paper 2 need to know

• State the environmental problem that chlorodifluoromethane can cause.

  Give one reason why pentane does not cause this problem.

  Causes ozone depletion

  Pentane does not have C-Cl bonds
• Explain why the strength of the interaction between two cysteine R groups differs from the strength of the interaction between a serine R group and an aspartic acid R group.

  1. Two Cys R groups form a disulfide bridge
  2. Ser and Asp R groups form Hydrogen bonds
  3. Disulfide bridges are stronger than Hydrogen bonds
  4. Because disulfide bridges are covalent bonds (while Hydrogen bonds aren’t)
• Give a reason for adding the distilled water in steps c and f.

  To remove (water) soluble impurities
• A suitable target titre for the titration is 30.0 cm3 of 0.025 mol dm−3 Br2(aq).

  Justify why a much smaller target titre would not be appropriate.

  Smaller titre will increase (%) uncertainty
• State the reason for inverting the flask several times.

  To ensure the solution is homogeneous
• What reagents and conditions are needed to produce a Halogenoalkane from an alkane?

  Halogen and UV light.
• What reagents and conditions are needed to produce a Nitrile from a Halogenoalkane?

  KCN, ethanol and reflux
• What reagents and conditions are needed to produce a Primary amine from a Halogenoalkane?

  ammonia, heat
• What reagents and conditions are needed to produce a Primary Amine from a Nitrile?

  $LiAlH_4$, dilute $H_2SO_4$
• What reagents and conditions are needed to produce an Alkene from a Halogenoalkane?

  KOH, ethanol, reflux
• What reagents and conditions are needed to produce a Halogenoalkane from an Alkene?

  HX, 20 degrees celsius
• What reagents and conditions are needed to produce Alcohol from a Halogenoalkane?

  warm NaOH, reflux
• What reagents and conditions are needed to produce an alcohol from an alkene?

  $H_3PO_4$ catalyst, steam
• What reagents and conditions are needed to produce an alkene from an alcohol?

  conc. $H_2SO_4$, reflux
• What reagents and conditions are needed to produce an Aldehyde/Ketone from an alcohol?

  $K_2Cr_2O_7$, $H_2SO_4$, heat in distillation apparatus
• What reagents and conditions are needed to produce an alcohol from an Aldehyde/Ketone

  $NaBH_4$ in water with ethanol
• What reagents and conditions are needed to produce a Carboxylic acid from a primary alcohol?


  $K_2Cr_2O_7$, $H_2SO_4$, reflux
• What reagents and conditions are needed to produce a Carboxylic acid from an aldehyde?

  $K_2Cr_2O_7$, $H_2SO_4$, reflux
• Explain why 3-aminopentane is a stronger base than ammonia.

  In 3-aminopentane

  Lone pair on N more available

  because of alkyl electron pushing /inductive effect
• Justify the statement that there are no chiral centres in 3-aminopentane

  No carbon (atom is) attached to 4 different groups
• State why cyclohexene can be separated from the aqueous solution using the separating funnel.

  Liquids are immiscible
• Give one observation that the student made to confirm that the cyclohexene was dry.

  Liquid goes clear
• Give a reason why this type of stereoisomerism arises.

  Restricted rotation about the C=C or double bond
• Golf balls recovered from lakes and ponds can be used again even after being in water for several years.

  Explain why these isoprene golf balls do not biodegrade

  Carbon Carbon bonds cannot be hydrolysed
• In practice, ethanoic anhydride is used in the industrial synthesis rather than ethanoyl chloride.

  Give one reason why ethanoyl chloride is not used in the industrial synthesis.

  Corrosive
• Suggest a suitable reagent for the hydrolysis of a protein

  Conc HCl
• Suggest how the positions of the amino acids on the TLC plate were located.

  Using ninhydrin or ultraviolet light
• Suggest why it was necessary to use two different solvents.

  Some amino acids have the same Rf value or have the same affinity with the first solvent
• The dicarboxylic acid in question 10.1 and the isomers of C6H14O2 in Questions 10.3 and 10.4 all have a relative molecular mass of 118.

  State why the dicarboxylic acid can be distinguished from the two diols by high resolution mass spectrometry using electrospray ionisation.

  The precise (relative molecular) masses are different
• Explain how carbon dioxide causes global warming.

  C=O Bonds in CO2 absorb infrared radiation (of 2350 cm-1 )

  IR radiation emitted by the earth does not escape (from the atmosphere)
• State the meaning of the term complementary when it is used to refer to DNA strands.

  (Complementary means the two strands must have base sequences) that match (all) A to T and C to G
• Explain why NaBH4 reduces 2-methylbutanal but has no reaction with 2-methylbut-1-ene.

  $H^-$ ion / nucleophile is attracted to $\delta^+$ C

  electron rich C=C

  $H^-$ ion / nucleophile is repelled by C=C
• Heptane can be obtained from the catalytic cracking of hexadecane (C16H34) at a high temperature.

  Identify a suitable catalyst for this process.

  Give one condition other than high temperature.

  Zeolite

  Slight pressure
• Explain, with reference to intermolecular forces, why distillation allows propanal to be separated from the other organic compounds in this reaction mixture. (Propan 1 ol, Propanoic acid)

  1. Aldehyde/propanal has dipole-dipole forces (between molecules)
  2. Alcohol/propan-1-ol AND Carboxylic acid/ propanoic acid have hydrogen bonding (between molecules).
  3. The forces between the molecules in aldehyde are weaker (than those in alcohol and acid so it will evaporate first.)
• Describe how you would carry out a simple test-tube reaction to confirm that the sample of propanal obtained by distillation does not contain any propanoic acid

  Add named carbonate/hydrogen carbonate to a sample of the distillate.

  Effervescence/fizz/bubbles would confirm presence of acid
• Solution X reacts with liquid ketones to form a crystalline solid.

  This reaction can be used to identify a ketone if the crystalline solid is separated, purified by recrystallisation, and the melting point determined.

  Describe how the crystalline solid is separated and purified.

  filter / decant

  dissolve in minimum vol

  of hot solvent

  cool and leave to crystallise AND filter under reduced pressure

  Wash with cold solvent/water, and dry (with method)
• State the hazard associated with the use of KCN

  Suggest a reason, other than safety, why KCN is used instead of HCN.

  toxic

  HCN weak
• Describe how you distinguish between separate samples of the two enantiomers of the branched chain aldehyde C5H10O

  Use Plane polarised light

  rotates (the plane of) in opposite directions
• Suggest why aqueous ethanol is a suitable solvent when heating the coconut oil with KOH.

  Give a safety precaution used when heating the mixture. Justify your choice.

  Allow to dissolve both oil and KOH

  Use a water bath for heating mixture

  Prevents risk of fire / Ethanol is flammable
• What reagents and conditions are needed to produce a carboxylic acid from an Ester

  dilute $H_2SO_4$ catalyst, $H_2O$, reflux

  or

  dilute $NaOH$, reflux