Unit 9 - Metals Flashcards
Reason for electrical conductivity in metals
Presence of delocalized electrons which can conduct electricity
Reason for thermal conductivity in metals
High density makes heat easier to pass through particles via vibrations
Reason for high melting and boiling points in metals
Strong forces of attraction need high temperatures to break bonds
Malleability
The ability to shape a substance
Ductility
The ability to pull a substance into stretched out wires
Reason for malleability and ductility in metals
Metals are arranged in layers with delocalized electrons that allow them to slide past each other easily
Reactions with metals and dilute acids
Metal + Acid –> Salt + Hydrogen
Reactions with metals and water
Metal + Water –> Metal hydroxide + Hydrogen
Reactions with metal and oxygen
Metal + Oxygen –> Metal oxide
Aluminum features
- Exceptionally low density but relatively strong
- Conducts electricity
- Corrosion resistant
Uses of aluminum
- Aircrafts - strong but low density
- Overhead cables - good conductor, low density
- Storing food - corrosion resistant
Uses of copper
- Wiring - high conductivity, very ductile, flexible
Alloys
Mixture of a metal and another element - tend to be stronger and harder than pure metals
Bronze composition
Tin and copper
Brass composition
Copper and zinc - causes it to be corrosion resistant and gold color
Steel composition
Group of alloys made with iron
Uses of steel
- Car engines
- Drill bits
- Cutting tools
Stainless steel composition
- Iron mixed with carbon and other metals e.g. chromium and nickel - protects rusting
Uses of stainless steel
- Cutlery
- Specialist equipment that process corrosive substances in chemical industry
Reasons for alloys’ lack of malleability and ductility
The admixture of particles of different sized causes the layers to not be able to slide/ interlocks them
Order of reactivity series
1.Potassium - K
2.Sodium - Na
3.Calcium - Ca
4.Magnesium - Mg
5.Aluminum - Al
6.Carbon - C
7.Zinc - Zn
8.Iron - Fe
9.Hydrogen - H
10.Copper - Cu
11.Silver - Ag
12.Gold - Au
Elements of the reactivity series and their reaction with water
- Aluminum and below don’t react
- Magnesium only reacts with steam
- Calcium reacts strongly
- Sodium reacts vigorously/violently
- Potassium reacts the most vigorous/violent
Elements of the reactivity series and their reactions with dilute HCl
- Magnesium - strong, forms bubbles quickly
- Zinc - bubbles form slowly
-Iron - Very slow, must be powdered iron - Rest don’t react
Displacement reaction
When a more reactive element takes the place of a less reactive element in a compound
Relationship with the reactivity of a metal and its ions
- The more reactive the metal, the less reactive the ions
- The less reactive the metal, the more reactive the ions
Reason for aluminum being corrosion resistant
When aluminum is exposed to air, it creates a microscopic layer that is a perfect barrier around the metal and prevents corrosion
Corrosion
Caused by metal reactions with oxygen
Rusting
The oxidation of iron
Rust chemical equation
- Iron + Water + Oxygen –> Hydrated iron(III) oxide
-2Fe(s) + 2H2O(l) + O2(g) –> Fe2O3·H2O(s)
Barrier methods for corrosion prevention
- Painting - Protects and colors
- Plastic coating - Protects and colors with thick-polymer based coating
- Lubricants - e.g. grease or oil - prevent corrosion and reduce friction to assist movement
- Electroplating
Sacrificial protection
Covering a metal like Iron with a more reactive metal e.g. zinc, magnesium, aluminum - more reactive metal would lose electrons that would prevent iron from oxidizing
Galvanizing
- Uses barrier method and sacrificial protection
- Coated in a thin layer of zinc + barrier e.g. paint
Hematite
Iron ore
Bauxite
Aluminum ore
Extraction of Iron
1.Carbon + oxygen –> carbon dioxide - hot air blasted in, complete combustion of carbon
2.Carbon dioxide + carbon –> carbon monoxide - oxygen gets used as hot air moves into the furnace, carbon dioxide reacts with coke, incomplete combustion of carbon makes carbon monoxide gas
3.Iron(III) oxide + carbon monoxide –> iron + carbon dioxide - carbon monoxide moves higher and reacts with iron (III) oxide, iron ions in iron(III) oxide are reduced to molten iron and is collected
Reducing impurities of Carbon
Carbon + oxygen –> carbon dioxide - most coke is combusted and can dissolve into the liquid iron, carbon reacts with oxygen and carbon dioxide gas is released and flows out the blast furnace
Reducing impurities of Sulfur
Sulfur + oxygen –> sulfur dioxide -
Sulfur impurities react with oxygen in air blast to form Sulfur dioxide which flows out the blast furnace
Reducing impurities of Silicon
1.Calcium carbonate –> calcium oxide + carbon dioxide - calcium carbonate in limestone thermally decomposes to become more reactive than calcium oxide
2.Calcium oxide + silicon dioxide –> slag - acidic impurity, calcium oxide and silicon dioxide react to make molten liquid slag, less dense and floats to top of liquid iron to collect at the bottom
Problems with Aluminum electrolysis
- Aluminum is more reactive than hydrogen - can’t be electrolyzed from an aqueous solution
- Melting point of aluminum oxide is too high
How to overcome problems with aluminum electrolysis
- Aluminum oxide is dissolved into a salt - cryolite
- Cryolite - doesn’t have any elements less reactive than aluminum or oxygen and has a high melting point but lower than aluminum oxide
- Cryolite heated to molten and then aluminum oxide added
- Dissolved solution has a melting point of 900-1000˚C
- Steel bath can be used due to lower melting point
- Anode and cathode made of graphite - good conductor
- Oxygen reacts with carbon anode to make CO2
-Molten aluminum is denser and sinks to the bottom to be removed and collected
Chemical half equations for aluminum oxide electrolysis
- Anode: 2O^-2 –> O2 + 4e^- oxide ion loses electrons - oxidized
- oxygen gas produced reacts with graphite anode: O2 + C –> CO2
- Cathode: Al^3+ + 3e^- –> Al aluminum ion gaining electrons and is being reduced
Overall balanced equation of aluminum oxide electrolysis
2Al2O3(l) –> 4Al(l) + 3O2(g)
