Practical Chemistry

States of matter [2]

The activities in this topic provideopportunities to link experimentalevidence and simple particle theory tohelp explain the properties of solids,liquids and gases, changes of state, gaspressure, and diffusion.

Bonding, structure, properties [3]

This topic includes activities which focuson how structure and bonding affect theproperties and uses of materials such aspolymers, fibres, ceramics, composites,glasses, metals, alloys and salts.Activities with dyes, detergents, waterand hydrogels explore the effects ofintermolecular forces.

Mixtures and separation [4]

The activities in this topic cover thedifferences between compounds andmixtures, and techniques for separatingmixtures and purifying substances. Theyinclude investigations into solubility, andprecipitation reactions to form insolublesalts. More advanced activities deal withthe solubility of solutes in aqueous andnon-aqueous solvents, saturated

Topics

There are over 200 class practicals and class demonstrations on this site. Each onecan help to develop students' skills and knowledge of chemistry. To help you find whatyou are looking for, we have grouped them into the following topiics.

Page 1 of 5Topics

2/2/2012http://www.nuffieldfoundation.org/print/2805

solutions, solubility curves and sparinglysoluble salts (Ksp).

Analysis [5]

The activities in this topic cover methodsfor qualitative and quantitative analysis.Activities include, for example,colorimetric analyses, titrations,chromatography, and calorimetry as wellas a variety of observation exercises.

Elements, the periodic table [6]

The activities in this topic can be used toillustrate the trends in the properties ofthe elements and their compounds. Theyinclude activities which explore thephysical and chemical properties ofelements and compounds and provideexamples of chemical change which canbe explained by the rearrangement ofatoms.

Acids and bases [7]

Activities in this topic include the use ofindicators to classify solutions as acidic,neutral or alkaline, neutralisationreactions, and the preparation of solubleand insoluble salts. More advancedactivities explore strong and weak acid-base behaviour, pH, indicator chemistryand buffer solutions.

Redox and electrochemistry [8]

The activities in this topic illustrate thereactivity series of metals, and oxidationand reduction processes such ascorrosion and the extraction of metals.They also illustrate the many differentapplications of electricity in chemistryand include examples of electrolysis toextract and purify substances as well asexperiments involving fuel cells, forexample.

Energy and entropy [9]

Page 2 of 5Topics


The activities in this topic includeexperiments focusing on energychanges in chemical reactions. Theyillustrate, for example, what makes auseful fuel and how to measure theenergy given out by different fuels.Exothermic and endothermic processesfeature including combustion reactions,neutralisation reactions and solutionformation. Other activities also focus ona consideration of entropy changes.

Kinetics and equilibrium [10]

The activities in this topic provide arange of opportunities to measure therate of chemical reactions and toinvestigate the factors affecting rate. Thetopic includes activities which can beused to demonstrate reversible reactionsand reactions involving dynamicequilibria. There are activities relating toequilibria in solution, gaseous equilibria,acid-base equilibria and redox equilibria.

Chemical quantities [11]

The activities in this topic can be used toconsolidate knowledge andunderstanding of chemical formulae andbalanced equations, and how these canbe used to calculate how much productcan be obtained in a reaction. Moreadvanced activities provide opportunitiesto apply the concept of the mole.Empirical and molecular formulae,reacting masses, percentage yield,volumes of gases and titrationcalculations are all covered.

Organic chemistry [12]

The activities in this topic illustrate howuseful chemicals can be obtained fromcrude oil and the properties and uses ofhydrocarbons. Polymers are exploredthrough polymerisation reactions andinvestigations into polymer properties,such as making ‘slime’ and investigating‘hydrogels’. More advanced activitiesinclude the synthesis and testing of thecharacteristic properties of a wide range

Page 3 of 5Topics


of aliphatic and aromatic substances,alcohols, halogenoalkanes, organicacids and esters. The techniquescovered include: reflux, distillation,vacuum filtration, purification anddetermination of yield and purity.

Biochemistry [13]

The activities in this topic can be used toinvestigate the chemicals and chemistryinvolved in food, food production andcooking. They include analysistechniques such as chromatography,testing for starch, and the importance ofmicrobes in food production and foodspoiling. More advanced activities covertopics such as enzyme reactions, foodchemistry and metabolism,photosynthesis, and amino acids andproteins.

The Earth and atmosphere [14]

The practical activities in this sectionfocus on the chemistry associated withthe environment, including the rockcycle, gases in the Earth’s atmosphere,and the chemicals dissolved in water.The rock cycle reactions includecrystallisation and chemical weathering.The section on water includes analysistechniques, for example in watertreatment. Experiments coveringpollution are also included.

Chemistry applications [15]

The practical activities in this topic focuson applications (e.g. synthesis andanalysis) of chemistry in industrialcontexts.

Enhancement [16]

The class practicals and teacherdemonstrations in this section areperfect for chemistry clubs or todemonstrate spectacular effects.

Page 4 of 5Topics


Source URL: http://www.nuffieldfoundation.org/practical-chemistry/topics

Links:[1] http://www.nuffieldfoundation.org/practical-chemistry[2] http://www.nuffieldfoundation.org/../../states-matter[3] http://www.nuffieldfoundation.org/../../bonding-structure-properties[4] http://www.nuffieldfoundation.org/../../mixtures-and-separation[5] http://www.nuffieldfoundation.org/../../analysis[6] http://www.nuffieldfoundation.org/../../elements-periodic-table[7] http://www.nuffieldfoundation.org/../../acids-and-bases[8] http://www.nuffieldfoundation.org/../../redox-and-electrochemistry[9] http://www.nuffieldfoundation.org/../../energy-and-entropy[10] http://www.nuffieldfoundation.org/../../kinetics-and-equilibrium[11] http://www.nuffieldfoundation.org/../../chemical-quantities[12] http://www.nuffieldfoundation.org/../../organic-chemistry[13] http://www.nuffieldfoundation.org/../../biochemistry[14] http://www.nuffieldfoundation.org/../../earth-and-atmosphere[15] http://www.nuffieldfoundation.org/../../chemistry-applications[16] http://www.nuffieldfoundation.org/../../enhancement

Page 5 of 5Topics


>States of matter

The activities in this topic provide opportunities to link experimental evidence andsimple particle theory to help explain the properties of solids, liquids and gases,changes of state, gas pressure, and diffusion.

Experiment collections

•Solids, liquids and gases[2]

•Changing state [3]

•Particles in motion [4]

Page 1 of 2>States of matter


Source URL: http://www.nuffieldfoundation.org/practical-chemistry/states-matter

Links:[1] http://www.nuffieldfoundation.org/practical-chemistry[2] http://www.nuffieldfoundation.org/node/2811[3] http://www.nuffieldfoundation.org/node/2812[4] http://www.nuffieldfoundation.org/node/2813

Page 2 of 2>States of matter


Solids, liquids and gases

Experiments

•The density of carbon dioxide [2]

The density of carbon dioxide relative to air is illustrated by pouring carbondioxide gas from a flask over a burning candle, which is promptly extinguished...

Source URL: http://www.nuffieldfoundation.org/practical-chemistry/solids-liquids-and-gases

Links:[1] http://www.nuffieldfoundation.org/practical-chemistry[2] http://www.nuffieldfoundation.org/node/2893

Page 1 of 1Solids,liquids and gases


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The density of carbon dioxide

Demonstration

This experiment provides a clear demonstration of the higher density of carbondioxide relative to air.A flask is filled with carbon dioxide from a cylinder or generator.The gas is then poured over a lighted candle, extinguishing the flame.

Lesson organisation

This is a quick, simple, teacher demonstration taking about 2 minutes.Although thiscould be done as a class experiment, it is probably not worth the extra time that itwould take.However, pupil assistance with the demonstration could enhance theimpact.

Chemicals

Candles (short 1-2 cm pieces), 2 (Note 1)

Carbon dioxide cylinder with regulator (Note 2)orSolid carbon dioxide (dry ice), a few small pieces (Note 3)

Refer to Health & Safety and Technical notes section below for additionalinformation.

Apparatus

Eye protection: safety spectacles, or goggles if handling dry ice

Thermal protection gloves and handling tongs (if using dry ice)

Beakers (100 cm3), 2

Page1of3Thedensityofcarbondioxide


Conical flask (250 cm3), with cork or bung to fit

W ooden splints

Health & Safety and Technical notes

Read our standard health & safety guidance [1]

W ear eye protection and thermal (insulated)gloves.

1 Nightlights or tea-lights may be used in place of short pieces of candle.

2 Carbon dioxide cylinder -see CLEAPSS Hazcard and also Laboratory HandbookSection 9.9 about the safe storage and use of gas cylinders.

3 If using solid carbon dioxide (dry ice), this should be obtained within 24 hours of thedemonstration in substantially larger quantity than required for the experiment, andstored in a vented insulated container until required.All handling must be done usingthermal protection gloves and handling tongs -see CLEAPSS Hazcard.

If neither a carbon dioxide cylinder nor a supply of dry ice is available, carbon dioxidegas may be generated chemically –see Standard Techniques: Generating collectingand testing gases [2].Replace the thistle funnel with a tap funnel or unstoppered

separating funnel.Add the hydrochloric acid (100 cm3, 2 M –IRRITANT)a few cm3 ata time to the marble chips (10 g)to generate a steady stream of carbon dioxide, andallow the heavier gas to displace the air from the collection flask.This can be checkedby sampling the gas emerging from the neck of the flask using a dropping pipette tosuck up a sample of gas, then bubbling it through fresh limewater in a test-tube.Immediate and dense milkiness of the lime water should indicate the flask is full ofcarbon dioxide, which may then be securely corked until required for thedemonstration.

The 250 cm3 conical flask may be filled prior to the lesson, either with gas from thecylinder or by adding a few lumps of dry ice, and allowing these to evaporate in theflask.The flask should be lightly corked and clearly labelled so the class can read thelabel, but the teacher may prefer to prepare the flask when required during the lesson.

Procedure

a Place the two beakers side by side on the bench and put a short length of candle ineach.

b Light the candles with a splint.They will continue to burn.

c Pour carbon dioxide from the flask into one of the beakers and the candle will go outwhile the candle in the other beaker continues to burn.

d Attempt to re-light the first candle with a splint.This will fail and the splint will go out.



e Now pour the carbon dioxide out of the beaker, and try again to re-light the candle.This should now succeed.

Teaching notes

Point out the use of carbon dioxide in some types of fire extinguisher and the reasonsfor its use.

Carbon dioxide (relative molecular mass 44)is about one and a half times denser thanair (average relative molecular mass about 29), and mixing of gases of differingdensities by diffusion can be a slow process unless the mixture is deliberately stirred.Hence gases can be effectively poured from one vessel to another, and also of coursebe collected in a flask or gas jar by displacement of air.

As an additional demonstration the presence of a layer of dense gas in the beakercontaining carbon dioxide can be shown by blowing a small soap bubble (using acommercial bubble mixture)and ‘catching’it in the beaker (a larger beaker will makethis easier!).W ith luck the bubble will descend into the beaker without bursting andthen proceed to ‘float’on the carbon dioxide layer.

Carbon dioxide can also be poured into a test-tube containing a little limewater.Onshaking the limewater will turn milky.

Health & Safetychecked March 2009

W eblinks

A homely variant on this experiment can be found at Reeko's Mad Scientist Lab [3]

An informative demonstration of the reason why carbon dioxide is not suitable forextinguishing fires involving burning metals such as magnesium is described at TheGeneral Chemistry Demo Lab [4]

This site includes an impressive video clip of magnesium turnings burning inside alarge block of dry ice!

carbon dioxide density gas Key stage 3 (11-14 years) Key stage 4 (14-16 years)Key stage 5 (16-19 years) States of matter

Source URL: http://www.nuffieldfoundation.org/practical-chemistry/density-carbon-dioxide

Links:[1] http://www.nuffieldfoundation.org/node/1634/[2] http://www.nuffieldfoundation.org/node/3139[3] http://www.reekoscience.com/[4] http://www.ilpi.com/genchem/demo/co2mg/index.html



Changing state

Experiments

•Chocolate and Egg [2]

By comparing the effects of heat on chocolate and on egg white, students areintroduced to the difference between physical change and chemical change...

•Liquefying chlorine gas [3]

This experiment shows how easy it is to liquefy chlorine gas by cooling alone.•Melting and freezing stearic acid [4]

In this class practical solid stearic acid (a constituent of wax) can be heated untilit melts and allowed to cool again until it freezes.

•Money to burn [5]

A striking demonstration that different fuels have different ignition temperatures.•Rate of evaporation [6]

In this experiment a drop of propanone is placed on a microscope slide underdifferent conditions and the time taken for it to evaporate is measured.

•Recovering pure water from a solution using a water condenser [7]

Copper sulfate solution is boiled and the water vapour produced is cooled andcondensed to a liquid.

•Supercooling - the energetics of freezing [8]

This experiment demonstrates the phenomenon of supercooling and illustratesthe various associated energy changes which occur.

•The density of ice [9]

The unusual density of ice compared to liquid water is brought out vividly in thisquick and simple demonstration.

•The sublimation of air-freshener [10]

The sublimation of air freshener can be observed by heating it in a water bathand cooling the resulting vapour. A fume cupboard is required for this.

•The thermal properties of water [11]

A paper cup containing water will not burn and a balloon containing water will notpop when heated.

•W ater expands when it freezes [12]

This demonstration shows that water expands when it freezes. It is useful forexplaining how rocks can be broken up when they absorb water

Source URL: http://www.nuffieldfoundation.org/practical-chemistry/changing-state

Page 1 of 2Changing state


Links:[1] http://www.nuffieldfoundation.org/practical-chemistry[2] http://www.nuffieldfoundation.org/node/2894[3] http://www.nuffieldfoundation.org/node/2895[4] http://www.nuffieldfoundation.org/node/2896[5] http://www.nuffieldfoundation.org/content/money-burn[6] http://www.nuffieldfoundation.org/node/2897[7] http://www.nuffieldfoundation.org/node/2898[8] http://www.nuffieldfoundation.org/node/2899[9] http://www.nuffieldfoundation.org/node/2900[10] http://www.nuffieldfoundation.org/node/2901[11] http://www.nuffieldfoundation.org/node/2902[12] http://www.nuffieldfoundation.org/node/2903

Page 2 of 2Changing state


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Chocolate and Egg

Class practical

The different effect of heat on chocolate and egg white provides a clear introductionto physical and chemical changes.This experiment could also be used to introducestudents to the safe use of Bunsen burners.

Lesson organisation

A straightforward, if somewhat messy, class experiment in which students heat the twomaterials alongside each other in a water bath until the changes have taken place,followed by cooling.This should take no more than 30 minutes.

Chemicals

Chocolate, a few grams

Egg albumen (egg white), about 4 cm3

Refer to Health & Safety and Technical notes section below for addtionalinformation.

Apparatus

Eye protection

Each working group will require:

Test-tubes, 2 (Note 1)

Beaker (250 cm3)

Page1of4Chocolateand Egg


Bunsen burner

Heat resistant mat

Tripod

Gauze

Test-tube rack

Test-tube holder



W ear eye protection.Do not taste foods in a laboratory.The food or the apparatus maybe contaminated.Do not sit down while heating the beaker or handling the hot test-tubes.

The ‘no tasting’rule should be strictly enforced.

Chocolate -cooking chocolate is the best type of chocolate for this experiment –othertypes melt too slowly.The chocolate should be grated and pre-loaded into a test-tubefor each working group, sufficient to give about a 2 cm depth of molten chocolate whenheated –this may require trials to establish the correct amount of grated chocolate.

Egg albumen -use eggs with the 'lion brand'stamp'as these should be salmonellafree.The egg white needs to be separated from the yolks of sufficient eggs to provide

enough for about 4 cm3 of egg white for each working group.The egg white shouldthen be pre-loaded into a test-tube for each working group.

1 At the end of the lesson, the students can be asked to hand back their test-tubes withthe contents still inside, as recovery and cleaning may cause less mess than leaving itto the students!The chocolate is best removed by re-melting and pouring out of thetubes.

Procedure

1 Add cold water to the beaker untilit is about one-third full, and place iton the tripod and gauze.

2 Place a test-tube with egg whiteand a test-tube with chocolate in thebeaker.

3 Heat the beaker of water with thetest-tubes carefully until the water inthe beaker boils.Allow the water toboil gently for about 5 minutes.



4 W atch what happens to the eggwhite and the chocolate in the tubeswhile they are being heated.

5 Turn off the Bunsen burner anduse the test-tube holder to transferthe tubes to the rack to cool.

6 W atch what happens to the egg white and the chocolate in the tubes as they cool.

Teaching notes

This experiment is appropriate for classes at an early stage in their science education,so students are likely to be fairly inexperienced in the safe and skillful use of theBunsen burner.This is therefore a good opportunity to develop their ability to use theBunsen burner and emphasis safety points, such as standing up when doingexperiments that involve heating.

The main purpose of the experiment is of course to introduce physical and chemicalchange, and the associated ideas of reversible and non-reversible changes.Thechemical change in the egg white should take no more than 5 minutes once the wateris boiling, and grated cooking chocolate should melt in about the same time.Manychildren will have met this in primary school.

On cooling, the chocolate will of course solidify to a solid mass, and students may bedistracted by the change of form from the grated material at the start.If so, thetechnician could be asked to pre-melt the chocolate in the tubes and allow it to solidifyagain before the lesson, but note that it will then take longer for the chocolate to melt inthe experiment.

Health & Safetychecked May2008

W eblinks

There are many websites, especially from North America, that provide a variety ofapproaches to teaching physical and chemical changes, but mainly for students olderthan those for whom this experiment is designed.These two examples seem to matcha similar stage of student learning;the first includes a useful demonstration that couldbe used to reinforce the class experiment:

Saskatchewan schools [2]

Teachers'domain [3]

A discussion of the nature of the chemical changes involved in cooking eggs, suitablefor teacher background information, can be found at:



Science of Cooking: The accidental scientist [4]

chemical change food Key stage 3 (11-14 years) Key stage 4 (14-16 years) Keystage 5 (16-19 years) physical change States of matter

Source URL: http://www.nuffieldfoundation.org/practical-chemistry/chocolate-and-egg

Links:[1] http://www.nuffieldfoundation.org/node/1634/[2] http://www.saskschools.ca/curr_content/science9/chemistry/lesson8.html[3] http://www.teachersdomain.org/resource/phy03.sci.phys.descwrld.lp_chemical/[4] http://www.exploratorium.edu/cooking/eggs/eggscience.html



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Liquefying chlorine gas

Demonstration

In this demonstration the gaseous halogen, chlorine, is liquefied by passing it over a‘cold finger’condenser cooled using a dry ice/ethanol mixture.Yellow drops of liquidchlorine are collected for comparison with other Group7 elements bromine and iodine.The demonstration can be extended toinclude changes of state for bromine and iodine.

Lesson organisation

This is a class demonstration used to show that chlorine gas is relatively easilyliquefied (boiling point -35 °C)by cooling alone.It must be done in a fume cupboard.

The yellow liquid formed can be compared with the other halogens –bromine andiodine –in the condensed state as part of a study of the trends in the physicalproperties of the halogens.

The demonstration can be done in 5 mins once the chlorine generator is set up andconnected to the ‘cold finger’.If the freezing of bromine and the melting andvaporisation of iodine are included allow 15 mins in total.

Chemicals

Sodium chlorate(I)solution, 14% (w/v)available chlorine (CORROSIVE)about 100 cm3

Hydrochloric acid, 5M (CORROSIVE)about 50 cm3

Ethanol (HIGHLY FLAMMABLE)or industrial denatured alcohol (IDA)(HIGHLY

FLAMMABLE, HARMFUL)about 20 cm3

Page 1 of 5Liquefying chlorine gas


A few small pellets of dry ice (solid carbon dioxide)(Can cause serious frostbite ifhandled without tongs or suitable gloves)

Optional:

Crushed ice -about 100 cm3

Sodium chloride –crushed rocksalt will do, about 100 g .

Bromine liquid (VERY TOXIC, CORROSIVE, DANGEROUS FOR THEENVIRONMENT), use a sealed ampoule

Iodine (HARMFUL, DANGEROUS FOR THE ENVIRONMENT), a few crystals


Apparatus

Eye protection

Access to a fume cupboard

Protective gloves -for handling pellets of dry ice (-78 oC).Tongs or insulating (notrubber)gloves should be used

Chlorine generator (Note 1)

‘Cold finger'condenser (Note 2)

Bosses, clamps and stands

Optional:

Boiling tube with cotton wool plug

Test-tube holder

Beaker (100 cm3)

Bunsen burner



W ear appropriate eye protection and gloves.

Sodium chlorate(I)solution, NaClO(aq), (CORROSIVE at this concentration)-seeCLEAPSS Hazcard.

Hydrochloric acid, HCl(aq), (CORROSIVE at this concentration)-seeCLEAPSS Hazcard and CLEAPSS RecipeBook.



Chlorine, Cl2(g)and (l), (TOXIC, DANGEROUS FOR THE ENVIRONMENT)-seeCLEAPSS Hazcard and CLEAPSS RecipeBook.

Ethanol, C2H5OH(l), (HIGHLY FLAMMABLE)or industrial denatured alcohol (IDA)(HIGHLY FLAMMABLE, HARMFUL)-see CLEAPSS Hazcard.

Solid carbon dioxide -see CLEAPSS Hazcard.Dry ice (solid carbon dioxide)can oftenbe obtained from a local university, hospital or industry.Larger chunks can be brokenup by enclosing them in a cloth, such as a tea towel, and hitting them with a mallet.The fragments can be stored for several hours in a box made of expanded polystyrene,or in a vacuum flask.A more powdery form of dry ice can be made using carbondioxide from a cylinder and a suitable dry ice making attachment.Tongs or insulating(not rubber)gloves should be used for handling dry ice.

Optionalitems

Bromine, Br2(l), (VERY TOXIC, CORROSIVE, DANGEROUS FOR THEENVIRONMENT)-see CLEAPSS Hazcard.

Iodine, I2(s), (HARMFUL, DANGEROUS FOR THE ENVIRONMENT)-seeCLEAPSS Hazcard.

1 Chlorine generation: see Generation, collecting and testing gases [2] (for chlorinescroll to bottom of page).

2 The ‘cold finger’condenser apparatus should consist of a 1 dm3 Buchner flask fittedwith a two-holed rubber bung.One hole in the bung should be big enough to take atest-tube and the other hole fitted with a short length of glass delivery tubing –seediagram.



Procedure

a Set up the chlorine generator in a fume cupboard.Make sure it is securely clamped.

b Connect the cold finger apparatus to the generator, using a short length of rubbertubing, and clamp it securely.

c Fill the ‘cold finger’test-tube about two-thirds full of dry ice chips and slowly add alittle ethanol.The mixture will bubble vigorously at first as the solid carbon dioxidesublimes.W hen the bubbling has settled down, add more ethanol until the test-tube isalmost full.(In CLEAPSS instructions for making freezing mixtures, the dry ice is addedto the solvent –with the quantities involved here it is unlikely to matter which wayround you add them.)

d Generate a gentle stream of chlorine by dripping the hydrochloric acid slowly on tothe sodium chlorate(I).The greenish-yellow gas will gradually fill both flasks.

e After about a minute, yellow drops of liquid chlorine begin to condense on the ‘coldfinger’and drop onto the bottom of the flask.At first these drops will vaporise but aftera few minutes they will begin to collect as the base of the flask cools down.Continuepassing chlorine gas through the apparatus until sufficient liquid chlorine has collectedfor the class to see.It is helpful to pre-cool the base of the flask with some dry ice orice/salt mixture.After stopping the flow of chlorine gas, the flask containing the liquidchlorine can be disconnected from the gas generator but should not be brought out ofthe fume cupboard.

Teaching notes

Liquid chlorine is transported around the country in bulk in rail or road tankers.Hereliquid chlorine can be compared with bromine and iodine as part of a study of thetrends in physical properties of the halogens.

This demonstration can be extended to include the freezing of liquid bromine (freezingpoint -7 °C)and the melting and vaporisation of iodine.

Bromine in a sealed ampoule can be solidified by cooling it in a mixture of equalmasses of crushed ice and salt (sodium chloride).

A few crystals of iodine gently heated in a boiling tube (containing a cotton wool plug atthe mouth of the tube to prevent the escape of iodine vapour)will melt (melting point114 °C)and then form a deep purple vapour.On cooling, iodine crystals form on thewalls of the tube.

Healthand Safetychecked October 2007

change of state chlorine gas Group 7 Key stage 4 (14-16 years) Key stage 5 (16-19 years) States of matter



Source URL: http://www.nuffieldfoundation.org/practical-chemistry/liquefying-chlorine-gas

Links:[1] http://www.nuffieldfoundation.org/node/1634/[2] http://www.nuffieldfoundation.org/../3139



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Melting and freezing stearic acid

Class practical

In this class practical students take the temperature of stearic acid at regular intervalsas they heat and cool it.They can observe the melting and freezing points of theacid and can plot a graph.This experiment could also be done using data-logging equipment.

Lesson organisation

This practical takes quite a long time to carry out.Students can begin by simplyrecording their data but, once they get the hang of what they are doing, most should beable to plot the graph at the same time as taking readings.If data-loggers are beingused then students will need another activity to be doing alongside the experiment.

Chemicals

Stearic acid (octadecanoic acid)


Apparatus

Eye protection

Per pair or group of students:

Beaker (250 cm3)

Boiling tube (Note 1)

Page1of3Meltingand freezingstearicacid


Thermometer (0-100 C̊)

Stop clock

Clamp, stand and boss

Bunsen burner

Tripod

Gauze

Heat resistant mat



W ear eye protection.

Stearic acid (octadecanoic acid), CH3(CH2)16COOH(s)-see CLEAPSS Hazcard.Thestearic acid in this practical can be used again and again.

1 If, after the practical, the boiling tubes are left containing both the stearic acid and thethermometer, immerse all the boiling tubes in hot water to remove the thermometers.The stearic acid can then be stored in the boiling tubes and recycled several times.

Procedure

a Put about 150 cm3 water into the beaker.

b Heat it on a tripod and gauze until the water juststarts to boil.

c Set up the apparatus as shown in the diagramand start the timer.Keep the water boiling, but notboiling vigorously.

d Using a suitable results table, record thetemperature of the stearic acid every minute untilit reaches about 70 C̊.Note on your results tablethe point at which you see the solid start to melt.

e Use the clamp stand to lift the tube from the hotwater.Record the temperature every minute asthe stearic acid cools down until it reaches about

50 C̊.Note on your results table the temperature at which you see the stearic acidbegin to solidify.



Teaching notes

Remind students not to attempt to move the thermometer in the solid stearic acid, as itwill break.

Energy must be supplied to melt a solid;this same energy is released when the liquidresolidifies.

This presents a good opportunity to demonstrate how to maintain a steady temperatureusing a Bunsen burner.This can be achieved by sliding the Bunsen burner aside asthe boiling becomes too vigorous;slide it back as the water stops boiling.It is notessential that the water bath is boiling.Students could be provided with anotherthermometer, and asked to maintain a lower temperature, say 80 °C.

A temperature sensor attached to a computer can be used in place of a thermometer.Itcan plot the temperature change on a graph and show this as it occurs.A slightmodification of the experiment can yield an intriguing result: W hen the test-tube is

cooling place it in an insulated cup containing a few cm3 of water.Use a secondtemperature sensor to monitor the temperature of the water.The water temperatureshould rise as the stearic acid cools and it should continue to rise even as it changesstate.

A slight alternative to this experiment is to plot only the cooling curve.Place all theboiling tubes with stearic acid into a large beaker.Place some hot water in the beakerand continue to heat with a Bunsen burner.Remove from the heat when all the stearicacid has melted.Students can place a thermometer into the stearic acid and place theboiling tube into a test tube rack or beaker.They take the temperature every 30seconds or every minute and plot a graph.Many students will anticipate that the stearicacid will continue to cool to zero –it is useful to discuss why the stearic acid stopscooling when it reaches room temperature.

In either version of the experiment it is good practice for students to draw a graph oftheir results.There should be a clear horizontal line in the graph which corresponds tothe change of state, however many school samples of stearic acid are not very pureand hence the line is often not perfetcly horizontal.The exact melting and freezingpoints of the stearic acid may not be exactly the same and will depend on the purity ofthe product and where it was purchased from, but are usually around 55-70 C̊.

Health & Safetychecked April 2008

changes of state Key stage 3 (11-14 years) Key stage 4 (14-16 years) Key stage 5(16-19 years) solids States of matter

Source URL: http://www.nuffieldfoundation.org/practical-chemistry/melting-and-freezing-stearic-acid

Links:[1] http://www.nuffieldfoundation.org/node/1634/



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Money to burn

Demonstration

A piece of paper (or a £5 or £10 note)soaked in a mixture of ethanol and water isignited.The ethanol burns but the paper does not.

Click to view a [1]video [1]clip of this demonstration experiment.[1]

Lesson organisation

This is a demonstration experiment which can either be used for fun as part of a publicevent or in a class to stimulate discussion of the conditions required for combustion.

Chemicals

Ethanol (HIGHLY FLAMMABLE)or

Industrial Denatured Alcohol (IDA)(HIGHLY FLAMMABLE, HARMFUL), 75 cm3

Sodium chloride (common salt), about 1 g


Apparatus

The quantities given are for one demonstration.

The teacher requires:

Eye protection

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Bunsen burner

Pair of tongs

Heat-resistant mats, 2

Beakers (250 cm3), 3

Paper, e.g.filter paper (Note 1)



W ear eye protection.

Ethanol, C2H5OH(l)(HIGHLY FLAMMABLE)-see CLEAPSS Hazcard.

Industrial Denatured Alcohol (IDA)(HARMFUL, HIGHLY FLAMMABLE)-seeCLEAPSS Hazcard.

Sodium chloride, NaCl(s)-see CLEAPSS Hazcard.

1 Prepare some pieces of absorbent paper, e.g.filter paper, about the size of a £5note.

2 Place about 50 cm3 of water in one beaker, a similar volume of ethanol in a second

beaker, and a mixture of 25 cm3 water and 25 cm3 ethanol in the third beaker.Add alittle (about 1 g)of sodium chloride to the third beaker and stir until it has all dissolved.Label the beakers.

Procedure

a Label the beakers.

b Place the Bunsen burner on the heat-resistant mat and adjust it to give a yellowflame.Ensure that the beakers of ethanol, water, and the ethanol-water mixture are asafe distance (2 m)away from the Bunsen burner.

c Using the tongs, soak one piece of paper in the water in the first beaker.Allow thepaper to drain.Try to ignite it by holding it in the Bunsen flame for a few seconds.Itdoes not ignite.

d Soak a second piece of paper in ethanol and use the tongs to hold it in the Bunsenflame just long enough for it to ignite.Take care to drip as little alcohol as possible onthe bench between the beaker and the Bunsen burner.The alcohol on the paperignites easily and sets fire to the paper, which burns away.

(If the alcohol in the beaker does ignite by accident during the demonstration, it can beeasily and safely extinguished by covering the beaker with a heat-resistant mat.)

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e Soak the third piece of paper in the alcohol-water mixture and use the tongs to hold itin the Bunsen flame just long enough for it to ignite.Swiftly remove the paper from theBunsen flame and observe as the alcohol burns with a yellow flame, but the paperdoes not burn.The paper will still be wet with water after the alcohol has burnt away.

Teaching notes

A wealthy and/or confident demonstrator can start this experiment with a £5, or evenhigher value, note and the alcohol-water mixture!More amusement can be added if amember of the audience ‘with money to burn’can be persuaded to part with themoney.It is important to use a yellow Bunsen flame, and to only hold the paper in theflame long enough for it to ignite, to prevent the note from burning.The demonstrationswith ordinary paper and the other liquids could then follow to provide an explanation.

The water in the alcohol-water mixture evaporates as the alcohol burns, keeping thetemperature of the paper below its ignition temperature (approximately 230°C).Converting this temperature to the Fahrenheit scale might remind some science fictionfans in the audience of the film ‘Fahrenheit 451’.See Fahrenheit 451 [3].

The flame from the paper soaked in alcohol alone should be visible but the flame froma burning alcohol-water mixture is often difficult to see.This is why the sodium chlorideis added, to give an orange-yellow colour to the flame.The demonstration looks evenmore impressive in subdued lighting.

The experiment could be extended to include different alcohol-water mixtures andother alcohols, such as methanol.

Health and Safetychecked November 2006

Key stage 3 (11-14 years) Key stage 4 (14-16 years) Key stage 5 (16-19 years)Chemistry

Source URL: http://www.nuffieldfoundation.org/practical-chemistry/money-burn

Links:[1] http://media.rsc.org/videoclips/demos/nonburningnote.mpg[2] http://www.nuffieldfoundation.org/node/1634/[3] http://en.wikipedia.org/wiki/Fahrenheit_451

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