Rocks and Building 1.4 Quicklime and slaked lime

Spot the mistakes Limestone is a metamorphic rock made up of the pure element calcium carbonate Limestone is a metamorphic rock made up of the pure element calcium carbonate Limestone is a sedimentary rock made up mainly of the compound calcium carbonate along with a mixture of other things Limestone is a sedimentary rock made up mainly of the compound calcium carbonate along with a mixture of other things

Learning objectives Understand how slaked lime is produced Understand how slaked lime is produced Know the process used to make a mortar Know the process used to make a mortar

Slaked Lime Heating calcium carbonate (limestone) produces calcium oxide (quicklime) Heating calcium carbonate (limestone) produces calcium oxide (quicklime) By adding water, we can produce slaked lime By adding water, we can produce slaked lime Calcium oxide + water calcium hydroxide Strongly basic – corrosive Strongly basic – corrosive Many uses Many uses Whitewash, soil treatment, brake pads and mortar Whitewash, soil treatment, brake pads and mortar

Lime water Dissolving slaked lime in water – lime water Dissolving slaked lime in water – lime water Tests for carbon dioxide Tests for carbon dioxide Turns cloudy Turns cloudy What is formed that makes it go cloudy? What is formed that makes it go cloudy? Ca(OH) 2 + CO 2 Ca(OH) 2 + CO 2 CaCO 3 + H 2 O

Investigation Investigate the reactions of limestone Investigate the reactions of limestone 1. Heat limestone – thermal decomposition 2. In a boiling tube, add a few drops of water to produce slaked lime – observe 3. Dissolve slaked lime in water to produce lime water 4. Blow through lime water using straw - observe

Why does the limewater turn cloudy? What is being formed? Why does the limewater turn cloudy? What is being formed? StageProductObservation Heating calcium carbonate Adding water to calcium oxide Dissolving calcium hydroxide Blowing through lime water

Using products of limestone 6000 years ago – Egyptians heated limestone and mixed it with water – made the pyramids 6000 years ago – Egyptians heated limestone and mixed it with water – made the pyramids 2000 years ago – Romans mixed slaked lime with sand – produced mortar 2000 years ago – Romans mixed slaked lime with sand – produced mortar Can hold building materials together Can hold building materials together Still used today Still used today

Mortar Doesn’t dry – it ‘goes off’ Doesn’t dry – it ‘goes off’ Chemical reaction Chemical reaction Gives out heat Gives out heat Calcium hydroxide + carbon dioxidecalcium carbonate + water Ca(OH) 2 + CO 2 CaCO 3 + H 2 O Important to get the right mix Important to get the right mix Not enough sand – shrinks and cracks Not enough sand – shrinks and cracks Too much sand – too weak Too much sand – too weak

Key Points When water is added to quicklime it produces slaked lime (calcium hydroxide) When water is added to quicklime it produces slaked lime (calcium hydroxide) Lime mortar is made by mixing slaked lime with sand and water Lime mortar is made by mixing slaked lime with sand and water