Lead in dry river sediment was extracted with 25 wt% HNO₃ at 358C for 1 h. Then 1.00 mL of filtered extract was mixed with other reagents to bring the total volume to V₀ 5 4.60 mL. Pb(II) was measured electrochemically with a series of standard additions of 2.50 ppm Pb(II).

(a) Volume is not constant, so follow the procedure of Figures 5-5 and 5-6 to find ppm Pb(II) in the 1.00-mL extract.

(b) Find the standard uncertainty and 95% confidence interval for the x-intercept of the graph. Assuming that uncertainty in intercept is larger than other uncertainties, estimate the uncertainty in ppm Pb(II) in the 1.00-mL extract.

Transcribed Image Text:

Pb(II) added (mL) Signal (arbitrary units) 1.10 0.025 1.66 0.050 2.20 0.075 2.81