Qualitative analysis Flashcards
What is the carbonate test
- carbonates react with acids to form carbon dioxide gas
Describe the steps for the carbonate test
- in test tube add dilute strong acid to solid or solution to be tested
- it will bubble
- bubble gas through limewater which will become cloudy if carbonates are present
What are the two ways to test for carbon dioxide
- bubble gas through lime water - saturated aquoeus solution of calcium hydroxide - Ca(OH)2
- carbon dioxide rects to form a fine white precipitate of calcium carbonate which turns lime water cloudy
What is the test for sulfates and why do we use it
- most sulfates are soluble in water excpet barium sulfate
- formation of a white precipitate of barium sulfate is formed
- aqueous barium sulfate (aqueous barium chloride or aqueous barium nitrate) is added to an unknown compound
What solution of aqeuous barium should you use if you are using halide test after and why
aqueous barium nitrate as if you use aquoues barium chloride you are introducing chloride ions into your solution
What is the steps for the halide test
- add aqueous silver nitrate of an aqueous solution of a halife
- the silver halide precipitate are different colors
- add aqueous ammonia to test the solubility of the precipitate
why is the halide test used
- most halides are soluble in water but silver halides are insoluble
- most silver ions react with aqueus halide ions to form precipitates of silver halides
What is the ionic equation for a halide test
Ag+ (aq) + X-(aq)->AgX(s)
x - halogen
Describe the test for chloride ions
- add aquous silver nitrate
- white precipitate forms
- soluble in dilute ammonia
Describe the test for bromide ions
- add aquous silver nitrate
- cream precipitate forms
- soluble in conc ammonia
Describe the test for iodide ions
- add aqueuous silver nitrate
- yellow precipitate forms
- insoluble in conc ammonia
What is the correct order to carry out the tests
- carbonate
- sulfate
- halides
Why do we do the tests in the order of carbonate, sulfate and then halide
- carbonates - add dilute acid looking for effervescence from co2 gas
- neither sulfate or halide produce bubbles with dilute acid
- if test produces no bubbles then no carbonate present and proceed to sulfate test
- in sulfate test add barium nitrate/chloridelooking for white precipitate of barium sulfate
- barium carbonte is white and insoluble in water so if you carry out sulfate test on a carbonate you will also get a white precipitate only carry out sulfate test when no carbonate present
- then in halide test add aqueous silver nitrate, silver carbonate and silver sulfate are both insoluble in water and will form as precipitates in this test
How do you identify a mixture of ions
- carry out the sequence of tests in the same sequence on the same solution
- add carbonate test if you see bubbles add dilute nitric acid until bubbling stop all carbonate ions removed and there will be none left to react
- to solution let from carbonate test add an excess of barium nitrate any sulfate ons will precipitate out as barium sulfate
- filter the solution to remove barium sulfate
- to solution left from sulfate test add aqueous silver nitrate
- any carbonate or sulfate ions initially present have been removed any precipitate fromed must involve halide ion
- add ammonia to confirm which halide you have
why do we not use hydrochloric acid or sulfuric acid and barium chloride when testing for a mixture of ions
- hydrochloric acid contains chloride ions interfere with halide test
- sulfuric acid contain sulfate ions that interefere with sulfate test
- barium chlorid chloride ions will show up in halide test
