Question
Redox reactions can be used to produce electricity.
(a) State the oxidation state of sulfur in copper(II) sulfate.
(b) A voltaic cell was constructed using a copper(II) sulfate/copper half-cell and a zinc sulfate/zinc half-cell.
(i) Outline why electrons flow from zinc to copper when these half cells are connected with a wire. Use section 25 of the data booklet.
(ii) Formulate equations for the reactions taking place at each electrode.
Anode (negative electrode): . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cathode (positive electrode): . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
(c) (i) Calculate the standard cell potential for the voltaic cell in part (b). Use section 24 of the data booklet.
(ii) Calculate the standard Gibbs free energy change, \(ΔG^{\theta}\), in kJ \(mol^{-1}\) , for this reaction. Use section 1 of the data booklet. (If you did not answer part (c)(i) use 1.05V, but this is not the correct value.)
Answer/Explanation
Answer:
(a) +6/VI
(b) (i) Zinc more reactive/ <<better>> reducing agent/ <<more>> easily oxidized/loses
electrons <<more>> easily.
(ii) Anode (negative electrode):
\(Zn_(s) \rightarrow Zn^{2+}_{aq} + 2e^-\)
Cathode (positive electrode):
\(Cu^{2+}_(aq) + 2e^- \rightarrow Cu_(s)\)
(c) (i) «\(E^θ_{cell}\) = +0.34-(-0.76) = +» 1.10 «V»
(ii) 
Question
(a) Oxidation of ethanol with potassium dichromate, K2Cr2O7, can form two different organic products. Determine the names of the organic products and the methods used to isolate them. [2]
(b) Write the equation and name the organic product when ethanol reacts with methanoic acid. [2]
Equation:
Product name:
Answer/Explanation
Ans
a.
ethanal AND distillation
ethanoic acid AND reflux «followed by distillation»
Award [1] for both products OR both methods.
b.
Equation: CH3CH2OH + HCOOH 
HCOOCH2CH3 + H2O
Product name: ethyl methanoate
Accept equation without equilibrium arrows. Accept equation with molecular formulas (C2H6O + CH2O2 C3H6O2 + H2O) only if product name is correct.