Organic pt3 ( Alcohols and organic analysis)

Question 1

What is the general formula for alcohol?

Answer 1

C_nH_2n+1OH

Question 2

What are the physical properties of alcohol?

Answer 2

• High melting and boiling points than alkanes = due to hydrogen bonding caused by OH
• Alcohols with short chains are soluble in water because the hydrogen bonding predominates
• Alcohols with long chains are insoluble in water because the hydrocarbon chain dominates

Question 3

How is ethanol made from crude oil? (where is ethene from, how does it turn into an alcohol, draw mechanisms and state conditions)

Answer 3

Ethene is produced when crude oil fractions are cracked

ethene is hydrated, which mean that water is added across the bond

steam 300 degrees and phosphoric acid

Electrophillic addition

Question 4

Name 2 ways ethanol can be produced

Answer 4

• Hydration
• Fermenation

Question 5

Describe how ethanol is made from the fermentation

Answer 5

• Fermentation (exothermic reaction) is carried out by yeast in anaerobic respiration
• Yeast produces an enzyme that converts sugars into ethanol and carbon dioxide
• Ethanol formed is separated by fractional distillation

Question 6

What is the chemical equation for the fermentation of ethanol?

Answer 6

Question 7

What are the conditions of fermentation?

Answer 7

Warm (25 to 42 degrees)

Aqueous

Yeast

Absence of oxygen

Question 8

Why is the yeast used in fermentation?

Answer 8

Because it provides a source of enzymes (biological catalysts) = speed up the rate of reactions

Question 9

Compare the Hydration of ethene to fermentation (Rate of reaction, use of resources, process type, waste products)

Answer 9

• hydration is faster,
• Hydration is made from non-renewable sources (ethene is from the cracking of crude oil) vs Fermentation is made from renewable sources (e.g. grapes and sugar canes)
• Hydration of ethene is a continuous process vs Fermentation is a batch process (have to start a new batch once yeast dies)
• Hydration produces pure ethanol vs fermentation produces impure (further processing needed)
• Hydration requires high temperature and pressure vs moderate temperature for fermentation so less energy needed
• fermentation releases co2 as a waste

Question 10

What is the definition of a biofuel?

Answer 10

a fuel derived or produced from renewable biological sources

Question 11

What is the definition of carbon neutral?

Answer 11

an activity on which the net carbon dioxide emission to the atmosphere is zero

Question 12

What are the reagents, conditions, and observations for oxidation to form an aldehyde from ethanol? Draw the mechanism for ethanol to ethanal.

Answer 12

Reagents: dilute sulfuric acid/ potassium dichromate or potassium permanganate

Conditions: distil, needs to be from a primary alcohol

Observations: color change from orange to green with potassium dichromate or purple to colorless with KMnO4

Question 13

What are the reagents, conditions, and observations for oxidation to form a CARBOXYLIC ACID from ethanol? Draw the mechanism for ethanol to ethanoic acid.

Answer 13

Reagents: dilute sulfuric acid/ potassium dichromate or potassium permanganate

Conditions: reflux, needs to be from primary alcohol

Observations: color change from orange to green with potassium dichromate or purple to colorless with KMnO4

Question 14

What are the reagents, conditions, and observations for oxidation to form a KETONE from alcohol? Draw the mechanism for ethanol to ethanoic acid.

Answer 14

Reagents: dilute sulfuric acid/ potassium dichromate or potassium permanganate

Conditions: reflux, needs to be from secondary alcohol

Observations: color change from orange to green with potassium dichromate or purple to colorless with KMnO4

Question 15

Why do we need to distil for aldehydes?

Answer 15

• Aldehydes have a lower boiling than alcohols and carboxylic acid : hydrogen bonds vs dipole-dipole
• To prevent further oxidation into carboxylic acids

Question 16

What is reflux and why is it used for aldehydes?

Answer 16

• allows mixture to be heated, but prevents the volatile components from escaping the reaction mixture (the condenser is placed above the reaction vessel)
• to further oxidise into carboxylic acids

Question 17

What is the mechanism and conditions for dehydration? Draw the mechanism for ethanol to ethene

Answer 17

Elimination

excess hot concentrated sulfuric acid

Question 18

When is it not possible to dehydrate alcohol?

Answer 18

when there is no hydrogen attached to adjacent carbon

Question 19

What is Tollens’ reagent?

Answer 19

Colourless solution of silver nitrate dissolved in aqueous ammonia

Question 20

What are the two tests for aldehyde?

Answer 20

Tollen’s reagent

Fehling’s test

Question 21

Describe how to carry out the Tollen’s reagent test and what happens when Tollens’ reagent is heated in a test tube with an aldehyde and when it’s heated with a ketone

Answer 21

Tollens reagent is made first: add some silver nitrate solution to a test tube, then add a few drops of sodium hydroxide so that pale brown precipitate appears. Add a few drops of ammonia until the precipitate disappears.

Add the aldehyde or ketone to the test tube. Place the test tube in a hot water bath

Aldehydes: Ag ions in Tollens’ reagent are reduced to Ag atoms. Silver mirror forms

Ketone: no precipitate forms.

Question 22

What is Fehling’s solution?

Answer 22

Blue solution of copper(II) ions dissolved in sodium hydroxide

Question 23

Describe the test and what happens to Fehling’s solution when it’s heated with an aldehyde

Answer 23

Fehlings solution is added to aldehyde or ketone

Place the test tube in a hot water bath

Aldehyde: Copper(II) ions are reduced to brick-red precipitate of copper(I) oxide

Ketone: no reaction

Question 24

Why can’t tertiary alcohols be oxidised by acidified potassium dichromate/permanganate?

Answer 24

Because there are no hydrogen atoms bonded to the carbon which is bonded to -OH

Question 25

Describe what happens when a reaction mixture is refluxed and why it is necessary for complete oxidation to ethanoic acid (3 marks - exam question)

Answer 25

* the mixture of liquids is heated to boiling point for a long period of time (allows the reaction to take place without losing volatile reactants/ products) * vapours cool in condenser + condense back to liquids + drip back into the reaction mixture * allows for the further oxidation of ethanal to ethanoic acid

Question 26

What do anti-bumping granules do?

Answer 26

Anti-bumping granules prevent explosive boiling by stopping bumping and therefore splashing, as they provide a large surface area for bubbles to form on. prevent large bubbles

Question 27

Use your knowledge of structure and bonding to explain why it is possible to separate ethanal during distillation

Answer 27

Hydrogen bonding in ethanol and ethanoic acid Ethanal has permanent dipole-dipole forces between molecules dipole-dipole are weaker than hydrogen bonding;

Question 28

Draw a reflux diagram

Answer 28

(the flask needs to be pear shaped) Also its a Liebig condenser

Question 29

**Draw a distil diagram**

Answer 29

make sure you label ethanol, (in the conical flask). Thermometer doesn't touch the liquid because it's measuring the gas IMPORTANT: Thermometer should be at the T Junction

Question 30

Describe how a student could use chemical tests to confirm that the liquid contained ethanal and did not contain ethanoic acid

Answer 30

Reagent to confirm the presence of ethanal: * Add Tollens' reagent * Result with Tollen's reagent: Silver mirror OR * Add Fehling's solution; * Warm; * Result with Fehling's solution: Red precipitate Reagent to confirm the absence of ethanoic acid: * Add sodium hydrogencarbonate; * Result: no effervescence observed, hence no acid present;

Question 31

What is meant by the term hydration?

Answer 31

Addition of water

Question 32

Why is high-resolution mass spectrometry useful?

Answer 32

useful for identifying compounds that appear to have the same Mr when they’re rounded to the nearest whole number it is extremely accurate as it measures the relative atomic mass to several decimal places

Question 33

How does infrared spectroscopy work?

Answer 33

a beam of IR radiation is passed through a sample of chemical Ir radiation is absorbed by the covalent bond in the molecules, increasing the vibrational energy bonds between different atoms to absorb different frequencies of IR radiation. Bonds in different places in a molecule absorbs different frequency too.

Question 34

What is the fingerprint region? Why does it have many peaks?

Answer 34

The area of an infrared spectrum below about 1500cm^-1 the many peaks are caused by the complex vibrations of the whole molecule, which unique for any particular substance

Question 35

How can you find out if a substance is pure using infrared spectroscopy?

Answer 35

impurities cause extra peaks

Question 36

Describe how infrared radiation absorption is linked to global warming

Answer 36

Some electromagnetic radiation emitted by Sun reaches Earth and is absorbed * Earth re-emits some of its infrared radiation (heat) Molecules of greenhouse gases (CO, CH, water vapour) in atmosphere absorb IR radiation (it's bonds of these molcules that absorb it)& re-emit some of it back towards Earth = keeps us warm (greenhouse effect) Means more heat being trapped and Earth getting warmer = global warming This energy is transferred to other molecules in the atmosphere by collisions (so all atmosphere is warmed)

Question 37

What causes an increase in greenhouse gas concentrations?

Answer 37

Human activities, burning fossil fuels & leaving rubbish to rot in landfill sites, caused rise in greenhouse gas concentrations

Question 38

How do you test for alkenes? Draw the equation

Answer 38

Add bromine water, shake, orange to colourless

Question 39

How do you test for halogenalkanes? Draw the equation

Answer 39

Place test tube in a hot water bath and add NaOH acidify with HNO3 add AgNO3 (aq) Precpitate of Ag X will form ( white, cream or yellow)

Question 40

Describe the test for primary/secondary alcohols

Answer 40

1. Add acidified potassium dichromate/ potassium magnate solution 2. Warm mixture gently in hot water bath 3. Watch for colour change Orange solution turns green/ purple to colourless

Question 41

What are the two tests for carboxylic acid. Draw the equations for them

Answer 41

Add sodium/magnesium or sodium carbonate

Question 42

What is the equation for tollens/Fehling’s

Answer 42

Question 43

Draw the mechanism for hydration of ethene and write the chemical equation

Answer 43

CH2CH2 + H2O→ CH3CH2OH

Question 44

Answer 44

The infrared spectrum shown an absorption/ peak in the range 3230 to 3550, which supports the idea that an alcohol is present the fingerprint region would match with a known sample

Question 45

Why are carboxylic acids more reactive than alcohols, aldehydes and ketones?

Answer 45

* more reactive than aldehydes and ketones due to containing hydrogen bonding * O−H bond in COOH is more strongly polarised due to the presence of electron withdrawing carboxy group (C=O) in adjacent position = stronger hydrogen bonds than alchols