qualitative analysis

Question 1

how can we identify the present cations in an unknown solution?

Answer 1

by adding aqueous sodium hydroxide or aqueous ammonia

Question 2

what happens when NaOH(aq) is added to Zn2+?

Answer 2

white ppt, Zn(OH)2 is formed
precipitate dissolves in excess to give a colourless solution

Question 3

what happens when NH3 is added to Zn2+?

Answer 3

white ppt, Zn(OH)2 formed
precipitate dissolves in excess to give a colourless solution

Question 4

what happens when NaOH is added to Al3+?

Answer 4

white ppt, Al(OH)3 formed
precipitate dissolves in excess to give a colourless solution

Question 5

what happens when NH3 is added to Al3+?

Answer 5

white ppt, Al(OH)3 formed
precipitate insoluble in excess

Question 6

what happens when NaOH is added to Pb2+?

Answer 6

white ppt, Pb(OH)2 formed
precipitate dissolves in excess to give a colourless solution

Question 7

what happens when NH3 is added to Pb2+?

Answer 7

white ppt, Pb(OH)2 formed
precipitate is insoluble in excess

Question 8

what happens when NaOH is added to Ca2+?

Answer 8

white ppt, Ca(OH)2 formed
precipitate is insoluble in excess

Question 9

what happens when NH3 is added to Ca2+?

Answer 9

no precipitate formed

Question 10

what happens when NaOH is added to Cu2+?

Answer 10

light blue ppt, Cu(OH)2 formed
precipitate is insoluble in excess

Question 11

what happens when NH3 is added to Cu2+?

Answer 11

light blue ppt, Cu(OH)2 formed
precipitate dissolves in excess to give a dark blue solution

Question 12

what happens when NaOH is added to Fe2+?

Answer 12

green ppt, Fe(OH)2 formed
precipitate is insoluble in excess

Question 13

what happens when NH3 is added to Fe2+?

Answer 13

green ppt, Fe(OH)2 is formed
precipitate is insoluble in excess

Question 14

what happens when NaOH is added to NH4+?

Answer 14

no precipitate formed
when heated, ammonia gas is produced and moist red litmus paper turns blue

Question 15

what happens when NH3 is added to NH4+?

Answer 15

no reaction

Question 16

how to test for carbonate?

Answer 16

add dilue nitric acid
bubble gas into limewater

Question 17

what is observed when carbonate is present in test for carbonate?

Answer 17

acid will react with CO3^2- ions to produce carbon dioxide. effervesence is observed
white precipitate (CaCO3) will form in limewater
gas produced is carbon dioxide

Question 18

how to test for chloride?

Answer 18

add dilute nitric acid
then add silver nitrate solution

Question 19

what is observed if chloride is present in test for chloride?

Answer 19

white precipitate of silver chloride (AgCl) formed

Question 20

how to test for sulfate?

Answer 20

add dilute nitric acid
then add barium sulfate solution

Question 21

what is observed if sulfate is present in test for sulfate?

Answer 21

white precipitate of barium sulfate (BaSO4) formed

Question 22

how to test for nitrate?

Answer 22

add dilute sodium hydroxide
then add a piece of aluminum foil
warm the mixture
test the gas given off with a piece of moist red litmus paper

Question 23

what happens if nitrate is present in test for nitrate?

Answer 23

moist red litmus paper turns blue
gas produced is ammonia gas

Question 24

what are the properties of hydrogen and how to test for it?

Answer 24

-colourless and odourless
-place a lighted splint at the mouth of the test tube

Question 25

how to tell if hydrogen is present?

Answer 25

a 'pop' sound is extinguished by the lighted splint

Question 26

what are the properties of oxygen and how to test for it?

Answer 26

-colourless and odourless -place a glowing splint into the test tube

Question 27

how to tell if oxygen is present?

Answer 27

the flame on the glowing splint reklindles

Question 28

what are the properties of carbon dioxide and how to test for it?

Answer 28

-colourless and odourless -bubble gas through limewater

Question 29

how to tell if carbon dioxide is present?

Answer 29

white precipitate (CaCO3) is formed in limewater

Question 30

what are the properties for chlorine and how to test for it?

Answer 30

-greenish-yellow gas with a pungent sme;; -place a piece of moist blue litmus paper at the mouth of the test tube

Question 31

how to tell is chlorine is present?

Answer 31

moist blue litmus paper turns red and then bleached (white)

Question 32

what are the properties of sulfur dioxide and how to test for it?

Answer 32

-colourless gas with a pungent smell -place a piece of filter paper soaked with acidified potassum manganate(VII) at the mouth of the test tube

Question 33

how to tell if sulfur dioxide is present?

Answer 33

purple acidified potassium manganate turns colourless (SO2 is a reducing agent)

Question 34

what are the properties of ammonia and how to test for it?

Answer 34

-colourless gas with a pungent smell -place a piece of moist red litmus paper at the mouth of the test tube

Question 35

how to tell if ammonia is present?

Answer 35

moist red litmus paper turns blue