MHS Chemistry
Identification of an Unknown Metal

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.


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..


DATA & RESULTS - show a complete sample calculation for each section.
 
mass of metal
__________
__________
__________
(g)
volume of water
__________
__________
__________
(mL)
volume of water + metal
__________
__________
__________
(mL)
 
volume of metal
__________
__________
__________
(mL)
density of metal
__________
__________
__________
(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
__________
__________
__________
(C)
         
specific heat of water
             4.18
             4.18
             4.18
(J/gC)
mass of cold water
__________
__________
__________
(g)
change in water temperature
__________
__________
__________
(C)
change in metal temperature
__________
__________
__________
(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.

[ID of Metal by Specific Heat score sheet][MHS Chem page]