Limestone and Building Materials, Calcium Carbonate, Metals and their uses

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Limestone and Building Materials

Uses of limestone

Limestone is a type of rock, mainly composed of calcium carbonate. Limestone is quarried (dug out of the ground) and used as a building material. It is also used in the manufacture of cement, mortar and concrete.                                           Reactions with acids:                                                                                                                                                   Carbonates react with acids to produce carbon dioxide, a salt and water. For example:                                             calcium carbonate + hydrochloric acid → carbon dioxide + calcium chloride + water

CaCO3 + 2HCl → CO2 + CaCl2 + H2O                                                                                       Since limestone is mostly calcium carbonate, it is damaged by acid rain. Sodium carbonate, magnesium carbonate, zinc carbonate and copper carbonate also react with acids: they fizz when in contact with acids, and the carbon dioxide released can be detected using limewater. 

Advantages and disadvantages of various building materials:                                                                         Limestone, cement and mortar slowly react with carbon dioxide dissolved in rainwater and wear away. This damages walls made from limestone, and leaves gaps between bricks in buildings. These gaps must be filled in or ‘pointed’. Pollution from burning fossil fuels makes the rain more acidic than it should be, and this acid rain makes these problems worse.               Concrete is easily formed into different shapes before it sets hard. It is strong when squashed, but weak when bent or stretched. However, concrete can be made much stronger by reinforcing it with steel. Some people think that concrete buildings and bridges are unattractive.

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Limestone and Building Materials

Calcium hydroxide

When limestone is heated strongly, the calcium carbonate it contains decomposes to form calcium oxide. This reacts with water to form calcium hydroxide, which is analkali. Calcium hydroxide is used to neutralise excess acidity, for example, in lakes and soils affected by acid rain.                                                                                                                                      Cement, mortar and concrete:                                                                                                                                                                        Cement is made by heating powdered limestone with clay. Cement is an ingredient in mortar and concrete:        mortar, used to join bricks together, is made by mixing cement with sand and water

  • concrete is made by mixing cement with sand, water and aggregate (crushed rock)                                          Limestone, cement and mortar slowly react with carbon dioxide dissolved in rainwater, and wear away. This damages walls made from limestone, and it leaves gaps between bricks in buildings. These gaps must be filled in or "pointed". Pollution from burning fossil fuels makes the rain more acidic than it should be, and this rain makes these problems worse.                                                                                                                             Concrete is easily formed into different shapes before it sets hard. It is strong when squashed, but weak when bent or stretched. However, concrete can be made much stronger by reinforcing it with steel. Some people think that concrete buildings and bridges are unattractive.                                                                                    Glass is usually brittle and easily shattered, but toughened glass can be used for windows. While glass is transparent and so lets light into a building, the use of too much glass can make buildings very hot in the summer
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Calcium Carbonate

Limestone is mainly calcium carbonate, CaCO3. When heated, it breaks down to form calcium oxide and carbon dioxide. Calcium oxide reacts with water to produce calcium hydroxide.

Limestone and its products have many uses: for example, in mortar, cement, concrete and glass.       Limestone, chalk and marble:                                                                                                                 Limestone, chalk and marble are all forms of calcium carbonate. They exist naturally in the Earth’s crust. Limestone is a very common building material and many tonnes are quarried in the UK every year. It is used for building - making concrete and cement - and the manufacture of glass, steel and iron.

Quarrying                                                                                                                    The limestone industry: environmental, social and economic considerations

Quarrying limestone is big business but the need for limestone has to be balanced against the economic, environmental and social effects. Some factors that have to be considered include:

  • effect on employment – increased job opportunities
  • pollution – noise, sound and air
  • traffic levels
  • visual effects of having a quarry
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Calcium Carbonate

Thermal decomposition

Metal carbonates such as calcium carbonate break down when heated strongly. This is called thermal decomposition. Here are the equations for the thermal decomposition of calcium carbonate:                                                       calcium carbonate right facing arrow with heat (http://www.bbc.co.uk/staticarchive/24ac5d1dcb82bc24e9ac3908069170de44a9b545.gif) calcium oxide + carbon dioxide                                CaCO3right facing arrow with heat (http://www.bbc.co.uk/staticarchive/24ac5d1dcb82bc24e9ac3908069170de44a9b545.gif) CaO + CO2

Other metal carbonates decompose in the same way. Here are the equations for the thermal decomposition of copper carbonate:         copper carbonate right facing arrow with heat (http://www.bbc.co.uk/staticarchive/24ac5d1dcb82bc24e9ac3908069170de44a9b545.gif) copper oxide + carbon dioxide      CuCO3right facing arrow with heat (http://www.bbc.co.uk/staticarchive/24ac5d1dcb82bc24e9ac3908069170de44a9b545.gif) CuO + CO2

Notice that in both examples the products are a metal oxide and carbon dioxide. The carbon dioxide gas can be detected using limewater. Limewater turns cloudy white when carbon dioxide is bubbled through it.

Metals high up in the reactivity series - such as calcium - have carbonates that take a lot of energy to decompose them. Metals low down in the reactivity series - such as copper - have carbonates that are easily decomposed. This is why copper carbonate is often used at school to show these reactions. It is easily decomposed, and its colour change, from green copper carbonate to black copper oxide, is easy to see.

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Metals and their uses

Metals are very useful. Ores are naturally occurring rocks that contain metal or metal compounds in sufficient amounts to make it worthwhile extracting them: most everyday metals are mixtures called alloys.                                                                                                                        Methods of extracting metals:

The Earth's crust contains metals and metal compounds such as gold, iron oxide and aluminium oxide, but when found in the Earth these are often mixed with other substances. To become useful, the metals have to be extracted from whatever they are mixed with. A metal ore is a rock containing a metal, or a metal compound, in high enough concentration to make it economic to extract the metal.                           Ores are mined. They may need to be concentrated before the metal is extracted and purified. The economics of using a particular ore may change over time. For example, as a metal becomes rarer, an ore may be used when it was previously considered too expensive to mine.                                   Reactivity and extraction method: Metals are produced when metal oxides are reduced (have their oxygen removed). The reduction method depends on the reactivity of the metal. For example, aluminium and other reactive metals are extracted by electrolysis, while iron and other less reactive metals may be extracted by reaction with carbon or carbon monoxide.

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Metals and their uses

Iron is extracted from iron ore in a huge container called a blast furnace. Iron ores such as haematite contain iron oxide. The oxygen must be removed from the iron oxide to leave the iron behind. Reactions in which oxygen is removed are called reduction reactions.                                                           Carbon is more reactive than iron, so it can push out or displace the iron from iron oxide. Here are the equations for the reaction:    iron oxide + carbon → iron + carbon dioxide  2Fe2O3 + 3C → 4Fe + 3CO2                                                                           In this reaction, the iron oxide is reduced to iron, and the carbon is oxidised to carbon dioxide. In the blast furnace, it is so hot that carbon monoxide will also reduce iron oxide:     iron oxide + carbon monoxide → iron + carbon dioxide       Fe2O3 + 3CO → 2Fe + 3CO2                                                                                                                                      Copper is soft and easily bent and so is a good conductor of electricity, which makes it useful for wiring. Copper is also a good conductor of heat and it does not react with water. This makes it useful for plumbing, and making pipes and tanks.                                                                                                           Some copper ores are copper-rich – they have a high concentration of copper compounds. Copper can be extracted from these ores by heating them in a furnace, a process called smelting. The copper is then purified using a process called electrolysis.                                                                                             Electricity is passed through solutions containing copper compounds, such as copper sulfate. During electrolysis, positively charged copper ions move towards the negative electrode and are deposited as copper metal.

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