Topic 13 - Transition Metals, Alloys and Corrosion Flashcards
5.1C - Where are transition metals found and what are their typical uses?
Transition metals are placed in the middle of the periodic table and between group 2 and 3.
Iron is a transition metal that is malleable and strong.
Copper is used for electrical wiring as it is ductile and good conductor of electricity.
Mirrors consist of a sheet of glass coated with aluminium as it is shiny.
A use of transition metal catalysts can be Iron in the Haber process.
5.1C - What are the physical properties of transition metals?
Physical properties - malleable ( can be rolled into shape without shattering ).
ductile ( can be stretched out to make thin wires )
good conductors of electricity
shiny when polished
Compared to other metals in other groups, transition metals have higher melting points and densities.
However there are exceptions, like mercury is liquid at room temperature although it is a transition metal.
5.1C - What are the chemical properties of transition metals?
Chemical properties - Metals in G1 and G2 form white or colourless compounds, however transition metal compounds are usually coloured.
Transition metals and their compounds are catalysts ( increase the rate of reaction without being changed chemically and by mass ).
5.2C - Why do metals corrode?
Corrosion happens when a metal continues so oxidise and become weaker. Rusting is the corrosion of iron or steel.
Oxidation of metals form rust flakes, exposing more metal to air and water, which continues to corrode the metal.
More reactive the metal, the faster it corrodes as it loses electrons quicker.
Metals oxidise and lose electrons when they react with oxygen and other components of the air.
5.3C - How can the surface of iron be protected from rusting?
Exclusion of oxygen - Storing a metal in an unreactive atmosphere of nitrogen or argon prevent rusting as oxygen isn’t present to react.
Exclusion of water - Rusting is prevented when water isn’t present, so using a desiccant powder that absorbs water vapour prevent rusting.
Painting, coating with plastic and oiling also prevent rusting.
Sacrificial Protection - A piece of Mg and Zn is attached to the iron or steel. As the attached material is more reactive the oxygen reacts with them than the iron or steel. This protection continues until the sacrificial metal corrodes away.
Metals may not corrode that much after a tarnish is formed, which is a thin layer of metal oxide preventing further oxidation.
5.4C - What is electroplating and how does it improve appearance, resistance to corrosion and conductivity?
Electroplating is the coating of a less reactive metal on a more reactive metal.
An example of this is with gold, which is electroplated to base metals like copper and nickel producing attractive jewellery which is cheaper than solid gold and improves the appearance of the metal.
Chromium is a metal that is resistant to corrosion, it is electroplated on car parts made of steel, the layer of chromium prevents air and water reacting with the steel under it, preventing corrosion.
Electroplating gold is used in expensive wiring as a tarnish would form on the equipment when unplugged, leading to oxidation. As well as being unreactive, gold is a good conductor.
5.4C - How do you carry out electroplating and explain the half equations at the electrodes?
To electroplate you need:
an anode made from the plating metal
an electrode made from the metal which is being electroplated
an electrolyte, with a solution containing ions of the plating metal (silver nitrate)
An example of this is a copper ring electroplated with silver :
A dc current flows through the electrodes and the electrolyte, the silver ions move to the electrode which is negatively charged.
The silver ions in the electrolyte gain electrons and are deposited as silver atoms on the ring.
At the silver anode - Ag (s) –> Ag+ (aq) + e-
At the copper cathode - Ag+ (aq) + e- –> Ag (s)
5.4C - What is galvanising and tin plating and how does it stop rusting?
Galvanising is the process of coating iron and steel objects with zinc. The thin layer of zinc resists corrosion as a sacrificial metal by stopping water and air reaching the metal.
Galvanising can be done by electroplating or dipping the object in molten zinc.
Food cans made of steel has tin electroplated on its inner surface to stop it from rusting.
Tin doesn’t react with air or water so protects the steel, but if damaged the steel will rust faster. This is because iron in the steel reacts with water and air.
5.5C - What are alloys and why does make the metal stronger?
An alloy is a mixture of different metal elements.
Alloy steels are stronger than pure metals they contain because in a pure metal like iron the atoms are all the same size and arranged regularly, meaning they can move past eachother making it malleable and ductile.
Alloys have other elements present, which distorts its regular structure making it difficult for the layers of atoms to slide over eachother, making alloys stronger than pure metals.
5.6C - Why is iron alloyed with other metals to produce alloy steels?
Alloy steels are made by adding other metals to iron, it can help reduce rusting by adding stainless steels like chromium which react with oxygen to form a layer of tarnish called chromium oxide, which is thick enough to prevent air and water from reaching the metal below and thin enough to be transparent.
Some alloy steels are strong and tough, so are used in drill bits and other tools. Alloys with high carbon content usually are stronger and used in these tools.
Mild steel has low carbon content and manganese for more strength while having malleability. This is used in building and cars.
Stronger steels with higher carbon content is less malleable but they can be pressed into shape with high force, making it useful for cars.
5.7C - What do the uses of metals and alloys depend on?
They depend on the properties of it, including :
chemical properties ( like corrosion resistant )
physical properties ( like ability to conduct electricity )
5.7C - What are some common uses of aluminium, copper and gold?
Copper and gold are used in electrical wiring as they both are resistant to corrosion and are malleable, ductile and good conductors of electricity.
However gold is very expensive, so used in tiny amounts for microprocessors, while copper is used for most wiring as it is cheap.
Aluminium resists corrosion but doesn’t conduct electricity as well as copper, this can be solved by wrapping more wires around one another making it more conductive.
However aluminium is stronger, cheaper and less dense making it useful in electrical cables.
5.7C - Why are different metals and alloys chosen for different uses?
Alloys like brass may be chosen rather than the metals copper and zinc it contains because copper and brass resist corrosion but brass is stronger, making it useful for plugs.
Another alloy is magnalium, which contains 95% aluminium and 5% magnesium. It is used in aircraft parts as it is less dense than its metals, much stronger and more resistant to corrosion this makes it strong but lightweight.
