4- test for ions

Question 1

silver nitrate test for halide ions-
general equation

Answer 1

X+ (aq) + Ag+ –> AgX (s)

Question 2

silver nitrate test for halide ions- reagent

Answer 2

aqueous silver nitrate acidified with dilute nitric acid

Question 3

silver nitrate test for halide ions- results

Answer 3

chloride ion= white ppt of AgCl
bromide ion= cream ppt of AgBr
iodide ion = yellow ppt of AgI

Question 4

silver nitrate test for halide ions- solubility of halide ion precipitates

Answer 4

AgCl= soluble in dil. ammonia(aq) and conc. ammonia(aq)
AgBr= insoluble in dil. ammonia(aq), soluble in conc. ammonia(aq)
AgI= insoluble in in dil. ammonia(aq) and conc. ammonia(aq)

Question 5

barium chloride test for sulfate ions- general equation

Answer 5

BaCl2+(aq) + SO4 2-(aq) –> BaSO4 (s)

Question 6

barium chloride test for sulfate ions- procedure and results

Answer 6

-add dilute HCl and BaCl2 to solution
-sulfate ions present= white ppt of BaSO4

Question 7

what is the carbonate ion problem (3)

Answer 7

-carbonate ions interfere with both tests (test for halide and sulfate ions)
-silver carbonate and barium carbonate are insoluble in water so give precipitates with test reagents
-cream ppt of Ag2CO3
-white ppt of BaCO3

Question 8

how to make sure carbonate ions dont interfere with tests (4)

Answer 8

-carbonate ions are destroyed by acid
-CO3 2- + 2H+ –> H2O + CO2
-add appropriate acid to reagent (nitric acid to silver nitrate, hydrochloric acid to barium chloride)
-bubbles of CO2 gas are observed

Question 9

test for hydroxide ions with magnesium chloride (3)

Answer 9

-produces white ppt of Mg(OH)2
-ppt isnt always obvious
-can test with litmus paper and it will go blue (OH- ions make pH alkaline)

Question 10

test for CO3 2- ions (3)

Answer 10

-add dilute HCl and Na2CO3 to solution
-attach bung with delivery tube. this will transfer gas produced into a 2nd test tube containing limewater
-CO3 2- ions react with H+ –> CO2. Limewater–> cloudy

Question 11

test for ammonium ions (4)

Answer 11

-10 drops NH4Cl in test tube. Add 10 drops NaOH and shake
-gently warm using water bath
-fumes released- hold damp red litmus paper with forceps to fumes
-dam red litmus paper–>blue due to ammonia gas

Question 12

test for group 2 metals- ammonium solution results

Answer 12

Mg2+ =white ppt of Mg(OH)2
Ca2+ = no change
Sr2+ = no change
Ba2+ =no change

Question 13

test for group 2 metals- excess NaOH results

Answer 13

Mg2+ =white ppt of Mg(OH)2
Ca2+ =white ppt of Ca(OH)2
Sr2+ =slight white ppt
Ba2+ =no change

Question 14

test for group 2 metals- excess H2SO4 results

Answer 14

Mg2+ =colourless solution
Ca2+ =slight white ppt
Sr2+ = white ppt
Ba2+ = white ppt