LEGO BRICKS, CRISPS AND A BIT OFBLING – THEY ALL COME TOGETHER IN

THIS SUPERB CHEMISTRY LESSONFROM DR JOANNA RHODES...

SUBSCRIBE AT TEACHSECONDARY.COM 33

Ionic substances provide us with useful compounds that are bothbeautiful and functional. Ionic compounds are used in products fromjewellery to batteries. They provide our bodies with essentialelectrolytes and they are essential for transmitting nerve impulseswithin the central nervous system. But how do we identify and makethese compounds and explain their properties and uses?

BIONICIONIC

LESSONPLAN CHEMISTRY | KS4

STARTER ACTIVITY

MAIN ACTIVITIES

1. Salt and Vinegar orReady Salted?

Students need to be able todescribe different ways to preparesalts, and understanding therelationship between a salt and anacid is a good place to start. I usethe term ‘Salt and Vinegar’ torepresent using an acid to make asalt whereas ‘Ready Salted’ is usedto describe making a salt fromother salts using precipitation.

In the ‘Salt and Vinegar’approach students first have toconsider which acid they will needto make the salt of their choice. Anitrate will require nitric acid, achloride will require hydrochloricacid and a sulfate will requiresulfuric acid. Once students havedecided which acid they need fortheir salt they need to decide thesource of the metal ion. A rule ofthumb is that if it is a group-onemetal it is the metal hydroxide. If itis a group-two metal or transitionmetal it is from the metal oxide.Variants include use of acarbonate, which fizzes andproduce carbon dioxide and use ofthe metal itself, which will bubbleas it produces hydrogen.

Students should also be able todescribe the experimental methodused. This lends itself well topractical work. Students canperform a titration usinghydrochloric acid and sodiumhydroxide with indicator and thenrepeat the titration using the samevolumes to produce sodiumchloride solution, which can beevaporated if desired. Whendealing with an insoluble base theyshould describe how to react anacid such as sulfuric acid withexcess base such as copper oxidefollowed by filtration andevaporation to make coppersulfate crystals, this approach also works for carbonates whichcan be added to the acid until theystop fizzing.

In the ‘Ready Salted’ approachstudents need to be able to spotthe use of two soluble salts tomake an insoluble salt. Studentsshould be on the lookout for thestate symbols given in examquestions to identify the presenceof soluble (aqueous) salts.Examples you can use to illustratethis include lead nitrate andpotassium iodide to make leadiodide, a bright yellow solid andbarium chloride and sodium sulfate

Electrochemistry is a very broadand exciting field of research inchemistry. Students can applytheir knowledge of electrodeprocesses to understand otherapplications such aselectroanalysis. Pioneeringapplications designed by theCompton Group in the OxfordUniversity Chemistrydepartment includeelectrochemical breathalysersfor alcohol and drug detectionand glucose sensors fordiabetics [AR 7]. Students couldbegin by carrying out a web-quest to investigate theseand other applications. Mystudents have attempted theelectrochemical determination ofthe heat of chilli peppersdesigned by the Compton Group[AR 8] on chilli peppers that theyhave grown themselves withgreat success!

HOME LEARNING

WHY TEACHTHIS?

the identity of the ion. To balancethe formula students must end upwith the same number of eachcolour of brick. Using this methodthey can work out for themselvesthat aluminium oxide must beAl2O3 because this is the onlyway to balance the Al3+ ion andthe O2- ion so that you have thesame number of red and bluebricks overall. To help studentstackle complex cations and anionssuch as ammonium (NH4+) andsulfate (SO42-) use the sameprocess with a single red brickrepresenting ammonium and twoblue bricks labelled with sulfate.Balancing (NH4)2SO4 thenbecomes a simple task of two redbricks to two blue. A commonmisconception that this avoids isfor students to attempt to breakapart these ions in order tobalance them. Most exam boarddata sheets supply a list of ionsand charges. Remind students touse this brick model to make eventhe most complex ion a simpletask to balance.

Balancing actDot-cross diagrams of ioniccompounds illustrate the transferof electrons from the metal to thenon-metal. A worksheet from theRoyal Society of Chemistry willprovide a quick reminder[Additional Resource 1]. A commondifficulty for students is producingthe formula of an ionic compoundwith the correct number of ionsand charges. Lego brick ions are auseful strategy to help. I usedifferent coloured bricks torepresent metal cations or non-metal anions with red as thecation and blue as the anion. Thenumber of bricks in the ionrepresents the charge and a stickylabel on the brick tells the student

In this lesson the aim is tohelp students appreciatethe strong connectionbetween chemistry and itsimportance within livingsystems covering ioniccompounds, electrolysis,nerves and cells; topicswhich are usuallyseparated into theirrespective subjectspecialism. Learners alsoexplore socialconsequences, gaining anunderstanding of howelectrochemicalbreathalysers for drug andalcohol testing and glucosesensors can protect andenrich lives. A novelapplication such as theheat of chilli peppers helpsstudents to attemptrelevant and interestingscience in their own schoollaboratories – why notcompete to see who canmake the hottest curry?

Lesson plan Chemistry_Layout 1 12/05/2014 11:43 Page 2

30 www.teachsecondary.com34 SUBSCRIBE AT TEACHSECONDARY.COM

CHEMISTRY | KS4

ARE YOU NERVOUS?Transmission of nerve impulsesacross a synapse would not takeplace if electrolytes includingNa+, K+ and Ca2+ ions were notpresent. To demonstrate thespeed of the central nervoussystem ask the whole class tostand in a circle and join hands.While closing their eyes they‘pass’ an impulse around thecircle by squeezing the hand ofthe person standing next to themwith the time for the ‘impulse’ totravel around the circle beingmeasured. Dividing by thenumber of people in the classgives and average response timewhich can be improved by a fewattempts. Students can thenbegin to appreciate how fast areflex action is and how fast theelectrochemical transmission ofan impulse across the synapsemust be.

SUMMARY

ADDITIONALRESOURCES[1] RICHARD DAWKINSTINYURL.COM/TSAPE1[2] CLIP BIRDS ACTIVITYTINYURL.COM/TSAPE2[3] BUILD-A-BEAST TINYURL.COM/TSAPE3[4] NHM EVOLUTION – DOWNLOADABLEFROM THE APPLE APP STORE[5] NATURAL HISTORY MUSEUM WEBSITETINYURL.COM/TSAPE5[6] BBC BANG GOES THE THEORYTINYURL.COM/TSAPE6[7] CREATION MYTHS – NUFFIELDFOUNDATION TINYURL.COM/TSAPE7[8] CHARLES DARWIN – CHRIST’S COLLEGECAMBRIDGE TINYURL.COM/TSAPE8

INFORMATIONCORNER

Dr Joanna L. RhodesM.Chem, D.Phil, MRSC is ateacher of science at ShelleyCollege, Huddersfield.

ABOUT OUR EXPERT

to make white barium sulfate.Students find it interesting to knowthat barium sulfate is so insoluble itcan pass through the body withoutpoisoning you even thoughsoluble barium salts are toxic. Thisis harnessed in the use of bariumsulfate in a barium meal that isingested to show up soft tissue onan X-ray [AR 2].

As a follow up activity orhomework ask students to work inteams to create a flowchart or akey based on yes/no questions tolink the different methods ofmaking salts.

2. Bling-BlingYour students work for a start-upcompany called Bling-Bling, whichcustom electroplates copper andsilver mobile phones. Bling-bling’sclients are very fussy and studentshave to investigate a method forensuring the same amount ofmetal is plated onto each mobilephone to ensure a perfect finish. Intheir preparatory work studentsshould identify the appropriateindependent variable, dependentvariable and control variables.Their independent variable couldeither be time or voltage on thepower supply and the dependentvariable should be the mass ofmetal plated onto the electrode.

Suitable solutions forelectroplating include coppersulfate solution and silver nitratesolution [AR 3]. Use a bulb in thecircuit to demonstrate to studentsthat dissolved ionic compoundsconduct electricity due to the

movement of charged ionsthrough the solution.

After their electroplating exerciseask students to predict theproducts of electrolysis of asolution of sodium chloride. Usingtheir knowledge of electrolysis it islikely that most will predict sodiumand chlorine. Use a HoffmannVoltameter to demonstrate thatthe products are in fact hydrogengas and chlorine gas. Both arevery useful gases extracted usingelectrolysis of seawater and thenbottled and sold. If you do nothave a gas voltameter one can beimprovised using burettes asdescribed in this Nuffield practicalworksheet [AR 4] or get pupilshands on by investing in a classset of low cost mini gas

voltammetry cells supplied withgraphite electrodes and graduatedtest tubes [AR 5]. To challengehigher ability students ask them touse the reactivity series (includinghydrogen) to predict whichsolutions will yield the metal andwhich will yield hydrogen gas.

A demonstration of the electrolysisof molten lead bromide [AR 6] toproduce lead and bromine showshow ionic compounds cannotconduct when solid but do conductwhen molten and the ions canmove freely. Higher ability studentsshould be encouraged to constructhalf equations for the processestaking place at the anode and thecathode in each of the threeelectrolysis experiments carriedout during the lesson.

The Royal Society of Chemistry’s education website, LearnChemistry, is a free, award-winning online platform of resourcesdesigned to enhance chemistry teaching and learning.

Through Learn Chemistry, you and your students can explorethousands of resource downloads, substance pages, articles andactivities. These free-to-access teaching materials relate toeveryday life and real-world challenges in areas such aspharmaceuticals; lifestyle; scarce natural resources; air quality;agricultural productivity; and energy. And resources are addedand updated every month.

Created for use with pupils of varying levels of ability, thematerials encourage students to approach challenges throughproblem solving and analytical thinking.

Royal Society of Chemistry, learn-chemistry@rsc.org,www.rsc.org/learn-chemistry

+KEY RESOURCE

Lesson plan Chemistry_Layout 1 09/05/2014 14:11 Page 3