Mid Term Question
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a) Vitamin C
b) Vitamin D
c) Vitamin A
The correct answer is 'b'.
Vitamin D is the vitamin that absorbs ultraviolet (UV) light. When our skin is exposed to UVB rays from sunlight, a precursor molecule in our skin, 7-dehydrocholesterol, is converted into vitamin D3 (cholecalciferol) through a photochemical reaction. This inactive form of vitamin D is then converted into its active form in the liver and kidneys, where it plays a crucial role in maintaining calcium and phosphorus levels in the body, supporting bone health, and aiding various physiological processes.
______________________________
a) 1934
b) 1940
c) 1970
The correct answer is 'b'.
The spectrophotometer was invented in 1940. It is an instrument used to measure the intensity of light absorbed by a substance at different wavelengths. It revolutionized scientific research and various fields, including chemistry, biochemistry, physics, and biology, by allowing precise analysis of the absorption spectra of substances. The invention of the spectrophotometer opened up new possibilities for studying the interaction of light with matter and paved the way for advancements in spectroscopy and related disciplines.
______________________________
a) Howard H. Cary
b) Arnold J. Beckman
c) None of these
The correct answer is 'b'.
The spectrophotometer was invented by Arnold J. Beckman. He was an American chemist, inventor, and philanthropist who developed the first commercial spectrophotometer, known as the Beckman DU, in 1940. His invention revolutionized scientific research and analysis, and spectrophotometers are now widely used in various fields to measure the intensity of light absorbed by substances at different wavelengths. Beckman's contributions to science and technology were significant, and he made numerous other inventions and founded the Beckman Instruments, Inc. company, which later became a major player in the scientific instrument industry.
______________________________
a) Ultracentrifugation
b) Beer’s law
c) Both
The correct answer is 'b'.
Beer's law, also known as the Beer-Lambert law, states that there is a linear relationship between the absorbance of light by a solution and the concentration of the solute in the solution. It is expressed as:
A = ε * c * l
Where:
A = Absorbance
ε = Molar absorptivity (also known as molar extinction coefficient), a constant for a particular substance at a specific wavelength
c = Concentration of the solute
l = Path length of the light through the solution
______________________________
a) I/Io = T
b) o/II = T
c) I/T = o
The correct answer is 'a'.
The Lambert-Beer law, also known as the Beer-Lambert law, is expressed as:
I/Io = T
where:
I = Intensity of light transmitted through the sample
Io = Intensity of the incident light (the initial light intensity before passing through the sample)
T = Transmittance, which is the ratio of the transmitted light intensity (I) to the incident light intensity (Io).
In other words, the Lambert-Beer law describes the relationship between the transmittance of light through a sample and the concentration of the absorbing solute in the sample. As the concentration of the solute increases, the transmittance decreases, and the amount of light absorbed by the sample increases. The law is essential for understanding the principles of spectrophotometry and quantifying the concentration of solutes in solutions based on their absorbance or transmittance of light at a specific wavelength.
______________________________
a) Concentration of sample
b) Light source
c) Path length
The correct answer is 'c'.
The path length refers to the distance that light travels through the sample in a spectrophotometer. It is an important parameter in spectrophotometric measurements because it affects the amount of light absorbed by the sample. As per the Beer-Lambert law, the absorbance (A) of a sample is directly proportional to the concentration (c) of the absorbing species and the path length (l) of the sample:
A = ε * c * l
where:
A = Absorbance
ε = Molar absorptivity (a constant for a particular substance at a specific wavelength)
c = Concentration of the absorbing species
l = Path length
By controlling the path length, scientists can ensure accurate and consistent measurements of absorbance, which allows for precise determination of the concentration of the sample's absorbing species in spectrophotometric analysis.
______________________________
a) Meters
b) Centimeters
c) Millimeters
Correct Answer:
The correct answer is 'b'.
In spectrophotometry, the path length represents the distance that light travels through the sample. It is typically measured in centimeters, as the light usually passes through a small volume of the sample in a cuvette or cell with standard path lengths ranging from 0.1 cm to 1.0 cm. Measuring the path length accurately is crucial for obtaining reliable absorbance measurements and calculating the concentration of absorbing species using the Beer-Lambert law.
______________________________
a) Log 10 I/Io = E lc
b) I/I o = T
c) 10 I/Io = log e lc
The correct answer is 'a'.
The Beer-Lambert Law is:
Log10(I/Io) = ε * c * l
where:
I = Intensity of light transmitted through the sample
Io = Intensity of the incident light (the initial light intensity before passing through the sample)
ε = Molar absorptivity (also known as molar extinction coefficient), a constant for a particular substance at a specific wavelength
c = Concentration of the solute
l = Path length of the light through the sample
The Beer-Lambert Law describes the linear relationship between the absorbance (A) of a sample and the concentration (c) of an absorbing species in the sample, as well as the path length (l) that light passes through the sample. It is a fundamental principle in spectrophotometry and is used to quantify the concentration of solutes in solutions based on their absorbance measurements at specific wavelengths.
______________________________
a) 2
b) 3
c) 4
The correct answer is 'a'.
There are 2 main types of spectrophotometry:
UV-Visible Spectrophotometry: This type of spectrophotometry measures the absorbance or transmittance of ultraviolet (UV) and visible light by a sample. It is widely used in various fields, including chemistry, biochemistry, environmental science, and pharmaceutical analysis, to quantify the concentration of substances in solutions based on their absorption of light at specific wavelengths.
Infrared Spectrophotometry (IR Spectroscopy): Infrared spectrophotometry measures the absorbance or transmittance of infrared light by a sample. It provides information about the molecular vibrations and functional groups present in the sample, making it valuable for structural analysis and identifying compounds.
These two types of spectrophotometry are commonly employed in scientific research, analysis, and various industries to gain insights into the properties and composition of different substances.
______________________________
a) 4
b) 9
c) 6
The correct answer is 'a'.
There are 4 types of electronic transitions that can be possible:
Singlet-Singlet Transition: This is a transition between two singlet electronic states, where the electron changes its spin from paired to unpaired or vice versa, but the total spin remains the same.
Singlet-Triplet Transition: This transition involves changing from a singlet state to a triplet state or vice versa. The electron's spin changes from paired to unpaired or vice versa, resulting in a change in the total spin.
Triplet-Triplet Transition: In this type of transition, the electron remains in a triplet state, but the spin configuration within the triplet state changes.
Forbidden Transition: These transitions are technically possible but occur at a much lower probability due to certain selection rules that restrict their occurrence.
These electronic transitions are important in spectroscopy and the study of electronic energy levels in atoms and molecules.
_____________________________
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