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[EOY 2019] Chemistry > Metals > Flashcards

Metals Flashcards

1
Q

Why are pure metals not widely used in industry?

A
  1. Pure metals are too soft. Layers of atoms slide easily over one another when a force is applied.
  2. Pure metals may react with air and water and wear away or corrode easily.
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2
Q

Define alloys.

A

An alloy is a mixture of a metal with one or a few other elements.

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3
Q

Why are metals used in the form of alloys?

A
  1. To make metals harder and stronger.
  2. To improve the appearance of metals.
  3. To lower the melting point of metals.
  4. To make metals more resistant to corrosion.
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4
Q

Why are alloys stronger and harder than their constituent metals?

A
  1. Atoms of added element have a different size.
  2. Regular/ orderly arrangement of atoms is disrupted.
  3. Layers of atoms cannot slide over each other easily when a force is applied.
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5
Q

How do you determine the reactivity of a metal referring only to the periodic table?

A
  1. Group I metals are more reactive than Group II metals.
  2. 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)
  3. Reactivity across a period decreases, as metallic character decreases across a period
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6
Q

How can the reactivity of metals be compared by the way they react with other substances?

A
  1. Reaction with water
  2. Reaction with steam
  3. Reaction with dilute HCl
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7
Q

Name the four metals that react with cold water, and state the observations.

A
  1. Potassium: reacts very violently. Highly exothermic. Hydrogen gas burns with lilac flame.
  2. Sodium: Reacts violently. Highly exothermic. Hydrogen gas burns with yellow flame.
  3. Calcium: reacts readily.
  4. Magnesium: reacts very slowly
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8
Q

State the general equation for the reaction between a very reactive metal and cold water.

A

Very reactive metal + water -> metal hydroxide + hydrogen

Group 1 metals react with water to form alkalis

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9
Q

Name the three metals that react with steam, and state the observations.

A
  1. Magnesium: reacts violently to produce a white glow
  2. Zinc: reacts readily. Zinc oxide formed is yellow when hot, white when cold.
  3. Iron: reacts slowly [Fe3O4, iron (III) oxide formed]
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10
Q

State the general equation for the reaction between a moderately reactive metal and steam.

A

Moderately reactive metal + steam [H2O (g)]-> metal oxide + hydrogen

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11
Q

State the 6 metals that react with dilute HCl and state the observations.

A
  1. Potassium: reacts explosively
  2. Sodium: reacts explosively
  3. Calcium: reacts violently
  4. Magnesium: reacts rapidly
  5. Zinc: reacts moderately fast
  6. Iron: reacts slowly
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12
Q

List the metals in the reactivity series from highest to lowest reactivity.

A 
Potassium
Sodium
Calcium
Magnesium
Zinc 
Iron
Lead
Hydrogen
Copper
Silver
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13
Q

State the general equation for the reaction between reactive metals and dilute HCl

A

Metal + HCl -> metal chloride + hydrogen

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14
Q

Name the 5 different reactions under the applications of the reactivity series.

A
  1. Metal displacement reaction (reaction between solid metal and metal salt solution)
  2. Metal displacement reaction (reaction between a metal and the oxide of another metal)
  3. Reduction of metal oxides with carbon
  4. Reduction of metal oxides with hydrogen
  5. Thermal decomposition of metal carbonates
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15
Q

Describe the metal displacement reaction between solid metal and metal solution.

A

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)

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16
Q

Describe the metal displacement reaction between a metal and the oxide of another metal.

A

A more reactive metal can reduce the oxide of a less reactive metal.

E,g, Zn (s) + CuO -> ZnO + Cu (s)

17
Q

Describe the reduction of metal oxides with carbon.

A

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)

18
Q

Describe the reduction of metals with hydrogen.

A

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)

19
Q

Describe thermal decomposition of metal carbonates.

A
  • 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.
20
Q

State the general equation for the thermal decomposition of metal carbonates.

A

MCO3 (s) -> MO (s) + CO2

*Assume that M has a charge of +2 -> true for almost all cases since group I metals cannot decompose

21
Q

Define rusting.

A

Rusting is the corrosion of iron. It is the gradual oxidisation of iron to form hydrated iron (III) oxide.

22
Q

State the equation IN WORDS to show the corrosion of iron (rusting)

A

Iron + oxygen + water -> hydrated iron (III) oxide

23
Q

What are the necessary conditions for rusting, and what are the conditions that will speed up rusting?

A

Necessary conditions:

  • Oxygen
  • Water

Conditions that will speed up rusting:

  • Sodium chloride
  • Acidic substances
24
Q

State and briefly describe the 3 methods of rust prevention.

A
  1. Using a protective layer
    - Principle: to exclude water & oxygen
    - Painting, greasing, plastic coating, electroplating
  2. Sacrificial protection: using a sacrificial metal
    - To protect iron/ steel with a more reactive metal
  3. Using alloys
    - Use of rust-resistant alloys, e.g. stainless steel
25
Q

What is the problem with protective layer?

A
  • When the protective layer is scratched, the iron beneath will rust faster as it is exposed to air & water
  • Thus, it is used for low-cost items such as tables and chairs
26
Q

How is a sacrificial metal used for rust prevention?

A
  • By attaching iron/ steel to a more reactive metal such as zinc or magnesium
  • Zinc/ magnesium will corrode preferentially instead of iron or steel
27
Q

Explain galvanised irons

A
  • Steel or iron blocks that are coated with zinc are known as galvanised irons.
  • Zinc is more reactive than iron
  • Zinc will oxidise preferentially and thus prevent iron from rusting
28
Q

Explain how the concept of using a sacrificial metal is used in attaching a magnesium pipe to an underground iron pipe.

A
  • Magnesium is more reactive than iron
  • Magnesium will oxidise more readily by losing electrons via a conducting cable to the iron pipe
  • Thus, iron will not undergo rusting
29
Q

State the 4 advantages of recycling metals.

A
  1. Conserve finite natural resources
  2. Reduce shortage of landfills required for disposal of unwanted items
  3. Reduce emission of pollutants caused by the extraction of metals, such as reduce the emission of CO2 and SO2
  4. Saves cost of extracting metals as less electrical energy/ fossil fuels are used
30
Q

State the 2 economic issues of recycling metals.

A
  1. Recycling can be more expensive than extracting metals directly from ores
  2. Recycling can cause pollution problems

[EOY 2019] Chemistry (3 decks)

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