Revision for C7

Flashcards

Questions to think about

1. What are the general properties of metals as solids?

• They are hard
• They are dense
• They have a high ultimate tensile strength
• They are lustrous and sonorous
• They are malleable and ductile
• They are good conductors of heat and electricity
• They have high melting points and boiling points (Mercury is an exception)

2. How is the bonding of metals like? describe it.

The bonding of metals is like a lattice of positive metal ions in a sea of delocalised electrons.

The sea of electrons

The electrons are no longer attached to any positive ions, so they are free to move around in the metal. They are delocalised. They can move through the metal when a potential difference or voltage is applied.

Conductors of electricity?

Electricity, heat, any state? All because of the moving electrons.

The layers that slide over

The perfect rows of ions tend to bend over, sliding over each other so they bend easy.

The bonds between the positive ions are flexible.

Metallic bonds are non-directional.

This means that metals can be bend, but it doesn't mean that the bonds are weak. In fact, metals have high melting and boiling points because they electrostatic bonds are very strong (although they are flexible)

In short, always attracted but can change shape.

3. What are alloys? Give some examples of it.

• Alloys are the mixture of metals and other elements (that can also be metals). Examples of it include brass and steel. Steel is the mixture of iron and carbon, while brass is the mixture of copper and zinc.

Steel

There are many types of steel, the most common ones are mild steel and stainless steel. Mild steel has a lower percentage of carbon than normal steel. This makes it more ductile and machinable. Stainless steel contains less than 11.5% of chromium, which makes it harder to rust to some extent.

Brass

Brass is the mixture of copper and zinc. Comparing to copper, it is very hard, has a higher strength and is more wear-resistance.

4. Why are alloys sometimes used instead of pure metals?

• Sometimes alloys are used as pure metals, because they have properties that are more useful than pure metals to human. For examples, some metals like brass becomes harder than the original metal copper, because the added element has a different atom size from the original metal, distorting the regular arrangement of atoms, so it is used to make weapons and tools in our daily lives. Stainless steel is resistive to corrosion, which makes it more durable.

5. How are the properties of iron changed by the controlled use of additives to form steel alloys?

There are many additives used while forming steel alloys, the most common one is chromium. Stainless steel is made out of more than 11.5% of chromium, while mild steel contains from 0.02% to 2% of carbon, making it cheaper. It has a lower ultimate tensile strength while more ductile. There is a tradeoff between hardness and toughness.

6. What are the diagrams of pure metal and alloys?

    

Pure Metal

Alloys

7. Place in order of reactivity:

   1. Potassium
   2. Sodium
   3. Lithium
   4. Calcium
   5. Magnesium
   6. Aluminium
   7. Carbon
   8. Zinc
   9. Iron
   10. Lead
   11. Hydrogen
   12. Copper
   13. Silver
   14. Gold

8. The higher the reactivity series, the more the metal tends to form its positive ion (by losing that extra one electron).

9. Can you deduce an order of reactivity from a given set of experimental result?

Well, probably.

10. How is Carbon used in the extraction of some metals from their ores?

Carbon is used to extract some metals that are less reactive than carbon from their ores. It does it by giving electrons to the less reactive metals, displacing the other metals and become carbon dioxide as a reducing agent.

11. List out the essential reactions in the extraction of iron from hematite in the blast furnace.

C + O₂ --> CO₂

// Coke combines with oxygen to form carbon dioxide

CO₂ + C --> 2CO

// Coke is combined with Carbon dioxide again to form Carbon Monoxide

Fe₂O₃ + 2CO --> 2Fe + 2CO₂

// Iron Ore Hematite is combined with Carbon monoxide to form pure iron and carbon dioxide

CaCO₃ --> CaO + CO₂

// Calcium oxide is produced. It is used to turn the sand into slag in the next step

CaO + SiO₂ --> CaSiO₃

// the sand, silica, is turned into calcium silicate and runs down

The Redox Reaction

Copper half equation: Cu(s) --> Cu²⁺(aq) + 2e^- // I throw electrons away and displace you

Silver half equation: Ag⁺(aq) + e^- --> Ag(s) // I get your electrons and become myself

12. How is aluminium extracted from its ore?

Since aluminium is more reactive than carbon, it is impossible to reduce it with Carbon. It needs to go through electrolysis.

13. Why do different metals have different methods of extraction?

Metals that are less reactive than carbon are displaced and reduced with Carbon, those that are more reactive than carbon need to be extracted from their ore by electrolysis.

14. Metal ores are finite resources, metals should be recycled.

15. Where are aluminium used and why?

They are used for airplane because of their light weight, and also for other tools in our daily lives because it does not rust. Aluminium oxide is formed on the surface of aluminium and it does not wear away, instead, it protects the rest of the aluminium from corrosion.

16. Why is aluminium unreactive?

A layer of aluminium oxide is formed on the surface of the piece of aluminium, protecting the rest of alumnium from reacting with oxygen and other substances.

17. What are the uses of

    1. mild steel?
    2. stainless steel?

18. What are the uses of zinc?

Zinc is mainly for galvanising steel (covering it up) and making brass (combined with copper).

Galvanising

Since Zinc is more reactive than iron (steel), it is able to do sacrifical protection, giving electrons to iron to reduce it and oxidize itself to prevent the corrosion of steel.

19. How and why do metals rust?

Metals rust in humid weathers because when there is more water in the air, electrons can be conducted away from the metal, making the metal positively charged and react with oxygen, forming rusts. Metals also rust in water.

20. What are the methods of rust prevention? Explain. (Especially sacrificial protecton)

21. What are the transition metals and what are their properties?

Transition metals

22. What is oxidation and reduction in a chemical reaction? Describe it in terms of:

    1. Loss and gain of oxygen
    2. Loss and gain of electrons

23. What is an oxidising agent and a reducing agent?

Confusing Points

The wearing away of metals due to the reaction with oxygen is called corrosion. Only the corrosion of iron is called rusting.