Part A. absorbance of a cationic iron(II) sample solution was measured in a spec

Question

Part A. 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 ?L of the sample and injecting it into a cuvette already containing 2.00 mL of water (total volume is 2.00 mL + 100.0 ?L). The absorbance value of the diluted solution corresponded to a concentration of 6.28×10?6  M . What was the concentration of the original solution? express the concentration to three significant figures with the appropriate units.

Part B. Molar Mass = Mass solute (in g)Moles solute

In order to prepare a certain volume of solution with a desired concentration, you would need to determine the required mass of solute. What mass of CaI2 would you need to prepare a 100. mL solution at a concentration of 0.420  M ? Express the mass in grams to three significant figures.

Part c.

Potassium cyanide is a toxic substance, and the median lethal dose depends on the mass of the person or animal that ingests it. The median lethal dose of KCN for a person weighing 145 lb (65.8 kg ) is 7.27×10?3 mol .

What volume of a 0.0820 M  KCN solution contains 7.27×10?3 mol of KCN?

Express the volume to three significant figures and include the appropriate units.

Explanation / Answer

part A )

total volume = 100 x 10^-6 x 10^3 mL + 2 mL

= 0.1 mL + 2 mL

= 2.1 mL

M1 V1 = M2 V2

M1 x 0.1 = 6.28×10?6 x 2.1

M1 = 1.32 x 10^-4 M

the concentration of the original solution = 1.32 x 10^-4 M

part B)

moles = 0.420 x 0.1 = 0.0420

mass = moles x molar mass

= 0.0420 x 293.9

= 12.3 g

mass of CaI2 = 12.3 g

part C)

molarity = moles / volume

0.0820 = 7.27 x 10^-3 / volume

volume = 0.0887 L

volume = 88.7 mL

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