Tests For Functional Groups/ions + Using Indicators

Front 1

Ammonia gas

Back 1

Damp red litmus paper

NH3 present - paper turns blue

Hint 1

Damp so ammonia gas can dissolve.

Ammonia gas is alkaline.

Front 2

Ammonium ions

Back 2

Add dil. NaOH + heat gently

If NH4+ present -> ammonia gas produced

Then test with red litmus paper for ammonia.

Front 3

Ca2+/Sr2+/Ba2+

Back 3

Flame test

1) dip niche one wire loop in conc HCl

2) Dip wire loop into unknown compound

3) Hold loop in clear blue part of Bunsen burner flame

4) Observe the colour change

Ca2+ = brick red

Sr2+ = red

Ba2+ = pale green

Front 4

Sulfate ions

Back 4

1) Add dil. HCl

2) Add Barium chloride solution (BaCl2)

Sulfate present = white ppt

(the white ppt is barium sulfate)

Hint 4

(works with all sulfates e.g. MgSO4/K2SO4)

Front 5

Hydroxides (OH-)

Back 5

1) Dip red litmus paper into solution

OH- present = paper turns blue

Front 6

Colour of red litmus paper at low pH (acidic)

Back 6

Red

Front 7

Colour of red litmus paper at high pH (alkaline)

Back 7

Blue

Front 8

Colour of phenolphthalein indicator at low pH

Back 8

Colourless

Front 9

Colour of phenolphthalein indicator at high pH

Back 9

Pink

Front 10

Colour of Methyl Orange indicator at low pH

Back 10

Red

Front 11

Colour of Methyl Orange indicator at high pH

Back 11

Yellow

Front 12

Phenolphthalein approx. pH of colour change

Back 12

8.3-10

Front 13

Methyl Orange approx. pH of colour change

Back 13

3.1-4.4

Front 14

Indicator for a strong acid/strong base titration

Back 14

Phenolphthalein or Methyl Orange

(There’s a rapid pH change over the range for both indicators)

Front 15

Indicator for strong acid/weak base titration

Back 15

Methyl Orange

(the pH changes rapidly across the range for Methyl Orange only)

Front 16

Indicator for weak acid/strong base titrations

Back 16

Phenolphthalein

(The pH changes rapidly over phenolphthalein’s range)

Front 17

Indicator for weak acid/weak base titrations

Back 17

No indicators work! (there’s no sharp pH change, the colour of any indicator would change too gradually)

• Use a pH meter.

Front 18

Halide ions (Cl-/Br- etc.)

Back 18

1) Add dil. nitric acid

2) Add silver nitrate solution

Fl- = no ppt

Cl- = white ppt (of AgCl)

Br- = cream ppt (of AgBr)

I- = yellow ppt (of silver iodide)

(HNO3 removes ions that might interfere with the test)

(AgI forms fastest, AgF forms slowest)

Front 19

Carbonates (CO32-) e.g. Na2CO3

Back 19

1) Add dil. HCl

(CO32- + 2H+ —> CO2 + H2O)

2) bubble the gas produced through limewater

If carbonate ions were present at the start = limewater turns cloudy

Front 20

Silver Halides (AgCl etc.)

Back 20

1) Add NH3 solution (NH3(aq))

AgCl = dissolves in dil. NH3

AgBr = dissolves in conc. NH3

AgI = insoluble in conc. NH3

(means AgI is least soluble)

Front 21

Alkene

Back 21

1) Add Bromine water

2) Shake

Alkene = solution orange to colourless

(not alkene = nothing happens)

Front 22

Primary/Secondary/Tertiary alcohol

Back 22

1) Add acidified K2Cr2O7

2) Warm the mixture gently

Primary = orange to green

Secondary = orange to green

Tertiary = nothing happens

(Problem - same result for primary and secondary alcohols, you’ll have to use distillation and collect the product, then use a test to see if aldehyde or ketone)

Front 23

Aldehyde vs ketone

Back 23

1) Add Fehling’s solution

2) Heat

Aldehyde: blue solution to brick-red ppt (Cu2+ -> Cu2O(s))

Ketone: nothing happens

OR

1) Add Tollen’s reagent

2) Heat

Aldehyde = silver mirror on walls of test tube

(Ag+ + e- -> Ag(s))

Ketone = nothing happens

Front 24

Alcohols (simple test)

Back 24

1) Add a small piece of Sodium metal (Na)

Alcohol = effervescence (H2 given off)

(Only works if alcohol is pure)

Front 25

What is the colour change?

Cr2O72- ———> Cr3+

Back 25

Orange to Green

Front 26

Carboxylic acids

Back 26

1) Add Na2CO3 (or NaHCO3)

(or any other carbonate)

Carboxylic acid = effervescence + CO2 evolved turns limewater cloudy

Not Carboxylic acid = nothing happens

Front 27

Carboxylic acids

Back 27

1) Add Na2CO3 (or NaHCO3)

(or any other carbonate)

Carboxylic acid = effervescence + CO2 evolved turns limewater cloudy

Not Carboxylic acid = nothing happens

(Problem - this test will give a positive result with any acid, only use it to distinguish between organic compounds where you know that one of them is a carboxylic acid)

Front 28

What colour is the end point when using Methyl Orange?

Back 28

Orange