Pastpaper Questions Flashcards by Stephen Baylis

Why would it be unexpected that ammonia reacts with benzene?

NH3 is a nucleophile

- Benzene repels nucleophiles

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Given that the Ka of HCN is very small, why would a reaction using this be slow?

HCN is a weak acid

- low concentration of [CN-]

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Which ion in fragmentation is detected in mass spectroscopy?

Positive ion

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How would you get [CH3N(CH3)3]+[Br]- from CH3NH2 ?(Reagents/conditions/mechanism)

CH3Br (excess)

- nucleophilic substitution

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State the meaning of the term “weak” as applied to carboxylic acids

It partially dissociates

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Suggest why chloroethanoic acid is a stronger acid than ethanoic acid

Chlorine is more electronegative so withdraws electrons

- Reducing the negative charge on the COO- group

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How does a buffer react when acid is added?

added acid reacts with A- (H+ + A- -> AH)

- ratio of [HA]/[A-] stays almost constant

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What happens when an amino acid is in a high pH?

COOH groups becomes COO- groups

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CH3CH2Br -> CH3CH2CH2NH2 Name the reagents,conditions for both stages of this reaction.Also name the intermediate compound in stage 1.

Stage 1
-  KCN aqueous
- intermediate, CH3CH2CN
Stage 2
- H2/Ni

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How to get CH3CH2CH2NH2 from CH3CH2CH2Br

Excess NH3

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How does increasing the concentration of a reactant or product affect Kc?

No effect

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Write an expression for Ka of the weak acid HX

Ka = [H+][X-]/[HX]

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What is the reaction between a polyester and NaOH?Why does it occur?

hydrolysis

- delta positive charge on C- which reacts OH-

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Give two industrials advantages, other than cost, of using ethanoic anhydride rather than ethanoyl chloride in the production of aspirin

less corrosive

- doesn’t produce toxic fumes (HCl)

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What colour does the indicator phenolphthalein cause with:- an acid- an alkali

acid = colourless

- alkali = pink

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What form does an amino acid take in a solid state?

It is a zwitterion

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Why would a solid amino acid have a higher melting boiling point than hydroxy carboxylic acid?

electrostatic forces between ions

- which is stronger than the hydrogen bonding in the hydroxy carboxylic acid

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Why would methylbenzene react faster than benzene with an acyl chloride?

methyl group has a positive inductive effect on the benzene group
benzene group becomes more negative and attracts electrophile a better

Give the formula of an organic compound that forms an alkaline buffer solution when added to a solution of ethylamine

CH3CH2NH3Cl (ethylammonium chloride)

Explain qualitatively how an alkaline buffer solution maintains an almost constant pH when a small amount of HCl added

extra H+ reacts with OH-

- ratio of H+/AH remains almost constant

State everyday use for CH3(CH2)17COO-Na+

Soap

State everyday use for CH3(CH2)19COOCH3

Biodiesel

State everyday use for [C16H33N(CH3)3]+ Br-

detergent
shampoo/conditioner
cleaning

Step 1: propanone is reduced to LStep 2: L is converted to MStep 3: M reacts to form 2-bromopropaneName L and M, name reagents and mechanisms for each step

L - propan-2-ol
M - propene
Step 1 - NaBH4, nucleophilic addition Step 2 - conc H2SO4, elimination
Step 3 - HBr, electrophilic addition

Why does the expression for Kw not include the concentration of water?

- [H2O] is very high (compared with [H+] and [OH-]) | - [H2O] is constant

Give a use for 1-amino,4-methylbenzene(Phenyl amines)

Making dyes

Describe the negative inductive affect in phenylamine

- benzene withdraws electrons from the lone pair on N | - lone pair on N delocalised into ring

State, in terms of its bonding, why benzene is more stable than cyclohexa-1,3,5-triene

Electrons are delocalised in benzene

Why is cyclohexa-1,3-diene more stable than cyclohexa-1,4-diene?

- C=C bonds are close together - some delocalisation - some extra stability

Give the meaning of the term "dynamic equilibrium"

- forward rate = backward rate | - concentration of reactants an products remain constant

Give the IUPAC name for two COOH adjacent groups attached to benzene

benzene-1,2-dicarboxylic acid

How would you identify an acyl chloride?

- AgNO3 | - white ppt

What happens to an amino acid when it reacts with an excess of NaOH?

The COOH groups become COO-

What happens when an amino acid reacts with an excess of methanol in the presence of concentrated sulfuric acid

COOH groups become COOCH3

Explain column chromatography how it could separate a mixture of amino acids

- phase is moving - stationary phase - separation depends on affinity in each phase

Suggest why CDCl3 is a more effective solvent than CCl4 for polar molecules

CDCl3 is polar

Suggest one advantage and one disadvantage of using a racemate rather than a single enantiomer in medicines

- no need to separate the enantiomers | - only half of the product works

What do you need to remember when working out the pH of sulfuric acid

H2SO4 | It forms 2 H+ ions, you need to double the conc of H2SO4 to get the conc of H+

Give a use for sodium salts

Soaps

Give a use for a mixture of methyl esters

Biodiesel

Why would Kevlar be biodegradable but a polyalkene would not?

- Kevlar has polar bonds | - polyalkenes have no polar bonds

Give the reagent and condition for adding a carbon in organic synthesis

- KCN | - aqueous and alcoholic

Two isotopes for Cl?

35 and 37

Give the conditions for elimination with KOH

- warm | - alcoholic