diamagnetic would require that every electron be paired, which a high-spin arrangement makes unlikely. Colorless is not a consequence of small splitting; many tetrahedral complexes, such as [CoCl4]2-, are intensely colored.
Category: Crystal Field Theory