2023 Paper 2

• Suggest why chloroethanoic acid is a stronger acid than ethanoic acid

  • The electron withdrawing effect of CH2Cl group
  • This weakens the O-H bond / increases the polarity of O-H Bond
• 2023 - Deduce the rate-determining step for this reaction, giving a reason

  • M1 Step 2
  • M2 (By the end of step 2) 1 × H+ and 2 × B have been used
  • Allow SLOWEST STEP
• Level 3 was much more difficult for Q4.2

  • Many failed to recognise that optical isomers were possible as a result of attack on planar secondary carbonation from above or below the plane
• Identify reagent that is warmed with isomer W in reaction 2. CBr to CCN

  • Reagent = KCN
  • Conditions = Aqueous AND ethanol (alcohol)

  
• Draw, on Figure 6, another section of nylon 4,6 polymer showing two hydrogen bonds

  between the two sections.

  • Surprising number failed to show the LONE PAIR OF ELECTRONS involved in each H bond
  • Linearity of H bond and single covalent bond from H to N
• • S - fractionating column was less well known
  • Why fractionating column is preferred to simple distillation to separate K and M
  • because K and M were likely to have similar boiling points was not well answered

  
• Bond enthalpy calculations

  • Better students showed values for the sum of bond enthalpies for bonds broken AND bonds formed
  • Even if mistake was made, final mark could be scared for calculating approximate value for enthalpy change