BBC Focus - 09.2019

Q&A

GETTY IMAGES X3 ILLUSTRATION: DAN BRIGHT

WHAT’SHAPPENING

Thekeytohowthe‘lavalamp’worksis thefactthatoilandwaterdon’tmix.

Whethertwoliquidsmixdependsontheinteractionsbetweentheirmolecules

andalsotheirfreedomtomovearound– thestrongerthearactiveforces,

andthegreaterthepossibilitiesofmovement,themorelikelytheyaretomix.

Watermoleculesare‘polar’– oneendis negativelycharged,andtheotheris

positivelycharged.Thismeansthatwatermoleculesaracteachothermore

stronglythantheyaractoilmolecules,whichare‘non-polar’.Also,the

watermoleculesendupforminga kindofcagearoundtheoilmolecules,

restrictingthemotionofboth.Thisis anunfavourablestate,andthe

waterandoilmoleculesquicklyseparate.Theoiloatsontopofthewater

becauseit is lessdense.

Thetabletscontaincitricacidandsodiumbicarbonate,whicharereleased

intothewaterwhenthetabletdissolves.Whenparticlesofthesetwo

chemicalscomeintocontactwitheachother,theyreact,producingcarbon

dioxidegas.Thegasformsbubblesinthewater.Thesearelessdensethan

boththewaterandtheoil,sooatupwards,draggingalongsomeofthe

colouredwater.Thebubblesburst once they reach the top of the oil, and the

water falls back down.AS

WHATTODO

1.Fillthecont ainerabout a third of the

wayupwithwater.

2.Pourcookingoilontopofthewater

untilthecontaineris nearlyfull.

3.Waitfortheoilandwatertoseparate.

4.Adda fewdropsoffoodcolouring

andwaitforthe water to become

coloured.

5.Breakthetabletinhalf and drop it

intothecontainer.

6.Watchthelavalampdoit sthing!

7.Addmorepiecesofthe t ablet to keep

the reaction going.

DIY

SCIENCE

HOMEMADE LAVA LAMP

WHATYOU’LL

NEED

Q Atall,open

container

suchasaplastic

drinks

boleoraglass

QCookingoil

QWater

QFoodcolouring

QFizzyvitamin

tabletor

Alka-Seltzer