IGCSE-chemistry-structure and bonding AND METALS

All the aluminium formed comes from the alumina not the cryolite.Suggest two reasons why the electrolyte must contain cryolite.

1. Dissolving aluminium in cryolite lowers the operating temperature. alumina melts at around 2000 degrees celcius while the cryolite and alumina solution melts at around 900 degrees celcius, this makes the process more economical and saves alot of energy. 2. the crylite acts as a solvent and increases the conductivity of he electrolyte.

Describe the basic extraction of iron from haematite (or magnitite)

1.) Haematite along with limestoe, and coke is loaded into a blast furnace 2. blasts of hot air are sent in from the bottom of the furnacethrough the tuyéres. 3. the carbon reacts with the oxygen forming carbon dioxide 4. the limestone decomposes into calcium oxide and carbon dioxide 5.the carbon dioxide produced reacts with the unreacted caron higher up in the furnace to form carbon monoxide. 6. the carbon monoxide produce acts as a reducing agent, it reacts with the iron oxide to form iron and carbon dioxide. 7.the dense molten iron formed is tapped out at the bottom. 8.the calcium oxide is basic and reacts with the acidic impurities in the iron ore forming a liquid slag. this is less denses than the molten iron. therefore floats on top of it. this is also tapped off and used in road foundations.

Suggest two reasons why chromium is used to electroplate steel.

1.) shiny, therefore acts as a decorative finish 2.) does not easily corrode as it is protected by an oxide layer therefore protecting the steel beneath.

Describe the basic extraction of aluminium from bauxite.

1.Bauxite is treated with sodium hydroxides to remove impurities. 2.the purified aluminium oxide is added to molten cryolite 3.the molten mixture is electrolysed in a halt-héroult cell 4.Due to alumina being a ionic substance, when its molten the ions become free to move. thus the oxygen anions become attracted to the anode, where on contact they turn into oxygen gas. and the aluminium cations become attracted to the cathode where on contact they recieve electrons and turn into molten aluminium. 5.molten aluminium is denser than the slag so is tapped off at regular intervals

define the term macromolecule. What are their typical properties?

A giant covalent structure, where atoms are covalently bonded to their adjacent atoms. 1.high mp/bp 2.brittle 3.insoluble in water 4.hard 5. poor conductor of heat/electricity.

The temperature inside the blast furnace can rise to 2000 °C. Write an equation for the exothermic reaction which causes this high temperature.

C+O₂→CO₂

Name two products formed at the anode during electrolysis of alumina with molten cryolite.

CO₂and O₂

Write an equation for the reduction of hematite by carbon monoxide.

Fe₂O₃+3CO→2Fe+3CO₂

Explain why graphite is a soft material used as a lubricant.

Graphite is composed of strong hexagonal rings forming layers with WEAK intermolecular forces between them. Thus these Van der waals forces are easily overcome so the layers will easily slide over each other. this is why it is soft and can be used as a lubricant.

Explain, using the idea of electron transfer, why zinc-coated steel does not rust even when the coating is scratched and the steel is in contact with oxygen and water.

Zinc is more electropositive than Iron therefore it will react to oxygen/water in preferance to iron. when the zinc oxidises it loses electrons these elctrons travel to the iron protecting it from corrosion even if exposed to oxygen and water.

A jet of oxygen is blown through the molten iron in the presence of a base, usually calcium oxide. Explain how the percentage of carbon is reduced and how the silicon is removed.

a. the carbon reacts with the oxygen to form carbon dioxide. and escapes. b. the silicon reacts with oxygen to form silicon oxide, which then further reacts with the calcium oxide to form liquid slag which is skimmed of the surface.

Why is copper a suitable material from which to make cooking utensils?

a.) good conductor of heat b.) malleable c.) unreactive, therefore wont react with your food d.) high melting point.

Predict two differences in physical properties and two differences in chemical properties between rubidium and the transition metal niobium.

a.) physical, rubidium will be softer and will have a lower density than niobium. b.) chemical, rubidium will react much more violently with cold water than niobium, and niobium has more than one oxidation sate unlike rubidium.

explain why diamond is a very hard material which is used for drilling and cutting.

diamond is composed of carbon atoms bonded to four other crbon atoms by strong covalent bonds in a tetrahedral lattice. this structure makes diamond very hard and suitable for being used as a drill bit or a cutting edge.

Why does neon exist as single atoms but fl uorine exists as molecules?

elements react to become more stable, single neon atoms already have a noble gas electron configuration (which is very stable). however flouring only has & valency electrons (its missing one) therefore it covalently bonds with another flourine to attain a noble gas configuration.

describe the bonding in a typical metal

metallic substances have a lattice of positive metal cores ( or positive "ions") in a "sea of delocalised electrons", forming metallic bonds and attractions between the positive "ions" and the delocalised electrons.

Explain why it is necessary to add limestone, calcium carbonate, to the blast furnace. Include an equation in your explanation.

the calcium carbonate decomposes into calcium oxide. CaCO₃→CaO+ CO₂ This is to remove silicon dioxide, the silicon dioxide reacts with the calcium oxide. CaO+SiO₂→CaSiO₃

explain how CO is produced.

the carbon dioxide produced from the decomposition of limestone and oxidisation of carbon reacts with the unreacted carbon higher up in the furnace to form carbon monoxide. C+CO₂→2CO

Why is aluminium used in the manufacture of airplanes?

this is due to it being light (low density) and strong simultaneously. it also resists corrosion due to it becoming protected by an oxide layer

why does aluminium appear to be much less reactive than its predicted to be?

this is due to the fact that aluminium reacts readily with the O₂in the ir to form a protective layer of Al₂O₃ on its surface.THis layer is inert and tough, it sticks to the metal thus preventing further oxidistion of aluminium. this disguises aluminiums true reactivity.

The boiling point of nitrogen is very low even though the bond between the atoms in a nitrogen molecule is very strong. Suggest an explanation.

when a substance boils its INTERMOLECULAR FORCES are the ones that are broken. here the strong covalent bonds between the atoms are INTRAMOLECULAR FORCES (these are not the ones broken during boiling). however the intermolecular forces between the nitrogen molecules are very weak. thus they are easily overcome wih little energy therfore leading o a very low boiling point.