An unknown amount of a compound with a molecular mass of 264.37 g/mol is dissolved in a 10 mL volumetric flask. A 1.00 mL aliquot of this solution is transferred to a 25 mL volumetric flask, and enough water is added to dilute to the mark. The absorbance of this diluted solution at 327 nm is 0.487 in a 1.000 cm cuvette. The molar absorptivity for this compound at 327 nm is ϵ 327 = 6503 M^(−1) cm^(−1).
(a) What is the concentration of the compound in the cuvette?
(b) What is the concentration of the compound in the 10-mL flask?
(c) How many milligrams of the compound were used to make the 10-mL solution?

a) 0.0019 M is the concentration of the compound in the 10-mL flask.

b) is the concentration of the compound in the cuvette.

c) 5.0 milligrams of the compound were used to make the 10-mL solution.

Explanation:

a)

Using Beer-Lambert's law :

Formula used :

where,

A = absorbance of solution = 0.487

C = concentration of solution = ?

l = length of the cell = 1.000 cm

= molar absorptivity of this solution =

is the concentration of the compound in the cuvette.

b) Concentration of solution in 25 mL of volumetric flask =

Volume of diluted solution =

Concentration of solution in 10 mL of volumetric flask =

Volume of solution taken before dilution =

0.0019 M is the concentration of the compound in the 10-mL flask.

c)

Concentration of solution in 10 mL of volumetric flask = 0.0019 M

Moles of unknown compound = n

Volume of the solution = 10 mL = 0.010 L

1 mL = 0.001 L

Molar mass of unknown compound = 264.37 g/mol

Mass of 0.00019 moles of unknown compound:

0.000019 mol × 264.37 g/mol = 0.0050 g

1 g = 1000 mg

0.050 g= 0.0050 × 1000 mg = 5.0 mg

5.0 milligrams of the compound were used to make the 10-mL solution.

definition

                    entropy is a measure of the randomness or the extent of disorder of a chemical process.

                      enthalpy is a measure of the heat change of a reaction occurring at a constant pressure.

measurement units:

                        entropy is measured in joule per kelvin (jk⁻¹)   whereas enthalpy is measured in joule per mole (jmol⁻¹)

requirements:

                            entropy has no requirements or limits, and its change is measured by the division between the heat change of the chemical process and the temperature.

                              in contrast, enthalpy can only be related to the heat change of the reaction under standard conditions.