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could you please help me writing the intro and conclusion for MEASUREMENTS LABEx: what are we going to do and what did we learn
MEASUREMENTS LAB INFO
Objectives:
The student will become familiar with some key pieces of glassware and instrumentation.
The student will learn to record measurements correctly, assess the precision of a piece of
glassware or instrument, and identify possible errors that can occur.
Background: (BBM section on Significant Figures)
The quality of experimental data is affected by the number of digits that can be reported for
a piece of equipment, the number of measurements, and the experimenter. When reading a
measurement, the investigator should report all digits that can be read with certainty plus one
additional digit that is the estimated or uncertain digit. The digits of a measurement are called
significant figures.
Precision refers to the reproducibility of measurements. The closer the measurements are
to one another, the greater the precision. Increased precision can be observed in measurements
obtained from instruments that can be read to a greater number decimal places with certainty.
Accuracy refers to how close a measurement is to the real value. The accuracy of the
measurement reflects the quality of the instrument. An instrument that can be read with more
digits of certainty typically yields a more accurate value assuming that the instrument has been
calibrated. See Signficant Figures section for a figure comparing the accuracy and precision of
measurements.
Errors occur during the collection of data. Errors are of two types: systematic and random.
Systematic errors are caused by a defect in the analytical method, by an improperly functioning
instrument, or by the analyst. Systematic errors cause a decrease in the accuracy of a set of
measurements. Systematic errors can be corrected by calibration of instrumentation, alteration of
the procedure, use of glassware and instruments that can be read to a greater number of significant
figures, and by attentiveness of the analyst. Random errors cause a reduction in the precision of a
series of measurements. Random errors are uncontrollable errors such as electrical fluctuations
experienced by balances.
A single measurement is insufficient to determine the accuracy and precision of an
instrument. It is therefore common practice to make three or more measurements for a material.
The precision of a series of measurements is indicated using the mean of the results ± the error.
(Example: A student measured the mass of a tennis ball three times on a lab balance that read to the
first decimal place. They recorded the mass as 54.4 g, 54.7 g, and 54.1g. To indicate the quality of
their readings, they reported the mass as 54.4 ± 0.3 g.) The accuracy of a series of measurements
can only be assessed if the true value is known. By using a calibrated instrument and making
several measurements the probability increases that the mean of the measurements and the true
value will be the same.
Procedure:
Measuring Lengths with the Rulers (printed on the next page)
1. On your data sheet, indicate the number of decimal places that a measurement made with
Ruler 1 should contain.
2. Record the length of the wooden block on your data sheet. Include units.
3. Repeat steps 1 and 2 for Ruler 2 and Ruler 3.
4. Report your data to the instructor.
5. Once all measurements have been obtained the class results will be posted. Record the
class results and determine the mean and error for each ruler.
Measuring Liquid Volumes using a Buret and Graduated Cylinder
1. On your data sheet, indicate the number of decimal places that should be recorded for the
buret and the number of decimal places that should be recorded for a 10-mL graduated
cylinder.
2. Fill the buret close to the 0 mL mark with tap water.
3. Record the initial water level of the buret under Trial 1. Include units.
4. Dispense exactly 5 mL of tap water from the buret into a 10-mL graduated cylinder.
5. Record the new volume of the buret under Trial 1. Include units.
6. Record the volume of the water in the graduated cylinder under Trial 1. Include units.
7. Empty and dry the graduated cylinder.
8. Repeat steps 3-7 for Trial 2 and Trial 3 beginning with the current volume in the buret.
9. Determine the mean and error for each piece of glassware.
Measuring Masses with Balances
1. On your data sheet indicate the number of decimal places that should be recorded for the
balance.
2. Tare the balance
3. Place a rubber stopper on the balance and record the mass as mass 1, balance 1. Include
units.
4. Remove the object. Let the balance come to zero and tare balance again.
5. Replace the stopper on the same balance and record the mass as mass 2, balance 1. Include
units.
6. Remove the object. Let the balance come to zero and tare balance for a third time.
7. Replace the stopper on the same balance and record the mass as mass 3, balance 1. Include
units.
8. Repeat steps 2-7 two more times using two other balances but the same rubber stopper.
The second balance used should be balance 2, and the third balance used should be balance
3.
Data and Results
Measuring Lengths with Rulers
# of decimal places listed for first ruler
________ reading 1st ruler
________
# of decimal places listed for second ruler
________ reading 2nd ruler
________
# of decimal places listed for third ruler
________ reading 3rd ruler
________
Class Results
Ruler 1
Ruler 2
Ruler 3
____________
____________
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Mean
Measurement
Difference between
Mean Measurement
and Lowest
Measurement
Difference between
Mean Measurement
and Highest
Measurement
Mean ± Error
Ruler 1
________
________
________
_________________
Ruler 2
________
________
________
_________________
Ruler 3
________
________
________
_________________
Measuring Liquid Volumes using a Buret and Graduated Cylinder
# of decimals that should be listed for a reading from a buret ________
# of decimals that should be listed for a reading from 10-mL graduated cylinder
________
Trial 1
Trial 2
Trial 3
Initial Buret Reading
__________
__________
__________
Final Buret Reading
__________
__________
__________
Volume of Water Dispensed by Buret
__________
__________
__________
Volume of Water in Graduated Cylinder
__________
__________
__________
Mean ± error of water dispensed by Buret
_____________________
Mean ± error of water in Graduated Cylinder _____________________
Measuring Masses with Balances
# of decimal places that should be listed for a reading from the laboratory balance
________
Balance 1
Balance 2
Balance 3
Mass 1
____________
____________
____________
Mass 2
____________
____________
____________
Mass 3
____________
____________
____________
Mean
Measurement
Difference between
Mean Measurement
and Lowest
Measurement
Difference between
Mean Measurement
and Highest
Measurement
Mean ± Error
Balance 1
________
________
________
_________________
Balance 2
________
________
________
_________________
Balance 3
________
________
________
_________________
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