2: INSTRUMENTAL MEASUREMENTS
- Page ID
- 506120
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)The purpose of this experiment is to:
- Record measurements of length, mass, volume, and temperature.
- Measure the mass and volume of an unknown rectangular solid.
- Demonstrate proficiency in using the following instruments: metric rulers, balances, graduated cylinders, and thermometers.
INTRODUCTION
Chemistry, a fundamental branch of science, is an experimental science. It is a qualitative science based on measurements that depends on careful observations of experiments, yielding accurate and precise results through the use of good laboratory techniques and instruments or devices.
In the chemistry laboratory, you must precisely measure length, mass, volume, and temperature for various experiments. To reinforce your understanding of common laboratory concepts and techniques and to gain knowledge in data gathering, this laboratory will explore and master fundamental operations using standard instruments and devices, thereby enhancing your success.
Measurements consist of two parts: a numerical part and a unit (sometimes called a dimension).
Example:
Please make it a habit to always include the unit with each number you use.
Measurements made are not always accurate. The size of the discrepancy depends on several factors, including the skill of the person performing the measurement and the instrument or device used. The margin of error for each measurement is the uncertainty associated with that measurement. The instrument itself limits how close one can come to a perfect measurement.
The measurements need to be precise and accurate. Exact measurements are those that consistently give close results. Accurate results are those that are close to the actual value. Precise and accurate measurements require instruments that are properly calibrated and functioning correctly. Additionally, the person performing the measurement must be familiar with using the instrument and follow the procedure carefully. By taking repeated measurements, one can estimate the instrument's and the operator's precision.
Measurement of Length
Length measurements in chemistry laboratories are typically made with rulers in metric units. The rulers (Figure 1) are marked with standard distances in centimeters at the top and in inches at the bottom, and the intervals on the ruler are called hash marks.
Measure the length of the yellow rectangle using a ruler
Solution
In measurements, all recorded figures are significant, including the estimated digit. On Ruler, the yellow rectangle appears to be 12.6 cm long. You can estimate one digit between the scale markings and measure 12.60 cm.
Measurement of Mass
Another common and essential operation in the chemical laboratory is determining the mass of given objects or samples. For that purpose, a suitable balance must be used. In the lab, you will primarily use the milligram or analytical balances in the balance room. The analytical balances weigh the nearest 0.001 gram, and all the digits should be recorded for the exact mass.
Figure 2. Milligram balance
Analytical balances are expensive and delicate, so care should be taken when using them. Always tare the balance, i.e., zero it before measuring the mass. Ensure the object you are measuring is always at room temperature, neither cold nor hot, to obtain an accurate mass measurement.
Many of the experimental procedures in this course require accurate quantitative values. In such instances, an analytical balance will be employed in weight determinations.
Measurement of Volume
Graduated cylinders, pipettes, or burets are commonly used to measure volume. Volume in the laboratory is generally expressed in milliliters (mL) or cubic centimeters (cm3)
Measure the volume of water in the graduated cylinder in Figure 3.
Figure 3: To measure the volume of liquid in this graduated cylinder.
Solution
The graduated cylinder with water above shows that the bottom of the meniscus lies between the 21 and 22 markings, indicating that the liquid volume is undoubtedly more than 21 mL but less than 22 mL. The meniscus appears closer to the 22-mL mark than the 21-mL mark, so a reasonable estimate of the liquid’s volume would be 21.6 mL. In the number 21.6, the digits 2 and 1 are specific, but the 6 is an estimate.dd example text here.
Calculate the volume of a regular rectangular solid whose length, width, and height are measured to be 12.00 cm, 4.00 cm, and 5.00 cm, respectively.
Solution
Volume of a rectangular solid is = L x W x h = 12.00 cm x 4.00 cm x 5.00 cm = 240.00 cm3
Measurement of Temperature
In chemistry laboratories, temperature measurement is performed using thermometers that contain colored liquid or are digital, typically in degrees Celsius. Other temperature scales that may be used are Fahrenheit and Kelvin.
Formulas for converting one temperature scale to another:
K = C + 273.15
°C = 
°F = (°C * 1.8) + 32.
Figure 4: A Comparison of Fahrenheit (°F), Celsius(°C), and Kelvin (K) Temperature Scales showing the difference between the freezing point of water and the boiling point of water.
A student measures the temperature of boiling water to 99.50 °C. What would boiling water temperature be in degrees Fahrenheit (°C) and Kelvin?
Solution
°F = (°C * 1.8) + 32 = (99.50 °C x 1.8) + 32 = 211.1 °F
K = C + 273.15 = 99.50 °C + 273.15 = 372.75 K = 372.8 K