Chemistry 350. The take-home least-squares problem will account for 15 possible points on this exam.

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Maximillian Spencer
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1 Chmtry 30 Sprg 08 Eam : Chaptr - Nam 00 Pot You mut how your work to rcv crt for problm rqurg math. Rport your awr wth th approprat umbr of gfcat fgur. Th tak-hom lat-quar problm wll accout for pobl pot o th am. Do four of problm -. Clarly mark th problm you o ot wat gra. (0 pt ach). A tattcal aaly a tal compot th valuato of prmtal rult. I our cuo of tattc, I tat vral tm that tattc oly tll u about th prco of a maurmt, ot th accuracy. Why th o? If th tru, how ca w u th cofc trval to prct how clo our rult ar to a tru or accpt valu? Wh w rfr to qualty of rult, w ar typcally corg th accuracy a prco of a valu. I trm of prco, tattc ar a uful tool to valuat how rproucbl our ata ar, wth a taar vato rvg a a tmat of th cattr of th ata. Th challg com th fact that w typcally hav a vry mall ata t a ar forc to rly o that mall t to appromat th taar vato. Th cofc trval alo allow u to mak om frc about th accuracy of a mtho by takg th fact that w hav a mall ata t to accout; aumg oly raom rror ar mpactg our maurmt. Thrfor, w mut rly o goo prmtal g to rmov ytmatc rror to mak a valuato ug th cofc trval raoabl.. Outl th proc that woul typcally b u lab to prform a tral taar prmt. (ht: you wll mor tha two oluto) Itral taar ar uful wh varabl ampl z ar u or wh trumt fluctuato prvt th rlabl u of a calbrato curv. Th matral cho for th tral taar mut rpo to th maurmt but hav a ffrt tty tha th aalyt.. Slct tral taar. Prpar a r of taar that cota varyg amout of th aalyt, but cotat amout of tral taar. 3. Prpar ukow oluto that hav th am amout of tral taar a th taar oluto cota.. Maur th rpo of ach oluto for th taar a th aalyt. Prpar a calbrato plot of th rlatv rpo of th aalyt a tral taar a a fucto of aalyt coctrato.. U th calbrato curv to trm th coctrato of aalyt th maur ukow oluto. 7. Accout for ay luto tp to trm th coctrato of aalyt th orgal ukow oluto.

2 3. I proucg a calbrato curv, raw ata typcally ubjct to a lar lat quar aaly. Dct th phra lar lat quar a crb qualtatvly what o a lar lat quar aaly. Why lar? Lat quar of what? No calculato ar cary. Th goal of a lar lat quar aaly to trm th lar rlatohp (y mb) that bt crb th tr a ata t. I th aaly, bt ma that th calculat valu for lop (m) a trcpt (b) crb a l whr th um of th quar of th rual (th ffrc btw th actual y-valu a tho prct by th l) mmz. Th accomplh by ttg th partal rvatv of th rual calculato wth rpct to th lop a trcpt to zro a olvg for m a b. A ky aumpto th aaly that th -valu ar kow to a hgh gr of prco, whl th y-valu hol th mot ucrtaty.. Th tvty of a aalytcal mtho oft cofu wth th lmt of tcto, v though thy ar ot th am. Epla th ffrc btw th tvty a lmt of tcto. Your cuo houl focu o th fact that tvty crb th ablty of a mtho to tguh btw mall chag coctrato (or amout) of aalyt throughout th rag of th maurmt. Th lmt of tcto crb th mmum coctrato (or amout) of aalyt that ca b tguh from th blak wth om lvl of crtaty. It crtaly pobl for a mtho to b tv a ot hav a mall lmt of tcto, a vc vra.. You hav b gv th tak of tachg a w tut, Al Thumb, th propr u of a Cla A burt for ttrato orr to obta hgh qualty quattatv rult. Clarly crb your tructo to th tut, clu rmr of commo ptfall Al houl avo. Your cuo for houl clu th followg: Procur for clag th burt (a tp) Takg car to avo ar bubbl th tp Bg ur to allow tm for th wall to ra a matral to ract bfor rag Rag th burt from th bottom of th mcu, wth th mcu at y lvl Etmatg rag to /0 of th mallt grauato (0.0 ml o a 0 ml burt) Shoot for cott pot color. Takg car to "cut" rop ar th pot

3 Do thr of problm -9. Clarly mark th problm you o ot wat gra. ( pt ach). You to prpar a 00.0 ml of oluto that 00.0 ppm calcum. Clarly crb how you woul prpar th oluto tartg from th pot blow. Iclu th quatt of ach tartg matral that you woul a. tartg wth ol calcum trat Rmmbr, calcum trat Ca(NO 3 ) (FW.088 g/mol) 00 mg Ca mol Ca mol Ca(NO 3 ).088 g Ca(NO 3 ) 0.00 L0.7 mg Ca(NO 3 ) L 0.08 g mol Ca mol Ca(NO 3 ) So, olv 0.07 g Ca(NO 3 ) a mall amout of watr a 00 ml volumtrc flak, m wll, lut to th mark a m wll aga. b. tartg wth a 0.00 M calcum trat oluto Sc ach mol of Ca(NO 3 ) that ocat lbrat mol of Ca, a 0.00 M Ca(NO 3 ) oluto alo 0.00 M Ca 00 mg Ca mol Ca 0.00 L L. ml L 0.08 g 0.00 mol Ca So, lut. ml of 0.00 M CaCl oluto a mall amout of watr a 00 ml volumtrc flak, m wll, lut to th mark a m wll aga. Th. ml coul b lvr by ppt or burt. 3

4 7. You hav ru a r of ttrato to trm th ukow coctrato of KHP a ol ampl. Th rult of ttrato cat KHP coctrato of 3.%, 3.9%, 30.%, 3.%, 3.07%, 3.98%. Th "tru" valu for KHP th ampl 3.9%. Evaluat th ata a trm f your rult ffr from th tru valu at th 9% cofc lvl. Lookg at th ata, t appar that th valu 30.% a outlr o try a Q-tt or a G-Tt: Q calc G calc Q tabl 0. < Q calc, a G tabl.8 < G calc o th ata pot houl b rjct. Ba o th rmag ata, th ma for th ata t 3.88 % wth a taar vato of 0. %. Do a t-tt: tcalculat t tabl for gr of from.77, c t calc >t tabl, th rult o ffr gfcatly. (NOTE: f you o ot o th Q-tt, th taar vato larg ough that look lk th rult o ot ffr. Alway look at th ata!) Altratvly, you coul hav calculat th rag trm by th cofc lmt a how that 3.9% l out th rag. Th 9% CI 3.9 ± 0.3 %

5 8. Ntrt (NO - ) wa maur rawatr a uchlorat rkg watr ug rplcat maurmt of a gl ampl by a tablh pctrophotomtrc mtho. Ba o th rult blow, o rkg watr ampl cota gfcatly mor trt tha rawatr ampl (at th 9% cofc lvl)? Rplcat 3 ma t. v. Rawatr (ppb) Drkg Watr (ppb) Th a comparo of two mtho, ug vral ru of a gl ampl to tablh th ucrtaty o ach mtho. Sc w hav two ma a taar vato, u pool to prform a t-tt. Chck th taar vato wth a F-tt frt: ( ) ( ) ( 7.77) (.8) Fcalculat.3 Sc F calculat l tha F tabl (.39), our ormal quato wll b f. (.8) ( ) ( 7.77) ( ) pool t calculat t tabl for (-) 8 gr of from.30 Sc t calculat > t tabl, th rult ar gfcatly ffrt

6 9. Th compoto of a ampl cotag a ukow amout of oum carboat combato wth a rt matral wa trm by olvg th ampl 0.0 ml of watr a ttratg th rultg oluto wth taarz trc ac oluto. Ug th formato blow, trm th prct by ma of oum carboat th orgal ampl, wth t abolut ucrtaty. You may aum that th cotrbuto of molar ma to th ovrall ucrtaty glgbl. Coctrato of trc ac taar Ma of carboat-cotag ampl Ital burt rag Fal burt rag 0.0 ± M 0.93 ± g.8 ± 0.0 ml 9.7 ± 0.0 ml Na CO 3 HNO 3 H CO 3 NaNO 3 Ucrtaty th volum lvr by th burt: (9.7 ± 0.0 ml) - (.8 ± 0.0 ml) 8. ± ml [(0.0) (0.0) ] / ml Coctrato calculato: (DON T FORGET THE STOICHIOMETRY!) 0.0±0.000 mol HNO 3 8.±0.07mL mol Na CO 3 L ±? mol L mol HNO ml ±? mol Na CO g Na CO 3 00% 33.30± % mol Na CO ±0.000 g ampl % M % o th prct oum carboat 33. ± 0. % ( ) 0.30 %

7 7 Pobly Uful Iformato m' m a w a Dty of ar 0.0 g/ml Dty of balac wght 8.0 g/ml t ± µ ) ( y σ µ π σ B A C B A C B A C kow valu t calculat ( ) pool calculat t ( ) ( ) pool t calculat ( ) ( ) y m y) (y k m ( ) y D y m D y b y LOD y blak 3 ( ) ( ) calculat F rag gap Q calculat valu upct G calculat

8 Valu of Q for rjcto of ata Valu of Stut t # of Obrvato Cofc Lvl (%) Dgr of From Q (90% Cofc) Grubb Tt for Outlr # of Gcrtcal Obrvato At 9% cofc Crtcal Valu of F at th 9% Cofc Lvl Dgr of from for Dgr of from for

Chemistry 222. Exam 1: Chapters 1-4

Chemistry 222. Exam 1: Chapters 1-4 Chtry Fall 05 Ea : Chaptr -4 Na 80 Pot Coplt two () of probl -3 a four (4) of probl 4-8. CLEARLY ark th probl you o ot wat gra. Show your work to rcv crt for probl rqurg ath. Rport your awr wth th approprat