Well, today, 25/4/11, is a lab lesson for my last lesson in Chemistry Olympiad. This lab lesson is on identification of metals in unknown solids. This could be done through a flame test. I believed that many people will ask about what am I talking about, I shall explain in a short while.
Rutherford has once demonstrated that atoms have a tiny, positively charged nucleus with electrons outside the nucleus. Evidence soon accumulated that the electrons were not randomly distributed but were arranged in a structured fashion.Chemists of the 18th and 19th centuries developed flame tests that used the colors of flames to identify elements. For example, lithium salt produces a brilliant red flame and sodium salt gives a persistent yellow flame.
An electron, by absorbing a quantum of energy, by heating, is elevated to a higher energy level. By giving up a quantum of energy, the electron can return to a lower energy level. All these would results ions to be formed. The energy released and absorbed in these transitions show up as a line of spectrum. An electron moves instantaneously from one energy level to another, and there are no intermediate stages. We can make sure of this phenomenon to identify elements by their characteristics emission colours through a flame test.
Now, having a better idea about flame test, I am going to reflect on my founding for flame test! :D
Firstly, we will need to clean the wire used for the flame test. To check that the wire is clean (free from contaminants), hold the metal loop in the hottest part of the Bunsen flame. If it is clean, there should be no change in the colour of the flame when the metal loop is heated in the flame.How to do it then?
1. Clean the nichrome wire loop by dipping it into a concentrated acid.
2. Hold the nichrome wire in the non-luminous Bunsen flame until there is no more changes in the colour of flame.
Now, we move on to conduct the flame test.
1. Dip the nichrome wire loop into the one of the known test solutions.
2. Hold the metal loop in the hottest part of the Bunsen flame.
3. Note down the colour of the flame in the chart below.
Note: Remember to clean your wire thoroughly before the next test!
Colour of flame for the compound containing:
Barium ion
Calcium ion
Copper(II) ion
Lead(II) ion
Yellowish green
Red
Green
White
Potassium ion
Iron(II) ion
Lithium ion
Sodium ion
Lilac
Orange sparkle
Red
Orange
Do you think that is all that I needed to test? You are wrong! There are more to this experiment.
There is an unknown substance A and B. Unknown substance A is a pure ionic compound while substance B consists of 2 substances, each containing 1 metal ion. Using separation technique, I have to obtain pure compounds in mixture B, I have to identify the metal or metal ion present in unknown A and B by performing the flame test.Since I know that the substance is in solid, I will have to react them with acid before they are in aqueous forms. These are the results below.
Test(s)
Observations
Conclusion
Unknown A (Flame test)
Flame of the colourless solution is greenish yellow.
The colourless solution is Barium ion.
Test(s)
Observations
Conclusion
Unknown B (Separation)
Filtrate is a colourless solution
Residue is a white solid
White solid is insoluble in the colourless solution
Unknown B1 (Flame test)
Flame of colourless solution is red
Colourless solution is Lithium ion. (Soluble in water)
Test(s)
Observations
Conclusion
Unknown B2 (Flame test)
Flame of the white solid is orange red
White solid is calcium ion. (Insoluble in water)
Just a simple flame test could determine what substance it is, what an amazing finding! Such experiments could helps us shorten our time span in finding unknown substances! Way to go!
Rutherford has once demonstrated that atoms have a tiny, positively charged nucleus with electrons outside the nucleus. Evidence soon accumulated that the electrons were not randomly distributed but were arranged in a structured fashion.Chemists of the 18th and 19th centuries developed flame tests that used the colors of flames to identify elements. For example, lithium salt produces a brilliant red flame and sodium salt gives a persistent yellow flame.
An electron, by absorbing a quantum of energy, by heating, is elevated to a higher energy level. By giving up a quantum of energy, the electron can return to a lower energy level. All these would results ions to be formed. The energy released and absorbed in these transitions show up as a line of spectrum. An electron moves instantaneously from one energy level to another, and there are no intermediate stages. We can make sure of this phenomenon to identify elements by their characteristics emission colours through a flame test.
Now, having a better idea about flame test, I am going to reflect on my founding for flame test! :D
Firstly, we will need to clean the wire used for the flame test. To check that the wire is clean (free from contaminants), hold the metal loop in the hottest part of the Bunsen flame. If it is clean, there should be no change in the colour of the flame when the metal loop is heated in the flame.How to do it then?
1. Clean the nichrome wire loop by dipping it into a concentrated acid.
2. Hold the nichrome wire in the non-luminous Bunsen flame until there is no more changes in the colour of flame.
Now, we move on to conduct the flame test.
1. Dip the nichrome wire loop into the one of the known test solutions.
2. Hold the metal loop in the hottest part of the Bunsen flame.
3. Note down the colour of the flame in the chart below.
Note: Remember to clean your wire thoroughly before the next test!
Colour of flame for the compound containing:
There is an unknown substance A and B. Unknown substance A is a pure ionic compound while substance B consists of 2 substances, each containing 1 metal ion. Using separation technique, I have to obtain pure compounds in mixture B, I have to identify the metal or metal ion present in unknown A and B by performing the flame test.Since I know that the substance is in solid, I will have to react them with acid before they are in aqueous forms. These are the results below.
Residue is a white solid
Just a simple flame test could determine what substance it is, what an amazing finding! Such experiments could helps us shorten our time span in finding unknown substances! Way to go!