Objective: Describe the difference between a physical change and a chemical change.
Data Table
Chemical Compounds
|
Elements Involved
|
Characteristics
|
Barium Chloride
|
BaCl
|
Green color
|
Calcium Chloride
|
CaCl
|
Orange color
|
Lithium Chloride
|
LiCl
|
Red color
|
Potassium Chloride
|
KCl
|
Blue color
|
Sodium Chloride
|
NaCl
|
Orange color
|
Strontium Chloride
|
SrCl
|
Red color
|
Mystery Substance
|
LiBa
|
Red and green colors
|
Aluminum Foil
|
Al
|
White and orange sparkles
|
Analysis Questions
1.) What characteristics determine that a chemical change (or reaction) has occurred?
Heat being emitted and the chemical change being irreversible.
2.) What is emitted when a chemical change takes place in the flame test?
Heat is emitted.
3.) What group, from the periodic table, do these elements exist?
They are apart of group 1-alkali metals.
4.) Do any two elements give the same spectrum of color? Explain why?
SrCl and LiCl give the same spectrum because they have similar wave lengths and frequencies.
5.) Recall what a catalyst is in a chemical reaction. What was the catalyst in these reactions?
The catalyst in these reactions is heat.
Critical Thinking
Obj: Explain how the data gathered in this lab can be used to solve crimes or convict criminals.
Sources used: http://www.nclark.net/Renters_Beware.pdf, http://www.webexhibits.org/causesofcolor/3BA.html, http://nj.gov/health/eoh/rtkweb/documents/fs/0532.pdf
The application of science to investigate and solve crime is forensics. A method that branches off of this field of science is flame testing. Flame testing-a form of emission spectroscopy-is a procedure that is used in chemistry to detect the presence of specific elements such as metal ions. This is a useful method because gas excitations-the excited state of an atom-produce a precise line emission spectrum for an element, thus allowing us to distinguish between certain elements based on their characteristic emission spectrum.
Flame tests can be used at crime scenes in a number of ways. One efficient way is to determine the contents used to poison a victim. Say someone was poisoned with copper chloride (CuCl)-a harmful and hazardous substance-and the criminal left behind evidence-a container with the poison-at the scene. Forensic technicians would take the evidence and run a flame test on it. The color given off-a green/yellowish color-would narrow it down to the possibility of the poison being copper chloride.
