Instrumental Analytical Chemistry Exam 2 Study Guide
questions with verified answers
??? Ans✓✓✓ Infrared absorption requires that a vibrational mode of
the molecule have a change in dipole moment or charge distribution
associated with it.
Abscissa Scales for NMR Ans✓✓✓ - It is impossible to determine the
definite value of a magnetic field's strength with accuracy
- It is possible to measure the magnitude of a change in the field
strength
- Using internal standard is advantageous b/c analyte can be measured
during experiment
Anharmonic Oscillation Ans✓✓✓
Chapter 18 Ans✓✓✓
Chemical shift & spin-spin splitting Ans✓✓✓ - Important for structural
analysis
- Both are easily distinguished because the peak separation resulting
from a chemical shift are directly proportional to the field strength or to
the oscillator frequency.
,Collision Product Peaks Ans✓✓✓ - Collisions between ionic molecules
make higher molecular weight ions
Collisional Deactivation Ans✓✓✓ - Atoms hit one another and loose
energy (external conversion) leading to non radiative relaxation.
Describe what happens after incident radiation is absorbed Ans✓✓✓ -
Following absorption, a number of vibrational levels of excited state are
populated.
- Molecules in these higher vibrational levels then relax to the lowest
vibrational level of the excited state (vibrational relaxation). From the
lowest vibrational level, several processes can cause the molecule to
relax to its ground state.
Detection of ion Ans✓✓✓ - As each separate population of ions passes
through detector, spectrometer needs to qualify & quantify them
Different Types of Mass Spec Ans✓✓✓
Double Focusing Mass Spec Ans✓✓✓ Resolution of mass is important
to consider for mass spec
Resolution definition R = M/∆M
where M is mass of particle observed
, ∆M is difference between M & the next highest particle that can be
observed
- Double focusing instruments are used to obtain higher resolution.
- Uses a magnetic analyzer & electrostatic analyzer (ions of same mass
are separated according to different energies)
- Cost us double focus is less ions passing through detector so decrease
sensitivity
Electrospray Ionization Ans✓✓✓ - Mostly used for analyzing
biomolecules with molecular weight 10^6 & more Da
- Needle has several 1000V above
- End up with fine droplets that have charges on them
- Needle pass through desolvating capillary
- Droplet shrinks --> charge density increases, desorption of ions into
gas occurs
Energy Levels in a Magnetic Field Ans✓✓✓ When a nucleus with a spin
quantum number of 1/2 is brought into an external magnetic field B_0,
its magnetic moment becomes oriented in one of two directions with
respect to the field depending upon its magnetic quantum state
Environmental Effects on NMR Spectra Ans✓✓✓ - The frequency by
which resonance frequency radiation is absorbed by a nucleus is
strongly affected by its chemical environment
questions with verified answers
??? Ans✓✓✓ Infrared absorption requires that a vibrational mode of
the molecule have a change in dipole moment or charge distribution
associated with it.
Abscissa Scales for NMR Ans✓✓✓ - It is impossible to determine the
definite value of a magnetic field's strength with accuracy
- It is possible to measure the magnitude of a change in the field
strength
- Using internal standard is advantageous b/c analyte can be measured
during experiment
Anharmonic Oscillation Ans✓✓✓
Chapter 18 Ans✓✓✓
Chemical shift & spin-spin splitting Ans✓✓✓ - Important for structural
analysis
- Both are easily distinguished because the peak separation resulting
from a chemical shift are directly proportional to the field strength or to
the oscillator frequency.
,Collision Product Peaks Ans✓✓✓ - Collisions between ionic molecules
make higher molecular weight ions
Collisional Deactivation Ans✓✓✓ - Atoms hit one another and loose
energy (external conversion) leading to non radiative relaxation.
Describe what happens after incident radiation is absorbed Ans✓✓✓ -
Following absorption, a number of vibrational levels of excited state are
populated.
- Molecules in these higher vibrational levels then relax to the lowest
vibrational level of the excited state (vibrational relaxation). From the
lowest vibrational level, several processes can cause the molecule to
relax to its ground state.
Detection of ion Ans✓✓✓ - As each separate population of ions passes
through detector, spectrometer needs to qualify & quantify them
Different Types of Mass Spec Ans✓✓✓
Double Focusing Mass Spec Ans✓✓✓ Resolution of mass is important
to consider for mass spec
Resolution definition R = M/∆M
where M is mass of particle observed
, ∆M is difference between M & the next highest particle that can be
observed
- Double focusing instruments are used to obtain higher resolution.
- Uses a magnetic analyzer & electrostatic analyzer (ions of same mass
are separated according to different energies)
- Cost us double focus is less ions passing through detector so decrease
sensitivity
Electrospray Ionization Ans✓✓✓ - Mostly used for analyzing
biomolecules with molecular weight 10^6 & more Da
- Needle has several 1000V above
- End up with fine droplets that have charges on them
- Needle pass through desolvating capillary
- Droplet shrinks --> charge density increases, desorption of ions into
gas occurs
Energy Levels in a Magnetic Field Ans✓✓✓ When a nucleus with a spin
quantum number of 1/2 is brought into an external magnetic field B_0,
its magnetic moment becomes oriented in one of two directions with
respect to the field depending upon its magnetic quantum state
Environmental Effects on NMR Spectra Ans✓✓✓ - The frequency by
which resonance frequency radiation is absorbed by a nucleus is
strongly affected by its chemical environment
