According to the Resource Conservation and Recovery Act (RCRA), waste material is classified as toxic and must be handled as hazardous if the lead concentration exceeds 5 mg/L. By adding chloride ion, the lead ion will precipitate as PbCl2, which can be separated from the liquid portion. Once the lead has been removed, the rest of the waste can be sent to a conventional waste treatment facility. How many grams of sodium chloride must be added to 500 L of a waste solution to reduce the concentration of the Pb2+ ion from 10 to 5 mg/L?

A student set up an experiment for six different trials of the reaction between 1.00-M aqueous acetic acid, CH3COOH, and solid sodium hydrogen carbonate, NaHCO3. CH3COOH(aq) + NaHCO3(s) NaCH3CO2(aq) + CO2(g) + H2O() The volume of acetic acid was kept constant, but the mass of sodium bicarbonate increased with each trial. The results of the tests are shown in the figure. (a) In which trial(s) is the acetic acid the limiting reactant? (b) In which trial(s) is sodium bicarbonate the limiting reactant? (c) Explain your reasoning in parts (a) and (b).

Chromium(VI) forms two different oxyanions, the orange dichromate ion, Cr2O72 , and the yellow chromate ion, CrO42 . (See the following photos.) The equilibrium reaction between the two ions is Cr2O72(aq)+H2O(l)2CrO42(aq)+2H+(aq) Explain why orange dichromate solutions turn yellow when sodium hydroxide is added.