Limestone

some rocks are very important building materials:

limesone and sandstone used as building blocks to make houses (the yellow stoned houses in the cotswolds are made out of limstone blocks)

polished marble and granite are used as decorative rocks ('important' buildings such as high street banks often have exteriors which are clad with granite)

slate is a rock that can be easily split into sheets. this makes it ideal for roofing tiles.

however, cheaper building materials can be manufactured from rocks, in particular from limestone

limestone is a rock that is made mainly of calcium carbonate. some types of limestone were formed from the shells and bones of tiny lifeforms that lived in the sea millions of years ago. we dig limestone out of the ground in quarries around the world. it has many important uses, including use as a building material.

compounds of metals and non-metals like calcium carbonate are generally ionic

limestone is used for the following

• as a building material (10%)
• to make glass (15%)
• to neutralise acid (5%)
• to make paper (10%)
• to make concrete (25%)
• to make steel (20%)
• to make cement

calcium carbonate is an alkali so when added to acidic soil or water it neutralises. CaCO₃+ 2HCl → CO₂+ H₂O

• copper, zinc, magnesium and sodium carbonates are tested for thermal stability
• limewater was used to test for CO₂and all of the carbonates gave it off
• Copper carbonate decomposed very easily and turned from green to black
• calcium carbonate had no colour change and decomposed slowly
• zinc carbonate decomposed very easily and turned yellow, but when it cooled down it turned white
• sodium carbonate decomposed very slowly and there was no colour change 
• the copper carbonate turned black because CuO (the product) is black

CaCO₃→ CaO +CO₂calcuim carbonate + heat → calcuim oxide + carbon dioxide

equation for thermal decomposition

Metal cabonate → metal oxide + carbon dioxide

the metal carbonates where aded to dilute hydrochloric acid and the gas was passed through lime water to test for carbon dioxide

all of the metal carbonated fizzed and produced carbon dioxide

Magnesium Carbonate + hydrochloric acid → water + carbon dioxide +magnesium Cholride

equation for effect on acid

metal carbonate + hydrochloric acid →  water + carbon dioxide + metal chloride

rainwater is usually slightly acidic because it contains  sulphuric acid from the atmosphere

rain can be more acidic near cities, industrial areas and factories. acid rain would slowly erode limestone buildings

calcium oxide reacts with water to give calcuim hydroxide which is an alkali (pH 11). both of these substances are bases that will react with acids in a neutralising reaction.

CaO + 2HCl →  CaCl₂+ H₂O

Ca(OH)₂+H₂SO₄→ CaSO₄ + 2H₂O

both calcium oxide and calcium hydroxide can be spread on fields to neutralise the acid in the soil. limestone (calcium carbonate) can be heated with clay to make cement. when cement is mixed with sand, morter is made (this is the substance used to 'stick' brick together in buildings. when cement is mixed with sand and aggregate (small stones and gravel) concrete is formed. glass  can also be made by heating limestone with sand and a littel sodium carbonate

• Limestone
• name: Calcuim Carbonate
• formula: CaCO₃
• uses: neutralising soil, building →
• Quicklime
• name: Calcium Oxide
• formula: CaO
• uses: glass →
• Slaked Lime
• name: Calcium Hydroxide
• formula: Ca(OH)₂
• uses: mortar →
• Lime water
• name: Calcuim Carbonate
• formula: CaCO₃
• uses: testing for CO₂→ (back to Limestone)

calcuim carbonate (limestone) is heated in a flame, CO₂is produced, and what is left is calcium oxide (quicklime). CaCO₃→ CaO + CO₂

water is added to the calcuim oxide, they react exothermically to produce calcium hydroxide (slaked lime). CaO + H₂O → Ca(OH)₂

the mixture is filtered. the filtrate contains dissolved calium hydroxide, which is also called limewater. when carbon dioxide is passed through the solution, the calcium hydroxied reacts to make calium carbonate and this makes the water cloudy. Ca(OH)₂+CO₂→ CaCO₃+H₂O

as we have seen limestone itself is used as a material in the construction of buildings. building with quarried stone was a slow and labour intensive process. each block had to be carefully cut to shape and fitted into place by expert craftsmen. this made it slow and expensive. today, however meset quarried limestone is used to make cement. the limestone is heated with clay in a big oven and thermal decompossition occurs. this oven is called a rotary kiln because it keeps turning to mix everything up. the roasted product is then ground to form a light grey powder. this is cement. it forms a paste with water which soon hardens back to rock.

previous to using cement a substance called mortar was used to stick bricks together - this was made by mixing slaked lime (ie calcium hydroxie) into a paste with water

cement is used to stick bricks together, but most cement is mixed with sand, gravel and water to make concrete. this is cheaper and stronger than pure cement.

concrete forms a thick liquid when first mixed, and can be poured into any shape. slow chemical reactions make it set after a few hours and eventually it becomes rock hard. it is used to make roads, bridges and the frameworks and foundations of buildings

Key: Limestone, concrete, disadvantages, advantages

• pretty
• simmple process
• can be moulded
• more resistant to chemicals
• destroyed by acid rain
• erodded easily
• has to be cut
• is ugly
• lots of carbon dioxide produced