Sulfate in soil on Mars. In 2008, Professor Sam Kounaves and his students at Tufts University had the thrill of their lifetime as their Wet Chemistry Laboratory aboard the Phoenix Mars Lander returned a steam of information about the ionic composition of Martian soil scooped up by a robotic arm. The arm delivered ~1 g of soil through a sieve into a "beaker" fitted with a suite of electrochemical sensors. Aqueous solution added to the beaker shown in the figure leached soluble salts from the soil while sensors measured ions appearing in the liquid. Unlike other ions, sulfate was measured by a precipitation titration with Ba²+: BaCl2(8) Ba2+ (aq) + 2 C1-(aq) so - (aq) + Ba2+(aq) → BaSO4(s) As solid BaCl, from a reagent canister slowly dissolved in the aqueous liquid, BaSO4 precipitated. A barium sulfate precipitation titration is shown in the figure. The initial concentration of Cl- before adding BaCl, was 0.00019 M in 25 mL of aqueous extract of Martian soil. At the end point, when there is a sudden rise in Ba2+, [C1-] = 0.0096 M. -2.0 log (concentration, M) - 1.0 Leaching solution added Cl- calibration solution added CI- Soil added and BaCl2 begins to enter cell Cl- = 0.009 6 M -3.0 at end point -Cl = 0.000 19 M before BaCl2 addition 4.0 Ba2+ End point -5.000 0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 Time (h) Write the titration reaction. titration reaction: How many mmol of BaCl, were required to reach the end point? millimoles of BaCl2: mmol How many mmol of So were contained in the 25 mL? millimoles of S02 : mmol If so2 is derived from 0.920 g of soil, what is the wt% of so in the soil?