Chapter 18 - Fundamentals of Spectrophotometry 20 To measure calcium in a breakfast cereal, 0.6590 grams of crushed cereal were reacted for 1 hour in warm 1 M HNO3. The reaction mixture was filtered and the filtrate transferred to a 100 mL volumetric flask. A series of eight standards are prepared by transferring 5.00 mL aliquots to 50-mL volumetric flasks to which increasing volumes of standard Ca2+ (containing 20.0 μg/mL) is added, diluting to the final volume with distilled deionized H2O. The samples were then analyzed by flame atomic absorption. Use the data and graph below to find the percent by mass calcium in the cereal. Ca2+ Stnd Absorb. (mL) 0 0.151 1.00 0.185 3.00 0.247 5.00 0.300 8.00 0.388 10.00 0.445 15.00 0.572 20.00 0.723 Absorbance Vs mg/mL Ca²+ 0.8 0.7 y=0.0705x+0.1579 0.6 0.5 Absorbance 0.4 0.3 0.2 0.1 -4.00 -2.00 -0.10.00 2.00 4.00 Concentration Ca2+ (mg/mL) 6.00 8.00 10.00 Answer: 0.340% Ca by mass Intermediate Solve the trendline equation for the x-intercept, then take the absolute value to get the concentration of the unknown as diluted when preparing the 50 mL standard solutions. Back dilute to the original solution, multiply by 100 mL, and convert mass calcium to grams and solve for the percentage. Chapter 18 - Fundamentals of Spectrophotometry 19. help Ni emits light at 345.85 nm and 346.17 nm in an atomic emission spectrophotometer. Can the spectrophotometer's monochromator successfully resolve 345.85 nm from 346.17 nm? The grating has a length of 5.0 cm in length and there are 5500 grooves per cm. Assume first- order diffraction. = 6 Answer: The required resolution to differentiate between the Ni emission lines is 345.85 nm/0.32 27448.4. The nm 1080.8. The resolution of the monochromator is calculated by first determining Aλ, 345.85 nm/A 1(27500 grooves) Aλ = 0.0126 nm. Resolution is 345.85 nm/0.0126 nm = actual resolution of the monochromator is 25.40 times greater than needed. Hard =