Chem 122
Name: Grace Cole
Section DM1
Name of Partner: Samuel Colclough
Spring 2015
Instructor: Dr. ric Cotton Date of !pt: "#1$#15 Date of Su%mission: "#2
Experiment #9: CALORIMETRY
Abstract: In Part I, the specific heat of an n!no"n meta, ea$, "as cacate$ to be %&'( ) *+-C sin+ a constant.pressre caorimeter& caorimeter& In Part II, the moar heat of netrai/ation for h0$rochoric aci$ "as $etermine$ to be 12 !)*mo 3C for the netrai/ation reaction of h0$rochoric aci$ an$ so$im h0$roxi$e "ithin a constant.pressre caorimeter&
ca lculate the specific heat of an un,no+n un,n o+n Intro$ction: 'or Part I( the o%)ecti*e +as to calculate metal. Specific heat is -the amount of heat neee to raise the temperature temperature of one gram of /a /a 1 pure su%stance % one egree either Celsius or ,el*in3.4 It can %e calculate through the follo+ing euation pro*ie % 6amilton et al.13: q s = 13 m ∆ T +here q 7 amount of heat transferre in 83 7 mass of su%stance in g3 m s 7 specific heat of the su%stance in 89g19;C13. It is a rearrangement of the follo+ing euation( the stanar formula for calculating the heat transfer in a reaction: 23
q =m × s × ∆ T
In Part I of this e!periment( the metal is consiere con siere the sstem an the calorimeter is consiere the surrounings. Ieall( the -surrounings4 account for the entire entire uni*erse minus the sstem3( %ut in this case( the calorimeter is assume to insulate the heat e!change completel an is also assume to to not ta,e in an heat. =hus( in our calculations( onl the +ater containe in the calorimeter is use to calculate the *alue of heat transfer. transfer. =he follo+ing euation 1 pro*ie % 6amilton et al. 3 relates the energ gaine or lost % the surrounings +ater in the calorimeter3 to the energ lost % the sstem un,no+n metal3.
q system
&3
qsurroundings
=−
=his euation is *er important %ecause it is not possi%le to etermine the heat of the sstem s stem irectl. 6o+e*er( the heat of the surrounings is a%le to %e calculate( so it is *er important to %e a%le to relate the heat of the surrounings to the heat of the sstem. In Part II( the o%)ecti*e is to fin the molar heat of neutrali>ation of hrochloric aci for the follo+ing reaction1: "3
6Claq 6Claq33 ? Na<6aq Na<6aq33
NaClaq NaClaq33 ? 62<l <l 3
=he molar heat of reaction is foun % first calculating the heat of reaction( the heat transferre uring a certain chemical reaction. =he heat of reaction is an e!tensi*e propert %ecause its *alue is reliant on the amount of limiting reactant use in the reaction. Molar heat of reaction is( ho+e*er( an intensi*e propert %ecause it is instea the amount of heat prouce per mole of a certain reactant( thus thus can %e calculate inepenentl of reactant amount. 6amilton et al.1 pro*ie the follo+ing euation to etermine the molar heat of neutrali>ation of hrochloric aci. 53
molar molar heat of neutral neutraliza ization tion =
qneutr heat transferred transferred ∈eachtrial = ¿ mol ¿ mol mol HCl HCl ∈ eachtrial mol HCl HCl
Experimenta 4ection Proceure % 6amilton et al.1 +as follo+e.
5ata 6 Obser7ations: =a%le =a%le 1. Data ta%le for Part I
=a%le =a%le 2. Data ta%le for Part II
Cacations 6 Rests: Part I: Specific Heat of an Unknown Metal
A. Mass Mass of of water water = 1. 66.841 g −9.763 g=57.078 g 2. 66.357 g− 9.662 g =56.695 g B. ∆T of of wat water er = 1. 22.7 ° C 22.1 ° C 0.6 ° C −
=
2. 22.8 ° C −22.2 ° C =0.6 ° C C. ∆T of of met metal al = =−76.9 ° C 1. 22.7 ° C − 99.6 ° C =− 2.
22.8 ° C −99.7 ° C =−76.9 ° C
D. qwater =
( )(
)( )(
1.
( 57.078 g )
4.184
J g∙°C
0.6 ° C =140 J
2.
( 56.695 g
4.184
J g∙°C
0.6 ° C =140 J
) )
E. qmetal = 1. 2.
(
)
− 140 J =−140 J
( 140 J )=−140 J
−
F. smetal = 1.
s
=
140 J
−
0.12
=
10.785 g ×−76.9 ° C
J g∙°C
s=
2.
−140 J 10.754
g ×−76.9 ° C
J g∙°C
=0.12
G. Average verage smetal =
( 0.12+ 0.12 ) 2
= 0.12
Part II: Molar Heat of Neutralization
A. Mass of Solut Solutio io Afte Afterr Mi!ig Mi!ig = 1.
100.00 mL ×
2.
100.00 mL ×
0.997 g 1 mL 0.997 g 1 mL
99.7 g
=
99.7 g
=
B. ∆T of of solu solutio tio = 1. 30.3 ° C −23.8 ° C = 6.5 ° C 2.
29.8 ° C −23.5 ° C = 6.3 ° C
C. qsol =
( )(
)( )(
1.
( 99.7 g )
4.18
J g∙°C
6.5 ° C =2700 J
2.
( 99.7 g
4.18
J g∙°C
6.3 ° C =2600 J
) )
D. qeutr = 1. qsol #
( 2700 J )
−
2700 J ×
$#"
qeutr"
2700 J
=−
2600 J ×
−
3
10
2.7 kJ
=−
J
( 2600 J ) =−2600 J
−
$#"
1 kJ
−
2. qsol #
qeutr"
1 kJ 3
10
2.6 kJ
=−
J
E. %um&er %um&er of mole moles s of 'Cl 'Cl = −
1.
mL × 50.0 mL×
−
2.
mL × 50.0 mL×
3
L 1.00 mol × 1 mL 1 L
10
3
L 1.00 mol × 1 mL 1 L
10
moles HCl 0.0500 moles
=
moles HCl 0.0500 moles
=
F. Molar 'eat of %eutr %eutrali(a ali(atio tio = 2.7 kJ
−
1. 2.
0.0500 mol HCl
−2.6 kJ
mol HCl HCl 0.0500 mol
=−
54
kJ mol HCl
=−52
kJ mol mol HCl HCl
'. Average Molar Molar 'eat of %eutrali(atio %eutrali(atio =
(
− 54
kJ kJ +−52 mol HCl mol HCl 2
)
=−53
kJ mol HCl
Please see attache for Summar of Calculate @esults page.
5iscssion of Rests: =he ta%le %elo+ contains the results of the a%o*e calculations an the ata through +hich the a*erage specific heat of un,no+n metal an the a*erage molar heat of neutrali>ation +ere foun.
=a%le =a%le &. @esults for Part I an II
In Part I of this e!periment( the heat e!change %et+een the un,no+n metal sample an a measure amount of +ater in an insulate coffeecup calorimeter +as o%ser*e an measure in orer to fin its specific heat. =he amount of heat transferre to the +ater +as calculate from its mass( specific specific heat( an temperature change. =he heat transferre to +ater +ater +as then use to fin the heat transferre from the metal through the
q system
qsurroundings
=−
relationship. 'rom
the metalAs mass( mass( temperature change( an heat e!change( the specific heat +as calculate to %e 8 0.12 #g9;C for %oth trials. =hus( the a*erage of %oth trials trials +as 0.12 8#g9;C.
sil*er+hite metal. =he un,no+n metal +as escri%e as gre( roun pellets( thus the ientit of the un,no+n metal must %e lea. In Part II of the e!periment( molar heat of neutrali>ation of hrochloric aci +as calculate % first etermining the heat of the neutrali>ation reaction %et+een measure amounts of hrochloric aci an soium hro!ie. hro!ie. sing the mass of solution solution after mi!ing calculate calculate using the final *olume an ensit of +ater3( its specific heat( an temperature change( the heat release % the reaction +as foun. foun. fter con*erting con*erting that heat into ,ilo)oules an calculating the moles of hrochloric aci use in the reaction( the molar heat of neutrali>ation in ,ilo)oules per mole of hrochloric aci +as o%taine. =he results from %oth parts of the e!periment +ere close to the accepte *alues of leaAs specific heat an hrochloric aciAs molar heat of neutrali>ation( respecti*el. respecti*el. =here +as( ho+e*er( a limitation limitation issue in Part I %ecause the calculate E= +as *er small. =he small E= allo+e for onl one significant figure in the calculations( e*en though the measuring e*ice shoul ha*e allo+e for t+o. solution to this issue +oul %e to measure a greater E= % using using either a larger amount of lea or a smaller amount of +ater in the e!periment. =he E= +ill then carr t+o significant figures an no longer hiner the calculations. n area +here an error coul ha*e %een introuce uring the e!periment +as in transferring the metal from Part I from from the %oiling +ater to the calorimeter. calorimeter. It +as e!pose to the air for a%out three secons secons %efore %eing safel containe +ithin the Strofoam. It is li,el that that some heat escape to the air( air( not to the +ater +ater to %e measure. =he final temperature +oul +oul ha*e %een too lo+ an force the calculations off( ma,ing the e!perimental specific heat to %e too lo+. secon area +here error coul ha*e %een introuce +as in Part II( +hen measuring the initial temperature of the solutions. If not gi*en enough time to cool o+n %et+een trials( the temperature pro%es ma not ha*e gi*en accurate reaings of the actual initial temperatures of the reactants. =he lo+ E= +ill translate to a lo+ heat of reaction. =his +oul s,e+ s,e+ the calculations %ase on euation 53 to iel a lo+ e!perimental molar heat of neutrali>ation of 6Cl %ecause the lo+ *alue +ill %e in the numerator.
Concsion: In Part I( an un,no+n metal lea3 +as ientifie % its specific heat( 0.12 8#g9;C( +hich +as etermine through calorimetr calorimetr an appearance. In Part II( the the aci%ase reaction %et+een hrochloric aci an soium hro!ie +as use to calculate the molar heat of neutrali>ation for hrochloric aci( 5& ,8#mol 6Cl.
References: '& 6amilton( P. Fau( C. an aman( H.( CHEM 122 Experiments in General Chemistry I Laboratory( Laboratory( caem! Pu%lishing ser*ices: el ir( MD( 201&J pp. 10511$
Ans"ers to Post.Lab 8estions: 1. Examine the initial and final temperatures temperatures in Part I. Explain ho the temperatures tell you hat type of rea!tion as in"ol"ed #endothermi! or exothermi!$. %re the si&ns of your qater and and qmetal !onsistent ith this' Explain. Ke measure measure the final temperature +ithin the calorimeter( an it +as higher than the initial temperature( inicating an e!othermic reaction. 6o+e*er( the -reaction4 -reaction4 here is a phsical e!change of heat( not a chemical reaction( therefore there +as no enothermic or e!othermic reaction in*ol*e. 2. In Part I( I( e see that that !opper and and )in! ha"e ha"e the same spe!ifi spe!ifi!! heat #*ee #*ee table in the the 01 01 Introdu!tion.$ If you obtained an experimental "alue of +.,- /& /C ( ho mi&ht you determine hi!h metal you ha"e as an unnon' Explain. Ke recore the appearance of the un,no+n metal( as +ell as etermining its specific heat. If the metal metal +as a sil*ergre( then +e coul assume that the metal +as >inc. If the metal +as a copper color( then +e coul assume that the metal +as copper. copper. Ke +ill not %ase our conclusion on onl specific heat. surroundin&s beyond the nested !offee !ups. In ,. 3e assumed that no heat is lost to the surroundin&s Part I( ob"iously there ould ha"e been some loss in heat as the hot metal is is transferred transferred to the !alorimeter. !alorimeter. Ho does that una"oidable heat loss affe!t your !al!ulated spe!ifi! heat of the metal' 3ould 3ould your !al!ulated spe!ifi! heat be too hi&h or too lo due to this error' Explain fully.
=he calculate specific specific heat +oul %e too lo+ ue to this error. error. =he calculate change in temperature for the +ater an the calculate transferre heat +oul %e too lo+ an the calculate change in temperature for the metal +oul %e too high. 'or e!ample( in an un,no+n metal e!periment( the final temperature +as &0.&2;C %ut +as incorrectl incorrectl recore as 2L.$";C. 2L.$";C. 'irst( the change in temperature for +ater +ill %e calculate to %e too lo+. Corre)t )al)ulatios of ∆T water" *)orre)t )al)ulatios of ∆T water"
30.32 ° C −23.80 ° C =6.52 ° C 29.64 ° C − 23.8 ° C = 5.84 ° C
Secon( the heat in 8oules +ill %e calculate to %e too lo+.
Corre)t )al)ulatios of q water"
( 100.0 g )
*)orre)t )al)ulatios of q water"
( 100.0 g
( )(
)( )(
4.184
J g∙°C
6.52 ° C =2730 J
4.184
J g∙°C
5.84 ° C = 2440 J
)
)
=hir( the heat transfer *alue is still incorrect.
( 2730 J ) =−2730 J
−
Correct calculations of metal: Incorrect calculations of metal:
( 2400 J )
−
2440 J
=−
'ourth( the change in temperature for the metal +ill %e calculate to %e too high. 30.32 ° C −100.00 ° C =69.68 ° C
Corre)t )al)ulatios of ∆T metal"
29.64 ° C −100.00 ° C = 70.36 ° C
*)orre)t )al)ulatios of ∆T metal"
'ifth( the specific heat of the metal is calculate to %e too lo+. Corre)t )al)ulatios of s metal"
*)orre)t )al)ulatios of s metal"
s
=
s
2730 J
−
10.000 g ×− 69.68 ° C
=
3.92
J g∙°C
3.47
J g∙°C
=
2440 J
−
10.000 g ×−70.36 C
=
4. In Part II( II( e assume assume that the the density density and spe!ifi! spe!ifi! heat heat of the soluti solution on is the same same as that that of ater. ater. 3hat 5ustifi!ations 5ustifi!ations do e ha"e to mae that assumption' Explain. In Part II( the reactants( hrochloric aci an soium hro!ie( reacte together to form salt an +ater. oth reactants +ere 1 M solutions( thus the amount of salt prouce in neutrali>ation compare to the +ater from the reagents plus the +ater prouce in the reaction is negligi%le. =hus( the final solution solution is mainl compose of +ater or -ilute4( an +e can assume that tha t the ensit an specific heat of the solution are the same as that of +ater. #assumin& it is +. 6sin& the molar heat of neutrali)ation obtained in your experiment #assumin& !orre!t$( !al!ulate ho mu!h heat you ould exp e!t to be produ!ed if you mixed 7+.+ 7 +.+ mL of +.27+ M HCl ith 7+.+ mL of +.27+ M 8a9H. *ho your !al!ulations. #Hint: Ho many moles of HCl are in"ol"ed'$ In the propose e!periment( there +oul %e the same num%er of moles of hrochloric aci as of soium hro!ie. Since( in euation "3( the t+o reactants ha*e a stoichiometric relationship of 1:1( there is no limiting reagent to +orr a%out. =hus(
accoring to the molar heat of o f neutrali>ation o%taine in m e!periment( fift milliliters of 0.250 M hrochloric aci +ill prouce 0.$$& ,ilo)oules +hen mi!e +ith soium hro!ie.
50.0 mLHCl×
10
3
−
L HCl 0.250 mol HCl 53 kJ × × 1 mL 1 L HCl 1 mol HCl −
0.66 kJ
=−
