Lab; Molar Enthalpy of the fusion of Ice.(melting of ice)

Purpose: To Calculate the molar enthalpy for the fusion of ice.

Materials:

• 100-200 ml sytrofoam coffee cup and lid
• 100 ml graduated cylinder.
• thermometer
• electronic scale or triple beam balance
• ice
• warm water (50°C)
• paper towel

Procedure:

• Mass a coffee cup and lid.
• Heat water in a 250 ml beaker to approximately 50°C.
• Fill a sytrofoam coffee cup with 100 ml of heated water measured with the graduated cylinder
• Take the temperature of the water.
• Mass the coffee cup, water and lid.
• Obtain some crushed ice. (Approximately 15 - 20 grams (two handfuls).
• Dry the ice with paper towel to remove the sweat on their surface.
• Record the temperature of the water in the coffee cup (this is temperature initial)
• Place the coffee cup, lid and water on the scale and add enough ice to increase the mass Approximately 15 grams.(Note the mass does not have to increase exactly 15 grams). Place the lid on the sytrofoam cup and record the final mass.
• Stir the ice until it all melts and record the final temperature in the sytrofoam cup.

Data:

Calculations:

1. Calculate the mass of water in the calorimeter in kilograms.
2. Calculate the mass of ice added to the calorimeter in kilograms.
3. Calculate the moles of ice that was added (mass of ice in grams ÷ molar mass of water) = n.
4. Calculate the temperature change in the water in the calorimeter (temperature before - temperature after).
5. Calculate the temperature change that happened to the ice after it melted (this is the change from 0 ^oC to the final temperature of the ice water mixture).
6. The heat that the water in the calorimeter lost was absorbed by the ice in first melting, and then later in the ice warming up to the final temperature of the water in the calorimeter. The formulas for calculating these changes are given below.

• Heat lost by the calorimeter Q calorimeter = m * c *t
  • Q = heat in KJ
  • m = mass of water in calorimeter in Kilograms (#1 above)
  • c = specific heat capacity of water (4.19 J/g * ^oC)
  • t = temperature change in calorimeter.(#4 above)
• Heat gained by the ice in melting is Q melting of ice = H * n
  • Q = heat in KJ
  • H = molar enthalpy of fusion of ice
  • n = moles of ice (#3 above)
• Heat gained by the ice as it warms up to the final temperature in the calorimeter is Q ice water = m* c *t
  • Q = heat in KJ
  • m = mass of melted ice (same as the mass of the ice) (#2 above)
  • c = specific heat capacity of melted ice (same as water = 4.19 J/g * ^oC)
  • t = temperature change that occurred in the melted ice (#5 above )

   

  Combined the formula is as follows:

Heat change in calorimeter

=

Heat needed to melt ice

+

Heat absorbed as ice warmed up

m

*

c

*

t

=

H

*

n

+

m

*

c

*

t

7. Plug in values from above into this formula and calculate the molar heat of fusion of ice ( H )

Discussion:

1. The accepted value for the molar heat of fusion of ice is 6.03 KJ/mol. Compare your values with this and with classmates (if any) . Calculate a % error as follows.
   • % error = |(measured value - accepted value (6.03 KJ))| ÷ accepted value
   • The bars indicate that you take the positive value of the difference between measured and accepted values.
2. What factors might have increased the error that you observed in this experiment? Discuss at least 2 ways.

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