48. A copper plate coated with an oxide film weighing 1.3489 g was dissolved in concentrated sulfuric acid. The solution was neutralized, diluted with water, bringing the volume to 1 liter, and mixed. A 10 ml sample was placed in a cell for conductometric titration, an acetate buffer solution with pH 5.0 was added and titrated with a 0.2511 M solution of complexone III. The titration results are shown in the table:
V, ml 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
R, Ohm 63 61 58 57 55 53 51 52 53 54 55 56 57
Determine the mass fraction of copper in the sample.

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