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    Theory

    the first high temperature superconductors were a group of oxides of yttrium, barium and copper formula YBA2Cu30x. The value of x depends on the oxidation state of the copper. To determine the oxidation state of the copper (and hence x), the copper from the superconductor is reacted with iodide ions. The copper is reduced to Cu 1+ and the iodide is oxidised to iodine. The iodide thus produced is titrated against sodium thiosulphate. n.b. Yttrium normally exists as a 3+ ion. Neither Yttrium nor barium reac with the iodide ions.

    Practical

    0.0100 moles of the superconductorwere used. The copper in it was reacted with excess iodide ions. The iodine produced was made upto 100cm cubed in a volumetric flask, and 10cm cubed portions were extracted with a pipette and titrated against 0.500 mol/dmcubed sodium thiosulphate. Concordant readngs of 8.00cmcubed were obtained.

    Question

    Calculate the oxidation state/s of the copper in the superconductor and hence the value of x.
 
 
 
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Updated: April 15, 2006
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