Limestone is a raw material used in manufacture of concrete, which, when heated, calcium carbonate it contains forms calcium oxide.
Calcium Carbonate ----> Calcium Oxide + Carbon Dioxide
CaCO³(s) ------> CaO(s) + CO²(g)
When water is added to calcium oxide a lot of heat is released and calcium hydroxide, a crumbly white solid, forms in the reaction.
Calcium Oxide + Water -----> Calcium Hydroxide
CaO(s) + H²O(l) ------> Ca(OH)²(s)
Calcium Hydroxide dissolves when more water is added forming a solution, commonly known as limewater.
A Test For Carbon Dioxide-
Limewater turns milky in the presence of Carbon Dioxide because white insoluble calcium carbonate forms:
Calcium Hydroxide + Carbon Dioxide -----> Calcium Carbonate + Water
Ca(OH)²(aq) + CO²(g) ------> CaCO³(s) + H²O(l)
Neautralising Acids With Limestone-
*Acids are neutralised by alkalis, called a neutralisation reaction.
*Calcium Carbonate, Calcium Oxide and Calcium Hydroxide can neutralise acids.
*If, for example, farmers need to reduce the acidity of their soil, they could spray any of the powdered chemicals mentioned over their fields.
*Coal naturally contains sulfur and compounds.
*When coal burns the sulfur forms sulfur dioxide.
Sulfur + Oxygen -----> Sulfur Dioxide
S(s) + O²(g) ------> SO²(g)
Key Words:
Limewater
Neutralisation Reactions
Questions:
1) What is the test for carbon dioxide?
2) Which calcium compounds can be used to reduce soil acidity?
3) How do they reduce acidity?
What you should know:
- 2.14 Be able to describe the effect of water on calcium oxide to form calcium hydroxide ('slaked lime')
- 2.15 Be able to describe how calcium hydroxide dissolves in water to form a solution, known as limewater.
- 2.17 Be able to explain how calcium oxide, calcium hydroxide and calcium carbonate can be used to neutralise soil acidity.
- 2.18 Be able to explain how calcium carbonate can be used to remove acidic gases from coal-fired power station chimneys, reducing harmful emissions and helping to reduce acid rain.
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