Name Period Date 6. Colorimetric Analysis * Driving Question H ow can you deter mine t h e con centrationof a colorf u l sol u t i on ? Pre-Lab Activity Setting the stage for the activityWhenl i gh t interact s w i t h l i gh t-absorbin g p articl es, som e of t he l i gh t i s r emoved . C on sequ entl y, obj ect s w i t h m an y l i gh t - a b sorbi n g p a rt i cl es a p p ea r d a rker th a n ob j ects wit h f ew er l i gh t-a b sorbi n g p arti cl es. T h e a b i l i t y t o a b sorb col or , as w el l as w h a t col or is t o b e a bsorbe d , d epen d s ont h e type of p arti cl e p resent. O ne can vary the n u m ber of pa rt i cl es w i t h w h i c h l i gh t interact s i n t w o w ays. I f you com pa re t w o sol u ti on s of t h e same col ored su bst an ce w it h di ff erent c on centr ati on s, you see t h at t h e on e w i t h t h e h i gh er c on centr ati on ap pea rs d arke r becau se it h a s m ore ab sorbi n g p arti cl es an d i t ab sorbs m ore of t h e i n ci d ent l i gh t . A l so, i f you p ou r t h e same solut i oninto a tes t tu be a n d a 1 00- mL bea ker , t h e sol u t ion i n t h e bea ker ap pea rs da rker. Even t h ou gh t h e con cen t rat ion i n t h e tw o sol u tions is th e sa m e, the l i gh t h as to travel a l on ger p ath int h e b ea k er. T h eref ore, p h ot on s h ave a h i gh er prob ab i l it y of bei ng ab sorbed so l ess l i gh t w i l l l eave t h e b eak er an d t h e sol u t ionap p ea rs da r ke r . N ext, if you p ou r a litt l e b i t of t h e 1 M cop p er(II) su l f ate solut i oninto a 1 -L be ak er n ea rl y f u l l wit h w ater , w h y i s t h e ori gi n al b ea ke r so m u ch d a r ke r? I t i s da rker be cau se t h e "l i gh t catc h i n g" pa rt i cl es in t h e more d i l u t ed sol ution are m uc h f art h er apart. F rom t h i s w e see t h at c on centr ation i s anot h er vari ab l e to consi der w h en l ook i n g a t ab sor bed l i g h t. T o measu re t h e a m ou n t of l i gh t absorbed, w e u se a col ori m et er . L i ke al l el ectronic m easu ri n g dev ices, t h e col ori met er prod u ces a vol t ag e ba sed on t h e a m ou n t of l i gh t t h at h i t s it. T h e vol ta ge i s c on vert ed to an ab sorban ce l ev el i n op ti ca l d en si ty u n i ts ( o. d .). Example calculation to tryI n an exp eri men t, f ou r calibratin g sol u t i on s are u sed t o d et erm ine the concent rat ionof a C u S O 4sol ut i on w i t h u n kn ow nconcent rat ion. G iven t he fol l ow in g d ata, create a cal i brat i on grap h , fi ndt h e eq u ati on , an d u se th e equ ati on t o sol ve f or t h e con cen t rat ion of t h e u n k n ow n sol u tion. * This is an AP Chemis try course recommended experiment.
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7/21/2019 AC 16 Colorimetric Analysis for Lab Notebook
3. Con!igure the data collection system to manually collect absorbance o! orange "#$ nm% light and the
concentration in a table. To do this scroll down and click on &'ser entered numeral data(. )or measurementtype in &concentration( and !or unit name type in &molarity(.
4. ext click on both absorbance orange and concentration. Then click on the table button and
ok. +n the bottom by the clock, click on it and change to manual.
5. Calibrate the colorimeter with the blank solution "use distilled water !or the blank%. To do this rinse a
cuvette with a small amount o! &blank( solution - empty. ext !ill the cuvette. ipe clean and dry and place itinto the colorimeter. Press the green button and the light will go on. /eave in until the light goes o!!.
6. ater absorbs a small amount o! light.
7. /abel !our clean, dry test tubes &( through &0( and place them into a test tube rack.
8. Pipet 1.$, 0.$, #.$, and 2.$ m/ o! the $.0$ 3 copper"44% sul!ate solution into test tubes through 0,
respectively.
9. 5eliver 2.$, #.$, 0.$, and 1.$ m/ o! distilled water into test tubes through 0 so that each test tube has
$.$ m/ o! solution.10. Thoroughly mix each solution with a stirring rod.
Note: Clean and dry t&e stirrin rod beore stirrin a dierent solution.
Table : olumes and concentrations or t&e calibration solutions
Trial # 0.40 M CuSO4 (mL) HO (mL) Concentration (M)
Colorimeter
"i&t -ti&t co'er
Calibration button
5*tension cable (o$tional)
1 3 4
) t o c 0
6 n 0 n o % n
7/21/2019 AC 16 Colorimetric Analysis for Lab Notebook
""# Start a new, manually sampled data set. Click on and then the arrow button. Click on theconcentration trials and enter the concentrations above !or the !irst 6 test tubes.
12. 3easure the absorbance o! the !ive known solutions !ollowing the steps below.
a. 7inse the cuvette twice with a small portion o! the !irst solution and then !ill the cuvette two8thirds !ull.
ipe the cuvette clean and dry and place it into the colorimeter.
b. &Turn on( the colorimeter by clicking the &on( button. A!ter the reading stabili9es, record a data
point by clicking on the green button again.
c. 5ispose o! the solution appropriately and rinse the cell thoroughly with water.
d. :ach time you place a new cuvette in, wait !or it to stabili9e and again click to record. hen you haverecorded all o! your data, stop the data set by clicking on;
Note: T&e data or test tube 2 is not yet recorded because it &as an unno%n molarity and it %ill not be $art o t&e
standardi7ation cur'e.
13. Save your experiment. To do this click on and then save as<.
=
Data Analysis
1. Create a data table to record the concentration an absorbance o! the 6 solutions. Also include a place torecord the unknown "to be done later in the lab%
2. To graph your data start a new page by clicking on . Select the absorbance orange and
concentration again, but now click on the graph button and ok.
3. Ad>ust the scale o! the graph to show all data, i! needed.
7/21/2019 AC 16 Colorimetric Analysis for Lab Notebook