Alcohols Flashcards

1
Q

what is the properties of alcohols?

A

they are less volatile, have high melting points, and greater water solubility

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2
Q

why do alcohols have higher boiling points than alkanes

A

alcohols have a polar 0-H bond because of the difference in electronegativity, therefore, are polar and form hydrogen bonds.

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3
Q

why do alcohols have low volatility?

A

in liquid form , alcohols gave hydrogen bonds which requires more energy to overcome

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4
Q

why are alcohol soluble in water>

A

they have polar 0H- group

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5
Q

what happens when hydrocarbon chain of alcohol increase?

A

influence of OH group becomes relatively smaller so solubility decrease

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6
Q

why does spraying ethylene glycol (ethane-1,2 diol) at ice help the ice to melt?

A

water freezes at 0 degrees but when ethylene glycol is added which has a freezing point of -13 degrees, it makes the mixture have a freezing point of -40 degree.

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7
Q

what is a primary alcohol

A

an OH group attached to a carbon which is attached to 2 hydrogen atoms and an alkyl group

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8
Q

what is a secondary alcohol

A

an OH group attached to a carbon atom which is attached to one hydrogen atom and 2 alkyl groups

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9
Q

what is a tertiary alcohol

A

an OH group attached to a carbon atom which is attached to no hydrogen atoms and 3 alkyl groups

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10
Q

is the combustion of alcohol exothermic or endothermic?

A

exothermic

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11
Q

what is the product for oxidation of primary alcohols?

A

aldehydes or carboxylic acids

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12
Q

what is used for oxidation of primary alcohols?

A

potassium dichromate , K2Cr2O7 , acidified with dilute sulfuric acid

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13
Q

what happens to orange solution contain dichromate ions, Cr2O7^-2 , when primary alcohol is oxidised

A

solution changes from orange to green as dichromate ions are reduced to chromium ion, Cr^3+

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14
Q

what is aldehyde prepared?

A

primary alcohol gently heated with acidified potassium dichromate

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15
Q

how is it ensured that an aldehyde is formed rather than a carboxylic acid

A

aldehyde is distilled out of the reaction mixture as it forms to prevent further reaction with oxidising agent.

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16
Q

how is carboxylic acid formed?

A

primary alcohol is heated strongly under reflux with excess of acidified potassium dichromate.

17
Q

what is the product for oxidation of secondary alcohols

A

secondary alcohols are oxidised to ketone under reflux

18
Q

can tertiary alcohols undergo oxidation reactions?

A

no

19
Q

how is an alcohol dehydrated?

A

alcohol is heated under reflux in presence of acid catalyst to form an alkene, removing h20

20
Q

what happens when alcohol reacts with hydrogen halide

A

forms haloalkane under reflux with sulfuric acid and a sodium halide which forms hydrogen bromide in situ
NaBr + H2SO4 —— NaHSO4 + HBR
the hydrogen bromide reacts with alcohol to form haloalkane

21
Q

what is the overall equation for the substitution reaction of alcohol with hydrogen halide to form haloalkane

A

NaBr + H2SO4 + CH3CHOHCH3 —— CH3CHBRCH3 + NAHSO4+ H20