Rocks and their formation
Rocks make up the earths crust
- formed when magma/lava solidifies
- made of interlocking crystals- makes them hard and resistant to erosion
- have small crystals if liquid rocks cools quickly (e.g. basalt)
- have large crystals if liquid rock cooled slowly (e.g. granite)
- formed when layers of sediment are compacted over a long period of time
- erode more easily than igneous and metamorphic rocks
- made of rounded grains and may contain fossils
- include chalk and limestone (natural forms of calcium carbonate)
formed from existing rocks by action of heat and/or pressure, causing new interlocking crystals. E.g. marble which is formed from chalk or limestone.
Limestone and its uses
- Limestone used for making buildings and as base for roads and railways
- Mostly made of calcium carbonate which is an important raw material for making glass, cement and concrete
- Limestone heated when making cement and glass. Heat decomposes the calcium carbonate in it to form calcium oxide and carbon dioxide. (Thermal decomposition)
- We need to quarry a lot of limestone, but quarrying has ecenomic, enironmental and social effects.
- We need to balance the effects with the demand.
- (Advantages and disadvantages on separate page)
- When heated strongly, calcium carbonate decomposes to form calcium oxide and carbon dioxide.
- The word equation for the decomposition of calcium carbonate is:
- calcium carbonate à calcium oxide + carbon dioxide
- CaCO3 à CaO + CO2
- Atoms are the smallest particles of an element that can take part in chemical reactions
- During chemical reactions atoms are neither created nor destroyed
- During chemical reactions atoms are rearranged to make new product with different properties from the reactants
- The total mass before and after a reaction in a sealed container is unchanged (shown practically by a precipitation reaction)
Reactions of calcium compounds
- When water is added to calcium oxide a lot of heat is released making the water boil and steam. It also fizzes.
- Calcium hydroxide dissolves when more water is added forming calcium hydroxide solution (known as limewater)
- Calcium oxide, calcium hydroxide and calcium carbonate can be used to neutralise soil acidity. Farmers spray them over the fields to reduce the acidity of the soil.
- Wet powdered calcium carbonate is sprayed through waste gasses from coal-fired powered station chimneys, this reacts with the acidic gases and neutralises them. This reduces harmful emissions and helps to reduce acid rain.