Classwork: Planning a Practical Investigation
The aim is to plan and write down an experimental procedure to find the specific heat capacity, c, of brass in the form of a small brass ball about 2cm in diameter.
The idea is that your plan will be handed out to a class of people who are going to do what it says on your sheet.
Apparatus you are allowed to use:
Brass ball attached to a thin heat-resistant rod.
Thermometer (0 to 100 0C)
Water – c for water is known; 4200 J/kg 0C
Lab balance for weighing
Thermocouple to measure the temperature of the Bunsen burner
Measure and record the mass of the empty beaker
Add sufficient water – perhaps about 100-200ml
Reweigh and subtract to find the mass of the added water
Measure and record the initial temperature of the water
Put the hot junction of the calibrated thermocouple in the Bunsen flame, meanwhile holding the brass rod as closely as possible to it for a short time so the temperature of the ball and flame you judge to be the same. The tip of the blue part is perhaps best.
QUICKLY transfer the hot ball to the cold water and stir gently, watching the temperature rise carefully. When the temperature has stopped rising and before it starts to lose heat to the room, record the final temperature of the ball and water. THIS BIT IS CRUCIAL.
Heat lost by the ball = heat gained by the water
mass x c(brass) x temp fall of ball = mass of water x 4200 x temp rise of the water. Hence find c. Repeat for different masses of water to check for accuracy.
NB: because the greatest energy loss is on transfer, the actual temperature of the ball as it hits the water is lower than that read by the thermocouple. So, the calculated value of c(brass) will be too high.