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Chemistry Unit 4 > Pastpaper Questions > Flashcards

Pastpaper Questions Flashcards

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1
Q

Why would it be unexpected that ammonia reacts with benzene?

A
  • NH3 is a nucleophile

- Benzene repels nucleophiles

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2
Q

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

A
  • HCN is a weak acid

- low concentration of [CN-]

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3
Q

Which ion in fragmentation is detected in mass spectroscopy?

A

Positive ion

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4
Q

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

A
  • CH3Br (excess)

- nucleophilic substitution

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5
Q

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

A

It partially dissociates

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6
Q

Suggest why chloroethanoic acid is a stronger acid than ethanoic acid

A
  • Chlorine is more electronegative so withdraws electrons

- Reducing the negative charge on the COO- group

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7
Q

How does a buffer react when acid is added?

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

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

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8
Q

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

A

COOH groups becomes COO- groups

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9
Q

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

A 
Stage 1
-  KCN aqueous
- intermediate, CH3CH2CN
Stage 2
- H2/Ni
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10
Q

How to get CH3CH2CH2NH2 from CH3CH2CH2Br

A

Excess NH3

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11
Q

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

A

No effect

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12
Q

Write an expression for Ka of the weak acid HX

A

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

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13
Q

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

A
  • hydrolysis

- delta positive charge on C- which reacts OH-

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14
Q

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

A
  • less corrosive

- doesn’t produce toxic fumes (HCl)

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15
Q

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

A
  • acid = colourless

- alkali = pink

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16
Q

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

A

It is a zwitterion

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17
Q

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

A
  • electrostatic forces between ions

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

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18
Q

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

A
  • methyl group has a positive inductive effect on the benzene group
  • benzene group becomes more negative and attracts electrophile a better
19
Q

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

A

CH3CH2NH3Cl (ethylammonium chloride)

20
Q

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

A
  • extra H+ reacts with OH-

- ratio of H+/AH remains almost constant

21
Q

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

A

Soap

22
Q

State everyday use for CH3(CH2)19COOCH3

A

Biodiesel

23
Q

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

A
  • detergent
  • shampoo/conditioner
  • cleaning
24
Q

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

A

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

25
Q

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

A
  • [H2O] is very high (compared with [H+] and [OH-])

- [H2O] is constant

26
Q

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

A

Making dyes

27
Q

Describe the negative inductive affect in phenylamine

A
  • benzene withdraws electrons from the lone pair on N

- lone pair on N delocalised into ring

28
Q

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

A

Electrons are delocalised in benzene

29
Q

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

A
  • C=C bonds are close together
  • some delocalisation
  • some extra stability
30
Q

Give the meaning of the term “dynamic equilibrium”

A
  • forward rate = backward rate

- concentration of reactants an products remain constant

31
Q

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

A

benzene-1,2-dicarboxylic acid

32
Q

How would you identify an acyl chloride?

A
  • AgNO3

- white ppt

33
Q

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

A

The COOH groups become COO-

34
Q

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

A

COOH groups become COOCH3

35
Q

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

A
  • phase is moving
  • stationary phase
  • separation depends on affinity in each phase
36
Q

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

A

CDCl3 is polar

37
Q

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

A
  • no need to separate the enantiomers

- only half of the product works

38
Q

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

A

H2SO4

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

39
Q

Give a use for sodium salts

A

Soaps

40
Q

Give a use for a mixture of methyl esters

A

Biodiesel

41
Q

Why would Kevlar be biodegradable but a polyalkene would not?

A
  • Kevlar has polar bonds

- polyalkenes have no polar bonds

42
Q

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

A
  • KCN

- aqueous and alcoholic

43
Q

Two isotopes for Cl?

A

35 and 37

44
Q

Give the conditions for elimination with KOH

A
  • warm

- alcoholic

Chemistry Unit 4 (3 decks)

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