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18. (1 point) A 2.74 g sample of a substance suspected of being pure gold is warmed up to 72.1 °C and submerged into 15.2 g o

21. (1 point each) Use standard enthalpies of formation (in Appendix G in text) to calculate AH° for each reaction. mAHor (pr

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Answer #1

18)
m(water) = 15.2 g
T(water) = 24.7 oC
C(water) = 4.184 J/goC
m(sample) = 2.74 g
T(sample) = 72.1 oC
C(sample) = to be calculated

We will be using heat conservation equation

use:
heat lost by sample = heat gained by water
m(sample)*C(sample)*(T(sample)-T) = m(water)*C(water)*(T-T(water))
2.74*C(sample)*(72.1-26.3) = 15.2*4.184*(26.3-24.7)
125.492*C(sample) = 101.7549
C(sample)= 0.811 J/goC

This is different than specific heat capacity of gold.
So, this substance is not pure gold
Answer: 0.811 J/goC, No

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