topic 9 - qualitative analysis

flame test - flame colour of a potassium ion (K+)

flame test - flame colour of a potassium ion (K+)

lilac

flame test - flame colour of a sodium ion (Na+)

yellow

flame test - flame colour of a lithium ion (Li+)

red

describe the test to identify halide ions

1. add dilute nitric acid to unknown solution

2. add silver nitrate to unknown solution

3. observe precipitate colour produced

results for test to identify halide ions (Cl-, Br-, I-)

• chloride ion (Cl-) = white precipitate

• bromide ion (Br-) = cream precipitate

• iodide ion (I-) = yellow precipitate

describe the test to identify carbonate ions

1. add dilute hydrochloric acid

2. observe whether bubbling occurs

results for test to identify carbonate ions

if bubbling occurs, carbonate ions are present

explain why the results of a test for presence of specific ions must be unique

in order to identify the specific ion without uncertainty

what is the precipitation colour of an aluminium ion (Al3+)

white (dissolves and goes colourless when excess NaOH is added)

describe the test to identify ions in solids or solutions using sodium hydroxide solution (NaOH)

1. add NaOH solution to unknown solution

2. observe the precipitate colour produced

3. if a white precipitate is formed add excess NaOH solution

flame test - flame colour of a copper ion (Cu2+)

blue-green

flame test - flame colour of a calcium ion (Ca2+)

brick red (orange-red)

precipitate test - precipitate colour of a iron 2 ion (Fe2+)

green

precipitate test - precipitate colour of a copper ion (Cu2+)

blue

precipitate test - precipitate colour of a calcium ion (Ca2+)

white

precipitate test - precipitate colour of a ammonium ion (NH4+)

white

precipitate test - precipitate colour of a iron 3 ion (Fe3+)

brown

describe the test to identify sulfate ions

• add dilute hydrochloric acid to unknown solution

• add barium chloride to unknown solution

• observe whether a white precipitate is formed

results for test to identify sulfate ions

if a white precipitate is formed, sulfate ions are present

describe the flame test to identify ions in solids

1. dip flame test loop into dilute hydrochloric acid

2. hold flame test loop in flame and then dip in beaker of water

3. dip clean flame test loop into one of the four known solids

4. observe and record the flame colour produced

describe the test for hydrogen gas

place a lighted splint in a test tube containing the gas. if the gas is hydrogen it will produce a squeaky pop

describe the test for oxygen

place a glowing splint in a test tube containing the gas. if oxygen is present the splint will relight

describe the test for carbon dioxide

bubble the unknown solution through limewater. if carbon dioxide is present, a white precipitate of calcium carbonate will be formed

describe the test for ammonia gas

dip a glass rod in concentrated hydrochloric acid and put this in the unknown gas. if ammonia is present, a white smoke of ammonium chloride will form

describe the test for chlorine gas

place a damp piece of litmus paper above a test tube containing the unknown gas. if the litmus paper is bleached, chlorine is present

what are the advantages of instrumental methods of analysis

• they are readily available

• can improve sensitivity of test

• can improve accuracy of test

• can improve speed of test