4 (2.3) Group 2 and 7 test tube reactions Flashcards
Test for grp 2 metal cations?
-group 2 compound on test tube
-add dilute NaOH dropwise into test tube, observe ppt forms
-keep adding NaOH until in excess
Results from magnesium (mg2+) with dilute sodium hydroxide solution
Initial- colourless solution
With OH- : slight white ppt
With excess OH- : white ppt
Observation of calcium ion (Ca2+) with dilute sodium hydroxide solution
Initial- colourless solution
With OH- : slight white ppt
With excess OH- : slight white ppt
Observation strontium ion (Sr2+) with dilute sodium hydroxide solution
Initial- colourless solution
With OH- : slight white ppt
With excess OH- : slight white ppt
Observation of barium (Ba2+) with dilute sodium hydroxide solution
Initial- colourless solution
With OH- : colourless solution (no change)
With excess OH- : colourless solution (no change)
Flame tests for group 2 ions?
Dip nichrome wire loop in conc HCl
Dip wire loop in unknown compound
Hold loop in clear blue part of Bunsen burner flame
Observe colour change of flame
Flame colour of each metal ion?
Ca2+ = brick red flame
Sr2+ = red flame
Ba2+ = pale green flame
Test for ammonium ions?
-add dilute NaOH to unknown solution + gently heat (ammonium ions will react with OH- ions to produce ammonia gas and water NH4+ (aq) + OH- (aq) —> NH3 (g) + H2O(l)
Ammonia gas- alkaline
-damp red litmus paper turn blue if ammonium ions present
Test for hydroxide ions?
-OH- ions make solution alkaline
-dip damp red litmus paper in solution- turn blue if hydroxide ions present
Test for carbonate (CO3^2-) ions
-add dilute hydrochloric acid
-solution containing carbonate ions will fizz (give carbon dioxide)
-test CO2 by bubbling gas through limewater - turn cloudy if carbonate ions
Test for sulfate ions (SO4^2-)
-add dilute hydrochloric acid, followed by barium chloride solution
-white ppt of barium sulfate forms if sulfate ions present
What is order of testing ions?
Carbonate —> Sulfate —> halide
-prevents false positive results occuring (ie unexpected insoluble ppt such as Ag2SO4, Ag2CO2)
How to test for group 7 ions (halides)
-add dilute nitric acid (HNO3)
-add silver nitrate solution (AgNO3)
Test for halides results?
Chloride (Cl-) = white ppt of silver chloride
Bromide (Br-) = cream ppt of silver bromide
Iodide (I-) = yellow ppt of silver iodide
Further test for group 7 halides?
-add dilute ammonia then conc ammonia to samples of dolution
Results with further halide testing?
Cl- - white ppt dissolves in dilute NH3 (solution go colourless)
Br- - cream ppt dissolves in conc NH3 (solution go colourless)
I- - yellow ppt remains in conc NH3
Equations for carbonate ion test?
Na2C O3 +2HCl→2NaCl+H2O +CO2
Ca(OH)2 + CO2 → CaCO3 + H2O
Test for group 7 ions: solid salts
-add few small spatulas of solid potassium halide salt
-add few drops conc sulfuric acid
-test any gas evolved with damp blue litmus paper
Observations for group 7 union solid salts test
KCl- white, steamy fumes
KBr- orange fumes
KI- purple fumes + purple/black solid
For all- turn damp blue litmus paper red
Safety for test of potassium halide salts
-conc sulfuric acid
-gases produced toxic & corrosive
Test for sulfate ions equation?
MgSO4 + BaCl2 —> BaSO4 (s) + MgCl2 (aq)
Why shake?
Ensure reactant combine properly
Simplest Ionic Equation for formation of Mg(OH)2 (s)
Mg2+ (aq) + 2OH-(aq)—>Mg(OH)2 (s).
Results for group 3 + OH-?
Aluminium salts will form a white precipitate of aluminiumhydroxidewhichwilldissolveinexcess sodium hydroxide to form a colourless solution
Ionic equation for Al + OH-
[Al(H2O)6]3+(aq) + 3OH- (aq) —> Al(H2O)3(OH)3 (s) + 3H2O (l) Al(H2O)3(OH)3(s) +OH-(aq)—>[Al(OH)4]-(aq)+3H2O(l)
