DM 1, 2, 3.1

Question 1

what is a transition metal

Answer 1

D block element that forms one or more stable ions with an incomplete D subshell

Question 2

what are the characteristic properties of transition metals

Answer 2

1. they have variable oxidation states
2. act as catalysts / catalytic activity (elements and compounds)
3. coloured compounds as solids and in solution
4. form complexes

Question 3

describe the electron configuration of d block elements

Answer 3

• across the first row, every element has one more proton and electron than the previous element and enters the 3d subshell which IS NOT the outermost shell because 4s gets filled first

Question 4

why are zinc and scandium NOT transition metals

Answer 4

• transition metal forms a stable ion with an incomplete d subshell
• Zn only forms the ion Zn 2+ with a FULL d orbital
• Sc only forms Sc 3+ with an empty d orbital
• they are not transition metals but they are d block elements

Question 5

why are chromium and copper different, and what are their electron configurations (with an argon core)

Answer 5

• electrons always arrange themselves to give the lowest energy and their electronic arrangements work out to give a lower energy than if they were arranged how you would expect them to be
• Cr [Ar] 3d5 4s1
• Cu [Ar] 3d10 4s1

Question 6

which electrons are lost first when transition metals form ions

Answer 6

• the electrons in the 4s orbitals are always lost first

Question 7

why does copper only have the oxidation state of +1

Answer 7

because d5 and d10 are particularly stable electronic arrangements

Question 8

how can iron content be analysed, describe the process

Answer 8

• using a redox titration
• depends on the variable oxidation states of transition metals
• iron (II) ion sare oxidised to iron (III) by potassium manganate (VII)
• known volume of iron (II) solution is titrated with potassium manganate solution of known concentration and volume
• end point is when the first permanent pink colour is observed (MnO4 is in excess)

Question 9

what can be used instead of potassium manganate (VII) solution in a redox titration

Answer 9

• acidified potassium dichromate

Question 10

what is a catalyst

Answer 10

• something that alters the rate of a chemical reaction without being used up in the process

Question 11

what makes transition metals such good catalysts

Answer 11

• the availability of the 3d and the 4s electrons and the ability to change oxidation state

Question 12

transition metals as heterogeneous catalysts

Answer 12

• usually a solid transition metal with liquid or gas
• they use the 3d and 4s electrons on the metal surface to make weak bonds (chemisorption) to reactants
• reaction occurs and the bonds break to release the products

Question 13

transition metals as homogeneous catalysts

Answer 13

• usually the reaction taking place in the aqueous phase
• usually a transition metal ion forms an intermediate compound with one or more of the reactants which breaks down to form the products

Question 14

what are the colours of the following transition metal ions
1. MnO4 -
2. Mn 2+
3. Fe 2+
4. Fe 3+
5. Cu +
6. Cu 2+

Answer 14

1. deep purple
2. pale pink
3. green
4. orange / brown
5. unstable in aqueous solution
6. blue

Question 15

why are transition metals coloured

Answer 15

• often related to their partially filled d-orbitals in the metal ion

Question 16

how do transition metals appear coloured

Answer 16

• when white light falls on transition metals, some light is absorbed, some is transmitted and some is reflected
• if the light absorbed is in the visible light region the the colour complementary to the frequency of light that was absorbed will be reflected

Question 17

describe the process of qualitative analysis with a transition metal

Answer 17

• add drops of sodium hydroxide OR ammonia to the sample solution containing transition metal ions
• this results in characteristic coloured precipitates

Question 18

describe the reaction of aqueous copper and ammonia

Answer 18

ammonia will donate OH ion to copper and pale blue precipitate of Cu(OH)2 will form
- Cu(OH)2 will re-dissolve on addition of excess ammonia to give a deep purple-blue solution
- containing a copper/ammonia complex ion