REQUIRED PRACTICAL 6 - Organic compound testing Flashcards
What bonding do alcohols have?
Hydrogen bonding - highest bp (out of aldehydes/ketones, alkanes/alkenes)
What bonding do aldehydes and ketones have?
Permanent dipoles - lower bp
What bonding do alkenes and alkanes have?
Van der Waal - low bp (lower group members are gases
During oxidation reactions, what does a primary alcohol produce?
Aldehyde. This can also be oxidised further to produce a carboxylic acid (carboxylic acid cannot be oxidised further)
During oxidation reactions, what does a secondary alcohol produce?
Ketone. This cannot be oxidised further
Can tertiary alcohols be oxidised?
No
What is the test for reagent acidified potassium dichromate? (K2Cr2O7/H+)
Must add acid 1st before dichromate
What is the result of acidified potassium dichromate on alcohols?
Bright orange to green solution for primary and secondary alcohols.
Tertiary alcohols - it will remain an orange colour
What is the result of acidified potassium dichromate on aldehydes?
Bright orange to green solution
What is the result of acidified potassium dichromate on Ketones?
No reaction as ketones don’t react further
What is the test for reagent potassium permanganate (KMnO4-/H+)
Must add acid 1st then permanganate
What is the result of potassium permanganate on alcohols?
Purple to colourless solution
What is the result of potassium permanganate on aldehydes?
Purple to colourless solution
What is the result of potassium permanganate on ketones?
No reaction
What is the test for Fehlings solution + warm?
MUST WARM SOLUTION
1) In lean test tube mix Fehling’s a and Fehling’s B solution of equal volumes resulting in dark blue solution
2) Add 5 drops of this test to 1cm3 sodium carbonate solution in test tube. Add antibumping granules. Then add 5cm3 ethanol/ propanal.
3) Warm test tube for 2 minutes and gradually bring to boil for a few minutes
4) Using test tube holder, remove from hot beaker and allow contents to stand for a few minutes
What is the result of Fehling’s test on alcohols?
No reaction
What is the result of Fehling’s test on aldehyde?
blue solution to orange/ red ppt
What is the result of Fehling’s test on ketones?
No reaction
What is the test for Tollen’s reagent + warm?
MUST WARM SOLUTION
1) Add 5 drops sodium hydroxide to 2cm3 soliver nitrate solution in test tube to prepare tollens reagent
2) Add enough dilute ammonia solution to dissolve brown ppt
3) Use beaker of hot water (50-60 degrees) to gently warm 5cm3 of this test reagent in test tube
4) Add 10 drops distillate containing ethanal to warmed tollen’s reagent in test tube.
5) Wait a few minutes
What is the result of Tollen’s reagent on alcohols?
No reaction
What is the result of Tollen’s reagent on aldehydes?
Silver ppt on sides of test tube (silver mirror)
What is the result of Tollen’s reagent on ketones?
No reaction
What is the test for reagent sodium metal?
Add small piece to ethanol in dry test tube
What is the result of reagent sodium metal on alcohols?
Hydrogen gas given off and colourless solution produced
What is the result of reagent sodium metal on aldehydes?
N/A as not alcohol
What is the result of reagent sodium metal on ketones?
N/A as not alcohol
Reduction reaction equation for dichromate
Cr2O7(2-) + 14H+ + 6e- goes to 2Cr(3+) + 7H20
orange to green
Reduction reaction equation for permanganate
Mn04- + 8H+ +5e- goes to Mn2+ + 4H20
purple to colourless / pale pink
2 oxidising agents:
Dichromate
Permanganate
Alkene reaction with bromine water
Shake, orange to colourless.
C2H4 + Br2 goes to C2H4Br2
Alkane reaction with bromine water
Shake, remains orange
Can bromine water test for halogenoalkanes?
No
Test for alkene method
1) Add 2 drops cyclohexene to test tube, add 1cm3 bromine water and shake contents vigorously side to side
2) Add 5 drops 1-bromobutane to about 1cm3 sodium hydroxide solution in test tube. Warm contents for a few minutes, by placing in beaker filled with hot water
3) Acidify contents of test tube bay adding 2cm3 dilute nitric acid and then add 1cm3 silver nitrate solution
3 ways of identifying carboxylic acid
- pH meter or pH probe attached to data logger
- Universal indicator - rough way and is colour subjective
- Chemical tests for identifying acids
What do all acids react with no matter if inorganic or carboxylic
Sodium carbonate or sodium hydrogen carbonate to release carbon dioxide gas (neutralisation reactions)
2H+ + CO3(2-) goes to CO2 + H2O
OR
H+ + HCO3- goes to CO2 + H2O
What would you witness if carbonates (CO3(2-)) or hydrogen carbonate (HCO3-) neutralised an acid?
Bubbling as co2 gas produced
Solid dissolves
Gas turns limewater from colourless to cloudy showing CO2 produced
Can dichromate or permanganate identify an alcohol group?
No because they can also oxidise aldehydes to carboxylic acids
Method to neutralise an acid
Place one small spatula measure of solid sodium hydrogen carbonate in a test tube and add it to about 2cm3 dilute ethanoic acid
What is the fingerprint region and what does it do?
Below the 1500cm3 region.
Gives a unique match to every compound including the isomeric forms of alcohols
What do you do with a spectrograph of an unknown compound?
Must be matched against a known spectrograph database
For an exact identification using this method both the functional group and the fingerprint region should match the unknown sample and not just one or other half of the spectrograph
