Metals Flashcards
Chemical properties of metals
- Metals that react with cold water form a metal hydroxide and hydrogen gas
metal + water → metal hydroxide + hydrogen
- Metals that react with steam form a metal oxide and hydrogen gas
metal + steam → metal oxide + hydrogen
- When metals react with a dilute acid it produces a salt and hydrogen gas
metal + acid → salt + hydrogen
- When metals react with oxygen a metal oxide is formed (unreactive metals don’t react e.g. gold)
metal + oxygen → metal oxide
Uses of aluminium
- Manufacture of aircraft
Because of its low density and high strength to weight ratio
- Manufacture of overhead power cables
Because of its low density and good electrical conductivity
- In food containers
Because of its resistance to corrosion and acidic food stuff, non-toxic
Why are alloys stronger than pure metals?
Alloys are harder and stronger than metals because they typically contain atoms of different sizes. When different sized atoms are added to the pure metal, they distort the regular lattice structure. This distortion disrupts the normally regular arrangements of atoms in metals. The distortion makes it more difficult for the layers toslideover each other. So, alloys are usually harder and stronger than pure metals but less malleable and ductile
Order of reactivity series
potassium, sodium, calcium, magnesium,
aluminium, carbon, zinc, iron, hydrogen, copper,
silver, gold
What makes metal ions more reactive?
Metal atoms formpositive ionsby loss of electrons when they react with other substances. Thetendencyof a metal to lose electrons is a measure of how reactive the metal is. A metal that is high up on the series loses electrons easily and is thusmore reactivethan one which is lower down on the series
- Therefore, the reactivity of metals can be demonstrated through displacement reactions. A more reactive metal will displace a less reactive metal from its aqueous solution of ions. This tendency to form positive ions and displace other metals can be used to deduce the reactivity order.
How can rust be prevented? + the conditions for rust
Presence of water and oxygen
- Some common methods are painting, greasing and coating with plastic
2 ways zinc is used to protect iron
- Barrier method
ZnCO3is formed when zinc reacts with oxygen and carbon dioxide in the air and protects the iron by the barrier method. This is because zinc carbonate forms a solid, stable layer on the surface of the zinc. This layer acts as a physical barrier. This zinc carbonate coating effectively prevents further exposure of the underlying zinc to air and moisture. Therefore, the zinc carbonate layer can prevent moisture and oxygen from reaching the iron, thus protecting it from rusting.
- Sacrificial protection
Zinc is more reactive (anodic) than iron in the electrochemical series. This means that zinc will corrode preferentially when exposed to moisture and air. When the iron or steel and the zinc coating are exposed to a corrosive environment, the zinc acts as a sacrificial anode. It corrodes instead of the iron, protecting the underlying metal. Even if the zinc layer is damaged, the exposed iron remains protected by the ongoing sacrificial corrosion of the zinc. The sacrificial protection will continue until the zinc is consumed. Once the zinc is depleted, the iron will be exposed to rusting.
extraction of iron from hematite
- In zone 1, cokeburnsin the hot air formingcarbon dioxide. The reaction is exothermic so it gives off heat,heatingthe furnace. C + O2→ CO2
- In zone 2, more coke reacts with carbon dioxide forming carbon monoxide. The carbon dioxide has beenreducedto carbon monoxide. C + CO2 → 2CO
- At zone 3, carbon monoxidereduces the iron(III) oxide in the iron ore to form iron. This will melt and collect at the bottom of the furnace, where it is tapped off. Fe2O3 + 3CO → 2Fe + 3CO2
- Also at zone 3, limestone (calcium carbonate) is added to the furnace to remove impurities in the ore. The calcium carbonate in the limestonethermally decomposesto form calcium oxide. CaCO3 → CaO + CO2
- Finally, the calcium oxide formed reacts with the silicon dioxide, which is an impurity in the iron ore, to form calcium silicate. This melts and collects as a moltenslagwhich is less dense than molten iron and floats on top of the iron. It helps to separate impurities from the molten iron and can be removed easily by being tapped off separately. CaO + SiO2 → CaSiO3
Half equation at the anode during electrolysis of aluminium
2O2-→ O2+ 4e-
How to test for the purity of water?
Use melting and boiling point
Impurities increase the boiling point and lower the melting point of water
Why is distilled water used in chemistry
Distilled water is used in practical chemistry rather than tap water because it
contains fewer chemical impurities
Water from natural sources may contain
(a) dissolved oxygen
(b) metal compounds
(c) plastics
(d) sewage
(e) harmful microbes
(f) nitrates from fertilisers
(g) phosphates from fertilisers and detergents
Substances in water that are beneficial
(a) dissolved oxygen for aquatic life
(b) some metal compounds provide essential
minerals for life
Substances in water that are harmful
(a) some metal compounds are toxic
(b) some plastics harm aquatic life
(c) sewage contains harmful microbes which
cause disease
(d) nitrates and phosphates lead to
deoxygenation of water and damage to
aquatic life
Water treatment
(a) sedimentation and filtration to remove solids
(b) use of carbon to remove tastes and odours
(c) chlorination to kill microbes
