Identification Tests

Question 1

The flame test results for Group 1 cations are:

Answer 1

Li+     red
Na+   yellow/orange
K+     lilac
Rb+   red/purple
Cs+    blue/violet

Question 2

The flame test results for Group 2 cations are:

Answer 2

Be2+    (no colour)
Mg2+    (no colour)
Ca2+    brick red
Sr2+    crimson red
Ba2+     apple green

Question 3

The method for conducting a flame test is:

Answer 3

-add concentrated HCl acid to the metal compound to partially dissolve it, then dip a silica or platinum wire loop into the mixture and hold the wire in the roaring flame of a Bunsen burner

Question 4

The test results for the reaction of transition metal hexaaqua complex ions with NaOH solution are:

Answer 4

[Cu(H2O)6]2+ + 2OH- → [Cu(H2O)4(OH2)] + 2H2O
pale blue solution → pale blue precipitate

[Co(H2O)6]2+ + 2OH- → [Co(H2O)4(OH)2] + 2H2O
pink solution → blue precipitate

[Fe(H2O)6]2+ + 2OH- → [Fe(H2O)4(OH)2] + 2H2O
pale green solution → green precipitate
[Fe(H2O)6]3+ + 3OH- → [Fe(H2O)3(OH)3] + 3H2O
yellow-brown solution → brown precipitate

[Mn(H2O)6]2+ + 2OH- → [Mn(H2O)4(OH)2] + 2H2O
colourless solution → pale yellow (off white) solution

[Cr(H2O)6]3+ + 3OH- → [Cr(H2O)3(OH)3] + 3H2O
green or violet solution → green precipitate
[Cr(H2O)3(OH)3] + OH- → [Cr(H2O)2(OH)4]- + H2O
green precipitate dissolves → green solution
[Cr(H2O)2(OH)4]- + 2OH- → [Cr(OH)6]3- + 2H2O
no further change in colour

[Ni(H2O)6)2+ + 2OH- → [Ni(H2O)4(OH)2] + 2H2O
pale green solution → darker green solution

[Zn(H2O)6]2+ + OH- → [Zn(H2O)4(OH)2 + 2H2O
colourless solution → white precipitate
[Zn(H2O)4(OH)2] + OH- → [Zn(H2O)3(OH)3]- + H2O
white precipitate dissolves → colourless solution

Question 5

the test results for halide ions with silver nitrate, then dilute and concentrated ammonia are:

Answer 5

Cl- + AgNO3  
white precipitate
dissolves with dilute NH3
Br- + AgNO3  
cream precipitate
dissolves with concentrated NH3
I-  + AgNO3   
yellow precipitate
does not dissolve in concentrated NH3

Question 6

the procedure for the halide test with silver nitrate and ammonia solutions is:

Answer 6

• add dilute nitric acid to remove any other anions present, especially carbonate ions, as they would also form precipitates
• add the silver nitrate
• add some dilute ammonia solution
• add some concentrated ammonia solution

Question 7

the test result and procedure for ammonium ions (NH4+) is:

Answer 7

• add NaOH solution to a solution containing NH4+ ions, and warm the mixture
• use damp red litmus paper to test for NH3 gas released, turning the paper blue
• alternatively, dip a glass rod in concentrated HCl acid and hold this above the mixture. the NH3 gas released will react with the acid and white fumes of NH4Cl will form (ammonium chloride)

Question 8

the test result and procedure for sulfate ions (SO4 2-)

Answer 8

• add dilute nitric acid to the sulfate compound (this removes any carbonate present, so preventing the formation of BaCO3, a white solid)
• add barium nitrate, Ba(NO3)2, and a white precipitate, BaSO4, will form
• BaSO4 is insoluble

Question 9

the test result and procedure for carbonate ions (CO3 2-) is:

Answer 9

• add an acid, such as HCl, to the sample and collect the gas produced
• bubble this gas through limewater, Ca(OH)2, which turns from colourless to cloudy as the CO2 gas reacts with the limewater to form insoluble CaCO3

Question 10

the test result and procedure for alkenes is:

Answer 10

• add 1cm3 of bromine water to 5cm3 of alkene
• shake the test tube
• mixture turns from orange to colourless

Question 11

the test results and procedures for aldehydes is:

Answer 11

• adding potassium dichromate(VI), K2Cr2O7, and sulfuric acid, H2SO4 to the substance
• colour change from orange to green solution as chromium 6+ ions are reduced to 3+ ions
• adding Fehling’s solution
• make the Fehling’s solution by dissolving CuSO4. 5H2O in distilled water and adding a few drops of dilute sulfuric acid
• add this to the substance
• the deep blue solution makes a red precipitate as the copper(II) complex is converted to copper(I) oxide
• adding Benedict’s solution
• the deep blue solution makes a red precipitate as the copper(II) complex is converted to copper(I) oxide
• adding Tollens’ reagent (ammoniacal silver nitrate)
• make the Tollens’ reagent by mixing aqueous silver nitrate with aqueous sodium hydroxide, then dilute adding ammonia drop wise until the silver oxide precipitate dissolves completely
• add the regant to the aldehyde, and a colourless solution produces a silver mirror as the silver(I) complex is converted to metallic silver

Question 12

the test result and procedure for carboxylic acids is:

Answer 12

-

Question 13

the test result and procedure for

Answer 13

-