Question

Dilution is a process in which the concentration of a solution is lowered by adding more solvent. Some of the reasons dilutions are performed are to minimize measurement errors when preparing a series of solutions at different concentrations, to save time and laboratory space, and to make more accurate measurements on an analytical balance when the target concentration is very low. The new concentration of a diluted solution can be determined from the following equation, sometimes called the dilution equation,

M1V1 = M2V2

where M1 is the concentration of the initial solution, V1 is the volume of the initial solution, M2 is the concentration of the final solution, and V2 is the volume of the final solution. The terms M1 and M2 are often expressed in molarity, M, which is equal to mol/L. Another way to write the equation is to replace subscripts of 1 and 2 with abbreviated notations representing concentrated and diluted, as follows:

MconcVconc = MdilVdil

Based on the inverse nature of this equivalency, small volumes of concentrated solutions can be used to prepare large volumes of diluted solutions with a known concentration, which is advantageous in areas involving solution chemistry.

The absorbance of a cationic iron(II) sample solution was measured in a spectrophotometer, but the instrument returned an error because the absorbance was too high. The sample was then diluted by using a pipette to take 100.0 μL of the sample and injecting it into a cuvette already containing 2.00 mL of water (total volume is 2.00 mL + 100.0 μL). The absorbance value of the diluted solution corresponded to a concentration of 8.76×10⁻⁶  M . What was the concentration of the original solution?

Express the concentration to three significant figures with the appropriate units.

Answer 1

MIVI = Mava AmL = 10-12 G ML 2 10 3 mL Mi (100x106L) = 8.768100Mx 2.1x10 L) M = 8.76 * 28 M x 2.181034 TA 100 x Loty IM = 1.8396x10-4 M M Mconc. = 0.000184