Cambridge IGCSE CHAPTER - 13 - Carbonates - More Resources

Other resources

Downloadable PDF file

• Colored PDF version

https://drive.google.com/file/d/12GzxOqTd-emrNGWCcot0cNwoJp0-Tefh/view?usp=sharing 

• Black and White version PDF

https://drive.google.com/open?id=1otNCm00MmueZUIfBaApGgO4i5Id2N_gR 

A fast quiz link from here

https://kanayatichemistry.blogspot.com/2019/03/chapter-13-carbonates-quiz_31.html

another presentation

http://www.knockhardy.org.uk/gcse_htm_files/gcaco3pps.pps

Notes in the form of pictures

Calcium Oxide and Calcium Carbonate

Core:

• Describe the manufacture of lime (calcium oxide) from calcium carbonate (limestone) in terms of thermal decomposition

• Name some uses of lime and slaked lime such as in treating acidic soil and neutralising acidic industrial waste products, e.g. flue gas desulfurization

• Name the uses of calcium carbonate in the manufacture of iron and cement

Manufacture of lime

• Limestone consists mainly of  calcium carbonate, CaCO₃.
• Lime which is calcium oxide, is manufactured from calcium carbonate by thermal decomposition:
  • CaCO₃ →  CaO + CO₂

• Slaked lime, calcium hydroxide, is made by adding a small amount of water slowly to calcium oxide:
  • CaO + H₂O →  Ca(OH)₂

• Limewater is a solution of calcium hydroxide in water, hence it is alkaline.

• The addition of carbon dioxide to calcium hydroxide produces the initial starting material, calcium carbonate:
  • CO₂ + Ca(OH)₂ → CaCO₃ + H₂O

• This reaction is the basis of the standard chemical test for CO₂

Ca(OH)₂ solution turns cloudy when in the presence of CO₂ gas due to the formation of insoluble white calcium carbonate

The combination of these three reactions constitutes the limestone cycle:

Uses of limestone and limestone products

• Limestone (calcium carbonate) is used in the manufacture of iron and cement.
• In the production of iron, limestone is added to the blast furnace where it decomposes to form lime (CaO) and carbon dioxide.
• The lime reacts with silica impurities to form calcium silicate, which floats to the top of the molten iron and is removed:
  • CaO + SiO₂ → CaSiO₃

• Cement is manufactured by heating a mixture of powdered limestone and clay in a rotary kiln.
• Once heated, calcium sulfate and water are added which produce cement.
• Cement is a hardened, interlocked structure of calcium aluminate (Ca(AlO₂)₂ and calcium silicate (CaSiO₃).
• CaCO₃ is also used in treating excess acidity in soils and lakes where it is often preferred to lime because it does not make the water in the soil alkaline. 

• Lime (calcium oxide) is used in lime mortar and in flue-gas desulfurization.
• Flue-gas desulfurization involves spraying acidic sulfur dioxide emissions with jets of slaked lime to reduce pollution by neutralising these gases before they leave the factory chimneys.
• Lime is also used in treating excess acidity in soils and lakes. If excess lime is used, however, the water in the soil may become too alkaline.
• Slaked lime (calcium hydroxide) is used in treating acidic soils and neutralising acidic industrial wasted products.

Thermal decomposition of metal carbonates

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Class practical

This experiment involves a comparison between the thermal stabilities of carbonates of reactive metals, such as sodium and potassium, and the carbonates of less reactive metals, such as lead and copper.

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Lesson organisation

This experiment can be carried out as a class exercise, individually or in pairs. Because of the toxicity of lead compounds, it may be best to leave lead carbonate out with less reliable classes.

The experiment should take about 40 - 45 minutes.

Apparatus	Chemicals
Eye protection Each group will require: Test-tubes, 2 (per carbonate) Delivery tube (right-angled) Spatula Bunsen burner Clamp and stand	Limewater (calcium hydroxide solution), 10 cm3 per carbonate About 2 g each of following solids: Copper carbonate (HARMFUL) Lead carbonate (TOXIC, DANGEROUS FOR THE ENVIRONMENT) Potassium carbonate (IRRITANT) Sodium carbonate, anhydrous (IRRITANT) Zinc carbonate Refer to Health & Safety and Technical notes section below for additional information.

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Health & Safety and Technical notes

Read our standard health & safety guidance

Wear eye protection. It is important not to inhale dust of lead carbonate or the oxide formed. Wash hands after using lead compounds.

Limewater (calcium hydroxide solution), Ca(OH)₂(aq), (treat as IRRITANT) -see CLEAPSS Hazcard and Recipe Book. 

Copper carbonate, CuCO₃.Cu(OH)₂(s), (HARMFUL) - see CLEAPSS Hazcard.

Lead carbonate, PbCO₃(s), (TOXIC, DANGEROUS FOR THE ENVIRONMENT) - see CLEAPSS Hazcard.

Potassium carbonate, K₂CO₃(s), (IRRITANT)  - see CLEAPSS Hazcard.

Sodium carbonate, anhydrous, Na₂CO₃(s), (IRRITANT) - see CLEAPSS Hazcard.

Zinc carbonate, ZnCO₃(s)  - see CLEAPSS Hazcard.

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Procedure

a Put a large spatula measure of the carbonate to be tested in a test-tube.

b Fit a delivery tube and then clamp the test-tube so that the delivery tube dips into a second test-tube containing 2-3 cm³ limewater.

c Heat the solid gently at first, then more strongly.

d Lift the delivery tube from the limewater before, or as soon as, the heating is stopped. This is to avoid "suck-back".

e Write down all observations. Notice what happens to the limewater and how long it takes to turn milky (if at all). Notice whether any melting occurs in the heated test-tube and any colour changes taking place. Write your results in tabular form.

f Repeat the experiment with the other metal carbonates supplied, and in each case write down your observations.

g Wash your hands thoroughly at the end of these experiments, since some of the metal carbonates are toxic.

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Teaching notes

It is important to emphasize how "suck-backs" are avoided before the students begin, otherwise there are bound to be mishaps.

It is also important to ensure that students wash their hands after using lead carbonate, and to ensure that dust is not raised when this solid is being used.

The relative ease with which the carbonates of some of the less reactive metals are decomposed has been used in the extraction of these metals from ores that contain the metal as a carbonate, for example zinc carbonate (calamine).

Students should find that sodium and potassium carbonates give no carbon dioxide or any other sign that decomposition has taken place, even after prolonged heating.

Those metal carbonates which do decompose leave a residue of the metal oxide and evolve carbon dioxide in the process:

eg ZnCO₃(s) → ZnO(s) + CO₂(g)

At an elementary level, the relative thermal stability of the carbonates of the metals cannot easily be explained in terms of simple ideas of bonding in these compounds. A simple relationship between the reactivity of the metal and the stability of its compounds, such as the carbonate here, will have to suffice.

With abler and older students it may be appropriate to refer to the polarization (distortion) of the electron cloud of the carbonate ion by the metal ion, and that this is bound to be more pronounced when the metal ion is doubly, rather than singly charged, and small. Polarization eventually leads to abstraction of oxygen from the carbonate ion, producing the oxide ion and a carbon dioxide molecule. The greater the polarization, the lower the temperature needed to decompose the carbonate.

Health & Safety checked, August 2016

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Resource

http://www.rsc.org/learn-chemistry/resource/res00000450/thermal-decomposition-of-metal-carbonates?cmpid=CMP00005971

you can move to from here

Carbonates Notes

Carbonates Quiz