Reading: Chapter 7 (sections 1, 3), Exploring Chemical Analysis 5 th ed., D. Harris Homework: Chapter 7:2-7, 9, 10, 14-16, 18, 21.a How many moles of green K (g) (FW=39.0983 g/mol) are evolved? STOP How many moles Cl - were in the initial solution (AgCl, FW=143.321 g/mol) are evolved? STOP As a group make a list of what you would want in a precipitate STOP In her Ph.D. research ( Radioactive Substances , 1903), Marie Curie measured the atomic mass of the element radium, which she discovered. She knew that radium is in the same family as barium, so the formula of radium chloride is RaCl 2 . When 0.09192 g of pure RaCl 2 was dissolved and treated with excess AgNO 3 , 0.08890 g of AgCl precipitated. How many moles of Cl - were in the RaCl 2 ? STOP A mixture containing only Al 2 O 3 (FW: 101.96) and Fe 2 O 3 (FW: 159.69) weights 2.019 g. When heated under a stream of H 2(g) , the Al 2 O 3 is unchanged, but the Fe 2 O 3 is converted to metallic Fe plus H 2 O (g) . If the residue weights 1.774g, what is the weight percent of Fe 2 O 3 in the original mixture? STOP A 1.475g sample containing NH 4 Cl (FW 53.492), K 2 CO 3 (FW 138.21), and inert ingredients was dissolved to give 0.100 L of solution. A 25.0 mL aliquot was acidified and treated with excess sodium tetrapheylborate, Na + B(C 6 H 5 ) 4 - , to precipitate K + and NH 4 + ions completely: \[\ce{B(C6H5)4- +K+ → (C6H5)4BK_{(s)}}\: \textrm{(FW 358.33)}\nonumber\] \[\ce{B(C6H5)4- + NH4+ → (C6H5)4B NH4_{(s)}}\: \textrm{(FW 337.27)}\nonumber\] The resulting precipitate amounted to 0.617g. A fresh 50.0 mL aliquot of the original solution was made alkaline and heated to drive off all the NH 3 : \[\ce{NH+4 + OH- → NH3_{(g)} + H2O}\nonumber\] It was then acidified and treated with sodium tetraphenyl borate to give 0.554 g of precipitate. Find the weight percent of NH 4 Cl and K 2 CO 3 in the original solid. STOP