9 - Developing Metals (DM)

Question 1

What is a redox titration?

Answer 1

Titration of a reducing agents by an oxidising agent or vice versa

Question 2

What equipment is used to carry out a titration?

Answer 2

-Pipette and pipette filler
-Burette

Question 3

Why is a pipette and pipette filler are used in a titration?

Answer 3

Measures out the volume of a reactant accurately before transferring it to a conical flask

Question 4

Why is a burette are used in a titration?

Answer 4

It is a controlled way to add small volumes of one reactant to another reactant

Question 5

What can MnO4- titrations be used to analyse?

Answer 5

Reducing agents, such as:
-Fe2+ ions
-Ethanedioic acid (COOH)2

MnO4- is reduced to Mn2+

Question 6

How do you do a titration with potassium maganate (VII)?

Answer 6

-Add potassium maganate into burette
-Other reactant is acidified with H2SO4
-Potassium maganate flows into the flask it become colourless
-When there is the first trace of a permanent pink solution, close burette tap

Question 7

Define coordination number

Answer 7

The number of coordinate bonds from ligands to the central metal ion/atom

Question 8

What are the 2 bond shapes in common with a complex with a coordination number of 4?

Answer 8

Tetrahedral and square planar

Question 9

What is the bond angle for a tetrahedral complex?

Answer 9

109.5º

Question 10

What is the bond angle for a square planar complex?

Answer 10

90º

Question 11

What is the bond shape for a complex ion with a coordination number of 6?

Answer 11

Octahedral

Question 12

What is the bond angle for a complex ion with a coordination number of 6?

Answer 12

90º

Question 13

Define half-cell

Answer 13

Contains the chemical species present in a redox half equation

Question 14

What is a metal/metal ion half cell?

Answer 14

A half cell where a metal rod is dipped into a solution containing an ion of the same metal

Question 15

What is an ion/ion half-cell?

Answer 15

Contains a solution of ions of the same element but different oxidation states. The electrode is usually graphite or platinium
e.g. Fe2+ and Fe3+

Question 16

How do you combine 2 half equations?

Answer 16

Make sure number of electrons in each equation are equal. Do the anticlockwise rule to determine which equation is oxidation/reduction

Question 17

Define standard electrode potential

Answer 17

Voltmeter/emf reading when a half-cell of interest is connected to a hydrogen half-cell via a salt bridge with all solutions having a concentration of 1mol dm^-3 under standard conditions

Question 18

What is a hydrogen half-cell?

Answer 18

Contains hydrogen gas and a solution containing hydrogen ions. Inert platinum electrode is used to allow electrons in and out of the half-cell

Question 19

How do you use standard electrode potential to calculate the standard cell potential?

Answer 19

More positive electrode - other electrode

Question 20

Define electrochemical cell

Answer 20

2 half-cell connected by a salt bridge with their electrode connected to a voltmeter, allowing the flow of electrons. It generates electrical energy from chemical redox reactions

Question 21

Define salt bridge

Answer 21

Allows the transfer of ions. Typically a concentrated solution of KNO3

Question 22

Why may a graphite or platinum electrode be used?

Answer 22

They are very unreactive and will not react with the half-cel solutions and will not affect the voltmeter readings

Question 23

How do you predict which half-cell is being oxidised and which one is being reduced?

Answer 23

Oxidation occurs at less positive side
Reduction occurs at the more positive side

Question 24

How do you predict the feasibility of a redox reaction?

Answer 24

If the oxidising agent has a lower standard cell potential than the reducing agent. The greater the difference in cell potential, the more likely the reaction is to occur

Question 25

Why may a reaction not occur?

Answer 25

-Non-standard conditions -Ambient energy of the system is lower than the activation energy

Question 26

What is rusting?

Answer 26

An iron oxide (usually red) formed from the redox reaction of iron and oxygen in the presence of water/moisture

Question 27

How can rusting be prevented?

Answer 27

-Surface needs to be separated from air and water, i.e. keeping the metal in oil -Coat the iron -Alloys (e.g. stainless steel) can be made to prevent rusting

Question 28

Define transition metals

Answer 28

d-block elements that can form one or more stable ions which have an incomplete d-subshell

Question 29

What is the electron configuration of chromium?

Answer 29

1s2 2s2 2p6 3s2 3p6 3d5 4s1

Question 30

What is the electron configuration of copper?

Answer 30

1s2 2s2 2p6 3s2 3p6 3d10 4s1

Question 31

What are the common oxidation states of copper and iron?

Answer 31

Copper - Cu+/Cu2+ Iron - Fe2+/Fe3+

Question 32

What is the colour of Cu+ in solution?

Answer 32

Colourless

Question 33

What is the colour of Cu2+ in solution?

Answer 33

Blue

Question 34

What is the colour of Fe2+ in solution?

Answer 34

Green

Question 35

What is the colour of Fe3+ in solution?

Answer 35

Yellow/Brown

Question 36

Why do transition metals have variable oxidation states?

Answer 36

d-subshell has a lot of stable states, so different numbers of electrons can be lost to produce ions that are all stable

Question 37

Define ligand

Answer 37

An electron donor that form a dative covalent bond with a central metal ion/atom

Question 38

Define complex ion

Answer 38

A central metal ion bonded via coordinate bonds to ligands that are either negatively charged, or posses a lone pair of electrons

Question 39

Define monodentate

Answer 39

Ligand forms 1 coordinate bond, donating 1electron pair

Question 40

Define bidentate

Answer 40

Ligand forms 2 coordinate bonds, donating 2 electron pairs

Question 41

Define polydentate

Answer 41

Ligand forms many coordinate bonds, donating many electron pairs

Question 42

Example of bidentate ligand

Answer 42

Ethanedioate, each O- has a lone pair of electrons which can be used to form a coordinate bond with the central metal ion

Question 43

Define ligand substitution

Answer 43

A reaction where one ligand in a complex ion is replaced by another ligand

Question 44

Define precipitation reaction

Answer 44

When 2 ionic aqueous solutions react together, forming an insoluble ionic solid

Question 45

How does iron (II) react with NaOH in a precipitation reaction?

Answer 45

Green solution --> green precipitate

Question 46

How does iron (III) react with NaOH in a precipitation reaction?

Answer 46

Yellow solution --> orange/brown precipitate

Question 47

How does copper (II) react with NaOH in a precipitation reaction?

Answer 47

Blue solution --> blue precipitate

Question 48

How does iron (II) react with NH3 in a precipitation reaction?

Answer 48

Green solution --> green precipitate

Question 49

How does iron (III) react with NH3 in a precipitation reaction?

Answer 49

Yellow solution --> Orange/brown precipitate

Question 50

How does copper (II) react with NH3 in a precipitation reaction?

Answer 50

Blue solution --> blue precipitate

Question 51

How does iron (III) react with excess NH3 in a precipitation reaction?

Answer 51

Blue precipitate --> dark blue precipitate

Question 52

Why do transition metals make good homogeneous catalysts?

Answer 52

They have various oxidation states, meaning they are able to oxidise and reduce reactants and intermediates to form the desired products

Question 53

Why do transition metals make good heterogeneous catalysts?

Answer 53

They can form weak bonds with reactant, using the 3d and 4s electrons, making them more reactive

Question 54

Why are transition metal complexes often coloured?

Answer 54

-When light is incident on an object, some is absorbed -Only absorbed if its energy equals the difference in energies between 2 energy levels of the atom -If it does, an electron becomes excited and is raised to a higher energy level -The difference in energy between the energy levels is equivalent to the frequencies of the visible region of the Em spectrum -So, they often appear coloured

Question 55

What is a colorimeter?

Answer 55

Measures the intensity of light/absorbance of light passing through a solution

Question 56

What is a visible spectrophotometer?

Answer 56

It measures the amount of light transmitted or reflected, when incident on a solution, as a function of wavelength

Question 57

How can you use a colorimeter/visible spectrophotometer to measure the concentration of a transition metal solution?

Answer 57

-Crease a series of solutions of known concentration -Measure their absorptions using suitable apparatus -Create a calibration curve (absorption against concentration) -This curve can then be used to identify unknown concentrations of transition metal solutions by their absorptions

Question 58

Where does oxidation happen in an electrochemical cell?

Answer 58

Less positive side

Question 59

Where does reduction happen in an electrochemical cell?

Answer 59

More positive side

Question 60

Define anode

Answer 60

Where oxidation occurs

Question 61

Define cathode

Answer 61

Where reduction occurs