Chem 2b Flashcards
Test for Halide ions
Silver nitrate solution followed by ammonia solution.
Uses of esters
Solvent
Plasticiser
Food flavouring
What reactions is NaOH used for?
Saponification of triglyerides/hydrolysis of esters
What reaction is K2C2O4 used in?
Oxidation of alcohols
What reaction is NaBH4 used in?
Reduction of ketones, aldehydes and carboxylic acids.
What reaction does conc. H2SO4 catalyse?
Esterification of water and carboxylic acid
Nitration of benzene
Nucleophiles which attack acyl chlorides?
Alcohol
Primary amine
Water
AMmonia
Nucleophillic addition elimination of acyl chloride by primary amine forms?
N-substituted amide
Nucleophillic addition elimination of acyl chloride by water forms?
Carboxylic acid
Nucleophillic addition elimination of acyl chloride by ammonia forms?
Amide
Nucleophillic addition elimination of acyl chloride by alcohol forms?
Ester
Why is formation of esters by acylation favourable?
Goes to completion; it is not an equilibrium
Does not need conc. sulphuric acid catalyst.
Why is ethanoic anhydride preferred to enthanoyl chloride for industrial level acylation?
Cheaper
Less corrosive
Less vulnerable to hydrolysis (reaction with water)
Safer.
What are nitration reactions used to make?
Explosives
Dyestuff
Why does atomic radius increase going down group VII?
- Number of electron shells increase
- Shielding increases
- Outer electrons are further from the nucleus
- Outer electrons are less strongly attracted.
Why does electronegativity decrease going down group VII?
- Number of electron shells increase
- Shielding increases
- Electrons in covalent bond are further from nucleus
- Electrons in covalent bond are less strongly attracted.
Why does boiling point increase going down group VII?
- Atomic radius increases
- Size of molecules increases
- Surface area increases
- Strength of van der Waal’s forces increases
Why does oxidising power of halogens decrease going down the group?
- Number of electron shells increase
- Shielding increases
- Ability to attract electrons from other atoms decreases
Trend in oxidising power going down group VII?
Decreases going down
A more powerfully oxidising halogen displaces a less powerful one from a solution of halide
Why does reducing power of halides increase going down the group?
- Number of electron shells increase
- Shielding increases
- Outer electrons are further from nucleus, less strongly attracted so lost more easily.
Test for halide ions
Silver nitrate solution followed by ammonia solution
Conditions for nitration of benzene
Benzene reacted with conc. HNO3 in the presence of conc H2SO4 at 50°C.
Initial reaction between reactant and catalyst in nitration of benzene
HNO3 + H2SO4 ⇋ NO2+ + HSO4– + H2O
What are nitration reactions used to make?
Explosives
Dyestuffs
Alkylation
Placing an alkyl group onto the benzene ring
Conditions for friedel crafts acylation
Completely dry, warm
AlCl3 catalyst was present
Initial reaction in friedel crafts acylation between reagent and catalyst
CH3Cl + AlCl3 —> +CH3 + AlCl4-
Relative strengths of amines in comparison to ammonia.
aliphatic amines are stronger bases than ammonia.
aromatic amines less strong bases than ammonia.
Preparation methods of amines
- Nucleophillic substitution of haloalkanes
- Reduction of nitriles.
- Reduction of nitrobenzene to form phenylamine
Poisonous sulfur gas with an unpleasant smell
H2S
State what is observed when concentrated ammonia solution is added to AgI.
No visible change
State why the silver nitrate is acidified when testing for iodide ions.
To remove carbonates and hydroxides that would form precipitates
Reaction between KCl and H2SO4
2KCl + H2SO4 → K2SO4 + 2HCl
Observations of the reaction of KBr(s) w/ conc. H2SO4
Brown choking gas
Misty fumes
Equation for redox reaction that occurs when KBr reacts with conc. H2SO4
2Br- + H2SO4 + 2H+ → Br2 + SO2 + 2H2O
Equation showing formation of SO2 when conc. H2SO4 oxidises halide
H2SO4 + 2H+ + 2e- → SO2 + 2H2O
All possible sulphur-containing reduction products formedwhen conc. H2SO4 oxidises halides
SO2
S
H2S
Equation showing formation of S when conc. H2SO4 oxidises halide
H2SO4 + 6H+ + 6e- → S + 4H2O
Equation showing formation of H2S when conc. H2SO4 oxidises halide
H2SO4 + 8H+ + 8e- → H2S + 4H2O
Explain why hydrochloric acid should not be used to acidify the silver nitrate.
COntains Cl- which would give a white ppt
State and explain what would be observed when acidified silver nitrate solution is added to a solution of sodium fluoride.
No visible change
AgF is soluble
Nucleophile
Electron pair donor
state and explain the stability of benzene compared with the hypothetical cyclohexatriene
Benzene is more stable than cyclohexatriene
Expected ΔHο hydrogenation of C6H6 is 360
Actual ΔHο hydrogenation of benzene is 152
Because of delocalisation of electrons
Equation showing the formation of NO2+
H2SO4 + HNO3 → HSO4– + NO2+ + H2
Conditions required for nucleophillic substitution of chlorocyclichexane by NH3
Excess NH3 under pressure in sealed tube
Reducing agents for hydrogenation of nitrobenzene
H2 or Ni
Why is nitrobenzene a worse reducing agent than ammonia
Lone pair on nitrogen less available as it is delocalised into benzene ring due to the negative inductive effect
Conditions for electrophillic substitution/nitration of benzene by HNO3
conc. H2SO4 and HNO3
Warm
Obervation when Na2CO3 is added to an acid
Gas evolves
Obervation when Na2CO3 is added to an ester/aldehyde
No visible change
How to distinguish between an acyl chloride and chloroethane?
Add water
Acyl chloride - Violent reaction/steamy fumes
Chloroethane - no visible change
Name (CH3)2NH
Dimethyl amide
Use of a quarternary ammonium salt
Fabric softener
Explain why the melting point of aminoethanoic acid is much higher than that of hydroxyethanoic acid, HOCH2COOH
aminoethanoic acid contains ionic bnding which is much harder to break than the hydrogen bonding in hydroxyethanoic acid.
Racemic mixture
Equimolar mixture of the enantiomers
State how separate samples of the stereoisomers could be distinguished
They rotate the plane of polarised light in opposite directions.
By considering the shape of the reactive intermediate involved in the mechanism of this reaction, explain how a racemic mixture of the two stereoisomers of 2-chlorobutane is formed.
The carbocation intermediate is planar. It will be attacked equally from above (forming one enantiomer) or below (forming the other).
Butylamine can be made in a two-step synthesis from CH3CH2CH2Br. Write an equation for the two steps in this synthesis.
CH3CH2CH2Br + CN- → CH3CH2CH2CN + Br-
CH3CH2CH2CN + 2H2 → CH3CH2CH2CH2NH
Explain why butylamine is a stronger base than ammonia.
R group increases electron density having a positive inductive effect
So lone pair on nitrogen is more available
Explain why polyamides can be made into fibres suitable for use in sewing and weaving, whereas polyalkenes usually produce fibres that are too weak for this purpose.
Polyamides have H bonding, polyalkenes have van der Waals forces
H bonding is stronger
What is the chemical used as a reference in NMR and why?
Si(CH3)4
Gives one single intense peak well away from others
Non-toxic, inert, volatile.
