30. Solving a chemistry problem

220. A sample of a copper-containing alloy weighing 0.6457 g was dissolved in a 100 ml volumetric flask. An aliquot of the resulting solution (20 ml) was titrated with 0.001 N sodium chromate solution Na2CrO4. Calculate the percentage of copper in the alloy using the following potentiometric titration data:
Volume of Na2CrO4, ml 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
E, mV - 252 - 210 - 150 - 108 16 178 234 295