- Created by: Lily O'Keefe
- Created on: 31-03-09 10:38
Atoms, elements and compounds
All elements are made up of atoms. When two or more atoms join together a molecule is formed. The atoms in elements and compounds are held together by giving, taking or sharing electrons. We say that they are held tightly together by chemical bonds.
Substances made up of only one type of atom are elements.
Different atoms joined together are called compounds.
Two or more atoms bonded together are called a molecule.
All substances are made up of atoms.
Limestone and its Uses
Limestone is made mainly of calcium carbonate. Its dug out of the ground from quarries. Its used sometimes as building material.
Processing limestone can make it into several other building materials. One of these being glass. Powdered limestone can be heated to a high temperature with a mixture of sand and sodium carbonate to make glass.
Powdered Limestone + heat + sand, sodium carbonate = glass
Powdered Limestone can be heated with Powdered Clay to make cement.
Powdered limestone+heat+powdered clay = cement
Cement powder mixed with water, sand and crushed rock makes concrete.
Cement powder + water, sand, crushed rock = concrete
Calcium carbonate is CaCO3.
When limestone is heated, it breaks down to a substance called quicklime (calcium oxide). Carbon dioxide is also produced. Breaking down a chemical by heating is called thermal decomposition. This is shown by an equation:
calcium carbonate -h-e-a-t-->calcium oxide+ carbon
Limestone is most made up of calcium carbonate (whose chemical formula is CaCO3) As well as being used to produce blocks of building material, limestone can be used to produce cement, concrete and glass that can also be used in building.
We represent decomposition of carbonates by using chemical equations. These use chemical formulae for elements and compounds and help us to see how much of each chemical is reacting.
When calcium decomposes, we can show the chemical reaction like this:
CaCO3 ---> CaO + CO2
Equations must be perfectly balanced. There must be the same number of each type of atom on both sides of the equation. The mass of the products formed in the reaction is equal to the mass of the reactants.
Count the number of each type of atom on either side of the equation, if the numbers are equal, then the equation is balanced.
Quicklime and Slaked Lime
When we add water to quicklime, slaked lime is produce.
Slaked lime is calcium hydroxide. And it gives out alot of heat.
calcium oxide + water ----> calcium hydroxide
CaO h20 -------> Ca(Oh)2
Dissolving calcium hydroxide in water, then filtering, produces lime water.
We use lime water to test for carbon dioxide. We do this by bubbling carbon dioxide through lime water. If the solution turns cloudy then co2 is present. This is becuase calcium carbonate is formed, which is insoluble in water.
Mix slaked lime with sand and water to produce mortar.
Mortar holds other building materials together.
Like stone blocks or bricks.
It works because the lime in the mortar
reacts with the carbon dioxide in the air
producing calcium carbonate again.
Limestone has been used in building for thousands of years. When it is heated, limestone produces quicklime, also called calcium oxide. If calcium oxide is reacted with water calcium hydroxide is produced. This can be combined with sand to produce mortar, used to hold building materials like bricks together. Mortar relies carbon dioxide in the air to produce a chemical reaction in which calcium carbonate is formed.
Cement, concrete and glass
Cement Lime mortar holds bricks and stone together very strongly but doesnt work in all situations. Lime mortar doesnt harden very quickly. It wont set where waster prevents it from reacting with carbon dioxide.
Heating limestone with clay in a kiln produces cement. Portland cement in particular is made from limestone, clay and other minerals which are heated then grinded to a powder.
Concrete Concrete is very strong. Very good at resisting forces. Pouring it around steel rods or bars then allowing it to set makes it even stronger, we call this reinforcing concrete.
Glass Limestone can be used to make another building material - glass. When powdered limestone is mixed with sand and sodium carbonate and mixed strongly to produce glass.
Glass is very usefull becuase its weatherproof and light. Disadvantages are that its more breakable than other materials.