Class notes
Chem 1405 Measurements Notes
- Course
- CHEM 1405
- Institution
- Lone Star College
This is a comprehensive and detailed note on; Measurements for Chem 1405. ***Essential Study Resource!!
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Module 1 Lab: MeasurementThe purpose of this lab is twofold:
To introduce you to your textbook and your CHEM 101 practice problems.
To introduce you to making measurements in the lab.
Directions
1) Read the Introduction on pages 1-4 which provides information from your textbook.
2) Then watch the seven-minute video which further explains how to make measurements.
https://youtu.be/-Ue-o_txQAw
3) Proceed to page 5 where you will find a data table for recording measurements. Use the
images shown on pages 6-10 for completing the data table. Submit page 5 for grading. (You
page 5 and submit the whole document.)
4) Watch a two-minute video comparing accuracy and precision.
https://youtu.be/TzLnO04uO30
5) You are now ready to complete your first CHEM 101 assignment on measurement.
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From Textbook; 2.1 Introduction to Measurements
Measurements provide the macroscopic information that is the basis for most of the hypotheses,
theories, and laws that describe the behavior of matter. Every measurement provides three kinds of
information:
1. the magnitude expressed as a number;
2. a standard of comparison included as units; and
3. a representation of the precision, or uncertainty.
The number included in a measurement indicates magnitude, but that number is meaningless without
a standard of comparison, the units. For instance, the distance between Washington DC and New
York City can be expressed as 230. The meaning of this number is not clear. Is it 230 kilometers? 230
blocks? 230 miles? In order to express the distance in a meaningful way, units must be included. The
distance between Washington DC and New York City is 230 miles.
1
, From Textbook; 2.5 Significant Figures: Measurements
When conducting an experiment, a scientist must determine how precise all the measurements are
by looking at what possible errors or sources of uncertainty exist. The amount of uncertainty depends
both upon the skill of the scientist and the quality of the measuring tool or instrument. While some
balances are capable of measuring masses only to the nearest 0.1 g, highly sensitive analytical
balances are capable of measuring to the nearest 0.001 g or better. Many measuring tools such as
rulers and graduated cylinders have small lines which need to be examined carefully when reading a
measurement. A scientific measurement consists of certain digits plus one uncertain or estimated
digit.
Consider the gray box in Figure 2.4. A ruler can be used to measure the length of the box. The box is
a little longer than 2 cm. Each small division on the ruler represents one-tenth of a centimeter, and the
edge of the box falls very close to the first line past 2 cm. This means that the length of the box is
around 2.1 cm. The ruler has a mark or gradation at the 2.1 cm point, so both digits are certain. The
actual measurement should also include one estimated digit. Because the edge of the box is exactly
at the 2.1 cm mark, the length is 2.10 cm. Look again at the gray box. Does it make sense to report
the length of box as simply 2 cm? What about 2.1000 cm? A measurement of 2 cm is approximate
does not convey the precision to which the measurement was made. A measurement of 2.1000 cm is
not possible with the detail on the given ruler.
The purple box in Figure 2.4 starts at the 3.0 cm mark and ends after the 3.8 cm mark. For the length
of the box, the estimated digit falls between 3.8 cm and 3.9 cm. This means that the purple box is
somewhere between 0.8 and 0.9 cm long. The edge of the purple box appears to fall half-way
between 0.8 and 0.9, so the correct measurement is 0.85 cm.
Figure 2.4 A ruler can be used to measure the length of the gray box and the purple box. The length of the
gray box can be measured to three significant figures and is 2.10 cm. The length of the purple box
can be measured to two significant figures and is 0.85 cm.
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