Chem-ex. 3 - Name: Section: Date: EXPERIMENT 1. Flame test...

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Unformatted text preview: Name: Section: Date: EXPERIMENT 1. Flame test for Ca“. As in Assignment 2, do flame tests on a dilute solution which contains Ca2+, a more concentrated solution which contains Ca”, and a pure salt of Ca2+. Report your results in the following table. Use CaC12(s) and CaCl2 solutions. Also do flame tests on CaCO3(s) and Ca§04(s). Then treat CaQQJs) and ca§04(s), respectively, with 1 M HCl and repeat the flame tests. (Note: The presence of anions such as C1’ are commonly necessary in flame tests to improve volatility of the ion being tested by flame analysis. Nevertheless, CaSO4(s) may not be sufficiently soluble in 1 M HCl to give a distinct Ca2+ flame test. So, note carefully your results for this investigation.) Substance Tested Color Time Q (In 2/ ' Dem limb “a M A CtiCO-g (as {Events v tell it”) are Germ is f ) Prepare a solution containing both K+ and Ca2+ in which [K+ ] and [Ca2+ ] are about equal. Similarly, prepare a solution containing both Na+ and Ca2+. Do a flame test on each. Q 3.1 Describe the preparation of eac ‘ solution. _ p _ , mus Mikaela. t NW“ WVNWMLKCJ$® q 6 PT) W\ L. ' Nata-ifl‘fi " i . , . Q 3.2 Describetéign I < testing?\l w about in the presence of Na+ ?\iiéomrnent based on your results. Do (and describe the results of) any further tests you think are necessary to r‘ d ' ' . s ~- a wet}; mm» ./ re me your ec1s1ons" A1 H 2? Qtufif § Veal-2 / «bl/\mfi Maggie [J /,,7/ KN a (1an {tag} as 0K 1' " ,\ ’ A series of investigations will now be performed in order to determine a reliable method of testing for Ca2+ by precipitation. Properties of Ca(0H)2 . Formation of Ca(0H)2. At 25°C, the pH of saturated Ca(OH)2 solution is about 12.60. Q 3.3 By calculation, estimate the molar solubility of Ca(OI—l)2 at 25“C. Show work and report y0ur answer to two S.F. MOM a... m9" 999 h F ,_ gin: oi :‘> fins—130M“leka MD “34 new: , y M , LscWaWQD—T tar tear 3.9%” Design an experiment to prepare Ca(OH)2. Q 3.4 Give solutions and amounts used for the Ca(OH)2 preparation. 51% Cute r w MW fimb Nab Q 3.5 Describe the Ca(OH)2 and comment on amount produced and apparent rate of formation. “9 ML/ C\m&~c\ VQWNL . i p 5: @5331 mix Safmrfix Um Q 3.6 If NH3 solution is mixed with 0.5 M CaClZ, should Ca(OH)2 form? Make a prediction based on the fact that the pH of 1 M NH3 is about 1 l .6. Give and defend . - has Pt: “'92 [fire 3; A»: \UN‘;S p Test your prediction to Q 3.6 by experiment. Q 3.7 Describe your experiment and results for the above. W9“? 3—14 —'“_'mm‘vmm'w “wan-— -m-—r- _' 1—- Q 3.8 Write the equation for the principal reaction which occurs when Ca(OH)2 solution is treated with /6 Wm (i) 1 M HCl. R706. my Qty“ ’9 Q “30 " 1 M NH Cl. \ ’ ‘ (u) 4 [outings Axum—2.. + Has wens Q 3.9 Regarding Q 3.8, do these reactions go to a small or large extent? Defend your answer. gem (@qu Wt .. u A, r I _ ’ OH I) 9%" v5» lost Q 3.10 Write sentences (Lot equations) to predict the result of treating Ca(OH)2(S) with (l) lMHCl. ‘ A I C ukUckvuh’tx ‘WUL €36le (ii) IMNH4C1. met-worm, Jew flew Km Test your predictions to Q 3.10 by experiments. Q 3.11 Describe experiments and results for the above. 10ml. Cmflljfl + 5 ML. HC\ : @rwmth Mukmlrefl \DML Qomth 3r Swat mam: (mm W mmme Pro erties of CaCO3. Formation of CaC03. At 25” C, the solubility of CaCO3 is about 1.4 x 10“ M. ’r—‘M___‘ “*--—_.._MIMH v, Use indicators to determine the pH (to one SF.) of saturated CECO3 so tion. w "H - ._...~, ,wr-v Q 3.12.. Give the indicators used, c lors and pH obtained for the above. ifflvwk b Misc—'1 biUJL ' Q 3.13 Write the equation for the reaction which acgts for the pH of CaCO3 solution. Q 3.14 Estimate [Ca2+] and [C032”] in saturated CaCO3 solution. (Note: Consider pH inJestirnating [CUE—l) E033: \J—i aw DCQng’B; 540/4; LOX'th‘i: AXEAS‘A Q 3.15 Which a ears to be the more sensitive test for Ca2+, recipitation as Ca(0H) or pp p 2 precipitation as CaCOfl Why? r459 5.25;,» weak: 5,9 we”? (Nb; is we: saint Design an experiment to prepare CaCO3. QA‘L‘J‘ *CU'QQ' '33 )0“? if W35" QMEM Q 1?:16 Give solutions an amounts use for the CaCO3 preparatio ml. 5M race sir—stew ML in Going. 15M Cam sigma A sates _\ v ’ a Q 3.17 Describe the CaC 3 and cm%%%%nount produced and apparent rate of formation. ‘ 3% N . _"6 ' k -“- a I «ult- L" r gs . \“xgmeM on WM‘W ‘ plsew‘ér MW e, #Cji WV) 1‘ . ‘h l A I P H I Rig“ 4/ HEB"? 3r H :32)? (if Ogfivigp‘qn . Q 3.18 Write the equation for he reaction‘i he above 6 per ent in which CaCO3 IS formed. \‘9‘5944 Cwsg’fammé Do experiments with various dilute solutions of Ca2+ to detennine the sensrtivity of testing for Ca2+ by precipitation as CaCO3 . Be sure to go as low as 0.0001 M Ca2+, and, if a precipitate does not immediately form in any of these tests, heat the test mixture almost to boiling and allow to stand and cool a few minutes. The development of turbidity means that a precipitate has formed. _ l I \ x we ’SM _m3(jb Q 3.19 Describe experiments andresults for the above. g\ M Chas: .Ol MQs-fgivfwlm . Wt- . A. 3% C991: fiXf'fi' hie—hatch .1 pi; one \ raw w some 3 \. 1. Prepare some fairly pure CaCO3 as follows: Mix 2 mL of 0.5 M CaCl2 with about 10 - 15 mL water in a small beaker. Add 3 mL of 0.5 M NaZCO3 and heat the mixture just to boiling. Filter while warm and wash the precipitate on the filter paper 2 or 3 times with water. Place small, approximately equal portions of the prepared CaCO3 in each of three small test tubes or in each of three hollows in the spot plate. (Note: Also save some of the CaCOZ for work in section 4., below.) By experiment, determine the effect exerted on CaCO3 by an excess of: l M HCl, 1 M HAc, and l M NH4C1, respectively. Q 3.20 (i) fiescribe results for the above with 1 M HCl. 1: ssh}? . ’7 iii-1"} .---. if » x n. at -|.- I '3". " ~- .V is; . - I” IV". Och-afar}: r-{;j:-- maxitfibla} Ki‘x ':\ t1 i: f .0 m. " »- a . ‘ 2’” ‘ t a t k, U J %i 1} (ii) Write the equation for the reaction. . -t ' rx. *“3 ' “"7 Mi» 3—17 $2.:- - "\ I. r Cs“: hr act; .1. p pct-ixcgcogst Q 3.21 0) Describe results for the above :with l M HAc. u gfio’bles mm a Ca CK}: (Emma. (ii) Write the equation for the reaction. § Wk; x CaCCg :3 Cf? 4' 3A7 flaws Q 3.22 (i) Describe results for the above with l M NH4C1. (If no reaction appeared to occur in this experiment, check the atmosphere over the test mixture for NH. Note results.) «~- . I A f N. y“ 3 \3 Vialbfit testis-1W1 ENC owe ' “ as. mac-fps» go .a .l’aty’i \x‘ Q {,3 (ii) Write the equation for the reaction?w . -- .V p a, )"K in; i"! i Cage... a as we‘ve .- Hews tub Mud"; '3 “ Place a few mL of saturated Ca(OH)2 solution in a medium test tube. Use a straw (available at stock window) and gently blow (DON'T INHALE!) your breath through the solution for a minute or two. Q 3.23 Describe your results for the above. kit’s Ky, flab» ‘ It). E36 :1 p Vi é Vi, ‘l’ Q 3.24 Given that your exhaled breath contains C02(g), write the equation for the reaction which has occurred in this experiment. Qatari}; tea; «a Properties of C032— and HOCO; (HCOs‘). Both C0327 and HCO; react with H3O+ to form C02. Treat different concentrations of COf—containin g and HCOJ—containing solutions with acid to try to determine a detection limit for CO2 formation. That is, try to determine the smallest [C0327] and smallest [HCO3_ ] for which acidification produces observable gas liberation. Also note any differences in the vigor of CO2 liberation by the solutions tested. Q 3.25 Describe experiments and resultsfor the above. t 9"}, “‘1‘-'-\‘§ 3:. n. .-= h M a 't -. , a. * 4/ aye twat? «A (g may ‘ "“ ‘Ul “ “4%) x xx»- 3 A ' ' -- ; in g; Wage} I. ‘ j r“ " a ewuvm(\3\ a In. \ if“- a a r' f. A ! “PP-v : J. "r ’1 ”e- this?“ :" W“: vat "I; s LU} yam: a mi 11% s I“ - — i- . ' J .3 (Lg; immig- wvj‘k 348 Q 3.26 Write the equation for each different gas—producing reaction which you just Performed (t my + (Amer as COM éfiafi ‘ -r v-y I) r” m. f- IV ‘ -" ‘- Log’r’ +23 Mao‘s fiv- l 3919,63 Distinction between (3032’ and HCO; rests mainly on the difference between their B/L basicities. Use indicators to determine the pH (one SF.) of the laboratory solutions of these ions. Q 3.27 Gi e solutions and indicators used, colors, and pH's obtained for the above. mgr-wit Elk/{Q CD)?“ Aluiavia Klé‘lalw ~—~ from? PH: 3 . ,fi‘flq“.vw'(" a), _I / {'4} 4mm em W2 “1 WM yawn-save w T.?Hagm _ Q 3.28 Write the equation for the reaction which accounts for the pH of each of the following. Remember to inventory! (i) NazCO3 solution. wg A; raga): 4, H _.. (ii) NaHC03 solution. Mix H69 k (Ago “(1+ aria-bf) JrCDa f 0 Ext, (iii) “(NH4)2CO3 ” solution. (Hint: What is the strongest B/L base present in high conciiptratlon In t s so w." C) as; pHLlAr _} CH / ion?) Q 3.29 Based on your work, how would you test for and distinguish between C0327 and HCO; ? Omit no pertinent detail. a «m w )M an,» loot bum. @fes’t pa; 3% too ‘W’t Cof’i’s 37in , u {fibuan m tic-US“ t3 ’Pfé’flfl‘l’ Q 3.30 Devise and perform an experiment to see if Ca2+ reacts with a dilute solution of NaHC03. Give an account of both experiment and result. (Remember that semisoluble M(HC03)2(S) salts can not be formed because the lattice stability of the corresponding MC03(sLs_alts is mucégreater.) ; M Calf/‘0 i f") Mall Osgwel) PP)“ cam/25 @5 W show}; “‘7 OK 3—19 Properties of C3804 - ZHZO. Formation of C3804 - 2H20. CaSO4 - ZHZO, known as gypsum, contains two moles of water per mole of CaSO4 in its crystal lattice. Such a compound is a "hydrate," and gypsum is also called calcium sulfate dihydrate. By careful heating, gypsum can be converted to CaSO4 - VzHZO, or calcium sulfate hemihydrate, which is commonly known as "plaster of paris." Treatment with water reconverts plaster of paris to gypsum which is the familiar, hard, white material contained in casts, molds, and wallboard. Place 2 mL of 0.5 M CaCl2 in a smali test tube and add 10 drops of 3 M HZSO4 (or 1.5 mL of 1 M H2804). If a precipitate does not immediately form, warm the solution cautiously but do not boil. Allow the mixture to stand. After precipitation appears to be complete, centrifuge the mixture (balance the centrifuge!) to pack the precipitate into the bottom of the test tube. The precipitate is CaSO4 - ZHZO. Carefully pour off and discard the supernatant liquid, leaving the precipitate in the tube. Add 1 — 2 mL of water to the precipitate, stir and recentrifuge. Again pour off and discard the supernatant liquid. Add about 3 mL of water to the precipitate, stir thoroughly for about one minute, and repeat centrifugation. This time pour off and save the supernatant liquid. Also save the precipitate. Q 3.31 Describe the CaSO4 - ZHZO and comment on amount produced and apparent rate of formation. Was it obvious that some time was required to maximize the amount of CaSO4 - ZHZO formed in this experiment? I ‘itfi/ Q 3.32 By visual examination alone, would you feel confident in distinguishing between CaSO4 - ZHZO and CaCO3 ? How about between CaSO4 - 2H20 and Ca(OH)2 ? Tell why or why not. file, oil We tildes Q 3.33 Give the [inventories for the principal ions in 0.5 M CaCl9 and 3 M H2804. “its! 1’ in -‘--*”\*~< ' Q 3.34 Write the equation for the reaction in this experiment in which CaSO4 - 21-120 is f f P ‘ \5 . ‘ a“ “mug-sea we? a was ‘* w 3—20 Q 3.35 How does the solubility of CaSO4 - ZHQO in acidic solution compare to its solubility in water? Defend based on the equation written in Q 3.34. ink) {KC/{lo Test your answer to Q 3.35 by experiment. Q 3.36 Describe experiments and results for the above. M0 4 Raga Lajos Qfifbct “ HQO 4’ H50 In each of four small test tubes (or vials) place 10 drops of the supernatant liquid from the CaSO4 0 2H2O preparation. Add 2 - 3 drops of 6 M NH3 to each and treat respectively, by dropwise addition, with: 0.5 M CaClz; 0.5 M (NH 40280 A; 0.25 M Ba(N03)2 ; and l M "(NH4)2CO3". Add two drops of each solution and observe. If no reaction occurs, add four extra drops of the indicated solution to the appropriate tube. Reobserve. Q 3.37 Indicate t 6 tubes in which a reaction occurred and write the equation for each. 5M (was? waemae * (has) ‘3 .0095 ‘ 95M 'qu ya gt Eng" «50.45" +2 EEO 3M (Wu); v-s Wt CW5» C059” 4‘» Q 3.38 What conclusions may now be drawn regarding the relative solubilities of CaSO4 - QHQO vsmnd CaSO4 - ZHZO vs. CaCO3 in dilute NH3 solution? Defend based on results of the above experiments. (Note that your defense must consider Species concentration.) “A .00 PP’T (DM_ {JO lam WT“ ., - estfioaiewwf a ism (as (NMaCEOW Cum“ C639“ A cacofi Q 3.39 Predict eépsult of treat’ g some CaCO3 with an excess of 3 M H2804. hawk ‘ W \\\ dimmer 4: CL W W will M Test your prediction to Q 3.39 by experiment. Q 3.40 (i) Describe your experiment and results for the above. bang «a. me bib‘idl'fi 3356.5 (ii) Write the equation for the main reaction which occurred. ‘ 3:- H‘TbOI/qu/igpi --%CQ 5614 viw ‘*‘ J‘ 09$ Treat the solid produced by the above experiment with l M HCl. Q 3.41 What evidence has just been obtained to support the conclusion that the solid produced above was CaSO4 - ZHZO rather than CaCOS? Explain as necessary. raw-7w More on the Formation of CaSO4 o ZHZQ. On occasion, students miss Ca2+ in a solution of an unknown because they test for Ca2+ by addition of SO 42' and decide that Ca2+ is absent if immediate formation of CaSO4 - ZHZO does not occur. To avert this error, try the following experiment. Prepare a solution containting Ca2+ at a concentration of 0.1 M and treat 10 drops of this solution with 10 drops of 0.5 M NaZSO4. Stir thoroughly and observe. Q 3.42 Note the time required for CaSO4 - 2H2O to begin to form. Also note the time required for precipitation to be essentially complete. Then repeat this experiment by heating the (Zak/S04; mixture as soon as it is prepared. Compare results with the heated mixture to the original room-temperature mixture. om ,, . OK 3—22 Name: Section: Date: PROBLEMS FOR ASSIGNMENT 3 P 3.1 Consider the preparation of a mixture which contains both M2+ and H0“ at fairly low concentration (less than 1 M). From a thermodynamic standpoint, which mixture: (i) [ix/12+] = 0.1 and [H0] = 0.01; or, (ii) [ix/12+ ] = 0.01 and [H07 = 0.1; gives the better chance to form a precipitate of M(OH)2? Why? . r {:CflM’) wrlélk)‘ mflm-je CF “Leno: 10:5 volume QC 003% lone myth 3M3 gamed W P 3.2 What evidence has been obtained in Assignment 3 which shows that the B/L basicity of an anion does not necessarily relate to its precipitate—forming t ndencies? . came-e Efi base ea no; ‘ >8)? 3* Jamming £9 (CH > (e abate-i kbb 5o} P 3.3 Based on work in Assignment 3, explain the outcome of sti ' g some CaSO4 - 2H20 in excess lgga CO3 for a long time. COK‘fi: ($3)? 444307;)? Glad; “\- r I . w 3 . (:9 we Keenan/to 3 f M Q MO)? : ate; a 6 d :7 fix 103 P 3.4 Based on work in Assignment3,whatis th most siensitive methodof testing forCaz+by precipitation from solution if (i) the solution is neutral or basic? Why? Wt (16 CO ’japCé @6333 i3 L233 cobble.- «lion +Cm®bbfi (ii) the solution is fairly acidic? Why? a y 0'3 0000179 L30 fined/e “Ti/n5 34kg CAL) ‘W‘&® x“ cm mm) m to meet/6 M my ‘Eftoiw comes core no CO!3 s. Gama _ P 3.5 Based on work in Assignment 3, tell how to convert pure Ca(OH)2 into pure CaSO4 - ZHZO with a minimum of Ca2+ loss. Provide sufficient detail so that a competent high school student could do this job by following/your instructions. ‘b‘itwot (W1 Cato“); w excess is @509 Celt. @LLQWQ) ‘bvl flt’fmim} WP‘Gt/‘(lwwe ACQM‘DQ/lebl of imam Quito * P 3.6 AS for P 3.5, tell how to convert pure CaSO4 - ZHZO into pure Ca(OH)2. (Note: this is more challenging than the P 3.5 case. r > n t 33330 " W M06055 «v gowftmug {g (M mumva @093 69L. @OLfi" EQMTlflété/Wflq NAM ‘M‘al‘figar View/v6 NJ L‘h PM 3m Us bow 40 C98 KW" mm W (4% H2 N\Mo@i’\‘~ P 3.7 Based on work in Assignment 3, tell how to incorporate C032", HCOJ, and Ca2+ into the scheme of analysis which you developed at the end of Assignment 2. Note that for Ca“, both a "test for" an a "se aration" must be considered. , get C%?KAC@§’ {gem w/ Hybotremace «<9 mewvg oémmvw of ®W3/.WW5 Q%..J¥¥\ 0? saw a? Efltntwhk 6WLg Lit/L 0% tea. WM“; M we at “Wmfliflfik WT“ fifty/5%! VG?» 56476205580 4*. Wu/L bg wwjmeffit) , fl 6 to age/awféf’z’w" 56w“ “flag; M K I CD3 LXU-(rg‘, WW5 [U/ and mam/lab; T a??? ‘d “m (’65 i */ $292di mm QC» :5 w 3724 ...
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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. 3 - Name: Section: Date: EXPERIMENT 1. Flame test...

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