chemistry chapter 3 (important chemical reactions) PART 1 : RUSTING

other causes of iron/steel corrosion

1. local rainfall is acidic in nature 2. area is surrounded by heavy industries that release plenty of acid fumes 3. marine environments lower lifetime of galvanized iron roofs and similar products as the high electrical conductivity of seawater encourages and increases the rate of corrosion

disadvantages of electroplating

1. electroplating is more expensive than galvanizing 2. chromium is only slightly more reactive than iron hence the sacrificial protection is poorer than zinc

effects of rusting

1. sudden failure of machines or structures 2. safety issues on railway tracks 3. performance and safety of cars, trains, airplane, ships and oil tankers will be affected 4. wastage of material and energy resources 5. failure of military weapons 6. leakage in water pipes

advantages of electroplating

chromium plating is more attractive in appearance as it is shiny

bronze is an alloy of what two metals?

copper and tin

brass is an alloy of what two metals?

copper and zinc

galvanization

galvanization is a method whereby zinc is used to coat iron or steel dustbins and gates. zinc is more reactive than iron, so oxygen in the air reacts more readily with zinc to form zinc oxide rather than iron. zinc is "sacrificed" to protect the iron. zinc oxide serves as a protective layer to the iron underneath from the damp air, thus preventing it from rusting.

steel is an alloy of what two elements?

iron and carbon

how does alloying prevent rusting?

iron and steel can be mixed with other metals to form alloys which do not rust. these stainless steels contains chromium or nickel. they are used for cutlery, tools and other expensive items which might easily rust.

why iron + HCl → iron chloride + hydrogen

iron is more reactive than hyrdrogen, hence it can displace hydrogen

rusting definition

iron reacts with oxygen and water present in damp air to form rust, hydrated iron (III) oxide

how does greasing/oiling prevent rusting?

moving parts of machines like bicycle chains cannot be painted hence they are greased or oiled as the oil prevents the moving parts of machines from coming into contact with oxygen and water so it would not react with them to form rust. greasing and oiling also help to lubricate the moving parts, which reduces friction.

how to remove rust

since rust is a metal oxide, adding acid will form salt and water (metal oxide + acid → salt + water) and hence the metal oxide will be removed

how does painting prevent rusting?

the paint covers the iron, preventing it from coming into contact with oxygen and water so it would not react with them to form rust. however once the paint is scratched, rusting starts.