Welcome back  Extracting metals Units 14.1 – 14.4

Learning objectives: Describe bauxite as an ore of aluminium Describe how the ease of obtaining metals from their ores depends on the positive of the metal in the reactivity series. Describe the extraction of zinc from zinc blende.

What’s an ore? Most metals found in the Earth’s crust are present as compounds in the rocks. A rock from which a metal can be extracted is called an ore. Most ores are oxides or sulfides. Some important ores are hametite (iron ore), bauxite (aluminium ore), and zinc blende (zinc ore).

Composition of the Earth crust

Metal extraction and reactivity series The reactivity series of metals is an arrangement of the metals (and carbon and hydrogen) in order of their reactivity starting with the most reactive metal at the top and ending with the least reactive metal at the bottom. The reactivity of a metal is determined by its ability to form a positive ion. For example, potassium is extremely reactive because it has only one valence electron, so it is very easy to lose it forming a positive ion. On the other hand, copper is a weakly reactive metal because it has more valence electrons so it is harder for it to become a positive ion.

Reactions with Dilute Hydrochloric Acid: Metals Reactivity with Dilute HCl Potassium, Sodium & Calcium React extremely violently with rapid effervescence and splashing Magnesium & Aluminum React violently with rapid effervescence Zinc, Iron & Lead React slowly with bubbles Copper, Silver, Gold & Platinum Do not react

Some quick revision Metal + HCl → Metal Chloride + Hydrogen Metal + Water → Metal hydroxide + Hydrogen Metal + Steam → Metal Oxide + Hydrogen

Ores are naturally occurring minerals from which a metal can be extracted. Most ores are metals oxide, carbonate or sulfide mixed with other impurities. The extraction of metal from ores begun long ago when people started purifying iron from its iron oxide ore by reducing it using charcoal. This was possible because carbon is more reactive than iron so it can reduce it take the oxygen ion from it. But then other metals were discovered which were higher than carbon in the reactivity series. Those metals were not possibly extracted from their ores until in the 19th century when a method of extracting them by electrolysis was invented. The method extracting a metal depends on its reactivity.

Metals - in decreasing order of reactivity · potassium · sodium · calcium · magnesium · aluminium Extract by electrolysis · carbon   · zinc · iron · tin · lead Extract by reaction with carbon or carbon monoxide · hydrogen · copper · silver · gold · platinum Extracted by various chemical reactions

Watch video-extraction of zinc

Extraction of zinc Step 1 The ore of zinc is called zinc blende and it is made of zinc sulfide. Zinc is obtained from zinc sulfide by converting it into zinc oxide then reducing it using coke, but first zinc sulfide must be concentrated. Zinc sulfide from zinc blende is concentrated by a process called froth floatation. In this process, the ore is crushed and put into tanks of water containing a frothing agent which makes the mixture froth up. Hot air is blown in and froth starts to form. Rock impurities in the ore get soaked and sink to the bottom of the tank. Zinc sulfide particles cannot be soaked by water; they are lifted by the bubbles of air up with the froth and are then skimmed off. This is now concentrated zinc sulfide.

Step 2 Then, zinc sulfide gets heated very strongly with hot air in a furnace. Zinc sulfide reacts with oxygen from the air to produce zinc oxide and sulfur dioxide gas which escapes as waste gas. 2ZnS + 3O2 → 2ZnO + 2SO2 Sulfur dioxide is used in the manufacture of sulfuric acid.

Step 3 Zinc oxide produced is put into a furnace with powdered coke. The mixture is heated till 1400oC. Carbon from the coke reduces the zinc oxide into zinc producing carbon monoxide which escapes as waste gas. ZnO + C → Zn + CO ZnO + CO → Zn + CO2 CO2 + C → 2CO Carbon monoxide produced is hot and is used to heat the furnace to reduce heating costs. The pure zinc produced is collected and left to cool down. Zinc is used in many ways like the production of the alloy brass, galvanization and making car batteries

Open books to page 176 please.

Extraction of Iron The ore of iron is called hematite. It consists of 60% iron in form of Iron oxide (Fe2O3) with other impurities such as silicon oxide (SiO2). This process takes place in a tower called a Blast furnace.

Steps Coke burns in oxygen from the hot air producing carbon dioxide; C + O2 → CO2 Carbon dioxide produced goes up the furnace and reacts with more coke up there producing carbon monoxide; CO2 + C → 2CO Carbon monoxide is a reducing agent. It rises further up the furnace where it meets iron oxide and starts reducing it producing iron and carbon dioxide; Fe2O3 + 3CO → 2Fe + 3CO2

Why do we add limestone? Because hematite contains sand (silicone (IV) oxide) as a major impurity. The limestone (CaCo3) helps remove most of the impurities by first decomposing into CaO + CO2 The CaO is then combined with SiO2 to produce CaSiO3 CaO + SiO2 → CaSiO3

Unit 14.3 L.O: Iron into steel Describe how Iron is converted into steel Understand the role of basic oxides and oxygen in steelmaking Describe the idea of changing the properties of iron by controlled use of additives

Quick revision: Raw materials for the reaction Contains Function Iron ore (haematite) Iron(III) oxide A compound that contains iron Coke Carbon Burns in air to produce heat, and reacts to form carbon monoxide (needed to reduce the iron oxide) Limestone Calcium carbonate Helps to remove acidic impurities from the iron by reacting with them to form molten slag Air Oxygen Allows the coke to burn, and so produces heat

Conversion of Iron into Steel Iron produced in the blast furnace is called pig iron. It contains 4% carbon as well as other impurities such as sulfur, silicon and phosphorus which make it hard and brittle. It got that name from the fact that it has to be poured into mold called pigs before it is converted into steel. Most of produced iron is converted into steel because steel has better properties.

Making steel out of pig iron is a process done in a basic oxygen furnace: Step 1: iron and scrap iron are poured in. Step 2: The converter is put back into a vertical position. A water-cooled tube called an oxygen lance is lowered into the converter. Step 3: Oxygen and powdered calcium oxide are blown onto the surface of the molten iron through the lance. Step 4: The oxygen oxidizes carbon, sulfur, silicon and phosphous to their oxides. Sulfur and carbon escape as gases (SO2 and CO2) Silicon and phosphorus are oxidized into silicon oxide and phosphorus pentoxide which are solids. Calcium oxide (lime) is added to remove the solid impurities as slag which is skimmed off the surface Throughout the process, sample of the iron are being taken and analyzed for the percentage of carbon present in it. When the percentage of carbon desired is reached, the furnace is switched off and the steel is collected.

Types and uses of metals Steel Composition Properties Uses Mild Steel 99.5% Iron 0.5% Carbon Easily worked lost brittleness Car bodies large structures Machinery Hard Steel 99% Iron 1% Carbon Tough and brittle Cutting tools and chisels Stainless Steel 87% Iron 13% Manganese Tough and springy Drill bits and springs and chemical plants Manganese Steel 74% Iron 18% Chromium 8% Nickel Tough and resistant to corrosion Cutlery and surgical tools, kitchen sinks Tungsten Steel 95% Iron 5% Tungsten Tough and hard even at high temperatures Edges of high speed cutting tools

Uses of aluminium Construction of air-craft bodies because aluminum is very strong and very light and it is resistant to corrosion Food containers because it is resistant to corrosion Overhead power cables because it conducts electricity, is very light, malleable and ductile. Although it is strengthened with steel core

Uses of copper In electrical wires because it is a perfect electrical conductor and very ductile, malleable and cheap Making alloys such as bronze and brass Cooking utensils because it conducts heat and it is has high melting and boiling points and also resists corrosion Electrodes because it is a good conductor of electricity Water pipes because it is resistant to corrosion

1. why are hydrogen and carbon good reducing agents? Carbon is a good reducing agent, especially at higher temperatures, because it is a non-metal and it combines with oxygen and forms its gaseous non-metallic oxides. Its dioxide CO2 being a gas, escapes away, hence it's a good by-product as we don't have to separate it further. Hydrogen is abundant and when it reduces metal oxides it forms water!

2. How is calcium metal extracted from the Earth crust? By electrolysis By heating with carbon It is found pure, so no need to extract it at all

3. How is platinum extracted from the Earth's crust? By electrolysis By heating with carbon It is found pure, so no need to for chemical extraction

4. How is zinc extracted from the Earth's crust? By electrolysis By heating with carbon It is found pure, so no need to for chemical extraction

5. Which is a typical property of metals? Malleable Brittle Low melting point

6. How are metals bonded? Positive and negative ions strongly attracted in a lattice Atoms bonded by sharing electrons Positive ions in a lattice with delocalized electrons in between

7.Why are metals good conductors of electricity? The positive ions are free to move through the lattice Electrons can move through the lattice The metal ions are locked in place

8. What is the name of Aluminium ore? Haematite Magnetite Bauxite

Water Ethanol Cryolite 9. What solvent is used to dissolve Aluminium oxide in the extraction of Aluminium? Water Ethanol Cryolite

10. Why is limestone added to the blast furnace during the extraction of iron? To reduce the iron oxide To increase the temperature To remove the impurities in the iron ore

11. Which of these metal ores is the most stable? Aluminium oxide Lead oxide Copper oxide

Question 11

Answer 11

Question 12

Answer 12