C15 - Using our resources

• What is corrosion caused by?

  Chemical reactions between metal and environment
• What is the effect of corrosion on metal?

  It affects strength and appearance
• What is rusting specifically the corrosion of?

  Iron
• What is rust?

  A soft crumbly substance on iron
• How does rusting differ from the protective oxide layer on aluminium?

  Rust flakes off, while oxide protects aluminium
• What conditions are needed for iron to rust?

  • Presence of air (oxygen)
  • Presence of water
• What does Tube A test in the rusting experiment?

  If air alone makes iron rust
• What does Tube B test in the rusting experiment?

  If water alone makes iron rust
• What does Tube C test in the rusting experiment?

  If air and water together make iron rust
• What is the chemical formula for rust?

  Fe₂O₃·nH₂O
• Why is it difficult to write a chemical formula for rust?

  It contains varying amounts of water
• List five ways to prevent iron rusting.

  1. Coating with paint
  2. Applying oil or grease
  3. Using plastic coatings
  4. Galvanizing with zinc
  5. Using sacrificial protection
• What is the purpose of a protective coating on iron?

  To keep air and water away from iron
• What happens if there is a gap in the protective coating of iron?

  Rust spreads under the coating
• What is sacrificial protection?

  Using a more reactive metal to protect iron
• Which metal is commonly used for galvanizing iron?

  Zinc
• Why does zinc protect iron in galvanization?

  Zinc reacts with water and oxygen instead
• What is the role of magnesium or aluminium in sacrificial protection?

  They can also protect iron sacrificially
• Under what conditions is sacrificial protection used?

  In harsh conditions like seawater
• What is the main advantage of using sacrificial protection?

  It protects iron even when exposed
• What are the properties of alloys compared to pure metals?

  • Alloys are harder than pure metals
  • Regular layers in pure metals are distorted
• What is bronze made from?

  Copper and tin
• Why is bronze used for ship propellers?

  Due to its toughness and corrosion resistance
• What is brass made from?

  Copper and zinc
• What are the uses of brass?

  Musical instruments and door fittings
• What is a key property of aluminium alloys?

  Low density
• How many aluminium alloys are available?

  Over 300
• How do different aluminium alloys vary in properties?

  They can be lightweight or strong
• What is the carat system used for?

  To express the purity of gold
• What is the composition of 18 carat gold?

  75% gold
• What are carbon steels made from?

  Iron with carbon
• What is the carbon content in low carbon steel?

  About 0.03% to 0.3%
• What are the properties of high carbon steel?

  Very strong but brittle
• What are the properties of low carbon steel?

  Soft and easily shaped
• What are alloy steels made from?

  Iron with 1% to 5% of other metals
• What is the use of nickel steel alloys?

  For long-span bridges and military armour
• What is the use of tungsten steel?

  For high-speed tools like drill bits
• What are stainless steels known for?

  Resistance to corrosion
• Why are stainless steels used in cooking utensils?

  They do not rust
• What is the main advantage of stainless steels in chemical industries?

  They withstand high temperatures and pressures