4. To determine tungsten, the oxidation reaction of iodide ion with hydrogen peroxide, catalyzed by tungsten compounds, was used. A differential variant of the tangent method was applied. In three volumetric flasks with a capacity of 50.0 ml made 3.00; 5.00 and 8.00 ml of Na2WO4 solution (T(Na2WO4/W)=1.045*10-7). The test solution was also placed in a 50.0 ml volumetric flask. After adding the necessary reagents, the optical density A was measured as a function of time t for all solutions. According to the data given in the table, build graphs in the coordinates А-t and tga-Cw and determine the content of tungsten in (g) in the studied solutions.

t, min 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0
Standard solutions ml 3.00 0.065 0.077 0.093 0.107 0.120 0.136 0.150 0.165 0.178 0.195 0.210 0.225 0.241
Standard solutions ml 5.50 0.115 0.140 0.166 0.192 0.220 0.246 0.275 0.300 0.327 0.355 0.380 0.410 0.425
Standard solutions ml 8.00 0.180 0.220 0.262 0.302 0.340 0.380 0.420 0.455 0.490 0.530 0.560 - -
Test solutions 0.085 0.102 0.123 0.140 0.156 0.176 0.196 0.214 0.230 0.250 0.268 0.287 0.306

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