{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

exam_3.key - 35 as 5an sew F‘ D 1 EXAM#3 CHEMISTRY 441 DR...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Background image of page 2
Background image of page 3
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 35/ as 5an + sew F‘ D? 1 EXAM #3 CHEMISTRY 441 DR. MURRAY 100 POINTS April I6, 2010 NAME KEY MASS SPECTROMETRY 1. Explain how a time of flight mass analyzer m detects ions of different rn/z ratio. Your answer should include an appropriate diagram of the analyzer, indication of Whether the ion source needs to be pulsed or is continuous, and a discussion of how the accelerating voltage is related to the time of flight and m/z (with equations if possible). 'V ‘y i. \ b ( l fi‘i""“"‘"""‘""“““”"‘”‘“ 1‘" , ‘ listd: (Lg/M S ‘9‘ M 9.4181}, {iv twig U C 2 1 If ml“ W‘ as W as”: iwfi ’ " a m { J w M \ MW {\(‘csl I a. {:le ngfike: aeAV’ 2 —{2 {WW \I i 12.. ... m 218% W— L \1 g “212%! im '2. What does “MALDI” stand for? Is it a “hard” or “soft” ion source, and What’s the difference? What does the “matrix” do? .0 mg‘l—M )4. Missing} “Li cl mg Mafia; vi. (WW: %gjalma J‘Afilfifiafil‘flm gr 3% b mwaiiflaWeM—W Jr 0 aloSo-Vl’JS lamp/oi”. Jim‘s/x any; merlly ,{y‘g‘KLacl KM M‘A + 5W9“. WW1 WWI; J2“) zé’teé\ 3. Shown below is a mass spectrum of CH3BI’. Assign as many of the peaks in the spectrum as you can, with formulas. +- 8k ‘5‘ ‘cug Ba 3 CH3 EA E E . E :3 4- 31 + lg 40 fl (l, g a: Bf}, u: A ) g 21] E 0 l3 massmh urge trntz} 20 4. The diagram below is of the new kind of mass analyzer called an “Orbitrap”. A tightly packed bunch of ions (the thin curvey line) are injected into the Orbitrap and undergoes rotation around the inner spindle. A dc voltage is applied between the inner spindle and the outer shell (fig). What kind of motion of the ion bundles takes place, and how is the ion m/z value determined from that motion? mammdfipafizi‘lié’n). (/7, odnm/ «Lagc‘dlaiiz (imam ( aw QXCLJLLL} @607.“qu n.1,, -_, ("W ._.._.:> . iii..‘533.1.5fn337 71' tea—w. Wmagsg Chdflsi’fi” % mg wax-:7 ‘ ‘QUCHB/L a [Owe/in. ogciiiamfii QW‘JW’ ELECTROCHEMISTRY 5. Consider the following electrochemical cell, where Pt is the working electrode. Pt/ Fe(CN)63' (3.0 mM), Fe(CN)64' (3.0 mM) // SCE For the reaction Fe(CN)63' + e- —> Fe(CN)64' E° = 0.120 V vs. SCE. a) What is the potential of the cell, measured at zero current? . 4. E z E0 d 054 ‘9: redraw“ C3»_L?-f>_ans. us 56;? i ii? (stingy b) Use the Pt electrode as a rotated disk, and apply various potentials to it (relative to the SCE). You observe steady state currents at each potential, that form a current—potential “wave” with limiting currents. Sketch (accurately!) and briefly explain the reactions occurring on different parts of this wave, and any differences between the values of the limiting currents. Label the axes on the plot, note where is E112, and where are the limiting currents. ) 0 “i” "" E u s EC‘E‘ but“) a, W L m ; ,3,me Cmg. ragwei r, .. 3~ , L“WC“ Limit? ‘ h? CC ”\ié “em? graffiti); L9“ in “mace stillii-"FWM 61L“? “it? 3 W" V65 c) If you rotate the electrode 4 times faster, the currents will be g -times smaller, or k -tirnes larger (enter a number in one blank). (1) If you use a Pt electrode with area 2 times larger, the currents will be 3 -times smaller, or k-times larger (enter a number in one blank). 1 ti 35 6. Briefly answer the following: / Law a) What is an ion selective electrode? Give an example. What must be a property of a component of the ion selecfive electrode, in order for it to be selective? Cat—“ll Corie/vita a, Wmloncwa 1;;Aztaggia'm J E aware E 57.2 - ' . p .. 7 lug} REF/CUPHN “M C ML wag. fl pacific-vi (M 440‘“ an M3” EMMLVS PERM 5E LE’CT‘l UE, —# Adm/mix cm‘t‘f it)“ @qfin‘culaau 53"”? 5: b) The reaction above in problem #5 is a “reversible” electrode reaction. Just what does that mean? 1’] = FAS‘LL. plea—breve» 4'7an (ibis) Nata/Jr'l‘W—J Wags WWL 7759 U; 53 bf‘r’fi NW??? if? a: . 7. Consider an electrochemical cell where a Pt disk is the working electrode and the (unstirred) aqueous solution contains 1 mM Ru(NH3)63+ with KN 03 as a supporting electrolyte. The reference electrode is SCE. . a) Sketch (accurately!) the cyclic voltammogram of the reversible one electron reduction of Ru(NH3)53+ to Ru(NH3)62+ . Pay attention to the shape of your sketch. Label the axes, the peak currents and peak potentials. l J Ll" 44 @ E94 99¢] a“ ia a) Both RuCNHg).53+ and Ru(NH3,)62+ are stable chemicals. What is the relation between the reduction and oxidation peak currents? v . r _ ' E ‘ l L?) 62-— : LP.) 60 mixed? at P4 (Jig. drama arses 4V) 55in mam, {Janie b) The electrode reaction is reversible. What in your diagram would you measure to know that? --, 5.5! 1+ E9): ‘ Ego. 1’ T "NV 0) How would the peak reduction current vary with the potential scan rate? The concentration of Ru(N H963 +1? The electrode area? ’2. g [Tic ac \I if CMCWEE? a A PLEDGE ...
View Full Document

{[ snackBarMessage ]}

Page1 / 3

exam_3.key - 35 as 5an sew F‘ D 1 EXAM#3 CHEMISTRY 441 DR...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon bookmark
Ask a homework question - tutors are online