Metals Flashcards
(30 cards)
Why are pure metals not widely used in industry?
- Pure metals are too soft. Layers of atoms slide easily over one another when a force is applied.
- Pure metals may react with air and water and wear away or corrode easily.
Define alloys.
An alloy is a mixture of a metal with one or a few other elements.
Why are metals used in the form of alloys?
- To make metals harder and stronger.
- To improve the appearance of metals.
- To lower the melting point of metals.
- To make metals more resistant to corrosion.
Why are alloys stronger and harder than their constituent metals?
- Atoms of added element have a different size.
- Regular/ orderly arrangement of atoms is disrupted.
- Layers of atoms cannot slide over each other easily when a force is applied.
How do you determine the reactivity of a metal referring only to the periodic table?
- Group I metals are more reactive than Group II metals.
- Reactivity down a group increases. The larger the atomic radius, the weaker the electrostatic forces of attraction between the positively-charged nucleus and the negatively-charged electrons, the higher the tendency to lose electrons, the greater the reactivity. (ease of losing electrons down a group increases)
- Reactivity across a period decreases, as metallic character decreases across a period
How can the reactivity of metals be compared by the way they react with other substances?
- Reaction with water
- Reaction with steam
- Reaction with dilute HCl
Name the four metals that react with cold water, and state the observations.
- Potassium: reacts very violently. Highly exothermic. Hydrogen gas burns with lilac flame.
- Sodium: Reacts violently. Highly exothermic. Hydrogen gas burns with yellow flame.
- Calcium: reacts readily.
- Magnesium: reacts very slowly
State the general equation for the reaction between a very reactive metal and cold water.
Very reactive metal + water -> metal hydroxide + hydrogen
Group 1 metals react with water to form alkalis
Name the three metals that react with steam, and state the observations.
- Magnesium: reacts violently to produce a white glow
- Zinc: reacts readily. Zinc oxide formed is yellow when hot, white when cold.
- Iron: reacts slowly [Fe3O4, iron (III) oxide formed]
State the general equation for the reaction between a moderately reactive metal and steam.
Moderately reactive metal + steam [H2O (g)]-> metal oxide + hydrogen
State the 6 metals that react with dilute HCl and state the observations.
- Potassium: reacts explosively
- Sodium: reacts explosively
- Calcium: reacts violently
- Magnesium: reacts rapidly
- Zinc: reacts moderately fast
- Iron: reacts slowly
List the metals in the reactivity series from highest to lowest reactivity.
Potassium Sodium Calcium Magnesium Zinc Iron Lead Hydrogen Copper Silver
State the general equation for the reaction between reactive metals and dilute HCl
Metal + HCl -> metal chloride + hydrogen
Name the 5 different reactions under the applications of the reactivity series.
- Metal displacement reaction (reaction between solid metal and metal salt solution)
- Metal displacement reaction (reaction between a metal and the oxide of another metal)
- Reduction of metal oxides with carbon
- Reduction of metal oxides with hydrogen
- Thermal decomposition of metal carbonates
Describe the metal displacement reaction between solid metal and metal solution.
A more reactive metal can displace ions of less reactive metal from its salt solution.
E.g. Fe (s) + CuSO4 (aq) -> FeSO4 (aq) + Cu (s)
Describe the metal displacement reaction between a metal and the oxide of another metal.
A more reactive metal can reduce the oxide of a less reactive metal.
E,g, Zn (s) + CuO -> ZnO + Cu (s)
Describe the reduction of metal oxides with carbon.
The oxides of zinc, iron, lead and copper can be reduced to their metals by heating with carbon.
E.g. 2CuO (s) + C (s) -> 2Cu (s) + CO2 (g) (carbon dioxide formed)
Describe the reduction of metals with hydrogen.
The oxides of iron, lead and copper can be reduced to their metals by heating with hydrogen gas.
E.g. PbO (s) + H2 (g) -> Pb (s) + H2O (g) (steam formed)
Describe thermal decomposition of metal carbonates.
- Most metal carbonates decompose upon strong heating to form metal oxide and carbon dioxide.
- The more reactive the metal, the more difficult it is to decompose its carbonate by heat.
- Group I carbonates such as NaCO3 and KCO3 are highly thermally stable and thus, do not decompose on prolonged heating.
State the general equation for the thermal decomposition of metal carbonates.
MCO3 (s) -> MO (s) + CO2
*Assume that M has a charge of +2 -> true for almost all cases since group I metals cannot decompose
Define rusting.
Rusting is the corrosion of iron. It is the gradual oxidisation of iron to form hydrated iron (III) oxide.
State the equation IN WORDS to show the corrosion of iron (rusting)
Iron + oxygen + water -> hydrated iron (III) oxide
What are the necessary conditions for rusting, and what are the conditions that will speed up rusting?
Necessary conditions:
- Oxygen
- Water
Conditions that will speed up rusting:
- Sodium chloride
- Acidic substances
State and briefly describe the 3 methods of rust prevention.
- Using a protective layer
- Principle: to exclude water & oxygen
- Painting, greasing, plastic coating, electroplating - Sacrificial protection: using a sacrificial metal
- To protect iron/ steel with a more reactive metal - Using alloys
- Use of rust-resistant alloys, e.g. stainless steel
