Electolytic Process, Obataining And Using Metals, Etc Flashcards
What is an electrolyte?
When an ionic solid is melted or dissolved in water, it’s ionic bonds break. This allow the ions to move. An ionic substance with freely moving electrons is called an electrolyte
What is electrolysis?
The process in which energy transferred by a direct electrical current decomposes electrolysis, it is used to brea down many substances
What is used in electrolysis?
Energy transferred by electricity to decompose electrolytes. Two electrodes are connected to a direct current (d.c) electricity supply and placed into the electrolyte. The two types of ions carry opposite charges and so migrate (move) towards the electrode with the opposite charge
What are cations?
Positive ions and are attracted to the negative cathode
What are anions?
Negative ions and are attached to the positive anode
What is oxidation?
Loss of electrons or gain of oxygen
What is reduction?
Gain of electrons or loss of oxygen
Where does reduction take place?
At the cathode
Where does oxidation take place?
At the anode
Show a cathode reaction
Zn + 2e ➡️ Zn
Show an anode reaction
2Cl ➡️ Cl + 2e
How is the electrolysis of molten or dissolved ionic salts carried out?
Using inert (unreactive) electrodes (usually graphite or platinum). When a molten salt is electrolysed, ions are discharged as atoms or molecules at the electrodes. When molten lead bromide is electrolysed, bromine is produced at the anode and lead is produced at the cathode
How can you predict the electrolysis products of any molten salt?
The salt will always decompose into its elements. The metal is produced at the cathode and the non-metal is produced at the anode
explain electrolysis of salt solutions using copper chloride as an example
At the cathode Cu 2+ and H+ ions are attracted. Copper ions are dirchsrged more readily tau. Hydrogen ions, so copper is formed as a brown solid.
At the anode Cl- and OH- ions are attracted. Chloride ions are discharged more readily than hydroxide ions, so chlorine is formed as a pale green gas. Overall the copper chloride decomposes but the water does not change
During the electrolysis of water acidified with dilute sulfuric acid what happens?
Water decomposes to form hydrogen and oxygen
How can copper be purified by the electrolysis of copper suk fate solution using copper electrodes?
The copper atoms in the anode lose electrons to be come copper ions. These dissolve in the solution and migrate to the cathode, where they are deposited as pure copper. Impurities from the anode do not from ions and collect below the anode as a sludge
What is the reactivity series?
A list of mental in order of reactivity, within the most reactive at the top
List the reactivity series
Potassium Sodium Calcium Magnesium Aluminium Zinc Iron Copper Silver Gold
The higher the metal is in the reactivity series, the mire easily…….
A metals atom loses eke robs
Metal atoms lose electrons to from what?
Positive ions
How can we use the reactivity series to predict whether reactions will take place?
Each metal will react with compounds of the metals below it in the series
What cannot copper displace zinc from its compounds!
Because copper is less reactive
What is a displacement reaction?
When a more reactive element displaces a less reactive element from one of its compounds
What is a redox reaction?
A reaction in which one substance is oxidised and another is reduced
What is an ore?
A rock that contains enough of a compound to extract a metal for profit.
More reactive metals have reacted with other elements to for, compounds in rocks. What is extraction?
The process of obtaining a metal from these compounds
Name some very unreactive metals found naturally in their native state as unconfined elements?
Gold and platinum
Metals higher than carbon must be extracted using a more powerful method called electrolysis. What does this involve?
Passing electricity through a molten ionic compound to decompose it into its elments
Why is electrolysis only used to extract very reactive metals that cannot be obtained by heating their oxides with carbon?
Because a lot of energy is needed to keep metal oxides molten for electrolysis, making it very expensive
What is bioleaching?
Uses bacteria grown on a low grade ore. The bacteria produce a solution containing copper ions, called leachate. Copper is extracted from the leachate by displacement using scrap ion, then purified by electrolysis. This method can also be used for metals such a nickel, cobalt and zinc
What is phytoextraction?
It involves growing plants that absorb metal compounds. The plants are burnt to for ash, from which metal is extracted
What are the advantages and disadvantages of bioleaching?
Does not require high temperature but toxic substances and suburbia acid can be produced by the process and damage the environment
What are the advantages and disadvantages of phytoextraction?
It can extract metals from contaminated soils but it’s more expensive then mining some ores and growing plants is dependent on weather conditions
What are the advantages and disadvantages of both bioleaching and phytoextraction?
No harmful gases are produced, it causes less damage to the landscape than mining and conserve supplies of higher grade ores, but they are very slow
When do oxidation and reduction always occur?
Together, is one substance is oxidised, another will be reduced
When does corrosion happen?
When a metal reacts with oxygen, making the metal weaker over time. The metal gains oxygen so it is oxidised. The corrosion of room requires water as well as oxygen and is called rusting. The more reactive a metal is,none faster it corrodes. Gold does not corrode at all, which is one of the reasons it’s used in jewellery
What is tarnish?
Some metals, such as aluminium are quite reactive and would be expected to corrode quickly. However they do not corrode because their surfaces form a protective oxide layer (a tarnish), which prevents further reaction
How can many metals be recycled?
By melting them down and making them into something new
What are the main advantages of recycling metals?
Natural reserves of metals ogres will last longer
The need to ins will be reduced. Mining can damage the landscape as well as create noise and dust pollution
Less pollution be be reduced
Many metals need less energy to recycle the, then to extract new metals for the ore
Less waste metal ends up in landfill sites
What are the disadvantages to recycling metals?
The costs and the energy using in collecting, transporting and sorting metals to be recycled. Sometimes it can be more expensing and require more energy to recycle than to extract a new metal
What can a life cycle assessment (LCA) be carried out for?
To work out the environmental impact of a product. It also helps people decide whether it is worthwhile to manufacture and recycle a product. LCAs can be used to compare the effect of using different materials for the same product.
What are the 4 stages of the life cycle assessment?
Obtaining and processing raw materials
Manufacturing and packaging the product
Using the product
Disposal of product
In some chemical reactions the reactions the products react to reform the reactants. What are these?
Reversible reactions
What is dynamic equilibrium?
When the forwards and backwards reactions in a reversible chemical reaction are occurring at the same rate
What is the double arrow used to show?
Used to show that both forward and backward reactions occur at the same time
What is the haber process?
An industrial process for producing ammonia leak from nitrogen and hydrogen, using an iron catalyst at high temperature and pressure
How is ammonia manufactured?
By the haber process, involves a reversible reaction between nitrogen (from the air) and hydrogen (from natural gas) that can reach a dynamic equilibrium. The equilibrium positions changes by the reaction conditions. In the haber process, and all similar industrial reactions, the reaction conditions are chosen to favour the forward reaction and make a large amount of product as cheaply as possible
What are the conditions in the haber process?
The temperature is 450 degrees C, a pressure of 200 atmospheres and the use of a iron catalyst
The equilibrium position can be altered in temperature, pressure and concentration. I general, the equilibrium position shifts to reduce the effects of any changes to the system. What are the effects of these changes?
Increasing temperature - in the endothermic direction (transferring energy from the surroundings, cooling them down)
Decreasing temperature - in the exothermic direction (transferring energy to the surroundings, heating them up)
Increasing gas pressure - in the direction that forms fewer gas molecules (as this increases pressure)
Decreasing gas pressure - in the direction that forms more gas molecules (as this increases pressure!
Increasing a concentration - in the direction that uses up the substance that has been added
Decreasing a concentration - in the direction that forms more if the substance that has been removed
What are transition metals?
These elements are placed in the central block of the periodic table, between groups 2 and 3. The transition metals include most of the metals used for construction, vehicles, electrical wiring, jewellery and other every day uses
What are the physical properties of transition metals?
Malleable (they can be hammered or rolled into a shape without shattering
Ductile (they can be stretched out to make thin wires)
Good conductors of electricity
Shiny when polished
High melting points
Why does iron have the typical properties of transition metals?
Iron is strong and malleable. And iron is a catalyst
What are the chemical properties of transition metals?
Transition metals are usually coloured, different transition metal hydroxides are different colours
Transition metals usually show catalyst activities
What do catalysts do?
Catalysts increase the rate of reaction without being changed either chemically or in mass at the end if a reaction
When metals react with oxygen in the air they oxidise to form what?
To form metal oxide
How fast do very reactive metals like sodium oxidise when they are freshly cut?
Rapidly
How fast do less reactive metals like silver oxidise?
Slowly. Gold and other very unreactive metals may not react with oxygen at all
When may metals form a thin layer of tarnish?
When they oxidise. This layer stops oxygen reaching the metal, preventing further oxidation
When does corrosion happen?
When a metal continues to oxidise and so the metal becomes weaker over time
What is rusting?
The corrosion of iron or steel (which is mostly iron). Iron rusts whe. It reacts with oxygen and water
How can rusting be prevented?
It can be prevented if air is kept away. This can be achieved by storing the metal in an unreactive atmosphere of nitrogen or argon. Rusting can also be prevented if water is kept away, for example using desiccant powder that absorbs water vapour. Other methods of rust prevention keep both air and water away, including painting, coating with plastic, oiling and greasing
What is sacrificial protection?
It is a method of rust prevention that does not rely on keeping air or water away. Instead, a piece of magnesium or zinc is attached to the iron or steel object. Magnesium and zinc oxidise more easily than iron, so oxygen reacts with them rather than with the iron or steel object. This protection continues until the sacrificial metal corrodes away
What does electroplating do?
Electroplating coats the surface of one metal with a thin layer of another metal. Silver and gold are attractive transition metals but they are expensive. Silver or gold can be electroplated onto cheaper base metals such as copper or nickel. This produces attractive jewellery that is cheaper than silver or gold. Electroplating may also be used to improve an,teals objects ability to resist corrosion.
What do you need to electroplating a metal object?
You need an anode made from the plating metal
An electrolyte, which is a solution containing ions of the plated metal
A cathode, which is the metal object itself
Describe how you could electroplate a copper ring with silver
A direct current (d.c.) flows through the electrodes and the electrolyte. Silver ions in the electrolyte move to the negatively charged copper ring. They gain electrons and are deposited as silver atoms. At the silver anode, silver atoms lose electrons to become silver ions, which go to the electrolyte. The longer the current flows, the thicker the silver layer on the ring becomes.
Go to page 101
And look at the electroplating diagram
Iron and steel objects can be protected from rusting by coating them with zinc. What is this called?
Galvanising. This improves corrosion resistance by stopping the water reaching the iron or steel and by acting as a sacrificial metal, this sacrificial protection can continue even is the zinc layer is damaged. Galvanising can be carried out using electroplating, or by dipping the object in molten zinc.
Food cans are made from steel. Their inner surface is protected from rusting by electroplating with tin. Tim does not react with air or water at room temperature. The tin layer stops air and water reaching the steel. However if the tin layer is damaged what will happen?
The steel can will rust faster. This is because iron is more reactive than tin, so it acts as a sacrificial metal to protect the tin.
What is an alloy?
An alloy is a mixture of a metal element with one or more other elements, usually metals.
How are alloy steels made?
By deliberately adding other elements to iron.mit is possible to create a huge range of alloy steels with different properties by varying their composition
What does stainless steels do?
They resist rusting, unlike other alloy steels and iron. Stainless steels contain cranium, which reacts with oxygen in the air. A layer of chromium oxide forms. This is thick enough to stop air and water reaching the metal below, but thin enough to be transparent.
What are alloys often stronger than?
The pure metals they contain
Why is iron alloyed with other metals?
Pure iron is too soft for everyday use, but wrought iron is stronger even though it contains only a small amount of other elements. Alloy steels are even stronger than wrought iron
In solids pure metal atoms are the same size and are arranged in regular layers, if enough force is applied these layers slide past each other, this is why metals are malleable and ductile. Why is this different for alloys!
In an alloy, the atoms of other elements present may be different sizes. They distort the regular structure, making it more difficult to slide past each other. This is why alloys are often stronger than pure metals, even though they are still malleable and ductile.
What are the properties of metals/alloys?
Chemical properties, such as resistance to corrosion
Physical properties, such as density and ability to conduct electricity
What can gold a copper be used for?
Electrical wiring, but cost may also be an important factor. Gold is thousands times more expensive than copper. So copper is chosen for most electrical wiring, while gold is used in tiny amounts to connect microprocecessors and memory chips
What is aluminium used for?
Overhead electrical cables, because it is stronger, cheaper, less dense and resists corrosion, but doesn’t conduct electricity
Explain why different metals and their alloys have different uses
Alloys have more useful properties than the metals they contain e.g. Brass is an alloy of copper and zinc. Copper and brass resist corrosion, copper is a better conductor of electricity than brass, but brass is stronger. This makes brass more suitable than copper for making electrical plug pins
