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CHM 2045- Midterm Exam Guide - Comprehensive Notes for the exam ( 12 pages long!)


Department
Chemistry
Course Code
CHM 2045
Professor
George Jeffrey Gower
Study Guide
Midterm

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UF
CHM 2045
MIDTERM EXAM
STUDY GUIDE

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A) Measurement
Volume measurement : meniscus readings:
“Known” Meniscus Readings:
In accord with the 10% rule, read the meniscus levels of the liquids in the graduated
cylinders and buret that are on display and labeled as “known”. Note that meniscus-
reading ability can be improved by marking a short, dark straight line on a small piece of
plain paper (or index card) and holding the paper behind the meniscus so that the line is
slightly (about 0.5 cm) below the meniscus. This makes the meniscus easier to see.
Beware of parallax error and multiple meniscus images. Read the lowest apparent
meniscus observable.
Compare your meniscus readings to the given meniscus readings. If you agree with the
“knowns” you probably know how to read meniscus levels correctly and may proceed to
the next. If, however, you do not agree with the “known” readings, ask your instructor for
assistance before continuing.
“Unknown” Meniscus Readings:
Read the meniscus levels in the graduated cylinders and buret labeled as “unknown”.
Complete the following table in your lab-notebook. Be sure to apply the 10% rule and to
include correct units on each entry.
Graduated Cylinders Buret
Total
calibrated
volume _______________ _______________
_______________
Smallest
calibrated
volume _______________ _______________
_______________
Uncertainty _______________ _______________
_______________
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Meniscus
level _______________ _______________
_______________
Estimation of the “Drop Volume” of 1 mL Water.
Add water using a dropping pipette to a 10-mL graduated cylinder until the meniscus
level coincides with the 1-mL calibration mark.
Now, count drops added, and add more water dropwise as the meniscus level rises and
becomes coincident with the 2-mL mark. Record this drop count below as the “number
of drops in 1 mL.”
At the 2-mL mark, start a new dropcount and continue to add water dropwise counting
the number of drops required to raise the meniscus from the 2-mL mark to the 4-mL
mark. Record this drop count below as the “number of drops in 2 mL.” Record in your
Lab-notebook the following:
Number of drops in 1 mL: _______ Number of drops in 2 mL: _______
Now, based on drop-count data, calculate the average number of drops per mL of
water. Calculate to the nearest 0.1 drop. Knowing the number of “drops per mL” is
valuable experimental information. This allows dispensing mL-quantities of aqueous
(water-solvent) solutions by counting drops rather than by measuring small,
inconvenient volumes. It is important to know that drop-size varies as a function of
dropper bore size and nature of solvent. Therefore, your “drops per mL” determination is
reliable in using your dropper with aqueous solutions.
Mass Measurement. Volumetric Measurement by Buret and Pipette. Mass and
Volume Measurement Related.
Mass of Flasks.
Label two clean and dry 125-mL (or 250-mL) erlenmeyer (conical) flasks (Figure 6).
.
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