Scientists clarify rocks based on how they were formed. The 3 different types are sedimentary, metamorphic and igneous. Sedimentary tend to be soft and igneous tend to be harder.
- Sedimentary rocks are made from layers of sediment in lakes or seas.
- Over millions of years the layers become buried under more layers and the weight squeezes out the water.
- Fluids running through the pores deposit natural mineral cement.
- Limestone and chalk are both sedimentary rocks that contain fossils.
- The rock isn't formed at high temperatures so the remains of dead orgainsms don't get destroyed.
- Limestone and chalk both get broken away easily by wind, waves and rain. This process is called erosion and can change the shape of our landscape.
Metamorphic rocks are formed from other rocks.
- Metamorphic rocks are made by the heat and preassure on sedimentary or igneous rocks over long periods of time.
- The mineral structure and texture has changed but the chemical composition is normally the same as the origional rock.
- As long as rocks don't melt, they're classed as metamorphic. But if they melt and turn to magma they're gone, however could re-surface as igneous rock.
- Marble is formed from limestone or chalk when high temperatures break down the limestone and it reformes as small crystals giving a more even texture and much harder appearance.
Igneous rocks are formed from fresh magma.
- Igneous rock is made when molten magma pushes up into the crust or straight through it befor cooling and solidifying.
- They hold different materials in randomly arranged interlocking crystals.
- There are 2 types of igneous rock, extrusive and intrusive:
Extrusive - igneous rocks that cool quickly above ground, making small crystals. (basalt, rhyolite)
Intrusive - igneous rocks that cool slowly underground, making big crystals. (granite,gabbro)
Calcium carbonate is found in the earth's crust as marble, chalk and limestone. Limestone'e great for building with but tearing from the ground causes problems.
Limestone is used as a building material...
- The grey/white colour rock is often fored from sea shells and even though the original shells are mainly crushed they're still some fossilised shells left.
- It's quarried out of the ground causing environmental problems.
- Limestone has been used to build old buildings like cathederals but also for statues and is crushed into chippings and used in road surfacing.
- It is virtually insoluble in plain water but acid rain is a big problem because the acid reacts with the limestone and dissolves it away.
- Limestone is the raw material used to make other building materials so it quarried on large scale.
- Powdered limestone is heated in a kiln to make cement, the cement can be mixed with sand, water and gravel to make concrete.
- Limestone can be used to make glass when heated with sand & sodium carbonate until it melts.
Quarrying limestone makes a mess of the landscape and can cause environmental problems.
- It creates huge holes the permenantly change the landscape.
- Quarrying creates lots of noise pollution from blasting rocks apart.
- It destroys habitats of animals and birds.
- The quarried limestone needs to be transported away in lorries causing more noise pollution and waste materials get taken to tips.
On the positive side...
- Limestone creates things in demand, like houses and roads and the chemicals used in dyes, paints and medicine.
- It can be used to neutralise acidic soil,acidity in lakes & sulfur dioxide. (which causes acid rain)
- Quarrying for limestone creates many jobs, putting money into the local economy which leads to local improvements.
- When projects are completed the landscape is normaly restored.
Thermal Decomposition & Limestone
- Limestone is mainly calcium carbonate - CaCO3
- When heated it themally decomposes to make calcium oxide & carbon dioxide.
Calcium carbonate → Calcium oxide + Carbon dioxide
CaCO3 → CaO + CO2
- Zinc carbonate and copper carbonate thermally decompose in the same way as calcium carbonate to form an oxide and carbon dioxide.
- Some carbonates undergo thermal decomposition more easily than others depending on the stability of the metal carbonate.
- Less stable carbonates will decomposte quicker and the limewater will turn milky sooner. Sometimes there can be a colour change.
- When water and calcium oxide are combined, calcium hydroxide is formed.
- This is an alkali that can be used to neutralise acidic soil and is much quicker than powdered calcium at doing this. It also dissolves in water to make a solution called limewater.
Atoms & Mass In Chemical Reactions
Atoms are the main part of chemical reactions and are only ever rearranged, they can't be lost or made in chemical reactions.
- Elements and compounds are made up of atoms. (The smallest particles you can get of every element) The atoms are the things that take part in chemical reaction.
- During that process things aren't created or lost. The same atoms are present at the start and end of chemical reaction, they're just rearranged in new ways to give new products with different properties from the reactants.
- Balanced symbol equations show the atoms at the start and end and how they're arranged. For example...
- Magnesium + Oxygen → magnesium oxide
- 2Mg + O2 → 2MgO
- Because atoms aren't gained or lost the mass of reactants is the same as the product. (6g of Mg reacted with 4g of O gives 10g MgO)
- Total mass before and after a sealed reaction is the same. A way of showing this is by a precipitation reaction.
- There must always be the same number of atoms of each element on both sides.
- The equation is balanced by putting numbers infront of fromulas, e.g...
- H2SO4 + NaOH → Na2SO4 + H2O
- The formula is correct but numbers of some atoms don't match up. (There are 3 Hs on the left but only 2 on the right)
- To correct this mistake, balance 1 atom at a time. Find an element that doesn't balance and pencil in a number & see where it gets you, if it creates another inbalance pencil in another number and see where that takes you instead. Keep playing around and sooner or later it will sort itself out. This means that the equation above would end up as...
- H2SO4 + 2NaOH → Na2SO4 + 2H2O
- The 2 on the right hand side of the equation is there because of the shortage of H atoms on that side. The only thing to do is put a 2 there. However this means that there are too many H & O atoms on the right of the equation. To sort this out, we put a 2 on the left infront of NaOH and everything balances.
- Remember that whatever number you put infront says how many lots there are
- State symbols tell us what physical state things are in. E.g.....
- (s)=Solid (l)=Liquid (g)= Gas (aq)=Dissolved in water