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HSC CHEM 2024 > 7.4 Alcohols > Flashcards

7.4 Alcohols Flashcards

How can alcohols be produced and what are their properties?

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1
Q

general formula

A

CnH(2n+1) OH

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2
Q

primary vs secondary vs tertiary alcohols

A

depends on number of carbons connected to terminal carbon

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3
Q

boiling point of primary -> tertiary alcohols increase/decrease? why?

A

DECREASES because more branching = less surface area = less forces of attraction = higher BP

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4
Q

at what point do alcohols become
(1) visibly insoluble
(2) completely insoluble

A

(1) 1-pentanol (C5)
(2) 1-octanol (C8)

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5
Q

complete combustion of alcohol equation

A

alcohol + excess oxygen

alcohol + O2 –> CO2 + H2O

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6
Q

incomplete combustion of alcohol equation

A

alcohol + O2 –> CO(g) + C(s) + H2O

*C + H2O = soot

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7
Q

(enthalpy of combustion prac) why is experimental value is much lower than published value? (4)

A

(1) heat loss to surroundings +
(2) heat absorbed by equipment,
(3) incomplete combustion (air = not in pure oxygen),
(4) evaporation of alcohol from spirit burner wick since alcohol has low BP

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8
Q

heat released per litre of fuel =

A

ΔH/MM x fuel density (g L⁻)

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9
Q

process to produce alcohol in beverages and biofuels =

A

fermentation

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10
Q

process to produce industrial alcohol = (2)

A

hydration of alkenes
OR substitution of haloalkenes

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11
Q

dehydration of alcohol process

A

alcohol –> alkene + H2O
using concentrated acid or alumina (Al2O3) catalyst

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12
Q

hydrohalogenation process

A

alcohol + HX –> alkyl halide + H2O

HX = hydro halides e.g. HBr, HI, HCl

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13
Q

alcohol reactivity order in hydrohalogenation process

A

°3 > °2 > °1

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14
Q

oxidation of primary alcohol

A

alkane + primary alcohol –> aldehyde + carboxylic acid

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15
Q

oxid. of secondary alcohol

A

alkane + secondary alc –> ketone

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16
Q

what type of reaction, and what catalyst?:

haloalkane + OH⁻ –> alcohol + halogen

A

substitution…

base catalyst e.g. NaOH

17
Q

common reagent for oxid. of secondary alcohols

A

chromic acid H2CrO4

18
Q

oxid. of tertiary alcohol

A

alkane <–> tertiary alc (no oxidation)

19
Q

hydration/hydrolysis of alcohols

A

alkene + H2O –> alcohol

*catalyst dilute H2SO4 or H3PO4

20
Q

two opposing solubility trends in alcohols

A

(1) polar -OH promotes solubility in water by forming H bonds
(2) NP hydrocarbon chain resisting solubility in water

21
Q

why ethanol is renewable

A

can be produced from re-growable plants AND manufactured from carbohydrates

22
Q

(2) pros using ethanol

A

(1) renewable, reduces greenhouse gas
(2) burns more completely = less pollutants

23
Q

(2) cons using ethanol

A

(1) large agricultural land devoted to growing suitable crops for ethanol
(2) problem disposing fermentation waste

24
Q

explain fermentation of alcohol

A

glucose breaks down into ethanol and CO2 by enzymatic action in yeast

25
Q

ingredients for fermentation

A

plant matter + yeast

26
Q

conditions for successful fermentation of ethanol (4)

A

(1) around 37deg
(2) anaerobic (no oxygen)
(3) pH 6.1 - 6.8
(4) dilute mixture maintained below 14% ethanol (w/v)

27
Q

step to remove ethanol from yeast mixture after fermentation

A

fractional distillation based on ethanol BP at 78deg

28
Q

what is molar heat of combustion

A

heat energy released in complete combustion reaction of 1 mol of a substance

29
Q

how to test 1deg and 2deg

A

2,4-DNPH
use 2,4-Dinitrophenylhydrazine

1deg changes colour

30
Q

how to test for 3deg

A

add acidifed Cr2O7 (2-) dichromate with H2SO4
reduces to Cr 3+ (green)
3deg does not turn green, stays orange

31
Q

what is reflux

A

heating the chemical reaction for a specific amount of time, while continually cooling the vapour produced back into liquid form, using a condenser

32
Q

easily oxidised alcohol is when

A

C in functional group is directly connected to H

HSC CHEM 2024 (30 decks)

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