1. A sample weighing 1.30 mg was analyzed to determine the concentration of a certain compound (FW =292.16 g/mol) using UV/Visible spectrometry. First, the sample was dissolved in 5.00 mL volumetric flask. A 1.00 mL aliquot was drawn up, placed in a 10.0 mL volumetric flask and diluted to the mark with DI water. The absorbance of this solution was measured at 530 nm and it gave an absorbance of 0.427 in a 1.00 cm cuvette. According to the Beer’s law, the molar absorptivity at 514 nm for this compound is 6130 Lmol-1cm-1. Find the concentration of this compound in the 5.00 mL volumetric flask. Calculate the mass percent of this compound in the sample.

Question

1. A sample weighing 1.30 mg was analyzed to determine the concentration of a certain compound (FW =292.16 g/mol) using UV/Visible spectrometry. First, the sample was dissolved in 5.00 mL volumetric flask. A 1.00 mL aliquot was drawn up, placed in a 10.0 mL volumetric flask and diluted to the mark with DI water. The absorbance of this solution was measured at 530 nm and it gave an absorbance of 0.427 in a 1.00 cm cuvette. According to the Beer’s law, the molar absorptivity at 514 nm for this compound is 6130 Lmol-1cm-1. Find the concentration of this compound in the 5.00 mL volumetric flask. Calculate the mass percent of this compound in the sample.

I really don't know how to do it, please help!!

Answer 1

A = ebc

0.427 = 6130*1*c
c in the 10 mL flask = ? M. c in c in 5.00 mL flask = 10x that = ?
mols 5.00 flask = M x L
g 5.00 flask = mols x molar mass = ?
mass% in sample = (g in 5.00 flask/mass sample)*100 =?
mass% =

Answer 2

To calculate the concentration of the compound in the 5.00 mL volumetric flask, we need to follow these steps:

Step 1: Calculate the molar concentration of the aliquot solution.
To do this, we need to use the Beer-Lambert Law, which relates the concentration of a substance in a solution to its absorbance. The equation is given by:

A = ε * c * d

Where:
A = Absorbance
ε = Molar absorptivity (given as 6130 Lmol-1cm-1)
c = Concentration of the compound (unknown)
d = Path length (1.00 cm in this case)

Rearranging the equation, we have:

c = A / (ε * d)

Using the given values, plug them into the equation:

c = 0.427 / (6130 Lmol-1cm-1 * 1.00 cm)

c ≈ 6.961 × 10^(-5) mol/L

Step 2: Convert the molar concentration to moles.
To convert the molar concentration to moles, we need to multiply it by the volume of the aliquot taken (1.00 mL) and divide by 1000 to convert from mL to L:

moles = (6.961 × 10^(-5) mol/L) * (1.00 mL / 1000 mL/L)

moles ≈ 6.961 × 10^(-8) mol

Step 3: Convert moles to grams.
To convert moles to grams, we need to use the molar mass of the compound (292.16 g/mol):

grams = (6.961 × 10^(-8) mol) * (292.16 g/mol)

grams ≈ 2.03 × 10^(-5) g

Therefore, the concentration of the compound in the 5.00 mL volumetric flask is approximately 6.961 × 10^(-5) mol/L, and the mass of the compound in the sample is approximately 2.03 × 10^(-5) g.

To calculate the mass percent of the compound in the sample, we need to divide the mass of the compound by the mass of the sample and multiply by 100:

mass percent = (2.03 × 10^(-5) g / 1.30 mg) * 100

Note that 1.30 mg is equivalent to 1.30 × 10^(-3) g.

mass percent ≈ 1.56%

Therefore, the mass percent of the compound in the sample is approximately 1.56%.