Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

UACE Chemistry > Transition Elements > Flashcards

Transition Elements Flashcards

1
Q

What is a transition element?

A

A transition element is an element whose atoms have partially filled d-orbitals or
forms at least one stable cation with partially filled d-orbitals.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Why are Scandium and Zinc not considered transition elements?

A

• Both the scandium ion (Sc3+) and zinc ion (Zn2+) lack partially d-orbitals.
• Both scandium and zinc do not form coloured ions.
• Both scandium and zinc ions are restricted to single oxidation state.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are the characteristics/ properties of transition elements?

A
  1. They have high densities, melting and boiling points.
  2. They have variable oxidation states.
  3. They form a variety of complex ions.
  4. They form coloured ions and compounds.
  5. They show ability to act as catalysts.
  6. They show paramagnetism
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

In what way does the Zinc ion show similarity to those of transition elements?

A
  • Able to form complexes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Why do transition elements have high density, melting and boiling points?

A

Explanation: The density, melting point and boiling point of metals increases with increase in the strength of the metallic bond.

Transition metals release electrons from both the inner 3d-sub energy level and the outer 4s-sub energy level towards metallic bonding resulting into very strong electrostatic attraction between the positively charged metal ions and the delocalized electrons (very strong metallic bonds) and high density/ high melting/high boiling point.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the trend in melting point of the first transition series (Scandium to zinc)? Explain?

A

Trend: It increases from scandium to vanadium and generally decreases from vanadium to zinc with manganese and copper having abnormally lower melting points than expected and zinc having very low melting point.

Explanation:
• The increase from scandium is due to the increases in the number of unpaired 3d- electrons per atom contributed towards metallic bonding and the general decrease in melting point from chromium to zinc is due to decrease in the number of unpaired 3d- electrons.

• Manganese and copper have abnormally lower melting points than expected. This is because manganese has a stable half-filled 3d-sub energy level while copper has a more stable completely filled 3d-sub energy level resulting into stable lattices in which the 3d- electrons are less available for metallic bonding. This results into weak electrostatic attractions between the metal ions and the delocalized electrons (weak metallic bonds) and low melting points.

• Zinc has very low melting point because its 3d-sub energy level is completely filled and the d-electrons do not take part in metallic bonding. Only the 4s-electrons are involved in metallic bonding resulting into weak electrostatic attractions between the zinc ions and the delocalized electrons and low melting points.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Why do transition elements form coloured compounds/ions?
Explanation:
Formation of coloured compounds by transition metal ions is due to presence incompletely filled 3d-orbitals.

When white light is shone onto transition metal ions or in presence of ligands, the 3d-orbitals split into two sub energy levels.

A photon of energy is absorbed in the visible spectrum when an electron jumps from the lower sub- energy level to the high energy level.

The unabsorbed visible light is transmitted and it is the observed colour.

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What factors affect the absorbed energy and the colour of the transition element ion?
• The nature of the metal ion
• The oxidation state of the cation e.g. Fe2+, Fe3+
• The nature of ligand e.g.
̅̅− 𝑂𝐻,𝐶𝑁,𝐶𝑙 ,𝐻2𝑂, 𝑁𝐻3
• The geometry of the complex e.g. tetrahedral, octahedral

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Explain how transition elements are paramagnetic (weakly attracted by a magnetic field).
Transition metal ions show paramagnetism due to presence unpaired 3d-electrons which spin on their axis creating a magnetic dipole.

The spins become temporarily aligned in the same direction the external applied magnetic field, causing the material to be attracted to the applied magnetic field.

Paramagnetic character increases with the number of unpaired 3d- electrons.
For example
(i) Mn2+ (1𝑠22𝑠22𝑝63𝑠23𝑝63𝑑5) is more paramagnetic than Mn4+
(1𝑠22𝑠22𝑝63𝑠23𝑝63𝑑3) because Mn2+ has five unpaired electrons while Mn4+ has only three unpaired electrons.

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Why do transition metals and their compounds make good heterogeneous catalysts?
- The presence of partially filled d-orbitals allows them to form weak bonds with the reactants on the catalyst surface, increasing the reactant concentration at adsorption sites. This weakens the reactant bonds resulting in an increased rate of reaction.
- their variable oxidation states which allows them to create an alternative path for the reaction with lower activation energy.

Note: During the reaction the catalyst undergoes change in oxidation state but it is regenerated at the end of the reaction.

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is a complex?
• A complex is a substance in which a central metal atom or ion is bonded to negative ions or neutral molecules with lone pairs of electrons through coordinate bonding.

• The negative ions or neutral molecules with lone pairs of electrons are called ligands.

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is coordination number?
• The number of coordinate bonds on the central metal atom or ion by ligands

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Why do transition metals form many complexes due to:
(i) their high polarizing power arising from their small highly charged ions enabling them to attract lone pairs from ligands.
(ii) the presence of vacant d-orbitals that can accommodate lone pairs of electrons from ligands.

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is Ionization isomerism?
These differ in the distribution of ions between those which directly bonded and those not directly bonded to the central metal atom or ion.

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is Hydration isomerism?
These differ in the number of water molecules directly bonded to the central metal atom or ion.

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Give the properties of vanadium
• It is very strong metal
• It is resistant to corrosion at ordinary conditions and only combines with air at high temperatures
• It is not attacked by cold dilute acids but slowly dissolves in hot concentrated nitric acid, hot concentrated sulphuric acid and concentrated hydrochloric acid.

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

How can the oxidation states of vanadium be demonstrated
By shaking a solution ammonium vanadate in dilute sulphuric acid with zinc amalgam.

The solution changes colour from pale-yellow to blue, to green and finally to lavender.

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Why don’t V5+ and V4+ exist as bare ions in aqueous solutions?

Both ions are highly charged and have very small ionic radii and as a result they exert a high polarizing effect on the neighboring water molecules and detaching oxide ions from the water molecules forming VO3- (or VO2+) and VO2+ ions respectively.

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How is Vanadium(V) oxide, V2O5 prepared?
- It is an orange solid prepared by heating ammonium metavanadate, NH4VO3.

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What type of oxide is vanadium (v) oxide
It is an amphoteric oxide.

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

How does vanadium (v) oxide react in strongly alkaline solutions?
It dissolves forming orthovanadate ion, VO43-

potassium hydroxide and potassium chlorate(V).
3MnO2 (s) + KClO3 (l) + 6KOH(l) → 3K2MnO4 (l) + KCl(l) + 3H2O(l)or − ̅ 2− −
3𝑀𝑛𝑂2(𝑙) + 𝐶𝑙𝑂3 (𝑙) + 6𝑂𝐻(𝑙) → 3𝑀𝑛𝑂4 (𝑎𝑞) + 𝐶𝑙 (𝑎𝑞) + 3𝐻2𝑂(𝑙)
• Potassium manganate(VI) is only stable in alkaline conditions.
In neutral or acidic conditions it disproportionates into manganate(VII) ions and manganese(IV) oxide.
18

3𝑀𝑛𝑂42−(𝑎𝑞) + 4𝐻+(𝑎𝑞) → 2𝑀𝑛𝑂4−(𝑎𝑞) + 𝑀𝑛𝑂2(𝑠) + 2𝐻2𝑂(𝑙)(𝑨𝒄𝒊𝒅𝒊𝒄 𝒎𝒆𝒅𝒊𝒖𝒎
2− −
3𝑀𝑛𝑂4 (𝑎𝑞) + 2𝐻2𝑂(𝑙) ⇌ 2𝑀𝑛𝑂4 (𝑎𝑞) + 𝑀𝑛𝑂2(𝑠) + 4𝑂𝐻(𝑎𝑞)(𝑨𝒍𝒌𝒂𝒍𝒊𝒏𝒆 𝒎𝒆𝒅𝒊𝒖𝒎)
Manganese(VII) compounds
Potassium manganate(VII)
This is the most important compound in the +7 oxidation state of manganese. It is a dark purple crystalline solid. It is moderately soluble in water.
Reactions of potassium manganate(VII)
̅
19

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

How does vanadium (v) oxide react in strongly acidic conditions?
It dissolves forming VO2+ ion
VO (s) + 2H+(aq) → 2VO +(aq)+H O(l)

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

How does chromium metal react with oxygen?
It burns in oxygen at 2300K forming chromium(III) oxide, a dark-green solid
4Cr(s) + 3O2 (g) → 2Cr2O3 (s)

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

How does chromium react with cold dilute hydrochloric and cold dilute sulphuric acid
- It reacts slowly but more rapidly on warming forming chromium(II) salts (blue solution) and hydrogen gas
Cr(s) + 2H+ (aq) → Cr2+ (aq) + H2 (g)

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What happens to chromium(II) salts in acidic conditions?
They are readily oxidized to chromium(III) salts (green solution).
4Cr2+ (aq) + 4H+ (aq) + O2 (g) → 4Cr3+ (aq) + 2H2O(l)

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What factors favor complex ion formation?
- Small highly charged cations / Cations with high charge density and polarizing power
- Presence of vacant orbitals on the central metal ion or atom
- Presence of lone pairs of electrons on the ligands

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

How does chromium react with concentrated sulphuric acid
It forms chromium(III) sulphate (green
solution), sulphurdioxide and water.

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

How does chromium react with nitric acid?
Chromium is rendered passive by nitric acid.

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What is the reaction between chlorine and chromium?
When heated in a stream of dry chlorine chromium(III) chloride is formed
2Cr(s) + 3Cl2 (g) → 2CrCl3 (s)

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

Which oxidation states does chromium exist in in compounds?
- +6 which is oxidizing
- +3 which is the most stable
- +2 which is reducing

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

How is chromium(II) chloride formed?
It is a white solid prepared by heating chromium in a stream of dry hydrogen chloride gas
Cr(s) + 2HCl(g) → CrCl2 (s) + H2 (g)

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

How is chromium(III) oxide prepared?
It is a green solid prepared by heating ammonium dichromate(VI)
(NH4 )2Cr2O7 (s) → Cr2O3 (s) + N2 (g) + 4H2O(l)

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

True or false
Chromium(III) oxide may be reduced by carbon and oxygen
False
Cr2O3 is very stable and resists reduction by both carbon and hydrogen

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

Is Cr2O3 basic, acidic or amphoteric?
Amphoteric with basic character being predominant.

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

How does Chromium(III) oxide react with acids?
It dissolves forming a green solution consisting of a chromium(III) salt.
Cr2O3 (s) + 6H+ (aq) → 2Cr3+ (aq) + 3H2O(l)

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

How does Chromium(III) oxide react with alkalis?
It dissolves forming a deep-green solution consisting of a complex of
hexahydroxochromate(III) ions or tetrahydroxochromate(III) ions

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

What color is Chromium(III) hydroxide?
It is a green solid

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

How is Chromium(III) hydroxide prepared?
By adding a calculated amount of aqueous sodium hydroxide to an aqueous solution of a chromium(III) salt.
Cr3+ (aq) + 3OH− (aq) → Cr(OH)3 (s)

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

Is Chromium(III) hydroxide basic, acidic or amphoteric?
Amphoteric

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

True or false, Chromium(III) hydroxide can react with both alkalis and acids.
True

With acids: Cr(OH)3(s) + 3H+(aq) Cr3+(aq) + 3H2O(l) ̅-
With alkalis: Cr(OH)3(s) + 𝑂𝐻(aq) [Cr(OH)4] (aq) ̅ 3-
Cr(OH)3(s) + 3𝑂𝐻(aq) [Cr(OH)6] (aq) c)

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

What color is Anhydrous chromium(III), CrCl3?
It is a reddish-violet solid

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

How is Anhydrous chromium(III) chloride prepared?
By heating chromium in a stream of dry chlorine gas.
2Cr(s) + 3Cl2 (g) → 2CrCl3 (s)

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

How may the three isomers of Hydrated chromium(III) chloride complex be distinguished?
By titrating each with standard silver nitrate solution to find the number of moles silver chloride precipitated per mole of the isomer.

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

Why are aqueous solutions of chromium(III) salts acidic?
The chromium(III) ion has a high charge density and polarizing power.

Therefore it exerts a strong attraction for a lone pair of electrons on water molecules forming a complex of hexaaquachromium(III) ions, [Cr(H2O)6]3+.

The strong chromium – oxygen coordinate bond formed weakens the oxygen-hydrogen bond (O – H) of the water molecule and releasing hydrogen ions.

The hydrogen ions make the solution acidic.
[𝐶𝑟(𝐻2𝑂)6]3+(𝑎𝑞) ⇌ [𝐶𝑟(𝐻2𝑂)5𝑂𝐻]2+(𝑎𝑞) + 𝐻+(𝑎𝑞)

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q

Explain what is observed when aqueous sodium carbonate is added to an aqueous solution of chromium(III) ions?

Observation: A green precipitate and effervescence of a colourless gas

Explanation: The green precipitate is chromium(III) hydroxide and the colourless gas is carbon dioxide.

The chromium(III) ions combine with carbonate ions forming chromium(III) carbonate.
2Cr3+(aq) + 3CO32-(aq) Cr2(CO3)3(s)

The chromium(III) ion has a small ionic radius and a big positive charge resulting into high charge density and polarizing power.

Chromium(III) carbonate is therefore readily hydrolyzed by water forming chromium(III) hydroxide and carbon dioxide gas.
Cr2(CO3)3(s) + 3H2O(l) 2Cr(OH)3(s) + 3CO2(g)

Overall equation:
2Cr3+(aq) + 3CO32-(aq) + 3H2O(l) 2Cr(OH)3(s) + 3CO2(g)

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
46
Q

Explain what is observed when chromium(III) ions is reacted with aqueous sodium hydroxide?

Observation: A green precipitate soluble in excess forming a green solution.

Explanation:
The green precipitate is chromium(III) hydroxide which is insoluble in water.
𝐶𝑟3+(𝑎𝑞) + 3𝑂𝐻(𝑎𝑞) → 𝐶𝑟(𝑂𝐻)3(𝑠)

Chromium(III) hydroxide is amphoteric and reacts with excess sodium hydroxide solution forming a soluble complex of tetrahydroxochromate(III) ions.
𝐶𝑟(𝑂𝐻)3(𝑠)+𝑂𝐻(𝑎𝑞)→[𝐶𝑟(𝑂𝐻)4] (𝑎𝑞)

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
47
Q

What happens when the green solution of tetrahydrochromate(III) ions is boiled with hydrogen peroxide?
A yellow solution containing chromate(VI) ions is formed.
2[𝐶𝑟(𝑂𝐻)4] (𝑎𝑞)+3𝐻2𝑂2(𝑎𝑞)+2𝑂𝐻(𝑎𝑞)→2𝐶𝑟𝑂4 (𝑎𝑞)+8𝐻2𝑂(𝑙)

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
48
Q

What is observed from the reaction between chromate(VI) ions and aqueous lead(II) nitrate or lead(II) ethanoate

When to the yellow solution of chromate(VI) ion is added aqueous lead(II) nitrate or lead(II) ethanoate, a yellow precipitate is formed.
Pb2+ (aq) + CrO 2− (aq) → PbCrO (s)

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
49
Q

What happens when to the yellow solution of chromate(VI) ions is added aqueous barium chloride or barium nitrate?
A yellow precipitate of barium chromate is formed.
𝐵𝑎2+(𝑎𝑞) + 𝐶𝑟𝑂42−(𝑎𝑞) → 𝐵𝑎𝐶𝑟𝑂4(𝑠)

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
50
Q

What happens when to the yellow solution of chromate(VI) ions is added a layer of butan-1-ol (or ether) followed by excess dilute sulphuric and hydrogen peroxide?
A blue solution is formed in the ether layer due to formation of chromium(VI) oxide peroxide which is more soluble in ether than water.
2𝐶𝑟𝑂42−(𝑎𝑞) + 4𝐻+(𝑎𝑞) + 4𝐻2𝑂2(𝑎𝑞) → 2𝐶𝑟𝑂5(𝑎𝑞) + 6𝐻2𝑂(𝑙)

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
51
Q

What is observed when to the yellow solution of chromate(VI) ions is added aqueous silver nitrate?
A brick red precipitate of silver chromate is formed.
2𝐴𝑔+(𝑎𝑞) + 𝐶𝑟𝑂 2−(𝑎𝑞) → 𝐴𝑔 𝐶𝑟𝑂 (𝑠)

What is observed when to the yellow solution of chromate(VI) ions is added dilute sulphuric acid or dilute
hydrochloric acid?
An orange solution is formed.
2𝐶𝑟𝑂 2−(𝑎𝑞) + 2𝐻+(𝑎𝑞) ⇌ 𝐶𝑟 𝑂 2−(𝑎𝑞) + 𝐻 𝑂(𝑙)

What is observed when to the yellow solution of chromate(VI) ions is reacted with aqueous ammonia? Explain.

Observation: A green precipitate soluble in excess forming a violet solution.
Explanation: The green precipitate is chromium(III) hydroxide which is insoluble in water.
𝐶𝑟 (𝑎𝑞) + 3𝑂𝐻(𝑎𝑞) → 𝐶𝑟(𝑂𝐻)3(𝑠)

The chromium(III) hydroxide reacts with excess ammonia solution forming a soluble complex of hexaamminechromium(III) ions.
3+ ̅ 𝐶𝑟(𝑂𝐻)3(𝑠) + 6𝑁𝐻3(𝑎𝑞) → [𝐶𝑟(𝑁𝐻3)6] (𝑎𝑞) + 3𝑂𝐻(𝑎𝑞)

What color is Chromium(VI) oxide, CrO3?
It is a dark-red crystalline solid

How is Chromium(VI) oxide formed?
When a saturated solution of potassium dichromate(VI) is acidified by concentrated sulphuric acid and cooled.
Cr O 2− (aq) + 2H+ (aq) → 2CrO (s) + H O(l) 2732

The crystals are filtered using glass wool not paper because the acid would attack the paper.

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
52
Q

What is the result of heating strongly, chromium(VI) oxide?
CrO3 decomposes forming a green residue of chromium(III) oxide and liberating oxygen gas.
4CrO3 (s) → 2Cr2O3 (s) + 3O2 (g)

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
53
Q

What type of oxide is Chromium(VI) oxide?
CrO3 is an acidic oxide

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
54
Q

How does Chromium(VI) oxide react with alkalis?
Reacts forming a yellow solution consisting of chromate(VI) ions

𝐶𝑟𝑂3(𝑠) + 2𝑂𝐻(𝑎𝑞) → 𝐶𝑟𝑂4 + 𝐻2𝑂(𝑙)

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
55
Q

How are Barium, strontium and lead chromates formed?
They are yellow crystalline solids prepared as yellow precipitates by reacting aqueous solutions of the metal ions with aqueous potassium chromate
Ba2+ (aq) + CrO 2− (aq) → BaCrO (s)
Sr2+ (aq) + CrO 2− (aq) → SrCrO (s)
Pb2+ (aq) + CrO 2− (aq) → PbCrO (s)

A
56
Q

How is Silver chromate made?
It is a red crystalline solid made by reacting silver nitrate with potassium chromate (VI)
2Ag+(aq)+CrO 2−(s) → Ag CrO (s)

A
57
Q

How do chromate(VI) ions react with dilute acids?
Aqueous solutions of chromate (VI) ions are converted to dichromate(VI) ions when reacted with dilute acids.

The yellow colour of chromate(VI) ions changes to orange of dichromate(VI) ions.
(Yellow) (Orange)

A
58
Q

What is the physical appearance of sodium dichromate(VI)?
- It is a red crystalline solid.

A
59
Q

How is sodium dichromate(VI) prepared?
- By reacting sodium chromate with dilute sulphuric acid.

A
60
Q

What precipitates out first when the mixture from the preparation of sodium dichromate(VI) is cooled?
- Sodium sulphate crystals (Na2SO4.10H2O).

A
61
Q

How are the red crystals of sodium dichromate(VI) formed after the initial precipitation?
- By concentrating the remaining solution through evaporation and then cooling it.

A
62
Q

Describe the solubility and deliquescent properties of sodium dichromate(VI).
- Sodium dichromate(VI) is deliquescent and soluble in water.

A
63
Q

Why can’t sodium dichromate(VI) be used as a primary standard?
- Because it is deliquescent.

A
64
Q

How is potassium dichromate(VI) made?
- By mixing hot, almost saturated solutions of sodium dichromate(VI) and potassium chloride.

A
65
Q

What happens to the sodium chloride formed in the reaction for making potassium dichromate(VI)?
- It is filtered out, and the hot filtrate is left to cool, forming crystals of potassium dichromate(VI).

A
66
Q

What is the equilibrium equation for the formation of dichromate(VI) ions from chromate(VI) ions in acidic solutions?
- 2CrO4^2−(aq) + 2H+(aq) ⇌ Cr2O7^2−(aq) + H2O(l)

A
67
Q

Why is potassium dichromate(VI) considered a primary standard?
- Because it is not deliquescent and can be obtained in a state of high purity.

A
68
Q

What is potassium dichromate(VI) used for in titration?
- It is used to standardize sodium thiosulphate solution.

A
69
Q

What happens to dichromate(VI) ions when they react with alkalis?
- They are converted to chromate(VI) ions, and the solution changes color from orange to yellow.

A
70
Q

What is the color change observed when dichromate(VI) ions are converted to chromate(VI) ions in alkali?
- From orange to yellow.

A
71
Q

What happens to dichromate(VI) ions in acidic media during redox reactions?
- They act as powerful oxidizing agents and are reduced to green chromium(III) ions.

A
72
Q

What is the balanced chemical equation for the reduction of dichromate(VI) ions to chromium(III) ions in acidic media?
- Cr2O7^2−(aq) + 14H+(aq) + 6e− → 2Cr3+(aq) + 7H2O(l)

A
73
Q

What color change occurs when dichromate(VI) ions are reduced to chromium(III) ions in acidic media?
- From orange to green.

A
74
Q

What does acidified potassium dichromate(VI) oxidize iron(II) ions to?
- Iron(III) ions.

A
75
Q

What is the balanced chemical equation for the oxidation of iron(II) ions by acidified potassium dichromate(VI)?
- Cr2O7^2−(aq) + 14H+(aq) + 6Fe2+ → 2Cr3+(aq) + 6Fe3+(aq) + 7H2O(l)

A
76
Q

What does acidified potassium dichromate(VI) oxidize aqueous potassium iodide to?
- Iodine.

A
77
Q

What is the balanced chemical equation for the oxidation of potassium iodide by acidified potassium dichromate(VI)?
- Cr2O7^2−(aq) + 14H+(aq) + 6I− → 2Cr3+(aq) + 3I2(aq) + 7H2O(l)

A
78
Q

What color change is observed when potassium iodide is oxidized to iodine by acidified potassium dichromate(VI)?
- From colorless to brown.

A
79
Q

What indicator is used in the titration of iodine with aqueous sodium thiosulphate?
- Starch indicator.

A
80
Q

What is the balanced chemical equation for the titration of iodine with aqueous sodium thiosulphate?
- I2(aq) + 2S2O3^2−(aq) → 2I−(aq) + S4O6^2−(aq)

A
81
Q

What is the most important ore of manganese?
- Pyrolusite (MnO2)

A
82
Q

How does pure manganese react with air when finely divided and heated?
- It burns to form Mn3O4.

A
83
Q

What is the balanced chemical equation for manganese burning in air?
- 3Mn(s) + 2O2(g) → Mn3O4(s)

A
84
Q

How does manganese react with hot water?
- It forms manganese(II) hydroxide and hydrogen gas.

A
85
Q

What is the balanced chemical equation for manganese reacting with hot water?
- Mn(s) + 2H2O(l) → Mn(OH)2(s) + H2(g)

A
86
Q

How does manganese react with dilute hydrochloric acid and dilute sulphuric acid?
- It dissolves, forming the corresponding salt and liberating hydrogen gas.

A
87
Q

What is the balanced chemical equation for manganese reacting with dilute acids?
- Mn(s) + 2H+(aq) → Mn2+(aq) + H2(g)

A
88
Q

What are the products of manganese reacting with hot concentrated sulphuric acid?
- Manganese(II) sulphate, sulphur dioxide, and water.

A
89
Q

What is the balanced chemical equation for manganese reacting with hot concentrated sulphuric acid?
- Mn(s) + 2H2SO4(l) → MnSO4(aq) + SO2(g) + 2H2O(l)

A
90
Q

In what oxidation states does manganese commonly exist?
- +2, +3, +4, +5, +6, and +7.

A
91
Q

Which oxidation state of manganese is the most unstable and least common?
- +5 oxidation state.

A
92
Q

Which oxidation state of manganese is the most powerful oxidizing?
- +7 oxidation state.

A
93
Q

Which oxidation state of manganese is the most stable?
- +2 oxidation state.

A
94
Q

Why is the +2 oxidation state of manganese the most stable?
- Because manganese has a half-filled 3d subshell in this state, which is thermodynamically very stable (Mn2+: 1s^22s^22p^63s^23p^63d^5).

A
95
Q

What is the appearance and preparation method of manganese(II) oxide, MnO?
- It is a grey-green solid prepared by heating manganese(II) carbonate or manganese(II) ethanedioate.

A
96
Q

What are the balanced chemical equations for preparing manganese(II) oxide from manganese(II) carbonate and manganese(II) ethanedioate?
- MnCO3(s) → MnO(s) + CO2(g)
- MnC2O4(s) → MnO(s) + CO(g) + CO2(g)

A
97
Q

What is the appearance and preparation method of manganese(II) hydroxide, Mn(OH)2?
- It is a white solid prepared by precipitation when aqueous sodium hydroxide is added to an aqueous solution of a manganese(II) salt.

A
98
Q

What is the balanced chemical equation for the precipitation of manganese(II) hydroxide?
- Mn2+(aq) + 2OH−(aq) → Mn(OH)2(s)

A
99
Q

What happens to manganese(II) hydroxide when it stands in air?
- It is readily oxidized to hydrated manganese(III) oxide, Mn2O3.xH2O, which is a brown solid.

A
100
Q

What is the balanced chemical equation for the oxidation of manganese(II) hydroxide by air?
- 4Mn(OH)2(s) + O2(g) → 2Mn2O3.2H2O(s)

A
101
Q

What happens to manganese(II) hydroxide when it reacts with hydrogen peroxide?
- It is oxidized to manganese(IV) oxide, a black solid.

A
102
Q

What is the balanced chemical equation for the oxidation of manganese(II) hydroxide by hydrogen peroxide?
- Mn(OH)2(s) + H2O2(aq) → MnO2(s) + 2H2O(l)

A
103
Q

What is the chemical formula for manganese(II) carbonate?
- MnCO3

A
104
Q

What is the appearance of manganese(II) carbonate?
- It is a brown-red solid.

A
105
Q

How is manganese(II) carbonate prepared?
- By precipitating it from a reaction between aqueous sodium carbonate and an aqueous solution of a manganese(II) salt.

A
106
Q

What is the balanced chemical equation for the preparation of manganese(II) carbonate?
- Mn2+(aq) + CO3^2−(aq) → MnCO3(s)

A
107
Q

What are the common manganese(II) salts and their appearance?
- Manganese(II) chloride, sulphate, and nitrate are all pink solids.

A
108
Q

How are manganese(II) chloride, sulphate, and nitrate prepared?
- By reacting excess manganese(II) oxide (MnO), manganese(II) hydroxide (Mn(OH)2), or manganese(II) carbonate (MnCO3) with the corresponding dilute acid.

A
109
Q

What is the process after reacting manganese(II) compounds with dilute acids to form manganese(II) salts?
- The excess solid is filtered off, the filtrate is concentrated by evaporation, and then left to cool to form crystals of the salt.

A
110
Q

How do Mn2+ ions exist in aqueous solutions?
- As [Mn(H2O)6]2+ complex, which is a pink solution.

A
111
Q

How can Mn2+(aq) be detected with aqueous sodium hydroxide?
- By adding it dropwise until in excess, forming a white precipitate that turns brown on standing.

A
112
Q

What is the balanced chemical equation for the reaction of Mn2+(aq) with aqueous sodium hydroxide?
- Mn2+(aq) + 2OH−(aq) → Mn(OH)2(s)

A
113
Q

How can Mn2+(aq) be detected with aqueous ammonia?
- By adding it dropwise until in excess, forming a white precipitate that turns brown on standing.

A
114
Q

What happens when Mn2+(aq) reacts with solid sodium bismuthate(V) or lead(IV) oxide and concentrated nitric acid?
- A purple solution is observed due to the formation of manganate(VII) ions.

A
115
Q

What is the balanced chemical equation for the reaction of Mn2+(aq) with sodium bismuthate(V)?
- 2Mn2+(aq) + 5BiO3−(s) + 14H+(aq) → 2MnO4−(aq) + 5Bi3+(aq) + 7H2O(l)

A
116
Q

What is the balanced chemical equation for the reaction of Mn2+(aq) with lead(IV) oxide?
- 2Mn2+(aq) + 5PbO2(s) + 4H+(aq) → 2MnO4−(aq) + 5Pb2+(aq) + 2H2O(l)

A
117
Q

What happens to manganese(III) compounds in aqueous solution?
- They tend to disproportionate, forming a pale-pink (or colorless) solution of manganese(II) ions and a black solid of manganese(IV) oxide.

A
118
Q

What is the balanced chemical equation for the disproportionation of manganese(III) ions in aqueous solution?
- 2Mn3+(aq) + 2H2O(l) → Mn2+(aq) + MnO2(s) + 4H+(aq)

A
119
Q

What is the chemical formula for manganese(III) oxide?
- Mn2O3

A
120
Q

What is the appearance of manganese(III) oxide?
- It is a brown solid.

A
121
Q

How is manganese(III) oxide prepared?
- By heating manganese(IV) oxide in ammonia gas.

A
122
Q

What is the balanced chemical equation for the preparation of manganese(III) oxide?
- 6MnO2(s) + 2NH3(g) → 3Mn2O3(s) + MnO2(s) + 3H2O(l) + N2(g)

A
123
Q

What is the chemical formula for trimanganese tetraoxide?
- Mn3O4

A
124
Q

What is the appearance of trimanganese tetraoxide?
- It is a red solid.

A
125
Q

How is trimanganese tetraoxide prepared by heating manganese(IV) oxide?
- By strongly heating manganese(IV) oxide.

A
126
Q

What is the balanced chemical equation for the preparation of Mn3O4 by heating manganese(IV) oxide?
- 3MnO2(s) → 2Mn3O4(s) + O2(g)

A
127
Q

How is trimanganese tetraoxide prepared by heating manganese(II) oxide?
- By strongly heating manganese(II) oxide in air.

A
128
Q

What is the balanced chemical equation for the preparation of Mn3O4 by heating manganese(II) oxide in air?
- 6MnO(s) + O2(g) → 2Mn3O4(s)

A
129
Q

What happens when Mn3O4 dissolves in cold concentrated sulphuric acid?
- It forms manganese(II) and manganese(III) sulphates.

A
130
Q

What is the balanced chemical equation for Mn3O4 dissolving in cold concentrated sulphuric acid?
- Mn3O4(s) + 8H+(aq) → Mn2+(aq) + 2Mn3+(aq) + 4H2O(l)

A
131
Q

What happens when Mn3O4 dissolves in hot concentrated nitric acid?
- It forms manganese(IV) oxide and manganese(II) nitrate.

A
132
Q

What is the balanced chemical equation for Mn3O4 dissolving in hot concentrated nitric acid?
- Mn3O4(s) + 4H+(aq) → MnO2(s) + 2Mn2+(aq) + 2H2O(l)

A
133
Q

What is the naturally occurring form of manganese(IV) oxide?
- Pyrolusite, MnO2

A
134
Q

What is the appearance of manganese(IV) oxide?
- It is a black solid and insoluble in water.

A
135
Q

How is manganese(IV) oxide prepared?
- By heating manganese(II) nitrate.

A
136
Q

What is the balanced chemical equation for the preparation of MnO2 by heating manganese(II) nitrate?
- Mn(NO3)2(s) → MnO2(s) + 2NO2(g)

A
137
Q

What property does manganese(IV) oxide have as an oxidizing agent?
- It is a powerful oxidizing agent.

A

UACE Chemistry (20 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions