Qualitative Analysis

Question 1

what is the formula for carbonate ions?

Answer 1

CO3(2-)

Question 2

what gas is formed when carbonates react with acids?

Answer 2

carbon dioxide gas

Question 3

how do you test for the presence of carbonate ions?

Answer 3

• in a test tube, add dilute nitric acid to an unknown solution
• if effervescence is produced/seen, test with limewater
• if limewater turns cloudy, CO2 is confirmed and thus carbonate ions present

Question 4

what is the formula for sulfate ions?

Answer 4

SO4(2-)

Question 5

how do you test for the presence of sulfate ions?

Answer 5

• add barium chloride (BaCl2) to an unknown solution
• if white precipitate (barium sulfate) is formed, sulfate ions are present

Question 6

what is the formula for halide ions?

Answer 6

Cl-, Br-, I-

Question 7

how do you test for the presence of halide ions?

Answer 7

• add silver nitrate (AgNO3) to the unknown solution
• coloured precipitate forms depending on the halide ion present

Question 8

what colour precipitate are chloride ions?

Answer 8

white

Question 9

what colour precipitate are bromide ions?

Answer 9

cream

Question 10

what colour precipitate are iodide ions?

Answer 10

yellow

Question 11

why do flouride ions not have a test?

Answer 11

they are soluble so dont give a precipitate

Question 12

how can you differentiate between the halide ions precipitates?

Answer 12

• add dilute aqueous ammonia to AgCl = dissolve precipitate
• add concentrated aqueous ammonia to AgBr = dissolve precipitate
• add concentrated aqueous ammonia to AgI = doesn’t dissolve

Question 13

what is the formula for ammonium ions?

Answer 13

NH4(+)

Question 14

how do you test for the presence of ammonium ions?

Answer 14

• add sodium hydroxide (NaOH) to the unknown solution
• ammonia gas is produced but cannot be seen as it is very soluble in water
• the mixture is warmed and ammonia gas is released
• to test if the gas is ammonia gas use damp red litmus paper which will turn blue

Question 15

what are the anions being tested?

Answer 15

sulfate, carbonate and halide ions

Question 16

what are the cations being tested?

Answer 16

ammonium ions

Question 17

what order do we test the ions?

Answer 17

carbonate, sulfate and halide (cringing so hard)

Question 18

what is the ionic equation for ammonium ions?

Answer 18

NH4+(aq) +OH-(aq) –> NH3(aq)+ H20(l)

Question 19

why does the sequence of test for ions matter?

Answer 19

BaCO3 and Ag2SO4 are insoluble