ch1 rocks as building materials

7/30/2019 CH1 Rocks as Building Materials

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Metal carbonates, including limestone, are attacked by acids: e.g.sulphuric acid + calcium carbonate calcium sulphate + water + carbon dioxide

H2SO4 + CaCO3 CaSO4 + H2O + CO2

Acid rain may contain sulphuric acid, from sulphurdioxide dissolving in rain droplets:

Acid rain is therefore capable of slowly

weathering limestone buildings and monuments,which is a disadvantage of this building material.

Limestone is mainly composed ofcalcium carbonate CaCO3from the shells of sea creatures. It is quarried and the cut

blocks can be used directly as a building material. For example,

St Pauls Cathedral in London is made from limestone.

Limestone rock is soft compared to

rocks such as granite, which makes

it easier to cut and shape. It is also

fairly readily available.


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Many metals form compounds called carbonates they contain carbon and oxygenas well as the metal. Here are some names and formulae:

Magnesium carbonate MgCO3 Potassium carbonate K2CO3Barium carbonate BaCO3 Copper carbonate CuCO3

Sodium carbonate Na2CO3 Zinc carbonate ZnCO3

Many carbonates decompose when heated in a Bunsen flame to give the metal

oxide and carbon dioxide gas. The carbonates of metals in Group 2 and Transition

metal carbonates both do this e.g.

metal carbonate metal oxide + carbon dioxide

e.g. magnesium carbonate magnesium oxide + carbon dioxideMgCO3 MgO + CO2

Reactions like this, where a compound breaks up when heated are called THERMALDECOMPOSITIONS

Some metal carbonates (e.g. sodium carbonate) dont compose when heated with a

Bunsen they require much higher temperatures to decompose.


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Social Impacts of quarrying limestone:

ADVANTAGES DISADVANTAGES

Better employment for local people Homes close by affectedby quarry company dust and noise

Growth of local community and perhaps Health of people affectedinvestment in social facilities, more by dust and/or noiseshops etc.

May develop better rail links if stone Limestone often found incarried by rail areas of natural beauty -

loss of tourism

Increased traffic to/from

quarry delays, noise

You dont have to learn these exact advantages and disadvantages but you do need to be able to suggest what advantages anddisadvantages there may be in a given situation, perhaps based on

some specific text information, or perhaps just in general terms.


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Economic Impacts of quarrying limestone:


Profit for company extracting limestone Tourism income may beso wages for their employees decreased

Employees spend money in local shops Disruption of traditionalbusinesses e.g. farming

More people move into the area for jobs with loss of profit

so more money being spent locallyTraffic jams etc. cause

Cheaper supply of limestone and limestone loss of business hours forproducts for local businesses which use it other companies




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Environmental Impacts of quarrying limestone:


Conservation schemes required of Loss of animal and plant habitatsquarry company may improve causing reduced numbersprotection of rare/endangeredspecies Dust and noise affecting people

and wildlife alikeArea might be restored after

quarrying complete Rare or endangered species mightdie out

Increased traffic causing pollutionof air (CO, nitrogen oxides, dust)




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As we have seen,calcium oxide is formed when limestone is heated strongly:

calcium carbonate calcium oxide + carbon dioxideCaCO3 CaO + CO2

Quicklime reacts with water to produce calcium hydroxide in an exothermicreaction (heat given out, which can cause burns).

calcium oxide + water calcium hydroxide [Exothermic]CaO + H

2

O Ca(OH)2

For this reasons farmers prefer to use calcium hydroxide rather than calcium oxide

for treating soil which is too acidic, although either would do the job perfectly well

because both are bases which can neutralise acids.

Calcium hydroxide is also used for remediationof lakes or rivers which have become

too acidic due to acid rain.


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Calcium hydroxide is a white solid

A solution of calcium hydroxide is colourless, and is called limewater. This is used totest for the presence ofcarbon dioxide.

Carbon dioxide turns a solution of limewater milky if the limewater is shaken with the

gas, or the gas is bubbled through.

This is because the carbon dioxide reacts with the

calcium hydroxide to form a precipitate of calcium carbonate.

Ca(OH)2 + CO2 CaCO3 + H2O

We have seen that in a cycle of reactions,calcium carbonate can be turned into calcium

oxide, which can be turned into calcium

hydroxide, which can be turned back into calcium

carbonate

limewater

CO2


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limestone

quicklime

slaked lime

limewater

reaction:CaCO3 CaO + CO2

reaction:CaO + H2O Ca(OH)2

reaction:Ca(OH)2 + CO2 CaCO3 + H2O

CaCO3

calcium oxide

calcium hydroxide

ADD WATERDISSOLVE &FILTER

BUBBLE CO2THROUGH Heat strongly

The limestone cycle


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MortarThe ancients used calcium oxide, mixed with water, as a

coating materials for building such as the Pyramids.

Calcium oxide mixed with sand and water forms lime mortarwhich was used for joining blocks of brick or stone together,however lime mortar needs carbon dioxide to be available in

order to set so it doesnt set under wet conditions.

Lime mortar sets because the calcium oxide reacts with water

to form calcium hydroxide, which then reacts slowly withcarbon dioxide to form calcium carbonate the mineral in

limestone.

Ca(OH)2 + CO2 CaCO3 + H2O

In other words as mortar sets a rock-like material is formedwhich bonds the blocks together.

The Romans first made mortar which could set when wet, by

adding volcanic ash or brick dust to the mortar mixture.

Modern mortars are made by using cement and sand.


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Cement is a powdered mixture of clay and limestonewhich has been roasted in a kiln at high temperature.

Cement is mixed with sand to make mortar which

will set when wet (unlike the lime mortar used inancient times). This is used for bonding together

bricks or stone blocks in buildings.

Cement is also used to make concrete

The Portland Cement which is used today has beendeveloped over the years to optimise its properties

endurance, speed of setting etc. It contains a variety

of other minerals as well as clay and limestone in

order to obtain these special properties.


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Concrete is a made from a mixture of:sand

cementsmall stones / crushed rock

water

Concrete sets to form a hard stone-like

material which is very useful for building

since it can be moulded before it sets.

Concrete is especially strong in resisting crushing forces

(i.e.under compression) so its good to use for pillarswhich will support weight.

Concrete can be made stronger in resisting stretching forces

(i.e. under tension) by pouring the concrete mixture into a

mould which contains a network of steel bars this is

reinforced concrete


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Glass is made from a powdered mixture of:limestone+ sand+ sodium carbonate

Very strong heating is required to melt and react thesematerials and form a viscous liquid which can be blown or

moulded.

Glass, like polymers, can be developed to have specific

properties which make it suitable for different applications.e.g. high refractive index glass for lightweight

spectacle lenses

toughened glass for automotive

windscreens

Pyrex glass for heat-proof ovenware

Glass is an important architectural material, being

relatively light, weatherproof, and transparent. Its strength

is sufficient to allow extensive use in modern buildings.

You might also like to find out about special glasses such as Pilkingtons self-cleaning glass. Seewww.pilkingtonselfcleaningglass.co.uk
http://www.pilkingtonselfcleaningglass.co.uk/http://www.pilkingtonselfcleaningglass.co.uk/

ch1 rocks as building materials

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