Background on flame test:
Metals change the colour of a flame when they are heated in it. Different metals give different colours to the flame, so flame tests can be used to identify the presence of a particular metal in a sample.
Every atom consists of a nucleus with tiny electrons whizzing around it. The further away from the nucleus they are, the more energy the electrons have. If a metal atom is heated, the electrons closer to the nucleus may gain enough energy to orbit further away from the nucleus. When they fall back closer to the nucleus, they give off this extra energy as light.
Next, we moved on to the practical part of the lesson. We were given a bunsen burner, a metal loop, lab glasses, and powdered samples of: barium, lead, calcium, potassium, copper and sodium. We were to observe the light emitted when putting these powdered samples into the flame using the bunsen burner and the metal loop.
We stuck the metal loop into the containers of powdered samples and took out a little powder. Then we put the metal loop in the flame and different colours were emitted. These were our results:
On the worksheet given, we were also given some questions as food for thought:
1.) How and what is it used for in "Crime scene investigations/ forensic science?"
2.) Is flame test sufficient to identify the trace metal(s) present?
3.) If there are more than one trace metal present, is the flame test still a suitable technique to identify the trace metals?
1.) Flame analysis is based on the physical and chemical principle that atoms after being heated by flame turn to their normal energy state by giving off the excess energy in the form of light. Frequencies of light given off are characteristic for each element. Flame analysis is a qualitative test and is designed to identify the components of a substance or mixture. Quantitative tests measure the amounts of the components in a reaction or substance. The unknown to be subjected to flame analysis is either sprayed into the flame or placed on a thin metal loop, then put into the flame. Volatile elements produce intense colours. For example: sodium, it produces a very bright yellow colour.
However, as useful as it is to forensic analysis, the flame test does not work on all elements.
2.) I don't think the flame test is sufficient to identify the trace metal(s) present because everyone perceives colours differently. If the flame given out seems red to me, it may seem bright orange to another person, so i think that the flame test is insufficient to identify the trace metals because everyone has different perceptions of colours and it will be inaccurate to just identify the trace metals by observing the light emitted by the metal. -> this is my opinion, may not be true though!
Moreover, impurities or contaminants may affect the test results. Sodium, in particular, is present in most compounds and will colour the flame. Sometimes a blue glass is used to filter out the yellow of sodium.
3.) If there are more than one trace metal present, is the flame test still a suitable technique to identify the trace metals?
No, the test cannot differentiate between all elements. Several metals produce the same flame colour. Some compounds do not change the colour of the flame at all.
This is a detailed interpretation of the flame test:
Red
Carmine to Magenta: Lithium compounds. Masked by barium or sodium.
Scarlet or Crimson: Strontium compounds. Masked by barium.
Red: Rubidium (unfiltered flame)
Yellow-Red: Calcium compounds. Masked by barium.
Carmine to Magenta: Lithium compounds. Masked by barium or sodium.
Scarlet or Crimson: Strontium compounds. Masked by barium.
Red: Rubidium (unfiltered flame)
Yellow-Red: Calcium compounds. Masked by barium.
Yellow
Gold: Iron
Intense Yellow: Sodium compounds, even in trace amounts. A yellow flame is not indicative of sodium unless it persists and is not intensified by addition of 1% NaCl to the dry compound.
Gold: Iron
Intense Yellow: Sodium compounds, even in trace amounts. A yellow flame is not indicative of sodium unless it persists and is not intensified by addition of 1% NaCl to the dry compound.
White
Bright White: Magnesium
White-Green: Zinc
Bright White: Magnesium
White-Green: Zinc
Green
Emerald: Copper compounds, other than halides. Thallium.
Bright Green: Boron
Blue-Green: Phosphates, when moistened with H2SO4 or B2O3.
Faint Green: Antimony and NH4 compounds.
Yellow-Green: Barium, manganese(II), molybdenum.
Emerald: Copper compounds, other than halides. Thallium.
Bright Green: Boron
Blue-Green: Phosphates, when moistened with H2SO4 or B2O3.
Faint Green: Antimony and NH4 compounds.
Yellow-Green: Barium, manganese(II), molybdenum.
Blue
Azure: Lead, selenium, bismuth, cesium, copper(I), CuCl2 and other copper compounds moistened with hydrochloric acid, indium, lead.
Light Blue: Arsenic and come of its compounds.
Greenish Blue: CuBr2, antimony
Azure: Lead, selenium, bismuth, cesium, copper(I), CuCl2 and other copper compounds moistened with hydrochloric acid, indium, lead.
Light Blue: Arsenic and come of its compounds.
Greenish Blue: CuBr2, antimony
Purple
Violet: Potassium compounds other than borates, phosphates, and silicates. Masked by sodium or lithium.
Lilac to Purple-Red: Potassium, rubidium, and/or cesium in the presence of sodium when viewed through a blue glass.
Violet: Potassium compounds other than borates, phosphates, and silicates. Masked by sodium or lithium.
Lilac to Purple-Red: Potassium, rubidium, and/or cesium in the presence of sodium when viewed through a blue glass.
PHOTOS+VIDEOS:
 |
| The powdered samples! :) |
 |
| Bunsen burner and lighter! |
 |
| Barium nitrate |
Flame test of sodium
No comments:
Post a Comment