Question

The Heat Capacity of Metals

Data Calorimeter Constant Determination:

Mass of cups and cool water(g) 27.15

Mass of cups and cool water(g) 56.12

Mass of cups, cool water, and hot water(g) 93.62

Initial temperature of cool water and calorimeter (c) 21.9

Initial temperature of hot water (c) 94.0

Final temperature of hot water, cool water, and calorimeter (c) 53.0

Calculate the calorimeter constant from your data.

1. How much heat (in Joules) is required to raise the temperature of 50 grams of water from 14c to 89c?

2. If 25.0g of cool water at 23.0c is mixed with 25.0g of hot water to give a final temperature of 34.6c, what was the initial temperature of the hot water? Assume no heat is lost to the calorimeter.

3. Give at least one probable cause for the heat loss caused by the calorimeter itself (c). Suggest a method to prevent or reduce this heat loss.

4. List at least two possible sources of error in this determination of the molar mass of an unknown metal.

5. Explain in terms of thermochemistry why hot water is so much more likely to cause a burn than a metal at the same temperature.

Answer 1

(1)

Heat reqd = Q = m*C*dT = 50*4.18*(89-14) = 15675 J

(2)

Using relation:

Heat lost by hot water = Heat gained by cold water

25*4.18*(T-34.6) = 25*4.18*(34.6-23)

Solving we get:

T = 46.2⁰C

(3)

A possible cause could be that the calorimeter is made up of a material which is not a perfect insulator and hence loses heat to the surroundings.

(4)

Possible sources of error include the heat loss to the surroundings because the system is not perfectly isolated.

Another error could be incorrect measurement of final temperature.

(5)

Hot water is more harmful because it has higher heat capacity that a metal, and hence it would give out more heat when placed in contact with our skin which is at a lower temp. If the heat capacity of water and metal would have been the same, then they would have been equally harmful.