1: LAB 1 - TAKING MEASUREMENTS IN THE CHEMISTRY LAB
- Page ID
- 505932
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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
• Become proficient in taking length, mass, volume, and temperature measurements.
• Experimentally determine the density of water.
• Calculate the density of various rectangular blocks and possibly identify the block based on its density.
INTRODUCTION
Welcome to the chemistry lab! This lab may be your first experience working in a lab setting for many of you. As you will learn in this class and other chemistry courses (should you need to take them in the future), many of the experiments you conduct will require you to record data of a measurement. Measurements are important not only in science courses but also in everyday life activities. For example, when cooking in the kitchen, you may be asked to measure certain ingredients. In this experiment, you will learn to take measurements associated with length, mass, volume, and temperature, four of the most common properties dealt with in the chemistry lab.
Length
Length measurements are often taken using a centimeter ruler. When we use a centimeter ruler that is subdivided into tenths of centimeters (like the ones we will be using in the lab), we always write our measurements to the hundredth place (two digits past the decimal point). For example, consider the object shown below in Figure 1:
Consider the red block shown below in Figure 1 and record its length.
Solution
Because it fits halfway between 2.3 and 2.4, we can record its length as 2.35 cm.
Note: If the measurement were exactly 2.3, we would record the length as 2.30 cm; if it landed on 2 cm, we would write that as 2.00 cm.
In all your experiments, a milligram balance (which measures to three decimal places) will be used for all mass measurements. When recording mass from a milligram balance, we write the exact number displayed on the balance. For example, if the mass of an object is given as 157.223 g, we write 157.223 g in the data table. Your instructor will demonstrate how to operate and zero the balance in more detail.
Volume
To determine a liquid's volume, we will use a graduated cylinder. The volume is read at the bottom of the curved line, called the meniscus, and recorded to one digit past the decimal point.
Consider the image below and measure the volume of liquid in the graduated cylinders.
Solution
The volume of liquid in the graduated cylinder on the left in Figure 2 below would read 36.5 mL. The volume of liquid in the rightmost graduated cylinder would be 40.0 mL.
In this experiment, we will also measure the volume of a rectangular solid using a centimeter ruler. Once we have measured the object’s length, width, and height, we can calculate its volume using the following formula:
Volume = (length) x (width) x (height)
Consider a rectangular object with dimensions of 6.50 cm in length, 3.00 cm in width, and 2.25 cm in height. Calculate the volume of the rectangular object.
- Answer
-
The volume would be recorded as
Volume = (6.50 cm) x (3.00 cm) x (2.25 cm) = 43.9 cm
(Note: In this class, we will always round the volume measurements of a rectangular block to three digits. These measurements will be further explained in future chemistry classes.)
Temperature
A thermometer is read to one digit past the decimal point, like a graduated cylinder. We will be using Celsius thermometers to measure temperature during our experiments. For example, if an object’s temperature is 11 °C, we would record the value as 11.0 ºC.
Density
Another property that we will explore in this lab is density. Density is defined as the amount of material in a given volume of substance and can be expressed as follows:
\[Density=\frac{mass}{volume}\]
Each substance has a unique density at a certain temperature. For example, the density of water at room temperature is 1.0 g/mL, regardless of the amount of water present. This density characteristic can be used to infer the identity of an unknown substance. However, other tests would also need to be performed to confirm the presence of a substance.
In this experiment, you will be asked to determine the density of water and various rectangular blocks experimentally. Based on the calculated densities of the rectangular blocks, you will then identify the blocks (if possible) based on a table of known densities. Consider the following examples:
9.0 mL of water was shown to have a mass of 9.010 g. Using this information, determine the density of water.
Solution
\[Density=\frac{Mass}{Volume} =\frac{9.010\ g}{9.0\ mL}=\ 1.0\ g/mL\]
(Note: We use g/mL as the units for the density of a liquid. In this lab, we will be rounding all density of liquid values to two digits, which will be explained in future chemistry courses.)
A small rectangular block with dimensions of 3.00 cm in length, 2.00 cm in width, and 1.00 cm in height was found to have a mass of 67.805 g. Using the information provided and the table of densities on the next page, calculate the density of the block and identify it (if possible, using Table 1).
Solution
First, we can calculate the volume of the block as follows:
Volume = (3.00 cm) x (2.00 cm) x (1.00 cm) = 6.00 cm3
Next, the density can be calculated:
\[Density=\frac{Mass}{Volume} =\frac{67.805\ g}{6.00\ cm^3}=\ 1.0\ g/cm^3\]
Referring to Table 1, we can identify the solid as lead because it has the same density value as lead.
(Note: We use g/ cm3 as the units for the density of a solid. In this lab, we will be rounding all density of solid values to 3 digits, which will be explained in future chemistry classes.)
Table 1: Densities of Known Solids
Substance |
Density |
|---|---|
|
Aluminum |
2.7 g/cm3 |
|
Bronze |
8.7 g/cm3 |
|
Gold |
19.3 g/cm3 |
|
Iron |
7.9 g/cm3 |
|
Lead |
11.3 g/cm3 |
|
Silver |
10.5 g/cm3 |
|
Steel |
8.0 g/cm3 |
|
Tin |
7.3 g/cm3 |
1) Always wear chemical splash goggles when working on this experiment.
2) Take caution while measuring the temperature of boiling water, as the beaker and equipment will be hot.
3) Clean up your work area when you are finished with the experiment and return all equipment and glassware to their designated places.
| Equipment | Equipment | Equipment | Chemicals |
|---|---|---|---|
| Centimeter ruler | Glass stirring rod. | Celsius thermometer | Tap water |
| Watch glass | 125.0 mL Erlenmeyer flask | Various rectangular blocks | A pail of ice (provided by the instructor) |
| Evaporating dish | 100.0 mL graduated cylinder | Test tube rack | Beaker of boiling water (provided by the instructor) |
| Large or medium test tube | 10.0 mL graduated cylinder | Milligram balance |
* Images of equipment needed in this lab can be found in the appendix (the equipment may be subject to changes, so follow your instructor’s directions).
EXPERIMENTAL PROCEDURE
Part A: Taking Measurements of Length, Mass, Volume, and Temperature.
1) Using a centimeter ruler, determine the following:
- The diameter of a watch glass
- The length of a large or medium test tube
- The length of a glass stirring rod
Record your measurements of the two digits past the decimal point.
2) Using a milligram balance, determine the mass of the following objects: watch glass, 125.0 mL Erlenmeyer flask, evaporating dish, and 10.0 mL graduated cylinder. Record your values in the data table. Record all the numbers shown on the milligram balance.
3) Fill a 100.0 mL graduated cylinder to the 100.0 mL mark. Record this as the initial volume in the data table. Pour water from the graduated cylinder to fill a large or medium test tube. Record the new volume in the graduated cylinder. Pour the water from the test tube into the sink and repeat the procedure twice. Record all measurements to one decimal place.
4) Using a Celsius thermometer, measure the following:
- Room temperature (hold the thermometer in the air and wait for the temperature to stabilize)
- Temperature of ice (place the thermometer in the pail of ice provided by the instructor)
- Temperature of boiling water (place the thermometer in the beaker of boiling water supplied by the instructor)
Record all measurements to one decimal place.
Part B: Density of Water
1) Determine the mass of an empty 10.0 mL graduated cylinder.
2) Add 1.0 mL to 9.0 mL of water to the graduated cylinder and record the correct volume.
3) Record the combined mass of the water and graduated cylinder.
4) Subtract the mass of the empty graduated cylinder from the combined mass of the water and cylinder to obtain the mass of water.
5) Using the mass of water and the volume of water (from step 2), calculate the density of water and record your answer in two digits.
6) Repeat steps 1-4 two more times, using a different amount of water each time.
7) Calculate the average density of water by adding up the three density values and dividing the sum by three.
Part C: Density of Various Rectangular Blocks
1) Obtain three different rectangular blocks and record either the color and the Unknown letter or the Unknown number for the unknown rectangular metal block whose density you will find.
2) Using a milligram balance, determine the mass of each rectangular block.
3) Using a centimeter ruler, determine each rectangular block's length, width, height, and volume.
4) Calculate the density of each rectangular block.
5) Using Table 1, provide a possible identity for each rectangular block. If an identity cannot be determined, enter 'N/A' in the data table.
PRE-LAB QUESTIONS
Name: ____________________________________
1) 15.5 mL of an unknown liquid had a mass of 12.050 g. Calculate the density of the unknown liquid.
2) A small rectangular block was shown to have the following dimensions: 2.85 cm by 1.75 cm by 3.50 cm. If the mass of the block was 127.432 g, calculate the density. Use the densities of known solids table above to infer the identity of the unknown block (if possible).
3) Click on the link below (or copy and paste it into your browser) to access a virtual simulation regarding density. https://phet.colorado.edu/sims/html/density/latest/density_all.html [phet.colorado.edu]
From here, click on mystery, and go through the following procedure using only set 1:
1: Drag box 1A to the balance and record the weight in kg.
2: Add box 1A to the 100.00 L pail and record the volume difference as the volume of box 1A. (For example, if the volume of water becomes 105.50 L once box 1A is added, the volume of box 1A would be 105.50 L – 100.00 L = 5.50 L.)
3: Calculate the density of box 1A in kg/L by dividing the mass by the volume.
4: Repeat steps 1-3 for the remaining boxes and record the density values in the table below.
5: Click on the density table, and using the densities you calculated, provide an identity (if possible) for each box.
Box |
Density (kg/L) |
Identity |
|---|---|---|
|
1A |
||
|
1B |
||
|
1C |
||
|
1D |
||
|
1E |
(Note: Simulation by Phet Interactive Simulations, University of Colorado Boulder, licensed under CC-BY-4.0(opens in new window) (https://phet.colorado.edu).
DATA AND OBSERVATIONS
| Type of Measurements | Data |
|---|---|
|
Diameter of the watch glass |
|
|
Length of test tube |
|
|
Length of stirring rod |
|
|
Mass of a watch glass |
|
|
Mass of 125 mL Erlenmeyer flask |
|
|
Mass of the evaporating dish |
|
|
Mass of 10.0 mL graduated cylinder |
|
|
The initial volume of water in a 100 mL cylinder |
|
|
The volume of water in the cylinder after the first pour |
|
|
The volume of water in the cylinder after the second pour |
|
|
The volume of water in the cylinder after the third pour |
|
|
Room temperature |
|
|
Temperature of ice |
|
|
The temperature of boiling water |
|
Trial 1 |
Trial 2 |
Trial 3 |
|
|---|---|---|---|
|
Mass of the empty graduated cylinder |
|||
|
Mass of the graduated cylinder and water |
|||
|
Mass of water |
|||
|
Volume of water |
|||
|
Density of water |
Average density of Water:
Part C: Density of Various Rectangular Blocks
Block Color or Number. |
|||
|---|---|---|---|
|
Mass of the Block |
|||
|
Length of Block |
|||
|
Width of Block |
|||
|
Height of Block |
|||
|
The volume of the Block |
|||
|
Density of the Block |
|||
|
Identity of the Block |
POST-LAB QUESTIONS
1) What was the biggest takeaway from this experiment?
2) Describe three possible sources of error in this experiment.
3) In pre-lab question 3, you determined the volume of each box by subtracting the initial volume of water in the pail from the total volume of water. Explain why this procedure can be used to determine the volume of the block.
4) How did your average experimental density in part B compare with the actual density of water?
5) Part A: When 8.0 mL of an unknown liquid was added to a 25.000 g graduated cylinder, the combined mass of the liquid and cylinder was 31.355 g. Using this information, determine the density of the unknown liquid.
Part B: Someone claims that the unknown liquid described in Part A is methanol. Can you prove this using only your calculation result? (Hint: Google search for the density of methanol, ethanol, and isopropyl alcohol.)
Please click here to access the Pre-Lab, Data Tables, and Post-Lab in Word or PDF format. Complete and upload as directed by your instructor.