Developing Metals

?
  • Created by: LBCW0502
  • Created on: 22-03-17 09:42
Name three metals which are found native
Gold, silver and copper
1 of 148
Name the uses of these native metals
Used in early art (and religious art), tools, money
2 of 148
Why were native metals used for the coinage bartering system?
Native metals have a lack of reactivity - relative ease of working
3 of 148
What does the term 'karat' mean?
Refers to the amount of gold in a particular item (measured in units of 24, where 24 karat gold is pure gold)
4 of 148
What does the d-block consist of?
Three horizontal series in Period 4, Period 5 and Period 6 with each series containing 10 elements
5 of 148
Describe the changes in the atomic structure of the elements across the first row in the d-block
Across the first row of the d-block each element has one more proton in the nucleus and one more electron than the previous element. Each additional electron enters the 3d shell (this is not the outermost shell because the outer 4s orbital is filled)
6 of 148
What is the core of the electron configuration for the transition elements?
The core is the electron configuration of the noble gas argon (Ar)
7 of 148
How is the electronic arrangement in the transition elements similar?
They have the same outer electronic arrangement as each other in the same way as elements in a vertical group all have the same outer shell structure
8 of 148
How do the transition elements differ in terms of electronic configuration?
They do not differ by a complete electron shell but by having one more electron in the inner, incomplete 3d sub-shell
9 of 148
Which elements do not fit the general patten in terms of electronic configuration in the first row of the d-block?
Copper and chromium
10 of 148
In the ground state of an atom, how are electrons always arranged?
Electrons are arranged to give the lowest total energy. Due to the negative charge, electrons repel one another so a lower total energy is obtained with electrons singly in orbitals rather than being paired in an orbital
11 of 148
Explain why two elements in the first row of the d-block do not first the patten for electronic configuration
In Cr, the orbital energies are such that putting one electron in each 3d and 4s orbital gives a lower energy than having two in the 4s orbital. With Cu, putting two electrons in the 4s orbital would give a higher energy than filling 3d orbitals
12 of 148
During ion formation, the electrons are lost from which orbitals?
4s orbitals
13 of 148
What are transition metals?
Metals which form one or more stable ions with partially filled d-orbitals
14 of 148
The range of oxidation states a transition metal can form depends on what?
The ability to lose 4s and 3d electrons
15 of 148
Why are Zn and Sc not considered to be transition metals?
Zinc only forms a 2+ ion with a completely filled d orbital. Sc only forms a 3+ ions with an empty d-orbital. Zn and Sc are not transition metals but are classified as d-block elements
16 of 148
Why can transition metals exist in a number of oxidation states?
There are several stable arrangements of the d-electrons and s-electrons (explains why copper forms a Cu+ ion and why Fe3+ has a greater stability than the Fe2+ ion)
17 of 148
How can iron content by analysed?
Using redox titration (this type of analysis depends on the variable oxidation states of the transition metals involved in the reactions)
18 of 148
Describe the chemical detail in a redox titration with iron and acidified potassium manganate (VII)
Iron (II) ions can be oxidised to iron (III) ions by potassium manganate (VII) in acidic solution
19 of 148
How do you know when the end point is reached?
If a known volume of iron (II) solution is titrated with potassium manganate (VII) solution of known concentration, the end point is when the first permanent pink colour is observed - when MnO4- (aq) is in excess
20 of 148
Why is no additional indicator required in the redox titration?
A colour change takes place when the end point is reached (colourless to pale pink)
21 of 148
Which alternative reducing agent can be used in the redox titration with iron (II) ions?
Acidified potassium dichromate solution
22 of 148
Describe the uses and properties of the element silver
Silver has antimicrobial properties (keeps water clean, prevents transmission of gonorrhoea, keeps milk fresh, wound dressings). Silver catalyses reactions in the cell walls of bacteria, resulting in the formation of disulfide bonds (prevent growth)
23 of 148
Give four uses of the catalytic properties of transition metals
Hydrogenation of alkenes (Ni or Pt), manufacture ammonia by Haber process (Fe), manufacture sulfuric acid (V2O5) and alloys of Pt, Rh, Pd used in car catalytic converters
24 of 148
What is a catalyst?
A substance which speeds up the rate of reaction by providing an alternative route with a lower activation energy. It is not used up in the process and remains chemically unchanged. Transition metals/compound are used in industry/biological systems
25 of 148
Describe heterogeneous catalysis (1)
The catalyst is in a different phase from the reactants (solid metal catalyst, gas phase or liquid phase)
26 of 148
Describe heterogeneous catalysis (2)
Transition metals can use 3d and 4s electrons of atoms on the metal surface to form weak bonds (chemisorption) to reactants. Once reaction has occurred, bonds break to release products
27 of 148
Give an example of heterogeneous catalysis
Manufacture of sulfuric acid catalysed by vanadium (V) oxide
28 of 148
Describe homogenous catalysis
Catalyst is in the same phase as the reactants (aqueous phase - transition metal ion)
29 of 148
Give an example of homogeneous catalyst
Reaction between 2,3-dihydroxybutanoate ions and hydrogen peroxide, which is catalysed by cobalt (II) ions
30 of 148
Describe the mechanism for the catalytic action of Co 2+
Reactants are combined (pink). Co 2+ reduce H2O2 and gets oxidised to Co 3+. Green intermediate formed. Co3+ oxidises 2,3-dihydroxybutanoate and gets reduced to Co 2+. Products are CO2, methanoate, H2O and Co2+ (pink)
31 of 148
Why are transition metal ions effective catalysts in redox reactions?
They can move readily from one oxidation state to another (e.g. Co2+ to Co3+)
32 of 148
What is Raman Spectroscopy?
A non-sampling, non-invasive and non-damaging spectroscopic and analytical technique. Used to identify pigments used in fragments of potters
33 of 148
Describe the process of Raman Spectroscopy
A single wavelength of coloured light from a laser source is shone upon a material. Majority of light bounces off the sample with the same energy (same colour). A tiny fraction comes off at different frequency and loses energy (different colour)
34 of 148
How is the Raman Spectra analysed?
By examining the difference between the light that goes in and the light that comes back, it is possible to identify the absorbing substance e.g. particular pigment used by an artist
35 of 148
Describe the appearance of compounds of d-block transition metals
Frequently coloured both in solid state and in solution (intensity of colour varies e.g. MnO4-)
36 of 148
What is the colour of transition metal compounds related to?
The presence of unfilled or partly filled d-orbitals in the metal ion
37 of 148
What are the colours of the following ions: Fe2+, Fe3+, Cu+ and Cu2+?
Green, orange/brown, Cu+ is unstable in aqueous solution and Cu2+ is blue
38 of 148
Describe the quantitative analysis used on transition metal compounds
Addition of drops of NaOH (aq) or ammonia solution to solutions containing transition metal ions can result in coloured precipitates forming
39 of 148
What colour precipitate is Fe(OH)2?
Green (gelatinous)
40 of 148
What colour precipitate is Fe(OH)3?
Orange/brown (gelatinous)
41 of 148
What colour precipitate is Cu(OH)2?
Pale blue
42 of 148
What would happen to Cu(OH)2 if the source of OH- ions was ammonia solution?
The pale blue precipitate would re-dissolve on addition of excess ammonia solution to give a deep blue-purple solution (copper/ammonia complex ion). Neither iron hydroxides form complexes with ammonia so they do not re-dissolve
43 of 148
What happens when a d-block compound absorbs light?
Light is absorbed if it matches energy gap between two energy states. Electrons become excited when radiation is absorbed
44 of 148
What does the frequency of light depend on?
The energy difference between two energy levels
45 of 148
What does the presence of ligands cause?
Orbitals split in such a way they some are slightly higher in energy than others. ΔE is now such that light absorbed falls in visible region (coloured)
46 of 148
What are complementary colours?
Colours opposite each other in the colour wheel (when one colour is absorbed, the complementary colour is reflected)
47 of 148
Give examples of ligands
H2O, NH3, CN-, OH- and halide ions
48 of 148
How do ligands attach themselves to the central ion?
By using a lone pair of electrons to form a dative or coordinate bond
49 of 148
What are monodentate ligands?
Ligands which form one dative bond to the central metal ion e.g. CN-, OH-
50 of 148
What are bidentate ligands?
Ligands which form two dative bonds to the central metal ion e.g. 1,2 diaminoethane, ethylenediamine
51 of 148
What is a hexadentate ligand?
Ligand which forms six dative bonds e.g. EDTA
52 of 148
Describe how ligands affect d-orbital electrons of the metal ion
Orbitals close to the ligands are pushed to slightly higher energy levels than those further away. 5 d-orbitals are split into two groups at two different energy levels
53 of 148
The energy needed to excite a d-electron to a higher energy level depends on what?
The oxidation state of the metal
54 of 148
What is a ligand substitution reaction?
Some ligands have a more powerful effect than others in splitting the d-sub-shell. So changing the ligand complexed with a metal ion often results in a colour change
55 of 148
What are the three factors does the colour of a transition metal complex depend on?
The number of d-electrons present in the transition metal ion, the arrangement of ligands (affects splitting of d-sub-shell) and the nature of the ligand (have different effects on relative energies of the d-orbitals in a particular ion)
56 of 148
From the complexes of chromium, the colour also depends on which factor?
The number of each kind of ligand present
57 of 148
Which technique can be used to measure the concentration of a coloured solution?
Colorimetry (the more concentrated the solution, the darker the colour and the more light is absorbs)
58 of 148
Describe the process of colorimetry
A narrow beam of white light is passed through a coloured filter (complementary colour that is most strongly absorbed by the solution)
59 of 148
What is the absorbance (A) proportional to?
The concentration of the solution (c)
60 of 148
For dilute solutions, what is the direct relationship between absorbance and concentration?
A = kc (k -constant, the concentration of a solution increases and the absorbance increases linearly)
61 of 148
Which alternative equipment can be used to measure the concentration of the solution?
A visible spectrophotometer
62 of 148
State the uses of metals in dentistry
Dental amalgam, manufacture of crowns and bridge restorations
63 of 148
What is the issue with using metals in dentistry?
Metals with saliva serving as the electrolyte can cause a shock to teeth
64 of 148
What are the several types of galvanism?
Silver/mercury filling placed by a tooth restored to gold, dissimilar metals in contact with upper/lower teeth, two adjacent teeth restored with dissimilar metals
65 of 148
What is the main principle of an electrochemical cell?
At one side of the cells (anode/negative terminal) electrons must be released and at the other (cathode/positive terminal) electrons must be gained
66 of 148
Why must an electrolyte be present?
To allow the movement of ions
67 of 148
Give an example of a primary cell
Zinc/Copper cells - not rechargeable
68 of 148
Give an example of a modern cell
Lithium ion cell - uses d-block compounds
69 of 148
What is a displacement reaction?
A more reactive element displaces a less reactive element in a compound e.g. zinc replaces copper in copper sulfate to form zinc sulfate and copper
70 of 148
What are spectator ions?
Ions which do not take part in the reaction (not in the overall ionic equation)
71 of 148
In a reaction between zinc and copper (II) ions, which reagent acts as the reducing agent?
Zinc acts as the reducing agent (Zn becomes oxidised to Zn 2+)
72 of 148
In a reaction between zinc and copper (II) ions, which reagent acts as the oxidising agent?
Copper (II) ions acts as the reducing agent (Cu2+ is reduced to Cu)
73 of 148
What happens when zinc sulfate is added to copper?
No reaction takes place
74 of 148
What happens when copper is added to silver nitrate (V) solution?
A grey precipitate is formed (Ag) and the solution turns from colourless to blue
75 of 148
What happens when silver is added to copper (II) sulfate?
No reaction takes place
76 of 148
What are the two methods to balance redox equations?
Balance using oxidation states and electron transfer method
77 of 148
Describe how to balance redox equations using oxidation states
Balance the oxidation states on either side of the equation, balance the number of atoms and then balance the charge on either side of the equation
78 of 148
Describe how to balance redox equations using the electron transfer method (1)
Form two half equations (oxidation and reduction), balance the number of atoms in each half equation, balance the charges in each half equation (use electrons), make sure there are the same number of electrons in each half equation.
79 of 148
Describe how to balance redox equations using the electron transfer method (2)
Combine the two half equations and cancel out the electrons
80 of 148
Describe the general arrangement for an electrochemical cell
Two half reactions occur separately with electrons flowing through an external wire from one half-reaction to the other. This system is used to batteries and dry cells
81 of 148
Describe the processes occurring in the general arrangement of the electrochemical cell
In one part of the cell, an oxidation reaction occurs. Electrons are produced and transferred through an external circuit to the other part of the cell, where reduction takes place and accepts electrons. Two half cells form an electrochemical cell
82 of 148
What is electric charge measured in?
Coulombs (C)
83 of 148
What is an electric current?
A flow of charge (measured in amperes - A). One ampere is a flow of charge of one coulomb per second
84 of 148
What is potential difference?
A measure of how each electrode is tending to release or accept electrons
85 of 148
What is potential difference measured in?
The potential difference between the terminals of the cell is measured in volts (V). The voltage of the cell tells you the number of joules of energy transferred whenever one coulomb of charge flows round the circuit (1 V = 1 JC^-1)
86 of 148
What happens to the energy given out?
The energy given out, instead of heating the surroundings, becomes available as electrical energy which is used to do work
87 of 148
What happens when a current flows in a circuit?
The voltage can drop - the higher the current drawn, the lower the voltage the cell may give
88 of 148
How can you compare and measure half-cells?
You can measure the potential difference between the terminals of the cell when no current flows (Ecell). To measure Ecell, a high-resistance voltmeter is used (zero current). The max potential difference between electrodes is recorded
89 of 148
How do you set up a simple half cell?
Use a ***** of metal and dip it into a solution of metal ions e.g. copper-zinc cell consists of two half cells. Zn is oxidised and Cu is reduced
90 of 148
The position of the equilibrium determines what?
The size of the potential difference between the metal ***** and solution of metal ions. The further to the right the equilibrium, the greater the tendency of the electrode to accept electrons and the more positive the electrode potential
91 of 148
How do you determine with half cell is positive and which half cell is negative?
When two half-cells are put together, the one with the more positive potential will become the positive terminal of the cell and the other one will become the negative terminal
92 of 148
Describe the formation of an electrochemical cell from two half-cells
A connection is needed between the solutions without the solutions mixing. A ***** of filter paper soaked in saturated potassium nitrate (V) solution can be used as a salt bridge
93 of 148
What is an ion bridge?
A junction between the half-cells. The circuit is completed by the movement of ions. Potassium and nitrate (V) ions carry the current in the salt bridge so there is electrical contact between the solutions but no mixing
94 of 148
What are the standard conditions for the standard hydrogen half-cell (standard hydrogen electrode)?
Concentration of hydrogen is 1 mol dm^-3 (concentration affects voltage), pressure of hydrogen gas is 10^5 Pa and temperature of 298K (electrode potentials vary with temperature). A platinum electrode is used
95 of 148
What is the standard hydrogen half-cell used for?
As a reference half-cell and all other half-cells are measured against it
96 of 148
What is the standard electrode potential of a half-cell E^o?
The potential difference between the half-cell and a standard hydrogen half-cell. E^o values have a sign depending on whether the half-cell is at a higher/lower positive potential than the standard hydrogen half-cell
97 of 148
What is the electrochemical series?
A list of redox equilibria arranged in order to electrode potential (most negative at the top to most positive at the bottom). The more negative the electrode, the greater the tendency to be oxidised
98 of 148
Give examples of other metal ions in half-cell reactions
Iron (III) ions, dichromate ions, manganate (VII) ions
99 of 148
How do you calculate Ecell?
Postive electrode - negative electrode
100 of 148
What are the uses of the table of standard electrode potentials?
Can be used to calculate the maximum voltage obtainable from any cell under standard conditions. Can be used to predict reactions and direction of redox reactions
101 of 148
What are electrode potential charts?
A useful way to display and use data. They can be used to make predictions about the direction of a particular redox reaction will take. Feasibility of redox reactions can be predicted (not rate of reaction)
102 of 148
What does a slow reaction indicate?
There is a high activation enthalpy (requires a catalysts). If you predict from electrode potentials that the reaction is not possible, no catalyst will make it happen (electrons can't spontaneously flow from the positive to negative terminal)
103 of 148
If it is predicted that a reaction is not feasible under standard conditions, what could you do to make the reaction feasible?
Change the conditions to alter the values of the electrode potentials
104 of 148
How do electrode potentials vary with concentration? (use hydrogen and hydroxide ions as an example)
E.g. if hydrogen or hydroxide ions are involved then pH changes will change the electrode potentials (reactions may become possible)
105 of 148
How can you use the electrochemical series to find the direction of redox reactions?
Follow the anti-clockwise direction (from top right to bottom right)
106 of 148
Are metal oxides more stable than metals?
Yes
107 of 148
What kind of conditions are required to extract a metal from its ore?
Lots a energy with high temperatures needed in the blast furnace
108 of 148
What is rusting?
The corrosion of iron
109 of 148
What are the half-reactions involved in rusting?
Oxidation of Fe to Fe (II) ions and the reduction of oxygen to hydroxide ions
110 of 148
Which half-reaction occurs at the more positive potential?
The reduction of oxygen to hydroxide ions
111 of 148
Which half-reaction occurs are the more negative potential?
The oxidation of Fe to Fe (II) ions
112 of 148
What determines the regions of the metal surface as sites of reduction or sites of oxidation?
The concentration of dissolved oxygen in the water droplet
113 of 148
At edges of the water droplet, is the concentration of dissolved oxygen higher or lower?
Higher - this means that oxygen is reduced to hydroxide ions
114 of 148
Where do the electrons needed to reduce oxygen come from?
The oxidation of iron at the centre of the water droplet
115 of 148
At the centre of the water droplet, is the concentration of dissolved oxygen higher or lower?
Lower
116 of 148
Why is corrosion always greatest at the centre of a droplet of water or under a layer of paint?
These are the regions where the oxygen supply is limited. Pits are formed here where the iron has dissolved away
117 of 148
Describe the secondary processes rust forms
Fe (II) ions and OH- ions diffuses away from the metal surface. They react to form Fe(OH)2 which reacts with oxygen to form a hydrated form of iron (III) oxide. It does not form as a protective layer in contact with the iron surface
118 of 148
Why is zinc used as a sacrificial metal?
It is a metal with a more negative value (Ecell) than iron. Zn half-reaction takes place from left to right, forming Zn2+ and 2e-. This shifts position of the iron half-reaction equilibrium to the right, effectively preventing the formation of Fe2+
119 of 148
Why is tin not used as a sacrificial metal to protect steel?
The less negative standard electrode potential of the tin half-reaction would mean that the Fe/Fe 2+ half-reaction would release electrons (go from left to right)
120 of 148
Why is chromium used to form a protective layer?
The standard electrode potential of the chromium half-reaction is negative. When chromium atoms are in contact with oxygen at the surface of stainless steel, it forms a protective layer of chromium (III) oxide
121 of 148
What is the simplest way of protecting steel against rust?
Provide a barrier between the metal and the atmosphere e.g. oil, grease or a coat of paint
122 of 148
Barriers are made from which type of material?
Organic polymers. Steel is coated with a plastic film (colourful/flexible). Sometimes iron is covered with a thin layer of another metal
123 of 148
What is galvanised steel?
It has a protective coating of zinc. As long as the galvanised surface remains undamaged, the zinc layer is protected from corrosion by a firmly adherent layer of zinc oxide.
124 of 148
Why is protection still maintained if the coating is scratched?
The zinc corrodes in preference to the iron - zinc is being used as a sacrificial metal
125 of 148
Give an example of the use of sacrificial metals
Protect metal sheathing on sailing ships from corrosion, used on car bodies (rusting problem is postponed, not eliminated)
126 of 148
Destruction oxidation of a metal occurs at which electrode site?
Anode site
127 of 148
Any technique that makes a metal a cathode site will ensure what?
That reduction occurs on that cathode surface and therefore ensures the metal is protected from corrosion
128 of 148
Apart from attaching sacrificial anode metals, what is an alternative way of protecting a metal?
Make the metal a cathode by supplying electrons to it by application of an emf from an external electrical source. This technique is used for protecting bridges, piers, pipelines, underground fuel tanks etc.
129 of 148
Using an impressed current to protect metal structures is another form of what?
Cathodic protection
130 of 148
What needs to be connected to the metal in order for it to be protected?
The negative terminal of a battery or DC power supply (electrons flow from anode to cathode)
131 of 148
What is the anode used in this technique?
An inert electrode which is corrosion-resistant and rather than the anode being oxidised, water is oxidised
132 of 148
Impressed current (applied emf) - underground steel pipeline
Consider an underground steel pipeline passing through moist soil where sufficient oxygen is present to result in severe corrosion to the pipe. An impressed current/applied emf technique would prove an ideal method of protecting the pipe
133 of 148
What does a complex consist of?
A central metal atom or ion surrounded by a number of negatively charged ions or neutral molecules possessing a lone pair of electrons (ligands). A complex may be charged (+/-) or neutral
134 of 148
What happens if a complex is charged?
It is called a complex ion - the overall charge is the sum of the charge on the central metal ion and the charges on the ligands. Charges on a complex ion are delocalised over the whole ion
135 of 148
In a complex, which atoms are electron donors?
The ligands
136 of 148
What type of bonding takes place in a complex?
Dative bonds (coordinate bonds)
137 of 148
What does the term 'coordination number' mean?
The number of bonds from the central ion to ligands
138 of 148
What are the most common coordination numbers?
Six and four (but two does occur e.g. in complexes of Ag (I) and Cu (I)
139 of 148
What does the shape of a complex depend on?
The coordination number
140 of 148
Complexes with a coordination number of six have what kind of shape?
An octahedral arrangement of ligands around the central metal ion
141 of 148
Complexes with a coordination number of four have what kind of shape?
A tetrahedral arrangement of ligands around the central metal ion or a square planar structure
142 of 148
Complexes with a coordination number of two have what kind of shape?
A linear arrangement of ligands
143 of 148
Give an example of a distorted/irregular shaped complex
[Cu(H2O)6]2+ - four water ligands are held more strongly than the remaining two, so that four of the copper-oxygen bonds are shorter. This produces a distorted octahedral arrangement
144 of 148
Give examples of a polydentate ligand
Ethanedioate ion and the 1,2-diaminoethane molecule are both bidentate ligands (form two bonds with a metal ion using electrons from two oxygen or nitrogen atoms). The metal ion is held in a five-membered ring (chelate ring). EDTA4- (hexadentate)
145 of 148
What happens when copper sulfate is dissolved in water?
The copper ions form a complex with a coordination number of six
146 of 148
What is a ligand substitution reaction?
One ligand displaces another. They only occur if the new complex formed is more stable than the previous complex - e.g. add c.HCl to [Cu(H2O)6]2+ then Cl- ions will displace the water ligands and the [CuCl4]2- complex forms
147 of 148
Which other type of molecule can displace water ligands in the complex?
Ammonia (add c.NH3 (aq) to complex ion) - the complex ion of copper (II) with ammonia ligands is more stable than with water ligands
148 of 148

Other cards in this set

Card 2

Front

Name the uses of these native metals

Back

Used in early art (and religious art), tools, money

Card 3

Front

Why were native metals used for the coinage bartering system?

Back

Preview of the front of card 3

Card 4

Front

What does the term 'karat' mean?

Back

Preview of the front of card 4

Card 5

Front

What does the d-block consist of?

Back

Preview of the front of card 5
View more cards

Comments

No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all Developing Metals resources »