Please enable JavaScript.
Coggle requires JavaScript to display documents.
CHEMICAL TESTS (Why do we need flame tests? (Mining (we use flame tests…
CHEMICAL TESTS
-
-
Testing for cations
When doing the flame test, firstly, grab a bunsen burner and have the hole open, the flame should be blue. Gather a metal loop and dip it into dilute hydrochloric acid and put it over the flame. The colour of the flame should be orange. Next, dip the metal loop in your cation, put it in the flames and observe the colour change of the flame.
This test uses sodium hydroxide or aqueous ammonia to test and identify metal ions by the precipitation formed. Sodium Hydroxide or Aqueous Ammonia is added to the solution being tested and the color of precipitation formed allows for identification of the compound.
Barium ions react with sulfate ions, SO42- to form insoluble white barium sulfate: Ba2+(aq) + SO42-(aq) → BaSO4(s)
To test for sulfate ions in solution: add a few drops of dilute hydrochloric to the sample, add a few drops of dilute barium chloride solution. A white precipitate forms if sulfate ions are present.
Testing for anions
This test has to be done in solution. If you start from a solid, it must first be dissolved in pure water. The solution is acidified by adding dilute nitric acid. (Remember: silver nitrate + dilute nitric acid.) The nitric acid reacts with, and removes, other ions that might also give a confusing precipitate with silver nitrate.
The hydrochloric acid is added first to remove any carbonate ions that might be present - they would also produce a white precipitate, giving a false positive result. Barium nitrate solution can be used instead of barium chloride solution. However, nitric acid is added first to acidify the test solution.
Flame tests are used to identify what metal is present. Although Magnesium and Iron are unable to be tested on because the flame will not give a specific colour change.
-
Gas tests are used to identify what gas is present around us but they all have different ways of testing which does not just include any ignited flames.
gas test
Hydrogen
Testing for Hydrogen involves the 'squeaky pop test'. In this experiment, you face the test tube, containing hydrogen bottoms up as Hydrogen gas is less dense and will go up. and get an ignited flint and insert it into the test tube. There should be a squeaky pop thus the name of the experiment, 'the squeaky pop test'.
Oxygen
Oxygen can be tested by reigniting a splint. Sounds a little ridiculous but since Oxygen is a good at supporting combustion, a glowing splint will reignite. Like the squeaky pop test, the test tube containing Oxygen should be held bottoms up, this is because oxygen is less dense and will go up. Then take your glowing splint and insert it into the test tube, the splint should reignite.
Carbon dioxide
There are two ways of testing for Carbon Dioxide. One way is putting in an ignited splint where the fire will go out but other gases do this as well so it is not as accurate as the limewater experiment. In this experiment, you can either put a bung on top of the tube with Carbon Dioxide and insert the other end of the tube in the limewater and wait for the limewater to start becoming milky white. Another way to test for Carbon dioxide is just opening the tube of carbon dioxide and adding in a little bit of limewater and just shaking the mixture until the limewater turns cloudy.
Ammonia
Ammonia gas gives off a very chocking smell and can be tested by damping a red litmus paper and inserting it into the test tube containing the Ammonia gas. The damp litmus paper should turn blue.
Chlorine
Chlorine gives off a chocking smell and to test for it's presence, simply get a damp blue litmus paper and insert it into the test tube. The damp litmus paper should turn red and then be bleached white.
-