7 Mole Relationships - Faculty.chemeketa.edu

10. After 10-15 minutes of intense heating, allow thecrucible to cool.11. After cooling to room temperature, measure the mass ofthe crucible, cover, and residue and record (Box ID)12. Place the crucible on the clay triangle once more andheat intensely for another 5 minutes.13. Cool to room temperature and reweigh the crucible,cover, and residue and record (Box IE). Compare themass of the second heating (Box IE) of the crucible,cover, and residue to the mass of the first heating (BoxID). If the mass difference is greater than 0.03 g, repeatthe intense heating then cooling until two successiveweighings are within 0.02 g of each other. 914. If advised by your instructor, repeat part I with a secondsample.15. Determine the mass of KCl residue left behind in thecrucible by subtracting the mass of the crucible & coverand report in Box IG. 1016. Determine the mass of the oxygen (O 2 ) produced fromthe reaction and report in Box IH. 11II. Examination of Residue17. Place three small (10 x 75 mm) numbered test tubes in arack. Number the tubes 1-3 with a pencil (not pen) onthe white surface or use a stick-on label.18. Make solutions consisting of the following:A. Test Tube No. 1: A pinch of stock potassiumchlorate (KClO 3 ) in 2 mL of deionized water.B. Test Tube No. 2: A pinch of stock potassiumchloride (KCl) in 2 mL of deionized water.C. Test Tube No. 3: A pinch of the residue 12 from thecrucible from your experiment in 2 mL of deionizedwater.19. To each of the three solutions add about 5 drops of 0.1Msilver nitrate (AgNO 3 ) solution and record yourobservations. The formation of a white precipitateindicates the presence of a chloride. 1320. Discard the three solutions in the "Waste Salts"container 14 . The KCl residue 15 can be disposed of in thegarbage or washed down the sink. Wash your hands.9 The only way to know if all thepotassium chlorate has decomposed isto continue heating and weighing untilthe mass no longer changes. This iscalled "heating to a constant mass."10 The residue left in the crucible willbe potassium chlorideMass = (Box IE or IF) – (Box IB)11 There is no direct way to measure themass of the oxygen gas since it willescape into the air. If the crucible andits contents lose mass during heating,the mass lost must be equal to the massof the oxygen.Mass of O 2 =(Box IA) – (Box IE or IF)Or Mass of O 2 =(Box IC) – (Box IG).12 You may have to use a spatula toscrape a small quantity of the residueinto the test tube. If any of the solidsdo not dissolve, gently heat it over aBunsen flame.13 The chloride ion (Cl 1- ) fromPotassium chloride (KCl) will reactwith the silver ion (Ag 1+ ) to make solidsilver chloride (AgCl).KCl + AgNO 3 KNO 3 + AgCl (s)The silver chloride precipitate consistsof very small pieces of suspendedsolid. Left undisturbed, the pieces willeventually settle to the bottom of thetest tube. All chlorides (e.g., NaCl andCaCl 2 ) give this same precipitate.Since tap water usually containschloride ions it is important thatdeionized water be used rather than tapwater.14 Silver ions, like mercury and leadions, are heavy metal ions and aretoxic. Silver nitrate left on your skinwill turn the skin black. Smallamounts on the skin are not consideredespecially dangerous but should beavoided. Swallowing silver nitrate canbe fatal. Wash your hands afterhandling the silver nitrate. Dilutesolutions of silver nitrate are used tokill bacteria in the eyes of newborninfants. Using the wrong concentrationof silver nitrate has caused permanentblindness.15 KCl is sold commercially as “LiteSalt”, a substitute for NaCl for personson a low sodium diet.96CH104 Lab 7: Mole Relationships (F14)