8.3 Qualitative Analysis Flashcards
What colour flame does lithium produce?
Crimson
What colour flame does sodium produce?
Yellow
What colour flame does potassium produce?
Lilac
What colour flame does calcium produce?
Orange-red
What colour flame does copper (Cu2+) produce?
Green
How can you test for hydrogen?
Place a lit wooden splint into a test tube containing the gas. You should hear a squeaky pop
How can you test for oxygen?
Place a glowing wooden splint into a test tube containing the gas. You should observe the splint being relit
How can you test for Carbon Dioxide?
Bubble the gas through limewater. It should turn the limewater cloudy
How can you test for Chlorine gas?
Add damp litmus paper to the gas. it should bleach it white
What do you use to test for positive metal ions?
Sodium Hydroxide
What colour precipitate is produced when Sodium Hydroxide reacts with Al3+ ions?
White
What colour precipitate is produced when Sodium Hydroxide reacts with Ca2+ ions?
White
What colour precipitate is produced when Sodium Hydroxide reacts with Mg2+ ions?
White
What colour precipitate is produced when Sodium Hydroxide reacts with Cu2+ ions?
Blue
What colour precipitate is produced when Sodium Hydroxide reacts with Fe2+ ions?
Green
What colour precipitate is produced when Sodium Hydroxide reacts with Fe3+ ions?
Brown
After testing Magnesium, Calcium and Aluminium ions with Sodium Hydroxide, what should you do to distinguish these ions?
-If excess sodium hydroxide is added, the aluminium hydroxide precipitate dissolves to form a colourless solution
-Calcium flame test, will get an orange-red flame
What should you use to test for Carbonate Ions?
An acid
Describe how to perform a carbonate ion test.
-Add dilute acid to the solid or solution
-If you see bubbles, the unknown compound could be a carbonate (should be CO2)
-Perform the CO2 test, bubble the gas through limewater, if it turns cloudy then CO2 is present.
Describe how to perform a sulfate ion test.
-Add aqueous barium ions to the unknown solution
-The formation of a white precipitate of barium sulfate indicates the presence of sulfate ions
What do you use to test for sulfate ions?
Barium Nitrate or Barium Chloride
What should you use to test for sulfates in a solution if you intend to test for halides afterwards? Why?
Barium Nitrate, because Barium Chloride adds Cl- ions to the solution
What do you use to test for halides?
Aqueous Silver Nitrate
Describe how to perform a halide test.
Add aqueous silver nitrate to an aqueous solution of a halide. Silver reacts and forms precipitates of different colours.
What colour precipitate forms when Silver Nitrate reacts with Chlorine?
White
What colour precipitate forms when Silver Nitrate reacts with Bromine?
Cream
What colour precipitate forms when Silver Nitrate reacts with Iodine?
Yellow
Describe what should be done if the colour of silver halide precipitates are difficult to tell apart.
-Add aqueous ammonia and test the solubility of the precipitate.
Describe the solubility of silver chloride in ammonia.
Soluble in dilute NH3
Describe the solubility of silver bromide in ammonia.
Soluble in concentrated NH3
Describe the solubility of silver iodide in ammonia.
Insoluble in concentrated NH3
List the sequence of the anion tests.
Carbonate test, sulfate test, halides test
Why should the carbonate test be performed first?
Because it can be carried out without the possibility of an incorrect conclusion. Neither sulfate nor halides bubble with dilute acid
Why should the sulfate test be performed second?
If you carry out a sulfate test on a carbonate, you will get a white precipitate too. So find out if carbonates are present before
Why should the halide test be performed third?
Because both carbonate and sulfate ions react with silver to form precipitates, so they will give misleading positive results.
If you are asked to analyse a mixture of chemicals in a test tube, should you carry them out in the same solution?
Yes
If you are performing several chemical tests on a single solution, what should you do during the carbonate test?
-If you see bubbles, continue adding dilute nitric acid until bubbling stops to remove all CO3 ions
-Use Nitric acid instead of sulfuric acid or hydrochloric acid
If you are performing several chemical tests on a single solution, what should you do during the sulfate test?
-Use barium nitrate, and filter out later
-Do NOT use BaCl2
If you are performing several chemical tests on a single solution, what should you do during the halide test?
Can continue as normal, because any carbonate or sulfate ions will have been removed
Describe how you would test for ammonium ions.
-Add aqueous sodium hydroxide to the solution
-Ammonia gas will be produced
-Test the gas with moist pH indicator paper, which will turn the paper blue (alkaline)
