HOW TO CALCULATE THE ATOMIC WEIGHT OF (Fe) AND (Cu) FROM : Initial temperature o

Question

HOW TO CALCULATE THE ATOMIC WEIGHT OF (Fe) AND (Cu) FROM :

Initial temperature of   20 C   Fe metal:

Final temperature of 100 C     metal:

Initial temperature of water from calorimeter: 20 C

Final water temperature from calorimeter: 28 C

Estimate of specific heat for metal:    0.628 J/g*C   

(use 1 cal/gm-°C for water)

Estimate the atomic weight of     69.7     metal:

Q=cmDT

AT=100-20=80

AT= 100-28=72 C Fe

AT=20-28= 8 C H2O

(100g)(80 C)(X)=(150ml)(8 C)(4.184 jg-1C-1)

7200 x= 5020.8

X=5020.8/8000

X=0.628 J/g*C

Atomic weight of Fe= ?????

2nd Metal (Cu)

Initial temperature of      20 C   Cu metal:

Final temperature of    100 C    metal:

Initial temperature of water from calorimeter: 20 C

Final water temperature from calorimeter: 27 C

Estimate of specific heat for metal:  .549 J/g*C   

(use 1 cal/gm-°C for water)

Estimate the atomic weight of    60.1      metal:

DT=100-20=80 C Cu     DT=20-27=7 C H2O

(100)(80)(X)= (150)(7)(4.184)

8000 X= 4393.2

X=0.549 J/g*C

Atomic weight of Cu= ?????

Explanation / Answer

Ist metal

Heat lost by metal = heat gained by water

(mCpdT)metal = (mCpdT)water

100 x Cp (100 - 20) = 150 x 4.18 (28 - 20)

Cp (metal) = 0.627 J/g. oC = 0.15 cal/g.oC

atomic mass of metal = 6/0.15 = 40 g/mol

IInd metal

Specific heat of metal = 150 x 4.18 x 7/100 x 80 = 0.55 J/g.oC

= 0.13 cal/g.oC

atomic weight of metal = 6/0.13 = 45.78 g/mol

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