Test for halides ions. Acidify with dil. nitric acid and add silver nitrate The following silver halides form | ||
F- | Colourless | No ppt to dissolve |
Cl- | White ppt produced (AgCl) | Re-dissolves in dil NH3 |
Br- | Cream ppt produced (AgBr) | Re-dissolves in conc NH3 |
I- | Yellow ppt produced (AgI) | Does not dissolve in NH3 |
Test for unsaturated carbon-carbon bonds C=C Add bromine water to organic compounds and shake |
Result: brown color disappear and solution becomes colorless |
Additionally When burned on a watch glass they produce a sooty flame (incomplete combustion) |
Test for sulphite anion SO32- |
Add acid and test the gas evolved is SO2 |
Test for sulfur dioxide |
Add potassium chromate paper goes from orange to green |
Test for carbonate and hydrogen carbonate (CO32- and HCO3-) |
Add universal indicator and if the solution is blue you have carbonate (pH 12), if it is dark green you have hydrogen carbonate (pH 9) |
Additionally you can add Phenolphthalein |
This goes dark pink with carbonate and light pink with hydrogen carbonate |
Add calcium chloride to CO32- or HCO3- |
Carbonate will form a white ppt |
Add MgSO4, then heat |
Cloudy solution |
Flame Tests
Salt | Colour |
Lithium | Red |
Sodium | Yellow |
Barium | Apple green |
Magnesium | Colorless |
Strontium | Crimson (dark red) |
Calcium | Brick red (orange) |
Potassium | Lilac |
Ammonium compounds |
Unlike ionic solids they sublime at low temperature |
Test for Halogenalkanes
Add sodium hydroxide and acidified silver nitrate. Refer to group 7 test for color of precipitate formed.
Test for alcohols –OH group
Add Phosphorous Pentachloride PCl5, misty fumes are produced which are acidic (hydrogen chloride HCl(g))
Test for gases
Gas | Test and result |
ammonia | Turns damp red litmus paper blue (alkaline gas) |
Hydrogen chloride gas (same for hydrogen bromide/ iodide) | Misty fumes turns blue litmus red |
Carbon dioxide | Turns limewater milky |
Chlorine (same for Br2 and I2) | Turns damp blue litmus paper red then bleaches |
Hydrogen | ‘pops’ with a lighted splint |
Oxygen | Relights a glowing splint |
Nitrogen dioxide | Brown gas turns blue litmus red (acidic gas test in fume cupboard) |
Sulfur dioxide | Yellow gas turns blue litmus red (acidic gas tested in fume cupboard) Turns potassium chromate paper from orange to green) |
Test for water
Test | Result |
Cobalt chloride paper | Blue paper turns pink with water |
Copper sulfate (anhydrous) | White compound goes blue with water |
Test for cations
Cation | Effect of aqueous NaOH | Effect of aqueous NH3 |
Aluminum (Al3+) | White ppt., soluble in excess giving colorless solution | White ppt., insoluble in excess |
Ammonium (NH4+) | Ammonia produced on warming | |
Calcium (Ca2+) | Slight white ppt., insoluble in excess | No ppt or very slight white ppt. |
Copper (Cu2+) | Light blue ppt., insoluble in excess | Light blue ppt., soluble in excess giving a dark blue solution |
Iron (II) (Fe2+) | Dark green ppt., insoluble in excess | Dark green ppt., insoluble in excess |
Iron (III) (Fe3+) | Brown/orange ppt., insoluble in excess | Brown/orange ppt., insoluble in excess |
Zinc (Zn2+) | White ppt., soluble in excess giving colorless solution | White ppt., soluble in excess giving colorless solution |
Test for anions
Anion | Test | Test result |
Carbonate (CO32-) | Add dil. acid | Effervescence, CO2 produced |
Iodide in solution (I-) | Acidify with dil. Nitric acid and add lead (II) nitrate | Bright yellow ppt produced PbI2) |
Nitrate in solution (NO3-) | Add sodium hydroxide and aluminium foil and heat gently | Ammonia gas produced |
Sulfate in solution (SO42-) | Acidify with dil nitric acid and add barium nitrate | White precipitate, BaSO4 |
Indicator tests – Titration information
Indicators: Phenolphthalein |
Goes from colorless to pink (acid to alkali) |
Methylorange |
Goes from yellow to orange |
Concordance: two titres need to be within 0.20 cm3 of each other, take an average and then multiply by the concentration to get the moles |
Sources of error: misreading meniscus, parallax error, bubbles in the burette, not rinsing with reactant before start, leaving the funnel at the top |
Points to consider: ratio of reactants in the equation e.g. 2:1 for NaOH + H2SO4 |
Organic compounds test
Organic molecules | Test |
Alkenes | · Shake with bromine water, goes from orange/brown to colorless Alkanes don’t react and the solution remains orange/brown · Also alkaline KMnO4 can be added, it goes from purple to colorless and a diol is made · Also when burned alkenes make a sooty flame |
Alcohols | · Acidified K2Cr2O7 is added, heated under reflux · Primary go from orange to green and aldehyde forms then carboxylic acid is made · Secondary go from orange to green and ketones are made · Tertiary do not oxidize and it stays orange Additionally you can add PCl5 and misty fumes of HCl are produced |
Aldehyde | Addition of Benedict’s solution causes a red ppt of Cu2O to be produced (Ketones do not react) |
Organic acids | Add a carbonate, effervescence of CO2 is observed |
Halogenalkanes | Add sodium hydroxide and heat, then acidified silver nitrate (see halides tests for results) |
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