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PHS2103 > UV spectroscopy > Flashcards

UV spectroscopy Flashcards

1
Q

What is a chromophore?

A

A covalently unsaturated group responsible for electronic absorption.

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2
Q

What is an auxochrome?

A

A saturated group with nonbonded electrons.

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3
Q

What happens when an auxochrome is attached to a chromophore?

A

It can increase the wavelength and the intensity of absorption of the UV rays.

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4
Q

What is a bathochromic shift?

A

When the maximum absorption gets shifted to a longer wavelength.

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5
Q

What is a hypsochromic shift?

A

When the maximum absorption gets shifted to a shorter wavelength.

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6
Q

What is the hyperchromic effect?

A

An increase in absorption intensity.

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7
Q

What is the hypochromic effect?

A

A decrease in absorption intensity.

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8
Q

How do you calculate wavenumber?

A

wavenumber = 1/wavelength

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9
Q

How do you calculate velocity?

A

velocity = frequency x wavelength

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10
Q

How do you calculate absorbance?

A

absorbance = lg ( incident light / transmitted light)
OR
absorbance = lg (1/ transmittance)

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11
Q

What is molar absorptivity?

A

The absorbance at a particular wavelength of a 1 mol/l solution in a 1cm cell.

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12
Q

What is the equation for Beer - Lambert law?

A

Absorbance = molar absorptivity x path length x concentration of solute in mol/l

OR

Absorbance = specific absorbance x path length x concentration of solute in g/100ml

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13
Q

What is path length?

A

The distance the light travels through the sample.

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14
Q

What is specific absorbance?

A

The absorbance of a 1g/100ml solution in a 1cm cell

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15
Q

What is the relationship between absorbance and concentration according to the Beer-Lambert law?

A

They have a linear relationship

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16
Q

How does conjugation affect the wavelength of maximum absorption?

A

More conjugation = greater wavelength

17
Q

What is lambda max?

A

The wavelength at which a substance has its strongest photon absorption

18
Q

What does the reference cell contain?

A

Pure solvent (so it doesn’t absorb a significant amount of light in the interested range)

19
Q

What is the relationship between wavelength, frequency and energy?

A

Higher wavelength = lower frequency = lower energy

20
Q

What is a homoannular and heteroannular diene?

A

Homoannular: both double bonds present in the same ring
Heteroannular: the double bonds are present in 2 different rings

21
Q

What is one property of the chemicals present in sunscreens?

A

They are highly conjugated so they can absorb UV, preventing it from getting into the skin

PHS2103 (4 decks)

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