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Appendices

12 Key Stage 3-4 example of theme: Limestone
The world's most useful rock

MODULE: LIMESTONE IN YOUR EVERYDAY LIFE

TEACHER'S NOTES

Level

This activity is most appropriate for students aged 14-16 to illustrate useful materials made from rocks.

English National Curriculum reference 4.3.2g
OCR A 1983 references 3.1.12 and 3.1.13
OCR B 1977 reference CD3
OCR C 1974 reference Sc3.2.3.4 and Sc3.2.3.6
AQA modular 3468 reference 15.1
AQA linear 3462 reference 11.5
Edexcel modular 1536 references 4.28 and 4.29
Edexcel linear 1522 references 3.25 and 3.26

Topic
Limestone has a relatively simple chemical composition - it is largely calcium carbonate, CaCO3. However, limestone and substances made from it have a diverse range of uses. This activity illustrates some of these uses by relating them to everyday activities of the students.

Description
Students fill in a timetable of their activities in the morning from waking up to leaving for school. Discussion with the teacher and / or reference book- or web-based research follows, and indicates that a surprising number of activities have a link to limestone in some way.

Context
This activity follows on well from The chemistry of limestone which points out some of the uses of limestone and products made from it.

Teaching points
The format is quite flexible. One approach is to ask the pupils to log and then report their activities from getting up in the morning until leaving for school. The degree of formality is a matter for the teacher. For example responses could be written logs or reports produced either individually or in groups, or they could be brainstormed and written up on the blackboard or presentation software. Students could then be challenged to suggest links between the various activities and limestone. To do this they can use knowledge from previous lessons, reference books and internet searches if web access is available. Entering 'Uses of limestone' into the Google search engine, for example, produces a large selection of websites with relevant information. Other links can be made by the teacher with reference to the notes and table below.

Alternatively, the teacher could discuss with the class in general terms some of the uses of limestone and its derivatives. This could be followed by students making a list of their activities between waking and leaving for school. They could then be asked to relate these general uses to specific activities in their morning routine. For example students might make the link between the use of limestone in the blast furnace to make iron and their use of an iron bath or the transport of water in iron pipes.

Another alternative would be for the teacher to supply the students with a copy of the table (or part of it) with selected parts (activities and / or applications of limestone) missing and ask the students to fill in the gaps.

Note that the table is largely for the teacher's reference. Students are unlikely to spot more than a few of the links in the table. Many links other than those in the table are also possible.

Uses of limestone and its derivatives

Some important uses of limestone follow.
Production of lime by thermal decomposition

limestone g lime + carbon dioxide

CaCO₃(s) g CaO(s) + CO₂(g)

This is the main reaction in commercial lime burning to make lime (calcium oxide) which is a base and has many uses, some of which are described below.

Controlling pH by the use of lime
In sugar refining, for example, lime is used to make the solution alkaline, causing impurities in the sugar to separate out for removal. Carbon dioxide (also from limestone) is then used to remove the lime by reforming calcium carbonate (limestone) which precipitates out. This is the same chemistry as the limewater test for carbon dioxide.

Neutralisation of acids
Lime is used to neutralise acidic soil and it is also used to remove sulfur dioxide from coal-fired power station gases (known as flue gas desulfurisation, FGD). The product is gypsum, used in building materials such as plasterboard. A very simplified form of the reaction can be represented by the following equation.

CaO(s) + SO₂(g) + 2H₂O(l) + ½ O₂(g) g CaSO₄.2H₂O(s)

Making iron in the blast furnace
The initial reaction is the thermal decomposition of calcium carbonate to form calcium oxide (lime):

CaCO₃(s) g CaO(s) + CO₂(g)

This is followed by the reaction of lime with sandy impurities (mostly silicon dioxide, silica, SiO₂) in the iron ore to form calcium silicate (slag):

CaO(s) + SiO₂(s) g CaSiO₃(l)

The reactions involved in the production of glass and Portland cement (the latter involving alumina and aluminium silicate) are very similar. Indeed some blast furnace slag is used to make glass and cement.

Manufacture of sodium carbonate
Sodium carbonate is made from salt (sodium chloride) and limestone by the Solvay (or ammonia-soda) process. The overall reaction is

CaCO₃(s) + 2NaCl(aq) ? Na₂CO₃(s) + CaCl₂(aq)

although the details are much more complex, see T. Lister (ed), Sodium carbonate - a versatile material, London: Royal Society of Chemistry, 2000.

Limestone powder as a filler
Limestone dust is frequently used as a filler to give bulk to or to extend expensive resins, adhesives, polymers etc. In the trade, fillers are often referred to as 'inert'; they are only 'inert' in the sense that they do not react significantly with the other materials used in that particular process.

The table gives a typical list of early morning activities and their links with limestone.

Time	Activity		Application of limestone
6.30 a.m.	Hot water switches on
	water is stored in dams made of concrete		limestone is used in cement and as aggregate to make concrete
	water		hardness is adjusted and purity improved by adding lime
	water is transported in	metal pipes (iron or copper)	limestone is used as a flux to remove impurities when refining metals
		concrete pipes	see above
		plastic pipes	limestone is used as a non-reactive filler to extend expensive resins in plastics
	water is heated by electricity	produced from coal	lime is used to remove (neutralise) polluting sulfur dioxide emissions from coal-fired power station gases
			limestone used in coal mines to prevent explosions (keeps dust down and doesn’t transmit sparks)
		produced from oil / nuclear sources	lime used in refining processes (for oil and uranium)
7.10 a.m.	Alarm clock rings
	plastics / metals		see above
7.11 a.m.	Look out of window
	glass		glass is made of sand (silica), limestone and soda ash (sodium carbonate), which is itself made from limestone and salt
	lead (leaded lights)		limestone removes sulfur (as calcium sulfate) from lead ore (lead sulfide) and acts as a neutraliser for the flue gas, which contains sulfur dioxide
7.12 a.m.	Step onto carpet
	carpet backing		limestone is used as a filler to extend latex (expensive) and bulk it out
7.13 a.m.	Go to the bathroom
	wash basin / wall tiles (ie ceramics)		ceramics are made from clays, sand and small amounts of limestone (eg in glazes)
7.14 a.m.	Stand on
	rubber mat		limestone used as a filler to extend rubber (expensive)
	Clean teeth
	toothpaste		fine limestone is used as a mild abrasive and also helps develop / maintain teeth  which are made up of calcium compounds
7.16 a.m.	Use the lavatory
	lavatory pan (ceramic material)		see above
	waste water		treated with limestone before being recycled or returned to river / sea
7.20 a.m.	Take a bath
	bath iron		see above
	bath enamel		enamel contains limestone
	soap		lime is used in soap making
	Clean bath
	bath cleaner		contains fine limestone as a mild abrasive
7.45 a.m.	Get dressed
	clothes		lime is used in preparing cotton and wool; dyes and washing powders use limestone
7.55 a.m.	Go downstairs
	paint		limestone is used in pigment-making and as a filler in extending expensive pigments, polymers, resins, etc
			limestone is used in treating acid waste from making white titanium pigments
			vinyl floor in kitchen has  limestone filler
7.57 a.m.	Make a cup of tea
	cup / saucer / teapot		ceramics, metals, hot water (see above)
	milk		cows have dietary calcium supplement derived from limestone
	sugar		lime is used to raise pH, causing impurities to separate out for removal; carbon dioxide (also from limestone) is then used to remove the lime by reforming calcium carbonate (limestone)
8.00 a.m.	Make toast
	wheat		limestone is used by farmers to neutralise soil
	bread		limestone is added to flour to maintain our calcium levels (to reduce risk of the bone disease rickets)
8.01 a.m.	Cook
	eggs		limestone is used in poultry grit
	bacon		limestone is used in pig feed to provide essential calcium
	salt		salt is made easier to pour by adding fine limestone
8.19 a.m.	Take indigestion tablet
	indigestion tablet		contains limestone filler / extender and  calcium salts (derived from limestone) as active ingredients (limestone is also used as a filler in many pharmaceuticals)
8.20 a.m.	Clean up
	surface cleaners		contain limestone filler
	unblock plug hole		caustic soda (sodium hydroxide) made from lime, salt and ammonia
8.29 a.m.	Pick up mail
	brochures		paper contains limestone filler and also provides a smooth coating
8.34 a.m.	Make phone call
	copper wire		limestone is used as a flux and to lubricate wire-drawing process
	optical fibre		is high grade glass (see above)
8.42 a.m.	Pick up school bag
	leather		tanning process uses calcium hydroxide (made from lime) to remove hairs and to plump up hides
	pencils		limestone filler in the pencil ‘lead’
	paper		see above
	typing corrector		limestone filler / extender / opacifier
	adhesive		limestone filler and lime in processing
	Blu-tack		limestone filler / extender

Further resources
When teaching about limestone, teachers may wish to do an activity such as Science and Technology in Society (SATIS) No. 602 The Limestone Inquiry, Hatfield: Association for Science Education, 1991. This is a role playing activity in which students debate the environmental impact of quarrying.

Further details of the blast furnace process can be found on the CD ROM Alchemy? London: Royal Society of Chemistry, 2002
Further details about flue gas desulfurisation can be found in D Warren, Green Chemistry, London: Royal Society of Chemistry, 2001
Further details of the sugar extraction process can be found D Warren, Chemists in Social and Historical Contexts, London: Royal Society of Chemistry, 2001