Spectral Analysis of Aqueous Copper II

  • 1. Purpose - learn to use the spectrophotometer for determining concentration, calculate percent yield for a potassium hydroxide and copper II sulfate reaction, plot and understand optical absorbance and its relation to concentration
    Procedure
    Rebreif on procedure and safety information
    Put on safety equipment
    Obtain equipment (test tubes, rack, 2 10mL pipet, pipettor, tape, pen, transfer pipets, beaker)
    MEASURE THICKNESS OF CUVETTE (inner and outer) (record inner ________ outer _______)
    Dilute the 1M copper II sulfate (see table) and record dilutions
    Follow spectrophotometer measurement procedures below to measure each sample
    Part II
    Rebreif on procedure and safety information
    Put on safety equipment
    Obtain equipment (2 100mL beaker, 2 150mL beaker, 120mL 1M CuSO4, 2 10mL pipet, pipettor, test tubes, rack, 2 funnels, 3g KOH, filter paper)
    MEASURE THICKNESS OF CUVETTE (inner and outer) (record inner ________ outer _______)
    in 100mL beakers, about 0.5g and 1.8g KOH (record A:_________ and B:_____________)
    add 25mL water from buret (record A:_________ and B:_____________)
    add 25mL CuSO4 stock to beakers (record A:_________ and B:_____________)
    stir
    filter until clear
    10mL from each into cuvettes
    follow spectrophotometer procedure
    Dilutions 
    • 2.00 mL 1M CuSO4(aq) ________  2.00 mL H2O________      .500M ________           

2.00 mL 1M CuSO4(aq) ________  3.00 mL H2O________      .400M ________           

2.00 mL 1M CuSO4(aq) ________  4.00 mL H2O________      .333M ________           

2.00 mL 1M CuSO4(aq) ________  6.00 mL H2O________      .250M ________

    Data Tables 

    Sample              A                    B                    C                    D                    

Molarity                                                                                                

(Zero)                                                                                                  

Transmitted                                                                                             
Intensity                                                                                               

[absorbance]                                                                                            

[concentration]

    PART II 

    Sample                     A                           B                          

mass KOH                                                                          

water                                                                             

[concentration]                                                                   

copper sulfate                                                                    

[theoretical                                                                      
concentration]                                                                    

zero                                                                              

transmitted intensity                                                             

[absorbance]                                                                      

[concentration]

    2. KOH is basic and can be caustic. Use protective gear and make sure that neutralizing vinegar is available. CuSO4 could possibly be poisonous. Check safety references for more information on skin contact, vapors, disposal, reactivity, etc.

  • 3. Take sample and place in cuvette.
    Initialize spectrophotometer to 620 nm.
    TAKE DATA ON EMPTY CUVETTE FOR QUANTIFICATION OF ERROR
    Place calibrating water cuvette and zero the instrument
    Replace calibrating cuvette and place sample and measure
    Repeat procedure with different intensities for more data points
    Repeat procedure for other samples
  • 4. Taking multiple readings at several concentrations lowers overall error and allows us to determine what curve (exponential, polynomial, linear, elliptic, etc.) will best fit the data. It also allows us to interpolate concentrations rather than extrapolate.
  • 5. 2KOH(aq) + CuSO4(aq) K2SO4(aq) + Cu(OH)2(s)
    2K+(aq) + 2OH-(aq) + Cu2+(aq) + SO42-(aq) 2K+(aq) + SO42-(aq) + Cu(OH)2(s)
    2OH-(aq) + Cu2+(aq) Cu(OH)2(s)
  • 6. See sheet