Precision Measurement Using UV/Vis Spectroscopy Lab Report

Experiment 2: Precision Measurement Using UV/Vis Spectroscopy Lab Report
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Abstract
This experiment examines the impact of varied dilution volumes and maximum dye absorbence
methods and then relates the findings to concept of precision in measurement. Out of the 3
method of measuring volume, statistical analysis of results obtained in this experiment shows
that bulb pipette is more precise that air-displacement pipette and measuring cylinder.
INTRODUCTION
Background theory
The quantity of solute per solvent solution forms the basis of most chemical solution preparaiton.
Chemical preparation of solutions thus requires accuracy and precision in measuring both the
volume and mass. In most cases, the analytical techniques require standard solution preparation.
The low concentration of hazardous substances (μg/L levels) complicates weighing of small
amount of chemicals in analytical balance. Often, majority of these chemicals are in the form of
crystals and granular where individual crystal has as low weight as milligram thus complicating
the measurement process thus complicating the possibility of getting desired weight in analytical
balance (Pedersen, Gammelgaard, & Halvorsen, 2019).
In these measurement, precision and accuracy are important. Precision is a term that is used to
describe a relationship between a series of measurement to indicate whether they give similar
results (Laksmiwati, Junaidi, & Hakim, 2017). A precise measurement may not necessarily
mean that the measurement is accurate. In reality, no single set of value can be considered
similar (Valcarcel, 2012). Analysts thus usually make reference to the experimentally values
with some uncertainty range
This experiment compares the reliability of air displacement pipette, bulb pipette and measuring
cylinder. The report reports precision in measurement in terms of standard deviation, range of
variance, 95 % confidence interval and relative standard deviation of the impact of various
dilution quantities and methods of maximum absorbance value of a dye and then relates the
obtained findings to the measurement precision.
Aims
 To use an air-displacement piston pipette

 To use analytical balance
 To calibrate glassware
 To provide a demonstration of measurement equipment precision.
 To statistically analyses data
METHODOLOGY
Part 1
The pipette was inspected to familiarize with its correct operation under the supervision of the
operator. The pipette scale was then set at 1.00Ml mark. A capped 20Ml liquid was then placed
in the scintillation vial onto the balance before taring the balance. The vial was then removed
from the balance and then the cap removed with the air displacement pipette, 1mL of water was
then dispensed and the cap via placed on the balance. The weight displayed on the digital display
was then recorded on the LNB. The balance was then tared. The above steps were then repeated
9 more times for the weight of the dispenser.
Part 2
This section of the experiment was carried individually. A stock solution containing methyl
orange in water was provided. For the solution preparation, the desired volume of the stock was
transferred using air displacement pipette or a bulb pipette and then diluted to specified volume
with deionized water.
For solution 1, using an air displacement pipette, 1000uL of the stock solution was take and
diluted to 10.0mL in a volumetric flask and absorbance measured at 473 nm on the UV/Vis
spectrometer. The solution was then discarded and 4 more identical solutions prepared using the
same pipette and volumetric flask and their absorbance measured.
For solution 2, 10mL of the stock solution was then taken using a bulb pippete and the volume
diluted in a 100.0mL volumetric flask before measuring the absorbance at 473 nm on the UV/Vis
spectrometer. 4 replicates were then prepared in different volumetric flask and their absorbance
measured.