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METALS
properties of metals mentioned in the periodic table chapter-characteristics of metals and non-metals Chemical properties - Metal reactions with warm or cold water, oxygen, steam and dilute acid.
Reactivity with water: Metal + water → metal hydroxide + hydrogen
Reactivity with steam: Metal + steam [H2O(g)] → metal hydroxide + hydrogen
Reactivity with acid: Metal + acid → Salt + hydrogen (hydrogen atom in the acid is replaced by the metal atom)
Reactivity with oxygen: Gold and platinum don’t react as they are unreactive metals Copper and iron do but very slowly Metal + oxygen → metal oxide
Uses - Aluminium: Aeroplane bodies - Low density, pretty strong for their lightweight Saucepans - Good conductor of heat Overhead power cables - Low density to be overhead, good conductors of electricity Used in storing of food (aluminium foil) - non toxic, resistant to corrosion, do not react with acidic substances in food keeping it clean Copper: Wires - conductors of electricity, malleable Water pipes - malleable, do not react with water
Alloys - ⭐Are mixtures of multiple metals or with a non-metal like carbon that gives it desired characteristics. Characteristics can be different from the metal used, more hardness, strength, resistance to corrosion, extreme temperatures, etc. ENHANCED properties that make them more useful than pure metals. Few alloys: Brass → copper and zinc [stronger than either of the metals]
Used in musical instruments, door knobs, ornaments Stainless steel → iron and (chromium, nickel, carbon) [harder, and more resistant to corrosion] Cutlery because they are resistant to corrosion.
Iron with tungsten improves its strength and restraint to high temperatures. Iron with chromium and nickel makes it more resistant to corrosion. Aluminium with other compounds like silicon, carbon and manganese makes it stronger but still maintains low density.
⭐Alloys are a mixture of different metals, giving it sizes of different sized atoms making it difficult for the layers to slide over one another, making it usually much stronger than pure metal.
Reactivity series - ⭐A reactivity series is produced after monitoring reactions of metals with acid and water. This can help deduce which metal is more reactive than the other. Carbon and hydrogen are also in this series as they are used to extract the metals. The more vigorously the metal reacts, the higher up on the reactivity scale they are.
- The highly reactive metals can be deduced by reactivity by making them react with a weaker reactant like water.
- The lesser reactive metals can be deduced by reactivity by reacting them with a stronger reactant like dilute acid.
- Temperature can also be used, the higher the change, the more reactive the metal is. Please - potassium Stop - sodium Calling - calcium Me - magnesium Cute - carbon Zebra - zinc I - iron Like - lead Her - hydrogen Call - copper Smart - silver Goat - gold
Cold water: Highly reactive metals react like potassium, sodium and calcium
Prevention of rust - Can be coated with a protective layer but it can chip off and lead to rust. Eg: pain, plastic, grease, oil.
Sacrificial protection: ⭐The use of a more reactive metal covering the less reactive metal (eg: steel, iron). This would lead to the more reactive metal to oxidise and corrode first, protecting the less reactive metal beneath it. Eg: zinc on iron on SHIPS [with direct exposure to water] Zn → Zn2+ + 2e- Zinc loses electrons more readily that iron [has to be replaced after corrosion]
Galvanising: ⭐Process when a layer of metal that is more reactive than the protected metal covers the protected metal, stopping it from corrosion. Can be done by electroplating or being dipped in molten metal. Eg: zinc on iron The zinc reacts with oxygen and carbon dioxide in the air forming zinc carbonate (ZnCO3), acting as a barrier to stop corrosion on iron. [as it has already reacted it is stabilised so it won’t react further, just acts as a barrier]. If it gets scratched or if it chips off, it still acts as a sacrificial protection.
[if metal is below iron on the reactivity scale, iron will rust, not protecting it] Extraction of metal - ⭐Metal ore is a rock that contains enough metal and some other substances, to make it useful enough to extract the metal. [usually oxides of the metal] ⭐Native metals are metals that exist in their pure form as they are chemically stable, and therefore exist in their uncombined forms.
Metals above carbon → electrolysis [electricity required in large amounts, expensive] Metals below carbon → heating with carbon [cheap, carbon is enough heat]
Extraction of iron from hematite: Occurs in a blast furnace Raw materials
- Coke (impure version of carbon)
- Iron ore (hematite)
- Limestone
- Hot air from the bottom
Iron part-
- Coke burns in the hot air to make carbon dioxide. This is exothermic heating the furnace. Carbon + oxygen → carbon dioxide C(s) + O2 (g) → CO2 (g)
- Coke burns further with the carbon dioxide due to the high temperatures, reducing the carbon dioxide to carbon monoxide. Carbon + carbon dioxide → carbon monoxide C(s) + CO2 (g) → 2CO(g)
- The carbon monoxide reacts with the iron (III) oxide, reducing it to iron. [the 3+ in iron is gone as it gains the electrons, reducing it] Carbon monoxide + iron (III) oxide → iron+ carbon dioxide 3CO (g) + Fe3O2(s) → 2Fe2(l) + 3CO2(g) Slag part - Calcium carbonate (limestone) is added to remove any impurities.
- Calcium carbonate in the limestone thermally decomposes to become calcium oxide Calcium carbonate → calcium oxide + carbon dioxide CaCO3 (s) → CaCO (s) + CO2(g)
- The calcium oxide now reacts with silicon dioxide to create slag Calcium oxide + silicon dioxide → calcium silicate CaCO (s) + SiO2 (s) → CaSiO3 (s) [iron and slag are tapped off separately]
Extraction of aluminium from bauxite: Higher than carbon in the reactivity series so it has to be separated through electrolysis.
- Bauxite is purified into aluminium oxide (Al2O3)
- It is then mixed with molten cryolite as aluminium oxide has a melting point of over 2000 C but molten cryolite lowers the MP without interfering.
- Placed into a cell made of steel with graphite lining which is the cathode (negatively charged) and has blocks of graphite as anode (positively charged) At cathode: The metal aluminium ions get discharged at the cathode, getting reduced. The aluminium deposits on the electrode (at the bottom as it is the lining) and gets tapped off as new aluminium oxide is added. Al 3+ + 3e- → Al
