chapter 9.2

Question 1

Redox reactions

Answer 1

• Most redox reactions can be balanced by inspection, some require specific technniques, particularly the ones that take place under acidic and basic conditions.
• The technique that is used to balance redox reactions is called the half reaction.

Question 2

Disproportionation Reactions

Answer 2

• In redox reactions one elements atoms are oxidizied and the other elements atoms are reduced.
• In a disproportionation reaction, the atom of one element can be oxidized and the atom of the SAME element can be reduced as well – In ONE SINGLE reaction.

Question 3

Reducing Iron ore

Answer 3

• the terms smelting and refining are applied to processing and purifying mordern ore.
• copper artifacts from the 3600 B.C.E show that anceitn people were extracting crude copper from copper ore, malachite, using it to make utensils.

Question 4

copper produced

Answer 4

• the copper produced could be shaped into utensils and other effective tools.
• For a thousand years after the discovery of how to prepare copper, the only source of iron for tools was meteorites.
• ancient people began to process iron ore at about 2500 B.C.E it was not a common practice until 1200 B.C.E.

Question 4

Extracting copper

Answer 4

• to extract the copper from the ore, it needed to be exposed to high temperatures, higher then the heat used to cook food.
• the only way to generate this heat was by using the ovens were clay pots were fired.
• speculated that potters discovered the process of preparing copper.
• when the ore would be placed in the oven it would melt and separate from other substances in the ore.

Question 5

1200 B.C.E

Answer 5

• by then they had discovered that heating iron ore, probably hematite, at very high tempartures in contact with charcoal produced iron suitable for making ornaments and tools.
• the fact that the mass of the iron obtained from ore was much smaller than the mass of origional ore was the basis of the term reduction.

Question 6

Heating with charcoal

Answer 6

• Iron ore is still heated with charcoal to extract metallic iron, which is now called smelting in which the chemical reduction of iron ions to iron atoms with carbon as the reducing agent.
• This process takes place inside a large blast furnace.

Question 7

1

Charge

Large blast furnace

Answer 7

• a mixture called the charge, contains pulverized iron ore, usually hematite, limestone and coke.

Question 8

2

Coke

Large blast furnace

Answer 8

• coke is prepared by heating coal in the absence of oxygen, driving of the impurities.
• When the process of making coke was developed, iron smelting became less expensive and more efficient.

Question 9

3

Levels of Blast furnace

Large blast furnace

Answer 9

• as the charge is poured into the top of the blast furnaces, blasts of hot air travel up through the particles as they fall.
• at the lowest level of the furnace, oxygen from injected air is available, carbon in the form of coke burns heating the air to 2000 degrees celsius.
• controlling the amount of air and the coke, the burning coke can be made incomplete, producing CO.

Question 10

4

As it falls

Large blast furnace

Answer 10

• CO acts as the reducing agent, as the iron ore is falling from the top it travels up and reacts with the compounds in the iron ore.
• a variety of reduction reactions occur throughout the furnace. Complete reduction of the hematite occurs in three steps, finally the metallic iron melts and pools in the bottom of the furnace.

Question 11

Purpose of Lime

Answer 11

• the purpose of the lime CaO(s), which is produced by heating the limestone in the charge, is to react with impurities.
• Signficat amounts of silicon dioxide and aluminum oxide are found in iron ore.
• The lime reacts with these compounds to produce a liquid called Slag.

Question 12

Slag

Answer 12

• The slag is less dense than the molten iron and thus floats on top of the iron. The slag and molten iron are drawn off at different levels.
• The iron still contains contaminants, mainly carbon (about 5%), silicon, phosphorus, manganese, and sulfur.
• –> This molten iron is poured into long narrow molds to form bars. In this form the metal is called the Pig Iron, it is then transported to other locations, where most of it is converted into steel.

Question 13

Making steel

Answer 13

• the process of smelting reduced the iron ions to the ore to metallic iron, several contaminants were also reduced to their elemetal form.
• Pig iron contains about 5 percent carbon from the coke
• Some of the silicon and phosphorus, small amounts of manganese and sulfur from the ore stay in the pig iron..

Question 14

Making steel: Impurities

Answer 14

• Most of these impurities must be removed because they cause the iron to brittle and branular.
• By the process of purifying or refining, pig iron is converted to steel.
• Many of the contaminants remain in the pig ironbecause they were reduced along with iron. The reasonable way to remove them is by oxidation.

Question 15

1

Making Steel: Molten pig iron

Answer 15

• Molten pig iron is poured into an upright vessel. Oxygen gas is pumped into the vessel over the iron.
• Lime, called flux, is poured into the mixture. The impurities oxidize much more readily than does the iron.
• The reaction produces a slag that is similar to the slag in the smelting process. The slag is less dense than the molten iron and therefore floats on it. When the reactions are complete the vessel is titled on its hinges, the slag is poured off the top, and the refined steel is recovered.
• Steel still contains some carbon (0.03% to 1.4%) but much less than pig iron does.