Chem-Ex. 1 - 33“”‘5 Piikmsrah Section: (97 Date: 8...

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Unformatted text preview: 33“”‘5 Piikmsrah Section: (97 Date: 8 [639) 069 EXPERIMENT V‘ 1. The Preparation of pH Standard Solutions. Solutions of known [H30+ ] are to be prepared and treated with appropriate indicators. These solutions will then be used as colorimetric pH standards. Name: Note: Be sure to write an acceptable response to Q 1.1 before coming to laboratory! Q 1.1 Tell how to prepare 30 mL of 0.1 M HCl by dilution of the laboratory 1 M HG. Show all calculations performed and provide all pertinent detail for your procedure recognizing that the 0.1 M HCl is to be prepared as carefully as possible by using standard locker glassware such as the 10emL and 100-rnL graduated cylinders. In ar'Jgr +9 'NVBLCE. “L. D;- O'F D.l by dilution! 3mL at ;M “a must be. aumfl‘ in Wu.— 750 ML. )oiufiofi. To do HMS, VD“) Hrs;- rgngp. m mat “a (Dam-L fired/dated «(W-“f” ‘70 do HHS! You "i evtw‘“ 2 ML 9“ I“ ’4“ l [MHcr V, - DJMHCI ~30nL \h :— 3M. . I cylimwi (“i-p.51. iJ:I and dwcari m (urn;me \Iou $0 5H“ ,3“ 4'0 We EDML firsdueki ‘ 4“ ‘ ' ‘ (Mr “to-4+ you "52 "DI: wrlrfir mm“ or t . wi+k W.» room, 3Wed who ‘ _ n q and put—l you t—ttt M9] JOML jugs/am; cytmur 04* _'W 3114— .+ \M H (no or am— {nLo MM. [00 “L tyund‘r‘, - ‘ ‘- Nerd‘ voo 9541 3 time. I D: _\,./3+[‘- .14, 44a» OK \‘ :t/ lB—mL cylinw 3‘”- ‘NNM- "’3 man Wil' “Tar at r; 355/. Fauna ital-o HA9- mom. a) li n‘ar. I LOSl-‘t You acid“ DI avg-Hr {-0 m [OOML glint? hum] [.5 Baal Note: Your mstructor may permit you to do the EXPERIMENT forgtIhis assrgnment 1n teams of two. BUT, FOLLOWING ASSIGNMENT 1, PARTNERSHIP WORK IS NO LONGER PERMITTED. After yourresponse to Q 1.1 has been approved, prepare the 30 mL sample of 0. 1 M HCl. Also prepare 30 mL each of 0.01 M HCl and 0.001 M HCl by appropriate dilution of 0.1 M HCl and 0.01 M HCl, respectively. Fill individual, clean, labeled vials (E)! test tubes) about twouthirds full with 1 M, 0.1 M, 0.01 M, 0.001 M HCl, and deionized water, respectively. Try to ensure that each vial is filled to about the same level. Save the unused portions of each HCi solution for use in section 2, below. Similarly, fill additional vials with the laboratory pH 4.0 and pH 5.0 standard solutions. Do fl()_t attempt to prepare these solutions by dilution of HCl solution as the corresponding dilution errors would be too great. To each vial add two drops of methyl violet (HMV) indicator. Stir each thoroughly, being sure that pendant drops of solution are n_ot transferred from vial to vial with the stirring rod. Stand the vials on a sheet of white paper. Observe colors by looking through each solution 1-9 from top to bottom. If the colors are too pale add more drops of indicator as necessary and restir. Be aware that best results are obtained if equal amounts of each test solution are treated with the same amount of indicator. If color intensities fade as this experi- ment progresses, add more indicator, restir, and reobserve. Give a concise description of the color of each solution in the following table. Be sure to draw a sharp and clear distinction between all solutions which are different in color. Note that for the listed solutions, only the pH 4.0 and pH 5 .0 standards and the deionized water should show essentially the same color with HMV. Also note that in describing different colors, it is necessary to distinguish between shades or tints, not intensities.* For instance, blue- green (like ocean water), azure blue (like the clear, daytime sky), navy blue (like some blue jeans), blue-violet (like HMV at a pH of about 3), blue-black (like certain inks), are all different shades of blue as the color descriptions indicate. Be sure that your color descriptions distinguish between colors which E different. * Note that the same blue color results on treating a liter of water with one drop of blue food dye versus treating a liter of water with ten drops of blue food dye. But the blue color of the ten-drop solution is much more intense. ON COMPLETION OF THIS WORK, SAVE THE VIALS WITH THE 0.01 M HCI 0.001 M HCI, AND THE pH 4.0 STANDARD FOR USE IN SECTION 2. Solution [H30+ ] * pH * Observed Color w. HMV (Watch SF!) 1 M HCI l 0 Y6 0.1 M HCI 0~ l I b 0.01MHCI n.“ 2 {5"} 0.001 M HCI 0 not g V pH 4.0 standard ,0 .06 o l ‘i L pH 5.0 standard 0 -' 9pm i K V deionized water” 0- 09000! U * [H30+ ] and pH values follow from the corresponding HCI-solution and standard-solution concentrations. These values are no; to be inferred from observed colors H from information appearing in the table on page 1-6. ** The laboratory deionized water may not have a pH of 7.0. See your instructor for information about this. Q 1.2 Based on your results, over what pH range does HMV appear to be a useful indicator? Why? a From {Jr-l 0 +0 3 (in) mm H“ W clif'lerm”. M,le MN" Cglwfif whlb— (H Li am} Of “6‘ ins di‘éktf‘m‘lt’ its—meow ‘lovlww‘ rmm -_—_—- __ .______ . __ __ ______.._————.——_. mm"‘—__— '—'_' _ '— pH 4.0 standard pH 5.0 standard “>000? pH 6.0 standard 9% deionized water a Dodge. (0 _____ __,y_ Q 1.3 Imagine that a colorless solution of unknown pH is treated with HMV. If this solution develops a color which is essentially the same as deionized water treated with HMV, what conclusions concerning the pH of the solution can be reached? (The answer is not "no conclusions".) Wu. ComclusiOn Mr Cém be. rmcluzdt 15‘ tin/.11- ‘l’kL ?H '0? +001 Coiuh‘an ,‘g above 0K 4‘ Repeat the above experiment using methyl orange (HMO) indicator instead of HMV. As the test solutions use your 0.01 M HCl and 0.001 M HCl solutions, the laboratory pH 4.0, 5 .0, and 6.0 standard solutions, and deionized water. (Be sure to save the HMV-treated vials and the HMO-treated vials with the 0.01 M HCl, the 0.001 M HCl, and the pH 4.0 standard for further work.) Report your observations for the HMO investigations in the following table. In order to summarize and compare your HMV results with your HMO results, reenter HMV observations as indicated. Also make the requested predictions (P), noting that you may test these predictions by experiment as you deem necessary. Solution [H301 pH Color w. HMV Color w. HMO 1 M HCI [ 0 y (7 (P) i7 0.1 M HCI ' ‘ 5 (P) _§>_ 5-1/ ? 0.01 M HCI ’00 I Bk 0.001 M HCI 3% ’3 V .0001: “i " r ‘3 U Q 1.4 Based on your results, over what pH range does HMO appear to be a useful indicator? 0; " u CUM We (“KL I- ‘ beg/ammo, my, \3 Wm— 0 color (“gt/L l—ll Q 1.5 What conclusions can be reached concerning the pH of a colorless solution which, when treated with HMO, develops essentially the same color as 0.001 M HCl treated with HMO? WM. can CoflCiucLL W“? H— (“35 a 12 H o? 9??““lm’fl‘fi 3 OK if The Approximation of K3 for a Weak Acid by Indicator Analysis. Acetic acid, HBCCOOH, (abbreviated as HAc), solutions of known concentration are to be prepared. Samples of these solutions will then be treated with HMV and HMO indicators. In order to determine [H30+ ] through estimation of pH, direct color comparisons of these solutions will be made to the pH standard solutions from section 1. The resuits obtained will allow [Ql for HAc to be approximated. Q 1.6 Write the equation for the principal acid/base equilibrium in 1 M HAc. ., f m CCODH Ir H20 :3 H30 ; H5 5600? Q 1.7 When 1 M HAc is diluted with water, what happens to the total number of H30+ ions in the system? Weft oF (Acct/35m. (on? wit-i Q 1.8 When 1 M HA0 is diluted with water, what happens to [H30+ ]? [(430 j "(K alum/as: W‘L «4 .6599: «Mam. Q 1.9 Write the equation for the principal chemical change which takes place when 1 M HAc is diluted with water. Note that this will be the reaction occurring on dilution that re—establishes equilibrium. .‘ if , MCCOOIMW) + H30“) 59550 69 “430sz out, Q 1.10 What [H301 lies halfway between [1130" ,j = 1.0 x 10’2 and [1130+] = 1.0 x 10’3? (Hint: Answer this based on pH and then reconvert to [H3O+ ] .) 0K l-12 :Ml4fie'x=°""‘" ,iHAL-erS‘fll I $55 :25 ‘.x=.3'§ Obtain about 25 mL of the laboratory 1 M HAc. By appropriate dilution prepare sufficient quantities of 0.1 M HAc and 0.01 M HAG for the colorimetric vial tests with each indicator, HMV and HMO. Prepare two labeled vials with 1 M HA0. Treat one with HMV and the other with HMO. Similarly, prepare vials with 0.1 M HAc and 0.01 M HAc, respectiveiy, and treat with HMV and HMO. Stand the HMV-treated vials next to the vials containing the HMV~treated pH standards. Stand the HMO—treated vials next to the HMO—treated standards. Note that only the 0.01 M HCl, 0.001 M HCI, and pH 4.0 standards should be necessary for this investigation. BY DIRECT COLOR COMPARISON OF HAc SOLUTION COLOR TO STANDARD SOLUTION COLOR (with a given indicator), make an estimate of the pH in each HAc solution. Note that both HMV color comparisons and HMO color - comparisons may be necessary in order to make a reliable pH estimate for the HAc solutions being studied. Remember that if an HAc solution shows a color which is the same as that of a standard having a pH inside the color change range of the indicator, the pH of the HAc solution is the same, or nearly the same, as that of the standard. On the other hand, if an HAC solution shows a color which is somewhere between that of two standards which span a pH range of l, the pH of the HAc solution lies somewhere between the pH's of the standards. In this case, very careful color observations/ comparisons must be made in order to make a reliable estimate of the pH for the HAc solution. (Recall section i in the Discussion.) Report observations and results in the following table. SAVE ALL VIALS WITH TEST SOLUTIONS UNTIL YOUR WORK IS APPROVED! THIS WORK MUST BE REPEATED IF TEST SOLUTIONS ARE DISCARDED PRIOR TO APPROVAL! Solution Color w. HMV Comparison of Color to HMV Standards* T, H 1 Blot-Vfolql‘ Corrfipnd‘s 4’0 .00! M .— 0_1 MHAC wear WWW" 0-01 M HAG _V‘i°l” M“ “M” Solution Color w. HMO ‘ Comparison of Color to HMO Standards" at! 1MHAC WI" WWI 0»; 0-1MHAC Mink ‘W M «3'2 0.01 M HAc F— Dramyé “(mew Y “(b .00! it Mr 3 * Be sure to identify standards by pH. 1-13 ———.—---—v _ w—t- mim— Solution Estimated pH (from [H30" ] (calculated from above color comparisons) estimated pH) t ’3’ 1 M HA0 1 L g X“ [0 , ft 0.1 M HA0 3 ‘i M > v. 2 Mi 0.01 M HAc ~ M x 1'0 OK i After your work has been approved (above), your instructor may ask that you check your HAc solution pH’s with a pH meter. (See instructions below for use of the-pH meter.) In this case, report your pH meter readings below. pH of 1 M HAc with meter pH of 0.1 M HAc with meter See Note. pH of 0.01 M HAC with meter NOTE: Student-type pH meters may not give accurate pH readings unless the meter has been calibrated for the pH range under investigation just prior to use. To compensate for any discrepancy between the colorimetric pH's and the corre- sponding meter pH's, check the meter reading with the laboratory pH 3.00 standard solution (M the 0.001 M HCl which you prepared). Any difference in the meter reading relative to 3.00 can be used to correct the meter readings recorded above. If necessary, consult your instructor for further advice. Using the pH Meter (1) CAREFULLY remove probe from probe-holder (probe is immersed in pH 4.0 buffer) and rinse probe with 2 — 3 squirts of deionized water. Catch rinsings in the sink or in a small beaker. DON‘T MAKE A MESS! (2) CAREFULLY pat probe tip with Kimwipe to dry. (3) Immerse probe to a depth of about 3 - 4 cm (1 - 11/2") in solution for which pH is to be determined. (4) Read and record pH arid ABIDE BY NOTE (above). 1—14 (5) Re-rinse probe as in Step (1), and pat dry as in step (2). (6) Repeat steps (3), (4), and (5) to complete all necessary pH measurements. probe-holder. MAKE NO METER ADJUSTMENTS! Any pH meter which appears to need adjustment or which appears to be malfunctioning is to be reported to the I (7) After final pH measurement repeat step (5) and GENTLY return probe to stockroom staff at the laboratory stockwindow. lg) exceptions! 3. Buffers. An HAG/AC_ buffer solution will be prepared. The properties of the buffer will then be compared to the properties of a solution which is not a buffer. This will serve to demonstrate how a buffer works. Obtain (prepare by dilution, if necessary) 0.5 M HAC and place 5 mL of this solution into each of two clean Vials. (Viais need not be thoroughly dry.) [' . K g. , 5 H . [13 ML = 5 Also prepare a solution which is both 0.5 M in HAc and 0.5 M in N aAc. Place 5 mL of this solution into each of two clean Vials. (Vials need not be thoroughly dry.) Q 1.11 Give details of preparation of the solution in which [HAO] 2 [Ac‘] 2 0.5. a? re mama-tag M Han, I «M '5'” o9 [M HA9 and Sm, of D1; mar, Proceed to p. l - 16. mm— Obtain (prepare by dilution, if necessary) a few mL of 0.5 M HCl and a few mL of 0.5 M NaOH. Use the laboratory pH meter to measure the pH of the 0.5 M HAc. Record below in Q 1.12. Use a clean dropper to add one drop of the 0.5 M HCI to one of the vials with 0.5 M HAc. Mix thoroughly. Measure and record pH (Q 1.12). Repeat this investigation at intervals of one drop until a total of 5 drops of 0.5 M HCl has been added. Take the second vial with 0.5 M HAc and repeat the above investigation, but this time treat with 0.5 M NaOH. Now repeat this entire experiment using the [HAc] = [Ac’] = 0.5 solutions. Treat one vial with 0.5 M HC1 and the second vial with 0.5 M NaOH. Q 1.12 Record pH readings for the above experiments. drops(d) added pH of 0.5 M HAc pH of [HAc] = [Ac' ] = 0.5 0 A 0!. £7 1dO.5MHC| 21.427 5/,(9‘7’ 2d 0.5MHCI 9.51 V/(sq 3d0.5MHC| 3.077 LL93 4d0.5MHCI Lq’c} he? 5d0.5MHC| \-3°l W55 1d 0.5 M NaOH -30 ‘fl § 2d 0.5 M NaOH 3'08“ ‘1. 7 5 3d 0.5MNaOH 7%? W177 4d 0.5 M NaOH WM ‘1'“? S 5d 0.5 M NaOH Mi 1-16 Name-L M [I E‘Seciion: 076 ‘7 Date: “ ‘05 PROBLEMS FOR ASSIGNMENT 1 P 1.1 Complete the following table based on your results in section 2. Solution [H30"] [Ac'] [HAc] (at equilibrium) I , v 7: 1M HA0 "(ac (0 3 YKIO g 0.1MHAC 4H0" ‘1: to" .I 0.01MHAC unto" Lfvwr -°‘ P 1.2 Based on the information reported in P 1.1, calculate an approximate Ka for HAc for each HAC SORQQJILLM _fi0‘71...l\&,~andn0~fll_ltfljnvestigated. Show work. . . t (:1 Km (Wk) ‘ ml. ‘. 14PM, P 1.3 Tell why your results prove that HAc is a weak acid. P 1.4 Your results should show that the extent or percent of ionization of a weak acid increases on dilution. Show this by using information reported in P 1.1 to calculate the percent (‘70) ionization ofHAc in each solution (1 M, 0.1 M, and 0.01 M). Note: %ionization = [W x 100% [lnttlal solute] _ [H.‘(Y3 to ? Ac, x (00°53. % ,mfl/i/hbfl ‘ Wtklou, [HHL]IM- A ° M, 139/“ rod/o c or! «Mr/l e H» mm = W”- l-l7 P'l.5 Consider a solution that has equal concentrations of both HAc and Ac'. Is this solution acidic, basic, or neutral? Defend. fa MSW HMS, m W51“ compare. in org;ch W WWW“ '5' Kat to Hm. mamm 0? Kb, TLL {PLcW-S with Fr?“ K “in dunk/rial Hu— ASW- 5M0?— Kq v's (M321 W (<5; H"); i soluhon 1" notatio- P 1.6 In solutions of (HO)ESO2 at concentrations greater than 0. 1 M, HOSO; ionizes only to a small extent. But, in 0.005 M (HOLSOZ, H050; ionizes to an extent of 60%. With this information predict the colors shown by HMV—treated 0.5 M (HO)ZSO2 and HMV—treated 0.005 M (HO)ZSOZ. Defend. in 0.5M MSG? {3420*}; 6? Pt—H'Sé a I. ou-I 5111.911 k 1‘ H, ‘p 0' 9W” MW 5 We“ H $41.0 {F ‘6: BL \ ' run (3" all. k M BJ‘r/cfip 0,005- M (4,1. goq [H39 £0,508 .a/ W. ill-l Wwfin Q-l. a gmce' WV :3 bh/L 310 War .4va m 1,,» 1:chL 9* (It 31‘ P 1.7 Calculate the pH of the following solutions. Show work. «H __ I 2 Sun" [We 7 2m 1m 43? (i) 0.5 M NaOH [0W3 (ii) ZMHCI [1450*]:a «r P“ = —o.% Pr QM M3034 [of—[’15) a' [H301]: Sxfo’ (iii) 2 M NaOH 3H s N I 5 (iv) 3 x 10—8 M HCl (Note that the ionization of water must be considered in order to calculate the pH of this acidic solution.) “H * ’ g F .k 4.“ m “'0‘” ” [[430 ND“ 3, 4‘ tso who 3;. #3020?! am; [OH‘JwI mm @130*};3+ 3x 10"? a, Lam—fl: ( 3* gx‘oflg)‘5 .53; r 3x if '04. sin“. Qe‘UHbfl (g Qa‘é'c: \j C M x \0'7, 4’ “n” EH 3‘ LONG"? .m /_ox(o"'M 146', 3 3 “[045 M r3. ‘- F W w my“ mm, 1 m #7 5« 9x10 I ma W) 8.8 Mo“. 1m (was - 9; $6404 9"“ LIX lo a! we 113 M 6105 {0 l-OMO—H‘ 60; [fiber ’3‘“) a LANG-1 anidlis PH : L4.) -K\g.:ess P 1.8 Based on work in Assignment 1, compare the acidities of HAc and HMV. Defend. (Hint: Consider the color shown by HMV at pH 3.0 and the extent of ionization of both HMV and HAc at pH 3.0.) M, PH 9 3.0 HE; I: M '3 H1“ 0? 3.0 HMV WV Ms WWW appmipbly h MV'V ‘ .1. W1 (1,? HMV r143.” H30*rMV’ “‘9‘” 9" PH (5'0 6? HM V M5 VomrUvA > 5.07» HMV . 3 M k fig — H g P 1.9 Whichgglution, l x 1044 lSVIHCl or0.01 shdu be the gect‘tedr con uctbr n ‘ of electricity? Why? _ e‘1 7M IX‘O'VM 3am [Motlfm] M0, " ‘1 lo’q‘Ac— co in 0.01/«Hm, [[4303 ‘ ’ . lee, (a, it» Mk9] M HH» {Ml/a) Ir {mam /7.. 6V which Ms ’3 a W I‘. fan coWrmhb/x M 0. 51 44M hm nr coma» cl-or. P 1.10 Imagine that 5 mL of 1 M HAc is mixed with 5 mL of 0.01 M HAc. What color will be observed if this solution is treated with an indicator that is yellow at pH 2.5, green at pH 3.0. and blue at pH 3.5? Defend. Maw/13 W5 aura m 9 ’4 [M P 1.11 How do the results from your work in section 3 demonstrate that 0.5 M HAC is not an effective buffer whereas [HAC] = [Ac’] = 0.5 is an effective buffer? Why? 71"” {UM 1" M geek-(on 3 (LN; mr m ‘3 H 0, S M HAC 0142.5 “waxy, Mgr; mu), um , My; “g Hm W NQOH an, Am, [rt/Aw] :fl.§ We) a (MQKW—W cmé’fzfl" LL wian MM» my ckrop‘; a; $6 KHz/x Nolan} T L} a" film J~ tiger”. l—l9 P 1.12 Again consider your work in section 3 where a sample of 0.5 M HAc was treated with 0.5 M HCl and a second sample of 0.5 M HAO was treated with 0.5 M NaOH. Which of these samples will eventually become an effective buffer? Why? New-“0‘9 as ,5 M {H655 a Ohm-2194i My [,‘ML, WG-6 MM: 9’5” Mick m4?“ Natl)?k 950V” lob a lawHtrlerFeg 1720 ...
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This note was uploaded on 10/11/2010 for the course CHM 2046L taught by Professor Horvath during the Fall '08 term at University of Florida.

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Chem-Ex. 1 - 33“”‘5 Piikmsrah Section: (97 Date: 8...

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