[From: ] [author: ] [Date: 11-07-08] [Hit: ]
8 = -29.(200*4.186*(-29.X = 1.molar mass = mass/mole = 410/1.675 = 244.......
A student performed an experiment on an unknown solid which melts in contact with hot water. The following data and information is known about the unknown solid.

Experimental Data
volume of water- 200mL
initial temp. of water- 59.8C
final temp. of water- 30C
mass of water and melted solid- 610g
initial temp. of the solid- 20C

Physical Properties of unknown Solid

melting point 20C
boiling point 136C
heat of fusion 10KJ/mol
Specific heat of unknown in liquid phase- 2J/gC

Calculate the molar mass of the unknown solid.

-
heat lost by water + heat gained by unknown solid = 0 [energy is conserved]
(m c delta(T))water + (m c delta(T))solid + moles(Lf)solid = 0
m water = 200 g
c water = 4.186 J/gC
delta(T) water = 30-59.8 = -29.8 C
m solid = 610 - 200 = 410 g
C solid = 2 J/gC
delta(T) solid = 30-20 = 10 C
moles solid = X
Lf solid = 10000 J/mol
(200*4.186*(-29.8)) + (410*2*10) + (X*10000) = 0
X = 1.675 mol
then
molar mass = mass/mole = 410/1.675 = 244.8 or about 245 g/mol

better double check all the numbers and math
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