Subject :
Chemistry
Type of Lesson:
Lecture
Grade:
10
CSEC OBJ:
State and apply Avogadro’s Avogadro’s Law (A3.! A3.3"
Term:
3
UNIT:
#$L% C$&C%'
Duraton:
)* minutes
Lesson:
0
!ee": #
Apply Avogadro’s Law in simple calculations
Objectives As a result o+ this lesson! the student will ,e a,le to: 1" Solve simple simple pro,lems pro,lems involving involving gas volumes volumes ,y applying Avogadr Avogadro’ o’ss Law " -enerate -enerate an euation euation that that can ,e ,e used to to +ind the the volume volume o+ a gas 3" ranspos ransposee the euation euation generat generated ed to solve solve +or other un/nowns
Prerequisite Student Knowledge he student should ,e +amiliar with: 1" " 3" )"
Avogad vogadro ro’’s Law Law #olar #olar volu volume me at at S' S' and and ' ' ranspos ransposing ing to ma/e ma/e a particular particular varia,l varia,lee the su,ect su,ect o+ the +ormula +ormula he he mean meanin ing g o+ mole moless
Important Points 2mportant points in this lesson: 1" Avogadro’ vogadro’ss Law only applies applies to gases gases and there+ore there+ore the calculatio calculations ns ,eing carried out here can only ,e done +or gases in this manner " $ne mole mole o+ o+ any any gas gas occupi occupies es .) .) dm3 at S' and ) dm3 at ' 3" %ncourage %ncourage students students to ma/e ma/e sure to use use the correct correct units units in carryin carrying g out their calculations
Key Terms Avogadro’s Law
Standard temperature and pressure
oom temperature and pressure
#olar volume
T eacher eacher I nstructional nstructional M aterial aterial
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Challenge Areas %plain why it would not ,e appropriate to apply Avogadro’s Law to solids and liuids. Show how the volume o+ a solid can ,e calculated.
quipment!"aterial #eeded Calculator! pencil! tet,oo/! set o+ uestions appropriate +or lesson #ote to Teacher
emem,er to emphasise that Avogadro’s Law applies to gases only! and there+ore calculations using the principles used in this lesson also apply only to gases. #any students o+ten do not pay much attention to the condition under which the volume o+ gas is measured! and do calculations at '. emind them that ' is not the only condition! and there+ore they must ensure that they are using the appropriate values +or the condition given. %mphasise that +ormulas should not ,e used without understanding. %ncourage students to use +ormulas only a+ter they have understood the steps and reasoning involved in the calculations. 4e patient. 4e especially care+ul not to rush this part o+ the topic. 2+ students understand these +undamental concepts well! you will ,e a,le to go at a +aster pace later.
Teacher$s %esson #otes
T eacher I nstructional M aterial
Introduction $% !or"n& '(o&adro)s La*+ a. ell students the in the last lesson we generated Avogadro’s Law. 2n today’s lesson! we will use Avogadro’s Law in the solution o+ simple pro,lems involving gas volumes.
&ody o' %esson $% Demonstraton , Group !or" a. 'ose the uestion ,elow! or a similar pro,lem. 5rite the uestion on the ,oard and also read it aloud. 6emonstrate how to solve the uestion using a similar method to that shown ,elow! then slowly allow students to solve other uestions on their own or in small groups! pro,ing understanding through uestioning! and providing support as needed. Continually chec/ that students are on trac/. %ncourage e++orts made ,y students. i. 5hat is the volume occupied ,y 0.* mole o+ car,on dioide at '7
Say to students: &ow! we will recall the +act that 1 mole o+ any gas occupies a volume o+ ) dm3 at '. Since 0.* mole is less than 1 mole! as/ students i+ we should epect an answer that is greater or less than ) dm37 ell students that we will there+ore ma/e the volume that we wish to +ind (i.e. the un/nown volume" ,e x 5e could there+ore ma/e two statements: 1 mole C$ occupies ) dm3 0.* mole C$ occupies x dm3 1 mol 8 ) dm3 0.* mol 8 x dm3 1 0.*
8
) dm
x dm
x 8
) 0.*
x =
1 dm3
3
3
T eacher I nstructional M aterial
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ii. Let’s try a second calculation: 5hat is the volume occupied ,y 0.9* mol nitrogen dioide at S'7 As in the +irst eample! we start with the statement that 1 mole o+ gas occupies .) dm3 at S' 1 mol &$ occupies .) dm3 0.9* mol &$ occupies x dm3 1 0.9*
8
.) dm3 x dm
3
x 8
.) 0.9* 3 x = 1.; dm iii.
As/ students to now attempt the calculation ,elow with a partner. -ive them a,out 3 minutes and then as/ selected students to report what they have got! and also the reasoning process that gave them that response. 'lace emphasis on the inclusion o+ units and clear steps.
iv.
v.
vi.
As/ students to get in groups o+ not greater than +ive. 'resent each group with a set o+ similar uestions (a,out 3" to +ind the volume o+ gas at S' and '. 5al/ around and loo/ at what each group is doing. #a/e comments on what is ,eing done! and provide tips and encouragement. As/ three groups to share their wor/ing and answers with the class (on the ,oard". Students must not only write down the wor/ing ,ut also eplain as they wor/. %ach student is wor/ing a di++erent pro,lem. =ollow this up ,y doing an analysis o+ each wor/ing and response! pointing out errors and misconceptions as well as good reasoning and structure. &ow as/ students to ta/e a loo/ ,ac/ at all the pro,lems that have ,een wor/ed. As/ them i+ they can identi+y any trend or pattern in the way the pro,lems have ,een wor/ed. -ive them a minute to discuss this with their peers. As/ them to share their thoughts! and have a very short discussion o+ this. hey should notice that that in order to +ind the volume o+ the gas! we always multiply the molar volume ,y the num,er o+ moles i.e. volume o+ gas 8 molar volume num,er o+ moles.
T eacher I nstructional M aterial
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vii.
viii.
ix.
'oint out to students that using the +ormula is a shorter route to the answer. >owever! emphasise to students that they should always use the route which is most com+orta,le +or them! and should only use short routes a+ter they have understood the reasoning ,ehind those routes. &ow tell students that we are now going to attempt to +ind the num,er o+ moles o+ gas given the volumes. %ample: how many moles o+ oygen are present in *. dm3 oygen at S'7 6emonstrate the wor/ing as +ollows: emind students that 1 mole o+ oygen occupies .) dm3 at S'. here+ore! help them to see that it would ,e reasona,le to epect a value o+ less than 1 mole to ,e represented ,y *. dm3. ell them that we will let the un/nown num,er o+ moles ,e x. 5e can there+ore write the +ollowing statements: 1 mole o+ oygen occupies .) dm3 3 x mole o+ oygen occupies *. dm 1 mol 8 .) dm3 3 x mol 8 *. dm 1 x
x
1
x x.
8
8
.) dm3 *.: dm3 *.: dm3 .) dm3
8 0.* mol
-ive students another similar pro,lem to +ind the num,er o+ moles o+ gas given the volume at '. ow many moles o+ sulphur dioide are there in )).; dm3 sulphur dioide at S'7 As/ them to identi+y the pattern used in ,oth calculations! that is! in ,oth cases in order to +ind the num,er o+ moles! we divide the volume given ,y the molar volume.
xi.
As/ students to transpose the +ormula that we generated +or volume o+ gas to ma/e num,er o+ moles the su,ect.
T eacher I nstructional M aterial
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? moles 8
volume o+ gas given molar volume
>elp them to recogni@e that this is the same operation as we have carried out. ell them that as in the case o+ +inding the volume o+ gas! this is a shorter route to the answer! ,ut they should ensure that they understand the reasoning ,e+ore using any shortcuts.
Closure In-C.ass 'ss&nments
1" 5hat is the volume occupied ,y: i. 0.1* mol sulphur dioide at ' ii. 3.) mol nitrogen dioide at S' iii. 0. mol ammonia at S' iv. * mol nitrogen at ' v. 0.0; mol chlorine at S' " 5hat is the num,er o+ moles represented ,y: i. )).; dm3 sulphur trioide at S' ii. 9 dm3 helium at ' iii. 33. dm3 car,on monoide at S'
Out-of-C.ass 'ss&nment
1" >elium gas is used to +ill ,alloons used at parties! weddings and special occasions. 5hat volume o+ gas would ,e needed to +ill 30 ,alloons needed +or a wedding i+ each ,alloon is to contain 0. mol o+ helium each7 " $ygen gas is partially solu,le in water. 2+ 1 cup o+ water contains .) dm3 o+ oygen! how many moles o+ oygen would ,e +ound in ; such cups o+ water7
T eacher I nstructional M aterial
Supplemental G.ossary of Terms '(o&adro)s La*
%ual volumes o+ gases! measured under the same conditions o+ temperature and pressure! contain eual num,er o+ molecules
/oom temperature and pressure
his is the condition when gas measurements are ta/en at a temperature o+ *0C and a pressure o+ 1 atm.
Standard temperature and pressure
his is the condition when gas measurements are ta/en at a temperature o+ 00C and a pressure o+ 1 atm.
0o.ar (o.ume
his is the volume occupied ,y 1 mole o+ any gas. At S'! this value is .) dm3 at ' the value is ) dm3.
CSEC 1uestons
&one availa,le /ecommended 0atera.s
http:BBwww.doc,rown.in+oBpage0)B)93calcs0Dmvg.htm
Bb.o&rap2y
6enial! #. 6avies! L. Loc/e! A. E eay! #. (1D;1". 2nvestigating Chemistry. London: >einemann %ducational 4oo/s Ltd. Lam,ert! &. E #ohammed! #. (1DD3". Chemistry +or CFC. London: >einemann %ducational 'u,lishers. indale! A. (1DD;". Chemistry: A concise revision course +or CFC. %ngland: Stanley hornes ('u,lishers" Ltd. Cari,,ean %amination Council (00". Chemistry Sylla,us. 4ar,ados: CFC.
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