'" -/ GENERAL CHEMISTRY LABORATORIES , . . A FRESHMAN WORKBOOK t 111111 Simon G. Bott and R. Geanangel Department ofChemistry, U..niversity ofHouston Second Edition \-\\'. '. \ . ,.' ..,-r ItllKENDALL/NUNT PUOLISNING CDIIPANY . 0050 We.t",.rk Driv. Dubuquo, lowo 52002 CONTENTS II v Acknowledgments 1 1. Introduction to Measuring Techniques 9 2. Properties ofMatter ~f 15 3. An Introduction toChemical Reactions , 25 4. CopperChemistry-ASeries ofReactions 31 5. Preparation and Properties ofGases 41 6. Gas Laws 53 7. Detennination ofMolAl'Mass bytheDumasMethod 61 8. Thermochemistry 71 9. Light fromAtoms 79 10. Periodicity and thePeriodic Table 87 11. PropertiesAssociated with Changes inPhysicalState 93 12. Determination ofMolarMass by ~reezing PointDepressi'on 101 13. Organic Chemistry 107 14. Ki:netic PropertiesofaChemical Reaction 119 15. Determination ofan EquilibriumConstant 129 • 16. Introduction toAcids and Bases 137 17. Acid-BaseTitration CUrves Using a pH Meter 18. Slightly Solub~le S~·a.l"t4s_......,-._~.,,~.~--.-......:Io-----:-:::•.-:'• ~.'.'...--"- -.... .-r,;o 147 157 19. Electrochemistry LGalvanic Cells 167 20. Electrochemistry II. Electrolysis 175 2t.·Synthesis ofAspirin 18i 22. Separation by Paper Chromatography 187 23. Redox Reactions 193 24. Acid-BaseTitrations: TheAnalysis ofVinegar 199 2S:'AntacidTitration ACKNOWLEDGMENTS- We would like to thank the following peoplefor their help in preparing this laboratory manual: Angela McGuffey, WilliamAbbott, Cathy May, SamaraKerawala, Alian Garay. Hung Nguyen, AdaKyriasoglar. Orly Klein, VictoriaClaus, RosanetteLuther, SipraGohel,ArianeArnold, TanyaBrown, EdwardGalvez, SuboohzHasan, ChrisTyler, John Venezia,Weihan Kan, Richard Perry. SujataPatil, and CasetRobertson for their help inproofreading. Any residual mistakes are our fault! ~, "\ Students at theUniversities ofHouston and NorthTexas who have worked with previous labora tory manuals and triedto show us how notto run alaboratory course! Ourfamilies and colleagues who have tolerated usduripg the time ofwriting! SimonBott Russ Geanangel Houston, 2000 v ________.--------~_=_="""""'=__===iiiiiiiiliiiililll Introduction,to Measuring Techniques ? INTRODUCTION Thepurpose ofthis experimentis to introduceyou t6a variety ofmethods ofmeasuring amounts of solids and liquids. Chemistry is an empirical(experimental) quantitativescience. Inother words, mostofthe experi ments you willdo involve measurement. Overthe semester, you will measure many differenttypes of quantities-pressure, temperature, pH, etc.-but the most common willbethe amountofa substance. The substances you will encounter most oftenwill 6e in either solid orliquid form. Itis, therefore, essential that you know how to determine how muchofa solid or liquid you have. The amount ofsolid is me~sured by massand the amount ofaliquidby mass or, usually, volume. Today, you will learn how to use the mostconunon lab equipmentfor mass and volume m~asurement. PROCEDURE A.," Identification ofApparatus Find the following pieces ofequipment in yourdrawer oraround thelab and sketchthem on the data sheet: " . 'I.,//,' .. ::-'. graduat~4 (g) (measuring) cylinder oJ / -- ~ -"(h)testtube :J (i) scoopula J "8. Balance Use Intl)ese generalchemistry laboratories, weonly useeasy-ta-read electronic balances-saving you a lot oftime and the teaching assistants (TA's) a lot ofheadaches. It is still importantthat you become adept at the use ofthese, however. Threeaspects ofabalance are important: (a) The on/offswitch. This iseitheron the front ofthe machine oron the back. Its use is obvious. (b) The "Zero" or "Tare" button. This resets the reading to zero. (c) CLEANLINESS. Before and afterusing abalance, ensurethatthe whole thing is spotless. Dirt on the weighing pancan mess up your measurements, and chemicals inside the machine can damage it. 1 r 1. Turnthe balance on. 2. Afterthe display reads zero, place a piece ofweighing paperon the weighing pan. 3. Read andrecord the mass (I-the nUrflher in italics refers to the line numberon the data sheet). th~ 4. Add about 1/3 ofateaspoonful of solid intothe pan. 5. Record the mass (2). 6. To determinehow much solidyou have, simply subtractthe mass ofthe weighing paper (I) from the mass ofthepaper and solid (2). Record this mass in line (3). You havejustdetermined themass ofan"unknown amount ofsolid."Asecond, slightly more com pleteuse ofthe balance involves weighing out a pre-deterrnined amount ofasolid. 7. Repeat steps 1-3 above, using a new piece ofweighing paper(4). 8. Press the ZeroorTare button. Themachine shouldreturn tozero. ( 9. Spoon outabout 1g ofthe solid(5). , Theuse ofthezero/tarebutton is obvious-iteliminates the need for subtraction. c. Dispensing Liquids . -. _"l:<_... . -/~__• ~:~-..........;...r_-...: -._~'0'.•~....-'-;JL,•.---.-..........---,...... When working with liquids, as discussed above, we usuallyaescribethe quantity 9fthe liquid ~', terms ofvolume (usualunits being milliliters (mL) orcubiccel~timeters(cm3)]. We use three types of glasswareto determinevolume-buret, pipet, or graduatedcylinder. Before discussing these individually, there is one thingcommon to all. 10. Examine eachpiece ofequipment. Notethatthe sidesofeach are graduated. Youcanreadeach with the precision ofhalfofthe smallestdivision. 11. Put some waterintothe graduated cylinger. Bend down and examinethe side ofthe waterlevel. Note thatithas a "curved shape."This is due to the waterclinging to theglass sides and is called the meniscus. When reading any liquidlevel, use thecenter ofthe meniscus asyoUrrefer encepoint. ~--=i........----Read here '- 2 a. Graduated Cylinder 12. Lookatthe graduations on the side ofthe cylinder. Notethat they go from0 atthe bottomand increaseupwards. Thus, togetthe mass of6 mLofa liquid from a graduated cylinder: 13. Add waterup to the 6 mLline as accurately as possible. 14. Dry yourbeakerand weighit (6). 15. Pourthe 6mLofwaterfrom the cylinderinto the beaker. Reweigh(7). b. Pipet 16. Look at t~ graduations on thepipet. You may findeither that0 is at the spoutend oratthe top ofthe pipet. You shouldbe aware ofhow thesegraduations go whenusing each pipet. 17. Half-fill abeaker with water. 18. Depress the plungeronthe pipetpump and then attach the pump to the top ofthe pipet. Putthe spout ofthe pipetunderwaterand tum the pump wheel clockwise.It shoulddraw thewaterinto thepipet. 19. When thewaterlevel is pastthe last graduation, remove the spout ofthepipet from the water. 20. Youcan dispense the liquideither by turning the wheel counter-clockwise(slow dispensing) or by pressing the lever on the side ofthe pump (fastdispensing). Always run some liquidinto a beaker orflask that you are using as a waste containerin order to leave the level atan easy-to readmark 21. Add6 mLofwater to apreweighed (8), dry be~er and weigh (9). c. Buret -22. Attach aburetclamp toa stand, andclamp abw;et. 23. Examine the graduations. Note that 0 is atthe top. 24. Using afunnel, addabout 6mLofw.ater. To do this, fir~t lower theburet so that the top is easy to reach. 25. Run a little.~terJrQm theburet;mto a wastecontainer. Then rema.wthe buret, tum it upside -;;~t wiifCttoru'i;-fn~o down"and allow the ofthe the cOOtainer(youwill have to openthe tap to equalizethepressure). 26. You h~vejust"rinsedyourburet". This should be done every timebefore using aburet-first rinse withwater, then repeatthe processusing -.yhatever liquidis needed inthe experiment. 27. Fillthe buret to any convenient level. Itis a good techniqueto "overfill" andthenallow liquid to run into a wastecontaineruntil you reachthe appropriate level. J 28. f>ry a beakerand weigh (10). 29. Measure 6 mLofwaterfrom theburetinto the beaker and reweigh (11). •J- 3 TA _ Name------------- DATA SHEET Introduction to Measuring Techniques A. Identification ofApparatus (a) beaker (b) flask f (c) watchglass (d) Bunsenburner (e) pipetand pump , (f) buret , '.: (g) graduated (measuring) cylind~r ,(h) testtube (i.l scoopula 5 B. Balance Use 1. Mass ofweighing paper(g) 2. Mass ofweighing paperand solid (g) 3. Mass ofsolid (g) (2- 1) ~.. Mass ofsecond weighing paper (g) 5. Mass ofsolid (afterzeroingbalance) (g) - ;;--......-_.~~..._:;.---- - ..-.~...._-...-..~_.---~ C. Dispensing Liquids 6. Mass ofbeaker(g) . " 7. Mass ofbeaker +water (g) 8. Mass ofbeaker (g) 9. Mass ofbeaker +water (g) 10. Mass ofbeaker (g) ,. 11. Mass ofbeaker+water (g) 6 u_------------------ POSTLAB QUESTIONS 1. Froma consideration ofthe masses ofwatermeasured in Part C, and given that the density ofwater is 1glmL, which is the most acu€ rate method ofvolume measurement--cylinder, pipet, or buret? 2. How precisely could each ofthe apparatus used beread (give number and units, forexample, to within 5 mL)? pipet balance buret cylinder 3 Givereasons for your answertoquestion-1inlightofyour abswer to question 2. ... 7 EXPERIMENT 2 Properties ofMatter INTRODUCTION Matter is anythingthat has mass andoccupies space..J.i. e., everythingyO\! see and alot ofthings that you don't see. In ordertodistinguishbetween differenttypes ofmatter, we considertheirproperties or characteristics. Properties areoftwo types-intensive and extensive. Intensive properties are those thatdo not depend onhow muchofa substance is present (forexample, whetherthe substance is a solid, liquid or gas under a given setofconditions), while extensiveproperties do depend on thequantity ofa substance (such as mass orvolume). Properties can befurther sub-divided intophysical and chemical. Physicalproperties arethose that may'be investigated withoutchangingthe composition ofthe substance, whereas chemicalproperties describe howthe substancemay changecomposition-eitli:er spontaneously, orincombination withother substances. Thus, boiling alcoholto give gaseous alcohol is a physical change, whereas burning alcohol with oxygento give carbondioxide and water is achemica\change. ,'.Inteday's laboratory, you will examinevarious properties oftwo liquids. The objectives oftheexperi- ment are: ' , . (1) toobserve how different substance~.havedifferent prqperties; ~2) to understant\the different types ofproperties; ""4 (3) tofa4millWe)<'.O. Ursetf-further-w_i•i.J-}Jb.e..1a;b.environment. . ~ PROCEDURE A. Physical Properties i Inthispart ofthe experiment, you will examine a variety ofphysical properties oftwo liquids. By comparing~ yourobservations to a listofproperties of"known" substances, you will be able toidentify your particular samples. .{i) Appearance and Odor .~ " 1. Obtaina~eachofunkn0':Yn~_~and!!!!-1 different 100mLbeakers. Describe their appearance on the datasheet(1). Use this 20mLofeachfor the restofthe experiment. 2. Raisethe beakercontaining Auntil itis level with, and about three inches away from, your nose. Wave yourhand overthetop ofthe beaker to waft-the vaportoward you. Describe any odor (2). I 3. Repeatforthe beaker containingB. / 9