Alcohols Flashcards
general formula of alcohols
CnH2n+1OH
describe a primary alcohol
one carbon is bonded to the carbon on the OH group
describe a secondary alcohol
two carbons are bonded to the carbon on the OH group
describe a tertiary alcohol
three carbons are bonded to the carbon on the OH group
general equation for reaction with oxygen (combustion)
ROH + O2 –> CO2 + H2O
what type of reaction is reactions with halogenoalkanes
substitution
Alcohol + phosphorus pentachloride –>
chloroalkane
general equation for reaction with phosphorus pentachloride (secondary + primary alcohols)
ROH + PCl5 –> RCl + HCl + POCl3
alcohol + hydrochloric acid –>
chloroalkane
general equation for reaction with hydrochloric acid (tertiary alcohols)
ROH + HCl –> RCl + H2O
alcohol + bromine ions –>
bromoalkane
conditions for reaction with bromine ions
- 50% concentrated H2SO4
(acid catalyst)
equations for reaction with bromine ions
KBr + H2SO4 –> HBr + KHSO4
ROH + HBr –> RBr + H2O
Alcohol + phosphorus triiodide –>
iodoalkane
equation for making phosphorus triiodide
2P + 3I2 –> 2PI3
(red phosphorus + iodine)
general equation for reaction with phosphorus triiodide
3ROH + PI3 –> 3RI + H3PO3
name of H3PO3
phosphonic acid
what type of reaction forms alkenes
elimination
what is needed for an elimination reaction
- concentrated acid catalyst
(concentrated phosphoric acid- H3PO4)
reaction of ethanol mixed with concentrated phosphoric acid
C2H5OH –> CH2=CH2 + H20
what products are formed in the reaction with conc phosphoric acid
two possible alkenes, depending on what side of the hydroxyl group the Hydrogen is eliminated from
how is the reaction with PCl5 a test for alcohols
produces white, steamy fumes that can turn damp blue litmus paper red
which types of alcohols can be easily oxidised
primary and secondary
name an oxidising agent
acidified potassium dichromate (VI)
what are primary alcohols oxidised to (with initial heating)
aldehydes
what are primary alcohols oxidised to under reflux
carboxylic acids
equation for oxidation of ethanol (heating)
CH3CH3OH + [O] –> CH3CHO + H2O
——————————-ethanal———-
equation for reflux of ethanol
CH3CHO + [O] –> CH3COOH
what are secondary alcohols oxidised to produce
ketones
ethan-2-ol oxidisation equation
CH3CH(OH)CH3 –> CH3CH3CO + H2
potassium dichromate formula
K2Cr2O2
what is potassium dichromate
an oxidising agent (is reduced when an alcohol oxidises)
colour change of K2Cr2O2 when primary + secondary alcohol oxidised
orange - green
colour change of K2Cr2O2 when tertiary alcohol oxidised
orange - orange (no colour change)
what is used to test for aldehydes
benedics/fehlings solution
describe how to use fehlings solution
add a few drops of solution to a gently warmed test tube containing the solution
- if aldehyde present a red precipitate will form
what occurs in a negative result in fehlings test
solution stays blue (Ketones will produce a negative result)
use of heating under reflux
allows reactions such as oxidation of primary alcohols all the way to formation of carboxylic acids
use of reflux condenser
ensures vapours condense and return to flask for further heating- product vapours don’t escape
role of separating funnel
separate two liquids of different densities
how does a separating funnel work
mixture is added, liquid will separate into two layers depending on their different densities (more dense liquid will be found at the bottom)
- open tap to remove denser liquid into a different flask
role of distillation
separate liquids with different boiling points
how does distillation work
- pear shaped flask heated, liquid with lower boiling point evaporates first
- vapour rises up flask into tubes
- condenser causes it to cool and condense into a liquid
- is then collected in a separate flask
how do you dry compounds
addition of anhydrous salts
how does drying work
absorbs moisture and water present, drying and purifying the compound
name a common anhydrous salt
sodium sulphate
how do you test the purity of a substance
boiling point determination
what kind of boiling point does a purer substance have
a closer boiling point to that of the database boiling point value
how do you determine a substances boiling point
- place into a thiele tube containing inverted capillary tube
- substance is heated above its boiling point, it then cools and condenses back into a liquid
- it is then drawn into the capillary tube (the temperature at which the change occurs is its boiling point)
