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3. A solution with a concentration of [tex]0.25 \, \text{M}[/tex] is measured to yield an absorbance of [tex]0.65[/tex]. Another solution of the same chemical is measured under the same conditions and yields an absorbance of [tex]0.45[/tex]. What is its concentration? (Hint: Use Beer's Law.)

4. Give an example of a molecule other than quinine that fluoresces.

Sagot :

GinnyAnswer
Certainly! Let's tackle each part of your question step-by-step.

Part 3: Finding the Concentration of the Unknown Solution Using Beer's Law

Beer's Law is a very important principle in chemistry, which states that the absorbance (A) of a solution is directly proportional to the concentration (c) of the solution, given that the path length (l) and molar absorptivity (ε) are constant. The formula is given by:

[tex]\[ A = \varepsilon \cdot l \cdot c \][/tex]

Where:
- [tex]\( A \)[/tex] is the absorbance,
- [tex]\( \varepsilon \)[/tex] is the molar absorptivity,
- [tex]\( l \)[/tex] is the path length,
- [tex]\( c \)[/tex] is the concentration.

Since the solutions are measured under the same conditions, [tex]\(\varepsilon\)[/tex] and [tex]\(l\)[/tex] are constant and can be cancelled out when comparing two solutions.

Given:
- Concentration of known solution ([tex]\( c_1 \)[/tex]) = 0.25 M,
- Absorbance of known solution ([tex]\( A_1 \)[/tex]) = 0.65,
- Absorbance of unknown solution ([tex]\( A_2 \)[/tex]) = 0.45.

We want to find the concentration of the unknown solution ([tex]\( c_2 \)[/tex]).

By the relationship of Beer's Law for two solutions:
[tex]\[ \frac{A_1}{A_2} = \frac{c_1}{c_2} \][/tex]
Rearranging to solve for [tex]\( c_2 \)[/tex]:
[tex]\[ c_2 = c_1 \cdot \frac{A_2}{A_1} \][/tex]

Substituting the known values:
[tex]\[ c_2 = 0.25 \, \text{M} \cdot \frac{0.45}{0.65} \][/tex]
[tex]\[ c_2 \approx 0.17307692307692307 \, \text{M} \][/tex]

So, the concentration of the unknown solution is approximately 0.173 M.

Part 4: Example of a Fluorescent Molecule

An example of a molecule that fluoresces is Fluorescein.

Fluorescein is a widely used fluorescent tracer in many applications, including microscopy, forensics, and medical diagnostics. It is popular for its strong fluorescence and can be excited with different wavelengths, making it a versatile tool in fluorescence-based studies.

So, to summarize:

1. The concentration of the unknown solution is approximately 0.173 M.
2. Fluorescein is a good example of a fluorescent molecule.
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