Many elements can be identifiied by the colour they give off when they are burned in a flame test.
Also, elements within compounds can be identified when the compound is burned by examining the colour of the flame.
For example - copper burns with a brigtht green colour. The compound copper sulfate will also give off the green colour flame of the copper elemnt in it.
This method of testing compounds for pecific elements is also known as the Positive Element Flame Test because it usually identifies the first element (the positive element) in the compound.
Flame tests can be applied to solids, liquids, solutions, and gases. Flame tests is a test for chemical properties of elements.
In the following activity you will test three gases and identify them by their chemical and physical properties. Specificlly hydrogen gas, which canbe identified by the blue flame it produces when it is burned.
The teacher will perform this activity for you in lab.
Watch the following video:
Gases were either collected using the downward displacement of water or supplied from stadardized laboratory bottles.
Hydrogen gas was produced by reacting calcium metal with water or magnesium metal with hydrochloric acid.
Oxygen gas was collected by decomposition of Hydrogen Peroxide, using Manganese Dioxide as a catalyst. The gas was collected using the upward displacement of air.
Carbon dioxide was collected by decomposition of Sodium Carbonate (Alka-Seltzer) in water. The downward displacement of water was used to collect the gas.
Observations and Summary:
The following flame tests were performed on the gases and the respective results are reported below.
|GAS||Physical Properties||Test (s)||Test Result|
|Hydrogen||odourless, colourless, less dense than air||Burning wood splint||
Burns with a light blue flame
explosive -- "pop sound" heard
|Oxygen||odourless, colourless, less dense than air||Glowing wood splint||Glowing splint burst into flames|
|Carbon Dioxide||odourless, colourless, more dense than air||
Burning Wood Splint
Clear Limewater Solution
Flame goes out
Limewater turns cloudy
Analysis and Follow-up Exercise:
- Complete the following table.
2. Summarize your Conclusions: