qualitative analysis

Question 1

list the anions that can be tested for using qualitative analysis

Answer 1

carbonate
sulfate
halide

Question 2

list the cations that can be tested for using qualitative analysis

Answer 2

ammonium

Question 3

describe the test for carbonates

Answer 3

1. add dilute nitric acid to the solution
   if bubbles appear, then a carbonate is likely to be present (produces CO2)
2. to test for carbon dioxide, bubble the gas through lime water
   if the limewater turns cloudy, then carbon dioxide is present, meaning the solution is a carbonate

Question 4

describe the test for sulfates

Answer 4

add aqueous barium ions (e.g. barium nitrate)
if a white precipitate forms, then a sulfate is present

Question 5

describe the test for halides

Answer 5

1. add silver nitrate
   if a precipitate forms, then a halide is present
   chlorine- white
   bromine- cream
   iodine- yellow
2. add aqueous ammonia to distinguish the precipitates if they are hard to tell apart
   siler chloride dissolves in dilute NH3
   silver bromide dissolves in conc. NH3
   silver iodide does not dissolve

Question 6

what is the correct order of the tests when testing for anions?

Answer 6

1. carbonate test
2. sulfate test
3. halide test

Question 7

why is there a correct order when testing for anions?

Answer 7

-the carbonate test can be carried out without the possibility of an incorrect conclusion, as none of the other ions produce bubbles with dilute acid
-both barium sulfate and barium carbonate produce white precipitates, so the sulfate test is carried out after the carbonate test
-silver ions also form precipitates with carbonates and sulphates, so the halide test is carried out last, once both the others have been ruled out

Question 8

describe the test for ammonium

Answer 8

1. add aqueous sodium hydroxide
   if ammonium is present, ammonia gas will be produced
2. warm the mixture and test the gas with moist pH indicator paper
   ammonia is alkaline and so a positive result will turn the paper blue