The sulfate ion concentration in natural water can be determined by measuring the turbidity that results when an excess of BaCl₂ is added to a measured quantity of the sample. A turbidimeter, the instrument used for this analysis, was calibrated with a series of standard Na₂SO₄ solutions. The following data were obtained in the calibration for sulfate concentrations, c_x:

Assume that there is a linear relationship between the instrument reading and concentration.

(a) Plot the data, and draw a straight line through the points by eye.

(b) Compute the least-squares slope and intercept for the best straight line among the points.

(c) Compare the straight line from the relationship determined in (b) with that in (a).

(d) Use ANOVA to find the R² value, the adjusted R² value, and the significance of the regression. Comment on the interpretation of these values.

(e) Compute the concentration of sulfate in a sample yielding a turbidimeter reading of 2.84. Find the absolute standard deviation and the coefficient of variation.

(f ) Repeat the calculations in (e) assuming that the 2.84 was the mean of six turbidimeter readings.

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C, mg So,?-L Turbidimeter Reading, R 0.00 0.06 5.00 1.48 10.00 2.28 15.0 3.98 4.61 20.0