Question

What is the concentration (in g/L) of FeCl3 in a 25 mL sample that has an absorbance of 0.325 at a wavelength of 535 nm, assuming an extinction coefficient of 976 L/mol/cm?

Answer 1

To find the concentration of FeCl3 in the sample, we can use the Beer-Lambert Law:A =  * c * lwhere A is the absorbance,  is the molar absorptivity  extinction coefficient  in L/mol/cm, c is the concentration in mol/L, and l is the path length in cm. In this case, we are given:A = 0.325 = 976 L/mol/cml = 1 cm  assuming a standard cuvette We can rearrange the equation to solve for the concentration:c = A /   * l Now, we can plug in the given values:c = 0.325 /  976 L/mol/cm * 1 cm c = 0.325 / 976 L/molc = 0.000333 mol/LNow, we need to convert the concentration from mol/L to g/L. To do this, we need the molar mass of FeCl3:FeCl3 = 1 *  55.845 g/mol  + 3 *  35.453 g/mol  = 162.204 g/molNow, we can convert the concentration:0.000333 mol/L * 162.204 g/mol = 0.054 g/LFinally, we need to find the concentration in the 25 mL sample:0.054 g/L * 0.025 L = 0.00135 gSo, the concentration of FeCl3 in the 25 mL sample is approximately 0.00135 g or 1.35 mg.