In this lab we will be using lab techniques and basic chemical concepts to identify an unknown metal. Every metal has a unique set of properties. We will be using density and specific heat (also known as "heat capacity" or "specific heat capacity"). Your periodic tables have adequate listings for the purpose of this experiment, but several other sources also have listings of these values for pure materials: check the indices of the CRC Handbook, the Merck Index, or the Exploring the Elements books on the shelves around the room.
NOTES: Goggles are necessary, and long hair must be tied back . Record all data to the correct decimal place in your lab handbook. NEVER stir anything with a thermometer, and never rest one on its bulb.
PROCEDURE - Density
To determine the density of your metal sample, you need to know the
mass (in grams), and the volume (in mL = cc = cm3). Determine
the volume as precisely as possible by measuring water displacement.
PROCEDURE - Specific Heat
To determine the specific heat of a metal sample, we will use a calorimeter,
and the concept that in a closed system, heat lost by a hot object is gained
by a cooler one.
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mDTCp(cold) = –mDTCp(hot) |
To determine the initial (high) temperature of your metal sample, suspend it in a beaker of boiling water and keep it there until boiling has proceeded steadily for about two minutes. Record the temperature of the boiling water with a thermometer in a rubber stopper (it should not touch the beaker glass). This is the same as the initial metal temperature.
While the water/metal mixture is boiling, record the mass of the empty calorimeter cup. Next, add just enough water to cover your piece of metal (estimate), and determine the combined mass. Keep track of the temperature of this water with a second thermometer.
Record the temperature of the cold water and of the metal just before combining them. Immerse the metal sample in the cold water and record the final temperature of the mixture. It should change quickly at first, then level off, then cool back down slowly. Record the level part.
NOTE: Perform one density trial then one specific heat trial,
then repeat the whole thing two more times. Make sure Everything
is dry for each trial..
| mass of metal |
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(g) |
| volume of water |
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|
|
(mL) |
| volume of water + metal |
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|
|
(mL) |
| volume of metal |
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|
|
(mL) |
| density of metal |
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|
(g/mL) |
Average density of metal: __________
| initial temperature of metal | |
|
|
(C) |
| mass of empty calorimeter cup | |
|
|
(g) |
| mass of cup with water | |
|
|
(g) |
| temperature of cold water | |
|
|
(C) |
| final temperature of mixture | |
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|
(C) |
| specific heat of water | |
|
|
(J/gC) |
| mass of cold water | |
|
|
(g) |
| change in water temperature | |
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|
(C) |
| change in metal temperature | |
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|
(C) |
| specific heat of metal | |
|
|
(J/gC) |
Show a complete sample calculation for heat capacity:
Average specific heat of metal (J/gCo): __________
Include a few sentences identifying the metal you examined. Be sure to use full sentences, and compare your experimental values with the "accepted values" for the density and specific heat of your chosen metal. Refer your periodic table.
A Final Reminder: Remember the labels in your calculations! This includes telling what each equation is calculating. Make sure you are consistent, and your calculations agree with your data labels. Do at least three trials for your metal.