Organics 2 Chemistry

opticlops's version from 2015-05-04 16:55

Section 1

Question Answer
What happens on combustion of an alcoholBurns with a clean colourless flame. C-C bonds and C-H bonds are broken as alcohol is completely oxidised to make Co2 and H20
What happens when a small piece of sodium is added to an alcohol (observations)Fizzes (reacts gently); steady stream of H2 gas forms; the metal DOES NOT MELT;
What does a reaction between sodium metal and alcohol produce (example of ethanol)?Ionic sodium ethoxide and hydrogen gas: 2CH3CH2OH + Na -> 2CH3CH2O-Na+ + H2
Relationship between chain length of alcohol and reactivity with sodiumThe longer the chain, the less reactive it is with sodium

Section 2

Question Answer
What type of reaction is the formation of a halogenoalkane from an alcohol?Substitution
What is the most reactive type of alcohol?Tertiary, then secondary, then primary
How do you make an impure chloroalkane from a tertiary alcohol>Shake a tertiary alcohol with HCl; produced H2O and chloroalkane
How do you make a halogenoalkane from Primary and Secondary alcohols w/ h2so4?1) Mix 50% H2SO4 with a metal halide to make a hydrogen halide in situ. 2) Heat the hydrogen halide with w/ the alcohol in presence of sulfuric acid
What is the problem with reacting KI w/ H2SO4?The iodine is too strong and oxidising agent- produces Iodine, H2S (g) HI etc.
How do you make a halogenoalkane from a primary or secondary alcohol with Phosphorus (III) Halides?just 'react' them with the acohol: PCl3 is easy to react with; however PB3 and PI3 are made in situ by refluxing the alcohol w/ red phosphorus and either bromine or iodine- then react.
Reacition of PX3 + alcohol equation3ROH + PX3 -> 3RX + H3PO3
PCl5 + alcohol?All alcohols react with PCl5 to produce choroalkanes.
What is the test for alcohols with PCl5?If an alcohol is present it will react with it to form HCl gas. The gas withh dissolve in water to form Cl- ions. Test for these ions with silver nitrate. The steamy fumes turn moist blue litmus paper red.
Equation of reaction of alcohol and PCl5ROH + PCl5 -> RCl + HCl + POCl3

Section 3

Question Answer
How do you oxidise an alcoholHeat with Acidified Potassium Dichromate VI
What alcohols oxidiseOnly primary and secondary, not tertiary.
What happens on heating (colour) Acidified Potassium Dichromate VI with alcoholsGoes from orange to green
What are primary alcohols oxidised to?Aldehydes and then carboxylic acids
What are secondary alcohols oxidised to?Ketones
What causes the potassium dichromate to change colour (ions)Cr2O7-(aq) -> green Cr3+
What produces ethanal (it is apple smelling)- why is it importsnt to control heatGently heating Acidified Potassium Dichromate VI solution & dilute sulfuric acid in a test tube- porduces ethanal- must control the heat to prevent further oxidation to carboxylic acid
how does one obtain an aldehyde (apparatus etc.)Must remove it from oxidising agent as soon as it is formed- gently heat reactant in a distillation apparatus
How do you produce a carboxylic acid + apparatus?Vigorously oxidise alochol. Mix with excess oxidising agent and heat under reflux/
How do you produce a ketone from a secondary alcohol?Reflux with Acidified Potassium Dichromate VI
What is the only way to oxidise a tertiary alcohol?Burn them.

Section 4

Question Answer
How do you distinguish between an aldehyde and a ketone?Distinguish using oxidising agents- aldehydes oxidise easily- ketones dont
What happens when warm Fehllings and benedicts with aldehyde and ketone?Both are deep blue Cu2+ complexes- reduced to brick red Cu2O when warmed with an aldehyde but stay blue with a ketone
Warm tollens with an aldehyde, and ketone?Reduced to silver when warmed with an aldehyde but not with a ketone- silver coats inside of the apparatus forming a silver mirror
What else can be used to detect functional group in organic molecules?IR spec

Section 5

Question Answer
What happens when mix halogenoalkane with water?Form an alcohol
Equation of water + halogenoalkane?RX + H20 -> r-OH + H+ + X-
What happens when you mix a halogenoalkane and an aqueous alkali- how do you do it?It is a subsititution reaction- forms an alcohol and a halogen ion. Add a e.g. NaOH to a drop of Halogenoalkane; acidify with dilute nitric acid- then add a few drop of silver nitrate solution to react with halogen ions-> ppt it is Sn2 reaction
What does water act as when mixed with halogenoalkaneA nucleophile- it is an Sn1 reaction (nucleophilic substitution)
What happens when react ha with excess ethanolic ammonia?Nucleophilic sub; ammonia swaps with halogen; an amine and a hydrogen halide forms which reacts with excess ammonia to form an ammonium salt; use excess ammonia to increase chance of ha reaction with ammonia; this is done UNDER REFLUX and
Overall equation of reaction between excess ethanolic ammonia and hac-X + 2NH3 -> C-NH2 + NH4BR
What happens when you react a warm alcoholic alkali with a HA?Forms an alkene- must be heated under reflux otherwise loose volatile stuff; in this case the OH- acts as a BASE not as a nucleophile when it is an aqueous alkali/ IT IS AN ELIMINATION REACTION

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