REQUIRED PRACTICAL 6 - Organic compound testing Flashcards by Jonny Billinton

What bonding do alcohols have?

Hydrogen bonding - highest bp (out of aldehydes/ketones, alkanes/alkenes)

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What bonding do aldehydes and ketones have?

Permanent dipoles - lower bp

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What bonding do alkenes and alkanes have?

Van der Waal - low bp (lower group members are gases

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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)

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During oxidation reactions, what does a secondary alcohol produce?

Ketone. This cannot be oxidised further

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Can tertiary alcohols be oxidised?

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What is the test for reagent acidified potassium dichromate? (K2Cr2O7/H+)

Must add acid 1st before dichromate

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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

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What is the result of acidified potassium dichromate on aldehydes?

Bright orange to green solution

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What is the result of acidified potassium dichromate on Ketones?

No reaction as ketones don’t react further

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What is the test for reagent potassium permanganate (KMnO4-/H+)

Must add acid 1st then permanganate

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What is the result of potassium permanganate on alcohols?

Purple to colourless solution

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What is the result of potassium permanganate on aldehydes?

Purple to colourless solution

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What is the result of potassium permanganate on ketones?

No reaction

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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

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What is the result of Fehling’s test on alcohols?

No reaction

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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?

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