Topic 5.1-5.7 - Transition metals, alloys and corrosion

Question 1

What are the typical properties of transition metals?

Answer 1

-high melting point
-high density
-the formation of coloured compounds
-catalytic activity of the metals and their compounds
as exemplified by iron, though most metals are transition metals.

Question 2

What does oxidation of metals result in?

Answer 2

Corrosion, which is the destruction​ ​of​ ​materials​ ​by​ ​chemical​ ​reactions​ ​with​ ​substances​ ​in​ ​the environment

Question 3

Explain how rusting of iron can be prevented by the exclusion of oxygen and/or the exclusion of water

Answer 3

-Rusting​ ​can​ ​be​ ​prevented​ ​by​ ​excluding​ ​oxygen​ ​and​ ​water​ ​e.g.​ ​by: painting, coating​ ​with​ ​plastic, using​ ​oil​ ​or​ ​grease
-Aluminium​ ​has​ ​an​ ​oxide​ ​coating​ ​that​ ​protects​ ​the​ ​metal​ ​from​ ​further​ ​corrosion​ ​– exclusion​ ​of​ ​oxygen​ ​and​ ​water
-Water​ ​can​ ​be​ ​kept​ ​away​ ​using​ ​a​ ​desiccant​ ​in​ ​the​ ​container​(absorbs​ ​water vapour)
-Oxygen​ ​can​ ​be​ ​kept​ ​away​ ​by​ ​storing​ ​the​ ​metal​ ​in​ ​a​ ​vacuum​ ​container

Question 4

Explain electroplating

Answer 4

Electroplating​ ​acts​ ​as​ ​a​ ​barrier​ ​in​ ​order​ ​to​ ​exclude​ ​oxygen​ ​and​ ​water
*It also​ ​improves​ ​appearance​ ​as​ ​you​ ​can​ ​electroplate​ ​a​ ​metal​ ​with​ ​an​ ​unreactive metal​ ​such​ ​as​ ​gold​ ​that​ ​is​ ​more​ ​attractive​ ​and​ ​will​ ​not​ ​corrode
*It​ ​is​ ​done​ ​using​ ​the​ ​metal​ ​to​ ​be​ ​plated​ ​as​ ​the​ ​cathode​ ​and​ ​the​ ​metal​ ​you’re plating​ ​it​ ​with​ ​as​ ​the​ ​anode,​ ​then​ ​have​ ​a​ ​solution​ ​containing​ ​ions​ ​of​ ​the​ ​metal being​ ​used​ ​to​ ​do​ ​the​ ​plating

Question 4

Explain how rusting of iron can be prevented by sacrificial protection

Answer 4

Sacrificial​ ​protection is ​where​ ​the​ ​metal​ ​you​ ​want​ ​to​ ​be​ ​protected​ ​from​ ​rusting​ ​is galvanised​ ​with​ ​a​ ​more​ ​reactive​ ​metal,​ ​which​ ​will​ ​rust​ ​first​ ​and​ ​prevent​ ​water and​ ​oxygen​ ​reaching​ ​the​ ​layer​ ​underneath

Question 5

Explain why iron is alloyed with other metals to produce alloy steels

Answer 5

Steels​ ​are​ ​alloys​ ​since​ ​they​ ​used​ ​mixtures​ ​of​ ​carbon​ ​and​ ​iron and some​ ​steels​ ​contain​ ​other​ ​metals.​
​Alloys​ ​can​ ​be​ ​designed​ ​to​ ​specific​ ​uses:
*Low-carbon​ ​steels​ ​are​ ​easily​ ​shaped​ ​-​ ​used​ ​for​ ​sheeting​ ​(malleable)
*High​ ​carbon​ ​steels​ ​are​ ​hard​ ​-​ ​used​ ​for​ ​cutting​ ​tools
*Stainless​ ​steels​ ​(containing​ ​chromium​ ​and​ ​nickel)​ ​are​ ​resistant​ ​to corrosion​ ​-​ ​used​ ​for​ ​cutlery

Question 5

Explain why converting pure metals into alloys often increases the strength of the product

Answer 5

In​ ​a​ ​pure​ ​metal,​ ​all​ ​the​ ​+​ ​metal​ ​ions​ ​are​ ​the​ ​same​ ​size​ ​and​ ​in​ ​a
regular​ ​arrangement,​ ​allowing​ ​the​ ​layers​ ​to​ ​slide​ ​over​ ​each​ ​other​ ​relatively easily,​ ​making​ ​the​ ​metal​ ​soft​ ​and​ ​malleable.​ ​In​ ​an​ ​alloy,​ ​you​ ​have​ ​+​ ​ions​ ​of different​ ​metals,​ ​which​ ​have​ ​different​ ​sized​ ​ions.​ ​This​ ​disrupts​ ​the​ ​regular structure​ ​and​ ​prevents​ ​the​ ​ions​ ​being​ ​able​ ​to​ ​slide​ ​as​ ​easily,​ ​leaving​ ​a​ ​much harder,​ ​stronger​ ​metal.

Question 6

Explain how the uses of aluminium are related to its properties

Answer 6

It has a low density so is used for aircrafts

Question 7

Explain how the uses of copper are related to its properties

Answer 7

It is a good conductor so is used in electrical cables

Question 8

Explain how the uses of gold are related to its properties

Answer 8

It has good resistance to corrosion so is used in jewellery

Question 9

Explain how the uses of magnalium are related to its properties

Answer 9

(It is aluminium + magnesium)
It has a low density so is used in cars and planes

Question 10

Explain how the uses of brass are related to its properties

Answer 10

(It is copper + zinc)
It is hard and resistant to corrosion so is used in coins