* KS4 Science GCSE/IGCSE Industrial Chemistry Revise 1. Limestone and thermal decomposition at Doc B's

DOC BROWN'S HOMEPAGE and WELCOME ALPHABETICAL SITE INDEX for chemistry KS3 SCIENCE QUIZZES and WORKSHEETS (~US grades 6-8) KS4 Science GCSE/IGCSE CHEMISTRY NOTES (~US grades 8-10) KS4 Science GCSE/IGCSE CHEMISTRY QUIZZES and WORKSHEETS (~US grades 8-10) KS4 Science GCSE/IGCSE CHEMISTRY SYLLABUS HELP LINKS (~US grades 8-10) ADVANCED LEVEL CHEMISTRY NOTES (~US grades 11-12) ADVANCED LEVEL CHEMISTRY QUIZZES and WORKSHEETS (~US grades 11-12) ADVANCED LEVEL CHEMISTRY SYLLABUS HELP LINKS (~US grades 11-12)  
TEACH YOURSELF CHEMISTRY
 Doc Brown's Chemistry  Industrial Chemistry

1. Limestone and thermal decomposition

Revision KS4 Science GCSE/IGCSE/O level Chemistry Information Study Notes for revising for AQA GCSE Science, Edexcel 360Science/IGCSE Chemistry & OCR 21stC Science, OCR Gateway Science  (revise courses equal to US grades 9-10)

Index of sections: 1. Limestone, lime - uses, thermal decomposition of carbonates, hydroxides and nitrates  *  2. Enzymes and Biotechnology  *  3. Contact Process, the importance of sulphuric acid  *  4. How can metals be made more useful? (alloys of Al, Fe, steel etc.) * 5. The importance of titanium  *  6. Instrumental Methods of Chemical Analysis * 7. Chemical economics of processes and sociological and environmental issues etc.

and other web pages of industrial chemistry: Ammonia synthesis/uses/fertilisers * Oil Products and Organic Chemistry *  Extraction of Metals * Halogens - sodium chloride Electrolysis * Transition Metals * Extra Electrochemistry

*****

limestone cliffs 1. Limestone - a very useful material useful limestone

  • GCSE Multiple choice QUIZ on Limestone and its uses:

  • Limestone, is a sedimentary rock formed by the mineral and 'shelly' remains of marine organisms, including coral, in warm shallow fertile seas. It is chemically mainly calcium carbonate and is a useful material that is quarried and used directly as a building material. It reacts with acids - 'fizzing' due to carbon dioxide formation - test with 'limewater' - milky white precipitate.

    • Marble is also made of calcium carbonate and is a metamorphic rock formed by the action of heat and pressure on limestone in the Earth's crust. It is a much harder rock than limestone and is used to make highly polished and finely carved stone sculptures, statues etc.

  • Chemically, limestone mainly consists of calcium carbonate, CaCO3, and is a valuable natural mineral resource, quarried in large quantities in many countries (see environmental impact at the end of the metal extraction web page).

  • Other uses of limestone rock are outlined below and it is an important raw material in the manufacture of cement and glass and iron.

  • Powdered limestone can be used to neutralise acidity in lakes and soils. (neutralisation chemistry). Like lime, it is a safe agri-chemical to use on the land and does produce the controversial side effects of artificial fertilisers, herbicides and pesticides etc.

  • When limestone is heated in a kiln at over 900oC, it breaks down into quicklime (calcium oxide) and carbon dioxide. Both are useful products. This type of reaction is endothermic (heat absorbing) and an example of thermal decomposition (and other carbonates behave in a similar way). 

    • calcium carbonate (limestone) ==> calcium oxide (quicklime) + carbon dioxide

    • CaCO3(s) (c) doc b CaO(s) + CO2(g)

    • This is a reversible endothermic reaction. To ensure the change is to favour the right hand side, a high temperature of over 900oC is needed as well as the continual removal of the carbon dioxide.

    • The high temperature needed is produced by mixing the limestone with coal/coke (a fuel of mainly carbon) and blowing hot air into the ignited mixture in a rotating kiln for a continuous production line (raw materials in at one end, lime out the other!)  ....

      • C(s) + O2(g) ==> CO2(g) is very exothermic - heat releasing!

    • Note on heating other carbonates - more thermal decomposition.

      • These also show a similar thermal decomposition to calcium e.g.

      • copper(II) carbonate(s, green)  ==> copper(II) oxide(s, black)  + carbon dioxide

      • CuCO3(s) ==> CuO(s) + CO2(g)

      • zinc carbonate(s, white)  ==> zinc oxide(s, yellow hot, white cold)  + carbon dioxide

      • ZnCO3(s) ==> ZnO(s) + CO2(g)

      • magnesium carbonate(s, white)  ==> magnesium oxide(s, white)  + carbon dioxide

      • MgCO3(s) ==> MgO(s) + CO2(g)

      • Zinc carbonate occurs as the mineral ores calamine/Smithsonite and the resulting zinc oxide can be used to extract zinc metal and zinc oxide itself is used as a whitening agent' in cosmetics and in 'calamine lotion' a mild antiseptic and antipruritic (anti-itching agent) for treating skin irritations.

    • FeCO3 and MnCO3 behave in a similar way (so just swap Zn/Ca/Cu with Fe or Mn)

    • Sodium hydrogen carbonate is used in baking powder because on heating it thermally decomposes releasing carbon dioxide gas that gives the 'rising' action in baking.

      • sodium hydrogencarbonate ==> sodium carbonate + water + carbon dioxide

      • 2NaHCO3(s) ==> Na2CO3(s) + H2O(l/g) + CO2(g)

      • This is just one of many chemical process that occur when food is cooked.

  • Quicklime reacts very exothermically with water to produce slaked lime (solid calcium hydroxide). 

    • calcium oxide (quicklime) + water ==> calcium hydroxide (slaked lime)

      • this is a very exothermic reaction, the quicklime 'puffs' up and steam is produced!

      • CaO(s) + H2O(l) ==> Ca(OH)2(s) 

      • with excess water followed by filtration you get calcium hydroxide solution or limewater.

diagram of the Limestone Cycle (c) doc bTop of page - sub-index and links

  • Lime (calcium oxide) and slaked lime (calcium hydroxide) are both used to reduce the acidity of soil on land, they are both faster and stronger acting than limestone powder. They are also used to reduce acidity in lakes and rivers due to acid rain. They are also used to neutralise potentially harmful industrial acid waste including sulphur dioxide in the flue gases of power stations.

  • In the test for carbon dioxide, calcium hydroxide solution (limewater) forms a white milky precipitate of calcium carbonate (back to where you started!). 

    • calcium hydroxide  + carbon dioxide ==> calcium carbonate + water

    •  Ca(OH)2(aq) + CO2(g) ==> CaCO3(s) + H2O(l)

  • Formulae of magnesium and calcium compounds (M = metal = Mg or Ca, same group 2, same formula!)

    • IONS: The metal ion in aqueous solution or solid compounds is M2+, which combines with other ions such as: oxide O2-, hydroxide OH-, carbonate CO32-, hydrogencarbonate HCO3-, chloride Cl-, sulphate SO42-, nitrate NO3- to form the calcium or magnesium compounds.

    • COMPOUND FORMULAE: oxide MO, hydroxide M(OH)2, carbonate MCO3, hydrogencarbonate M(HCO3)2, chloride MCl2, sulphate MSO4, nitrate M(NO3)2

  • The oxides and hydroxides readily react with acids.

    • general word equation: oxide or hydroxide  +  acid ==>  salt  +  water

      • examples ...

      • calcium oxide + hydrochloric acid ==> calcium chloride + water

      • magnesium hydroxide + nitric acid ==> magnesium nitrate + water

      • calcium hydroxide + sulphuric acid ==> calcium sulphate + water

    • since hydrochloric acid gives a chloride salt, nitric acid  gives a nitrate salt, sulphuric acid a sulphate salt ... the symbol equations are ... where M = Mg or Ca (or any other Group 2 metal)

      • MO(s) + 2HCl(aq) ==> MCl2(aq) + H2O(l)

      • MO(s) + 2HNO3(aq) ==> M(NO3)2(aq) + H2O(l)

      • MO(s) + H2SO4(aq) ==> MSO4(aq/s*)  + H2O(l)

      • if M(OH)2 involved, there is a 2H2O at the end NOT a single H2O to balance the symbol equation

      • M(OH)2(s) + 2HCl(aq) ==> MCl2(aq) + 2H2O(l)

      • M(OH)2(s) + 2HNO3(aq) ==> M(NO3)2(aq) + 2H2O(l)

      • M(OH)2(s) + H2SO4(aq) ==> MSO4(aq/s*)  + 2H2O(l)

      • * the sulphates of e.g. calcium and barium are not very soluble and this slows the reaction down!

  • Solubility of calcium compounds (and the chemically similar magnesium):

    • Magnesium and calcium oxides or hydroxides are slightly soluble in water forming alkaline solutions. They readily react and dissolve in most acids (see above).

    • Magnesium and calcium carbonate are insoluble in water but readily dissolve in most dilute acids like hydrochloric, nitric and sulphuric.

    • Equation examples for calcium carbonate (similar for magnesium carbonate) ...

    • calcium carbonate + hydrochloric acid ==> calcium chloride + water + carbon dioxide

      • CaCO3(s) + 2HCl(aq) ==> CaCl2(aq) + H2O(l) + CO2(g)

    • calcium carbonate + nitric acid ==> calcium nitrate + water + carbon dioxide

      • CaCO3(s) + 2HNO3(aq) ==> Ca(NO3)2(aq) + H2O(l) + CO2(g)

    • calcium carbonate + sulphuric acid ==> calcium sulphate + water + carbon dioxide

      • CaCO3(s) + H2SO4(aq) ==> CaSO4(aq,s)  + H2O(l) + CO2(g)

      • Calcium carbonate reacts slowly in dilute sulphuric acid because calcium sulphate is not very soluble and coats the limestone.

  • Magnesium and calcium hydrogencarbonate are soluble in water and cause 'hardness' i.e. scum with 'traditional' non-detergent soaps. Formulae are Mg(HCO3)2 and Ca(HCO3)2

  • Cement is produced by roasting a mixture of powdered limestone with powdered clay* in a rotary kiln. When cement is mixed with water, sand and crushed rock, a slow chemical reaction produces a hard, stone-like building material called concrete.

    • * Clay is also used directly to make pottery and other ceramics

  • Glass is made by heating together a mixture of limestone (CaCO3), sand (mainly silica = silicon dioxide = SiO2) and 'soda' (sodium carbonate, Na2CO3).

  • Limestone is used to remove acidic oxide impurities in the extraction of iron and in making steel.

  • Calcium oxide and calcium hydroxide also react with acids to form salts. You will find details of this kind of reaction on the Acids and Bases pages.

  • Limestone and hard/soft water are covered on the Extra Aqueous Chemistry page.

  • (c) doc bmultiple choice test on limestone etc.

Limestone Chemistry and Uses (c) doc bTop of page - sub-index and links
Other thermal decompositions (not needed by some syllabuses)

  • Decomposition of carbonates: see above.

  • Decomposition of metal hydroxides:

    • The Group 1 Alkali Metal hydroxides do not readily decompose on heating even 'up to red heat'.

      • Except for lithium hydroxide which forms lithium oxide and water.

        • 2LiOH(s) ==> Li2O(s) + H2O(l) 

      • These hydroxides are white solids and soluble in water to give an alkaline solution.

    • On heating, the Group II, Lead, Aluminium and Transition Metal hydroxides decompose to form the metal oxide and water vapour.

      • The original hydroxides are usually relatively insoluble solids, white in colour, except copper(II) hydroxide is blue and iron(III) hydroxide is brown.

    • M(OH)2(s) ==> MO(s) + H2O(l) 

      • M = Mg, Ca, Zn giving white oxide MO (ZnO yellow when hot),

      • M = Cu gives black copper(II) oxide CuO, M = Pb gives yellow lead(II) oxide PbO

      • e.g. if M = Zn: zinc hydroxide ==> zinc oxide + water

    • and 2M(OH)3(s) ==> M2O3(s) + 3H2O(l) 

      • where M = Al to give white aluminium oxide, and M = Fe to give reddish-brown iron(III) oxide.

  • Decomposition of nitrate salts:

    • The Group 1 Alkali Metal nitrates (NO3) decompose to form the nitrite (NO2) salt and oxygen gas.

      • 2MNO3(s) ==> 2MNO2(s) + O2(g) where M = Na or K

      • so when M = Na: sodium nitrate ==> sodium nitrite + oxygen

      • Nitrates are colourless crystals and nitrites are white solids and are all soluble in water giving neutral solutions.

    • Many metal nitrates decompose to form the metal oxide, nasty brown nitrogen dioxide gas (NO2) and oxygen gas (O2) when strongly heated.

      • These nitrates are all water soluble neutral salts, all colourless crystals except Cu is blue and Fe is pale brown-dark orange.

      • 2M(NO3)2(s) ==> 2MO(s) + 4NO2(g) + O2(g) 

        • where M = Mg, Ca, Zn giving the white oxide MO (ZnO yellow when hot),

        • when M = Cu, it gives the black copper(II) oxide CuO

        • if M = Pb it gives the yellow lead(II) oxide PbO.

      • 4M(NO3)3(s) ==> 2M2O3(s) + 12NO2(g) + 3O2(g) 

        • If M = Al, it gives white aluminium oxide, if M = Fe it gives give reddish-brown iron(III) oxide.

    • See gas preparation and collection page for methods.

  • -

CaCO3 Ca(OH)2 CaO CuCO3 ZnO ZnCO3 MgCO3 MgO

top sub-indexWebsite content copyright © Dr W P Brown 2000-2010 All rights reserved on revision notes, puzzles, quizzes, worksheets, x-words etc. * Copying of website material is not permitted * I do not personally endorse the adverts - but they do pay for the site!
(spanish) Doc Brown de Química Química Industrial Piedra caliza y de descomposición térmica Índice de secciones: 1. caliza, cal - los usos, la descomposición térmica de los carbonatos, hidróxidos y nitratos * 2. Enzimas y biotecnología 3. Proceso de Contacto, la importancia del ácido sulfúrico * 4. ¿Cómo pueden los metales sean más útiles? Aleaciones de Al, Fe, acero, etc) * 5. La importancia de titanio * 6. Métodos Instrumentales de Análisis Químico * 7. química de los procesos económicos y sociológicos y cuestiones medioambientales * (german) Doc Brown's Chemistry Industrial Chemistry Kalkstein und thermische Zersetzung Kalkstein - ein sehr nützliches Material Kalkstein ist ein Sedimentgestein und geformt durch das Mineral "Shelly" Überreste von marinen Organismen, einschließlich Korallen, in warmen flachen fruchtbaren Meere. Es ist chemisch hauptsächlich Calciumcarbonat und ist ein nützliches Material, und wird abgebaut verwendete Material(portuguese) de Química Industrial 1. e decomposição térmica da pedra calcária 1. calcário, calcário - que utiliza, a decomposição térmica dos carbonatos, hidróxidos e nitratos Calcário é uma rocha sedimentar formada pelos minerais e "Shelly" restos de organismos marinhos, incluindo corais, em águas rasas quentes fértil. It is chemically mainly calcium carbonate and is a useful material that is quarried and used directly as a building material . It reacts with acids - 'fizzing' due to carbon dioxide formation - test with 'limewater' - milky white precipitate. É quimicamente principalmente carbonato de cálcio e é um material útil que é extraído e utilizado diretamente como material de construção. Reage com ácidos - 'fizzing ", devido à formação de dióxido de carbono - teste com" água de cal' - precipitado branco leitoso. O mármore é também feito de carbonato de cálcio e é uma rocha metamórfica formada pela ação do calor e da pressão sobre pedra calcária em crosta da Terra. É um rock muito mais difícil do que o calcário e é usado para fazer muito polido e finamente esculpida esculturas de pedra, estátuas. Quimicamente, o calcário é constituído principalmente de carbonato de cálcio, CaCO3, e é um recurso natural precioso mineral, extraído em grandes quantidades em muitos países ( ver o impacto ambiental no final da página web da extracção de metais). Outros usos da pedra calcária são descritos a seguir e é uma matéria- prima importante na fabricação de cimento e de vidro e ferro. calcário em pó pode ser usado para neutralizar a acidez dos lagos e solos. ( neutralização química ). Como cal , é um seguro agro-químicos para uso na terra e não produzir os efeitos colaterais controversa de fertilizantes artificiais, herbicidas e pesticidas, etc Quando o calcário é aquecido num forno a 900 ° C, se decompõe em cal (calcium oxide) and carbon dioxide. (Óxido de cálcio) e dióxido de carbono. Both are useful products. Ambos são produtos úteis. Este tipo de reação é endotérmica (absorve calor) e um exemplo de decomposição térmica (e outros carbonatos se comportam de maneira semelhante). *  direkt als ein Gebäude. Es reagiert mit Säuren - "zischendes" durch die Bildung von Kohlendioxid - Test mit "Kalkwasser" - milchig weißer Niederschlag. *
TEACH YOURSELF CHEMISTRY