CHEM 106S Midterm 1

T/F: CHEM 106S encourages collaboration among students. Students work in groups of three or four and are expected to work together, share data, and discuss their experimental progress. Students may also consult with their SGS supervisor or the course instructor for additional suggestions

True

T/F: Cell phones and other mobile devices may be used freely while we are working in the wet laboratory at SGS Clovis

False

In chromatography, which term refers to the phase that remains in place inside the column?

Stationary Phase

What does the retention time, tr, represent on a chromatogram?

The time from sample injection until a component reaches the detector

Which statements about chromatographic separation are correct?

A) The widest possible peaks are desirable because they increase column efficiency.

B) A chromatogram plots detector response as a function of elution time.

C) Broader chromatographic peaks generally reduce separation quality.

D) Greater separation between peak retention times generally improves separation.

B) A chromatogram plots detector response as a function of elution time.

C) Broader chromatographic peaks generally reduce separation quality.

D) Greater separation between peak retention times generally improves separation.

Choose all that apply. Which statements about theoretical plates and column efficiency are correct?

A) Plate height, H, and plate number, N, are related to column length, L.

B) Increasing plate height always increases column efficiency.

C) A larger number of theoretical plates, N, generally indicates a more efficient

column.

D) Theoretical plates represent hypothetical equilibrium zones between stationary

and mobile phases.

A) Plate height, H, and plate number, N, are related to column length, L.

C) A larger number of theoretical plates, N, generally indicates a more efficient column.
D) Theoretical plates represent hypothetical equilibrium zones between stationary and mobile phases.

Which statement best describes the base peak in a mass spectrum?

C) The most abundant ion peak, assigned 100% relative abundance

Which ionization method is a hard source that often produces extensive fragmentation?

C) Electron ionization (EI)

Choose all that apply. Which statements about electrospray ionization (ESI) are correct?

A) ESI requires the analyte to be vaporized before ionization.

B) ESI can be coupled with HPLC or capillary electrophoresis.

C) ESI begins with a sample in solution.

D) ESI can produce multiply charged analyte ions.

B) ESI can be coupled with HPLC or capillary electrophoresis.

C) ESI begins with a sample in solution.

Choose all that apply. Which statements correctly describe mass spectrometer components?

A) Most MS components operate at atmospheric pressure to increase ion collisions.

B) The transducer converts the ion signal into an electrical signal.

C) The mass analyzer separates ions according to m/z.

D) The ion source converts neutral molecules into gas-phase ions.

B) The transducer converts the ion signal into an electrical signal.
C) The mass analyzer separates ions according to m/z.
D) The ion source converts neutral molecules into gas-phase ions.

Please list the four major experiment rotations that CHEM 106S students will complete during the semester.

GC, Metals, Wet lab, and PFAS

Which textbook chapter(s) does this experiment apply?

Chapter 26, Introduction to chromatographic separations, Chapter 27: Gas Chromatography

explain why the experiment is a practical application of those chapter(s).

Chapter 26 provides the theoretical framework for how pesticide molecules physically partition and separate between phases in a column, while Chapter 27 covers the specific instrumentation

What methods are used to provide feedback to students in this course?

Graded homework, lab reports, lab quizzes, and three midterm exams will offer timely and regular feedback. Also, students are always welcome to ask questions for additional feedback.

What does the concept of "theoretical plates" really represent, and why do we still use this traditional model to describe continuous, modern chromatographic columns?

Theoretical plates are hypothetical equilibrium zones where solutes partition between stationary and mobile phases. Although an idealized historical model, they remain useful for describing column efficiency: more theoretical plates indicate better separation.

Why can hard ionization be useful for structural identification, while soft ionization is often better for determining molecular mass?

Hard ionization, such as EI, produces extensive fragmentation that provides useful structural information. Soft ionization produces less fragmentation, making the molecular-ion-related peak easier to identify for molecular mass determination

GC calculation problems

N=16(tr/w)²

Nav=1/2 (N1+N2)

H=L/Nav

Analying a mass spec

C8H10

Base peak: 91

2 additional peaks: 65, 77

fragment ion with base peak: C7H7+

fragment ion with 77 peak: C6H5+

fragment ion with 65: C5H5+