What it shows
Different metals need different amounts of heat to warm by one degree. Dropping hot metal into cool water and measuring the final temperature gives the metal’s specific heat.
The science
When hot metal is dropped into cooler water, the heat lost by the metal equals the heat gained by the water (ignoring other losses): m_m c_m (T_m − T_f) = m_w c_w (T_f − T_w). So c_m = m_w c_w (T_f − T_w) / (m_m (T_m − T_f)), where c_w is 4200 J per kg per K. Metals of the same mass raise the water by different amounts: aluminium (about 900 J/kg K) gives a larger rise than iron (about 450) or copper (about 385).
Materials
Cost: under Rs 200. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Equal masses (about 50 g) of iron nuts, aluminium pieces and copper wire coils
- A kitchen scale
- A steel pot of boiling water (an adult heats it)
- A foam or plastic cup as the calorimeter, with 100 mL of water
- A thermometer to 0.5 degrees
- A thread to lower the metal into the water
- A cloth and a notebook
Safety
For this project: An adult must heat the water and move the hot metal with tongs or thread; boiling water and hot metal can burn badly.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
7 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Weigh each metal sample and the empty calorimeter cup, then add 100 g of water to the cup and wrap it in cloth.
Hang the iron sample from a thread in boiling water for 5 minutes so that it reaches about 100 degrees C.
Read the water temperature T_w in the cup, then quickly lift the metal out, shake off the drops and lower it into the cup.
Stir gently and record the highest temperature T_f reached.
Calculate c_m from the formula, with T_m = 100 degrees C, taking care with the units.
Repeat with fresh water for aluminium and copper, using the same masses and starting temperatures.
Compare your three values with a table of known specific heats and find the percentage error for each.
What you should see
Aluminium warms the water most, iron next and copper least, and the specific heats come out within about 20 percent of the table values (the error comes from heat lost to the cup and air).
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What is specific heat capacity?
The heat needed to raise 1 kg of the substance by 1 kelvin.
2Why does water warm slowly in sunshine?
It has a high specific heat of 4200 J per kg per K.
3Why must the metal be transferred quickly?
Otherwise it loses heat to the air and T_m is not 100 degrees C.
4Name a source of error.
Heat lost to the cup, the air and the drops of boiling water carried along with the metal.
Take it further
Plot the final temperature against the mass of metal used to show that the rise is proportional to the heat available.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
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