Question
(a) Explain why a colorimeter set at a wavelength of 500nm is not suitable to investigate reactions of \(Zn^{2+}\) compounds. Use section 3 of the data booklet.
(b) Nitrogen(II) oxide radicals (NO•) catalyse the decomposition of ozone \((O_3)\).
(i) Formulate equations showing how NO• acts as a catalyst in this reaction.
Chlorine also forms free radicals; the bond enthalpy for \(Cl_2\) is \(4.02 × 10^{-19}\) J.
(ii) Calculate the minimum frequency of light needed to break this bond.
Use sections 1 and 2 of the data booklet.
(iii) Calculate the formal charge on each atom in the two Lewis structures of the \(NO_2\)•(g) radical.
(iv) Lewis structure A is more stable. Suggest, giving one reason, whether the formal charge model supports this.
Answer/Explanation
Answer:
(a) \(Zn^{2+}\) does not form coloured compounds/ has a complete d subshell/orbital
500 nm/«the setting on the colorimeter» in visible region AND no absorbance will
be seen
(b) (i) «\(O_3\)(g) \(\rightarrow O_2\)(g) + O• (g)»
NO• (g) + \(O_3\) (g) \(\rightarrow NO_2\)• (g) + \(O_2\) (g)
OR
\(NO_2\)• (g) + O• (g) \(\rightarrow \) NO• (g) + \(O_2\) (g)
(ii) «v = E/h = \(4.02 x 10^{-19}\)/\(6.63 x 10^{-34}\) =» \(6.06 x 10^{14}\) «Hz»
(iii) 
(iv) No
AND
Structure B has all atoms of formal charge 0
Question
Esters and amides can be produced by condensation reactions.
Under certain conditions but-2-ene can react with water to form butan-2-ol.
State the names of two organic compounds required to produce ethyl methanoate and state suitable reaction conditions.[2]
Deduce the structure of the simplest repeating unit of the polymer formed from the reaction between 1,6-diaminohexane and hexane-1,6-dioic acid and state one use of this product.[3]
State and explain how the rate of step II would differ if 2-chlorobutane was used instead of 2-bromobutane.[1]
Answer/Explanation
Markscheme
ethanol and methanoic acid/methanoic anhydride/methanoyl chloride;
\({{\text{H}}_2}{\text{S}}{{\text{O}}_4}/{{\text{H}}^ + }\) and heat;
Award [1] for the correct amide link.
Award [1] if the rest of the structure is correct.
nylon fabric / clothing / ropes;
slower rate because carbon to chlorine bond stronger than carbon to bromine bond / OWTTE;
Examiners report
In part (a) most candidates correctly named both compounds but did not state both the catalyst and heat as necessary conditions for the production of ethyl methanoate.
Several candidates had difficulty in deducing the structure of the simplest repeating unit but most knew the uses of the product.
Assessment statements 10.6 and 20.5 state that reagents, conditions and equations are required. Most candidates correctly explained the effect of chlorine rather than bromine on the rate of the substitution reaction.