Chemistry 121: Experiment 1
Lab Techniques & Density Measurement
Materials
1 plastic 25 mL graduated cylinder 1 plastic 6 in clear ruler
10 pennies
Water (will need to be supplied by student)
Safety Precautions
The equipment and materials used in this lab do not pose any hazards.
Objectives
• Practice taking measurements and reporting observations with the correct significant figures.
• Calculate the density of 10 pennies using two techniques: measuring dimensions & displacing water.
Tasks:
1) Read the Introduction of the lab, it will explain how to make measurements. The information contained in the introduction will help you answer the questions at the end of the lab.
2) Follow the procedure and record all measurements in the Experiment 1 Student Worksheet.
3) Complete the calculations and questions in the Experiment 1 Student Worksheet.
4) Convert the completed Lab 1 Student Worksheet into a pdf file and submit to your instructor on canvas.
Criteria for Success
Calulations performed correctly with only small errors
Most evaluations of signficant figures are correct (at least 80%) Most evaluations of scale division and instrument precision are correct (at least 85%)
Short answer responses are formatted as paragraphs with complete sentences
Tables A, B1, and B2 are completed
Student shows calculation work in question 3, 4 and 7 Question 9 supports patient identification with evidence or reasoning
General Criteria
Question Specific Criteria
Lab 1 Grading Rubric
Introduction
Measuring volume, mass, length or height, time, and rate are common observations made in any lab or medical setting.
The tools used are often similar:
Variable Chemistry Lab Medical Environment
Volume Graduated cylinder, beaker,
volumetric flask, or pipet. Syringe or beaker.
Mass Electronic balance Electronic balance
Length Ruler Ruler or tape measurer
Time (Rate) Watch or stopwatch Watch or stopwatch
Reporting observations of volume, mass, length, and time require an accurate reading of the instrument, reporting the measurement with correct significant figures, and including the units of measurement (1 mg of a medication is very different then 1 g!).
Accuracy is related to the actual or “truthful’ value of the object measured. A ruler that can measure out to the millimeter is more precise than a ruler that can measure out to the centimeter. Precision is how close a series of measurements with the same instrument are to each other, or how reproducible a measurement is.
Significant figures are how a scientist or a medical professional communicate the precision of the instrument they used to perform a measurement. The last significant figure reported in a measurement is the estimated digit. If a nurse reports that 10 mL of a medication is administered intravenously to a patient we know they are estimating the “0” digit and were able to read a value that was greater than 10
mL and less than 20 mL. But if the nurse reports that 10.0 mL of medication is administered then we the nurse read a value of 10 mL on her instrument, and estimated that the volume was exactly 10 mL.
Laboratory Techniques
Measuring Units: The English System vs. The Metric System
The English system of measurement is most commonly used in the United States for non-scientific measurements (and a few medical readings). A car’s fuel efficiency is reported in miles per gallon; a person's height is given in feet and inches; ice cream is sold by the cup, pint or gallon; weight is measured in pounds and ounces; and temperature is reported in degrees Fahrenheit. Unfortunately, the English system can be difficult to use when units need to converted, because the ratios between units are not consistent. For instance, one pound is sixteen ounces, but one foot is twelve inches – and inches are often divided into fourths or even sixteenths. Converting a measurement like “4 and 7/16 inches” into feet can be tricky.
For most scientific measurements, and for many medical measurements, the U.S. (and the rest of the world) uses the much simpler metric system. The metric system is a decimal system of measurement whose basic units (e.g., gram, meter) can be easily converted into larger or smaller units by multiplying or dividing by 10 (e.g., kilogram or kilometer).
Because of its logic and simplicity, the metric system gained international acceptance with the Treaty of the Meter, establishing the International Bureau of Weights and Measures. Even the United States signed the treaty in 1875, but to date the U.S.'s use of the metric system is more limited. In hospitals, the cubic centimeter is often used, for instance.
(The most familiar metric unit to many Americans is the liter, because soda is sold in 2-liter bottles.) In science, the metric system is used almost exclusively, so most of the equipment and instruments used in a chemistry lab generally measure centimeters, millimeters, milliliters, grams, etc.
In this experiment, you will use electronic balances, rulers, graduated cylinders, burets, and syringes to measure the mass, dimensions, and volume of some solid metal cylinders and of various liquids. Although these measurements are not overly difficult, there are a few common mistakes you should learn to avoid.
Measuring the right number of significant figures
Don’t skip reading this section! It is not here to teach you how to use a ruler – we assume you know how to do that. The real purpose of this section is to teach you how to record the correct number of significant figures when using any graduated device, including rulers, graduated cylinders, burets, and pipets. Many students make mistakes in this area.
1. Always estimate a number between the lines when using a ruler (or other device with graduated markings)
EXAMPLE: In the example below, the centimeter ruler shown has numbers marked for each centimeter (cm), and the 10 smaller markings between each number represent 0.1 cm (the same as one millimeter (mm)).
The length of the metal bar in the example above is not exactly 8.5 cm or 8.6 cm – it is somewhere in between. We have 100% certainty that the length is 8.5 … something. Perhaps it is 8.52 or 8.57, for example. To use this measuring device accurately, you must estimate the final digit by closely looking at the space between the 8.5 and the 8.6 mark. In this case, the rod is about halfway between 8.5 and 8.6 cm. Therefore, a good estimate could be 8.55 cm, 8.54 cm, or 8.56 cm. The exact number a person comes up with depends on their eyesight, their perspective, and on their ability to accurately use the ruler. Because of this uncertainty in the last digit (+/- 0.01 cm), the last digit is the estimated digit.
On devices like this, the measurement is always recorded to one more decimal place than the smallest markings on the instrument.
2. If the length of the object is EXACTLY on a mark, don’t forget to write a zero after the number.
For example, in the ruler below, the end of the metal sample appears to line up with the marking for 4.7. Because this ruler is accurate to +/- 0.01, we must record the length as 4.70 cm. Although the number 4.7 is mathematically the same as the number 4.70, the final “0” in 4.70 is necessary in order to communicate the accuracy of the ruler.
It is more difficult to be highly accurate with graduated devices like rulers and graduated cylinders, but it is not impossible. Take the time to do the job right and you can indeed achieve 0.01 cm accuracy with a simple ruler.
Liquid Volume – Using Specialized Glassware
For all kinds of graduated glassware (i.e., glassware with measuring lines drawn on it): LOOK STRAIGHT ON AT THE BOTTOM OF THE LIQUID MENISCUS
When water is placed in a glass cylinder, a concave surface forms; this curve is called the meniscus. Calibrated glassware used in the lab is manufactured so that the volume is read where the bottom of the meniscus lines up with the markings on the equipment.
Your eye must be perpendicular to the bottom of the meniscus. Viewing the meniscus from above or below causes parallax, the deceptive displacement of the meniscus to be below or above the correct position, as shown at the right.
Graduated cylinders are used to hold and/or deliver measured amounts of liquid. They are available in many sizes. Those used in the lab can hold a maximum of 10 mL and 50 mL of liquid. For the greatest accuracy, use the smallest graduated cylinder that will hold the entire volume of sample.
For any graduated cylinder to be used accurately, it must be level (sitting on the counter, NOT handheld), because of issues with parallax (see above). Note that the graduations on all cylinders are read from the bottom up—that is, they indicate the volume contained in the cylinder.
The 25 mL graduated cylinder in each student’s kit has numbers every 10 mL and shorter lines every 1 mL. Because of the space between the markings on a graduated cylinder, one can estimate 10 divisions between the markings, so the volume can be recorded to 0.1 mL. The 10 mL graduated cylinder has markings every 0.1 mL, so the position of the meniscus between those divisions can be estimated to 0.01 mL.
Main Points: Accurately using graduated cylinders
1. Only make readings on level cylinders (sitting on the counter, NOT handheld), because of issues with parallax (see above).
2. Read the graduations the right way. All the graduations on all cylinders are read from the bottom up—that is, they indicate the volume contained in the cylinder.
3. Remember to estimate the level of the meniscus between the lines. Don’t just record the value of the marked line that is closest to the meniscus.
a. The 50 mL graduated cylinder in each student’s kit has numbers every 10 mL and shorter lines every 1 mL. One can estimate 10 divisions between the markings, so the volume can be recorded to 0.1 mL.
b. The 10 mL graduated cylinder has markings every 0.1 mL, so the position of the meniscus between those divisions can be estimated to 0.01 mL.
Density of Solid Objects
In this lab you will determine the density of 10 pennies in two different ways. Density is a physical property of matter that describes the relationship between the mass and volume of the object. For this experiment you will use the average mass of a penny to determine density.
Parallax error results when a meniscus is viewed from an
angle.
In the example to the left, the bottom of the meniscus is closer to the marking for 36 mL than for 35 mL, so the volume of liquid can be recorded as 35.7 mL or 35.8 mL, based on how close one sees it to the 36 mL mark.
For the second example to the right, the bottom of the meniscus appears to be between 1/4th and 1/3rd of the way from 32 mL to 33 mL, so the measurement can be recorded as 32.2 mL or 32.3 mL, depending on how one sees it.
𝑫𝒆𝒏𝒔𝒊𝒕𝒚 = 𝒎𝒂𝒔𝒔 𝑽𝒐𝒍𝒖𝒎𝒆
Method 1: You will measure the dimensions of pennies (length and diameter). From the dimensions you will calculate the volume of of 10 pennies by assuming they are perfect cylinders with a volume given by the following formula:
volume of a cylinder = πr2l where r is the radius and l is the length of the dowel.
Method 2: You will determine the volume of 10 pennies by displacing water in a graduated cylinder. When the pennies are submerged in the water the measured volume of water will increase. The difference between the initial water reading and final water reading will be the volume of the pennies.
Experiment 1 Procedure
Record all measurements in the Experiment 1 Student Worksheet.
Part A: Report measured values with the correct number of significant figures.
1. Read the measured physical property of each instrument shown in the picture below. Record the measurement with the correct number of significant figures in Table A of the Lab 1 Student Worksheet.
Part B: Volume of 10 pennies by measuring dimensions
2. From your lab kit find the clear 6 inch ruler and 10 pennies.
3. Measure the diameter of 3 pennies using the ruler. Record each measurement in millimeters to the correct number of decimal places.
4. Calculate the average diameter and radius of a penny. Be sure to show your work and report your answer with the correct number of decimal places.
5. Measure the length of 10 pennies stacked on top of each other using the ruler. Or measure the length of 3 pennies, calculate the average and multiply by 10. Record the measurement in millimeters to the correct number of decimal places.
6. Calculate the volume of the 10 pennies using the formula below. Be sure to use the average radius in your calculation and the length of 10 pennies stacked on top of one another.
volume = πr2l (remember, radius equals half the diameter)
Note that 1 mL is equal to 1 cm3. Be sure to record the volume with units of mL and with correct significant figures.
7. Use the calculated volume in step 4 to calculate the density of the 10 pennies if the average mass of one penny is 2.507 g or the mass of 10 pennies is 25.068 g. Be sure to show your work.
Part C: Volume of 10 pennies by water displacement
8. Obtain the graduated cylinder from your lab kit. Add water up to approximately the 15-mL mark in a plastic 25 mL graduated cylinder. It is not important whether you use exactly 15 mL of water, but it is important to record the exact volume of water you did use to the correct number of decimal places.
9. Tilt the graduated cylinder until it is at an angle, and carefully add the 10 pennies so as not to splash any water out of the graduated cylinder. Return the graduated cylinder to an upright position to read and record the new volume of water.
10. Subtract the original volume of water from the final volume of water, and record the difference with the appropriate units.
11. Use the volume determined in step 8 to calculate the density of the 10 pennies if the average mass of one penny is 2.507 g. Be sure to show your work.
Part D: Graphical Representation of Density
A lab needs to measure the density of a urine sample collected from a patient to calculate its specific gravity. 4 trials are performed, in each a syringe is filled with a volume of urine and the mass of the syringe both before and after filling with urine is used to calculate the mass of urine. Review the data below and answer the questions that follow.
Diameter (d)
Length (l)
Table D: Mass and Volume of urine samples
12. In Table D the mass and volume measurements of a urine sample are recorded. Calculate the average density of the four trials of measurements performed on the same sample. Report your answer with the correct number of significant figures
13. The urine samples were all kept at 23°C. If the density of water at 23°C is 0.9975 g/mL what is the specific gravity of the urine?
14. Diagnose the patient: Normal urine has a specific gravity range of 1.010 to 1.030, compare the specific gravity calculated in part b to this range of values. Identify your patient from the three choices below. Then provide an explanation using the data to support your diagnosis.
Patient A: A patient being treated for a benign brain tumor that complains of extreme thirst.
They are drinking excessive amounts of ice water and urinating extremely frequently. A urinalysis shows low potassium levels, the doctor suspects Diabetes Insipidus caused by the brain tumor the patient is being treated for.
Patient B: A patient diagnosed with type 2 diabetes reports that in the past six months they have quit smoking, jogged 3-4 times a week, and followed the nutrition plan their health team created.
The urinalysis does not detect excess glucose in the urine. The doctor congratulates the patient, these interventions have adequately managed their diabetes.
Patient C: A pregnant patient is emitted to the ER with abdominal pain and continued vomiting.
A urinalysis indicates glucose is present in the urine. The doctor suspects the patient has developed gestational diabetes mellitus.
B. Density of a Liquid Urine Sample
Unknown Urine Sample Number: __2_______
Temperature (°C) of the urine sample: _____25 C___________________
Trial 1 Trial 2 Trial 3 Trial 4
Mass of empty syringe (g)
3.921 g
Mass of syringe +
urine (g)
5.954
8.050 6.100 8.157
Mass of urine (g)
2.033
4.129 2.179 4.2365
Volume of urine (mL) 2.00 mL
4.10 mL 2.10 mL 4.10 mL
Density of urine (g/mL)
Measured Specific Gravity of urine sample (use hydrometer): _______1.020__________________
Post Lab Questions: Complete only questions 2 – 4.
1. DO NOT complete question 1, it requires hands on experience measuring flow rate from an IV.
2. In part 1B which measurement do you trust more: a single trial measuring the flow rate, or the average flow rate that you calculated? Why?
3. In Part 2A the density of a metal rod was measured in two ways:
1) by measuring the length, width, and height of the rod with a ruler and calculating the volume.
2) by displacing water to measure the volume.
Explain which method was the most accurate, use your data to support your answer.
4. Diagnose your patient: Normal urine has a specific gravity range of 1.010 to 1.030, compare your unknown patient urine sample to this range of values. Identify your patient from the three choices below. Then provide an explanation using your data to support your diagnosis.
Patient A: A patient being treated for a benign brain tumor that complains of extreme thirst. They are drinking excessive amounts of ice water and urinating extremely frequently. A urinalysis shows low potassium levels, the doctor suspects Diabetes Insipidus caused by the brain tumor the patient is being treated for.
Patient B: A patient diagnosed with type 2 diabetes reports that in the past six months they have quit smoking, jogged 3-4 times a week, and followed the nutrition plan their health team created. The urinalysis does not detect excess glucose in the urine. The doctor congratulates the patient, these interventions have adequately managed their diabetes.
Patient C: A pregnant patient is emitted to the ER with abdominal pain and continued vomiting. A urinalysis indicates glucose is present in the urine. The doctor suspects the patient has developed gestational diabetes mellitus.
B. Density of a Liquid Urine Sample
Unknown Urine Sample Number: __2_______
Temperature (°C) of the urine sample: _____25 C___________________
Trial 1 Trial 2 Trial 3 Trial 4
Mass of empty syringe (g)
3.921 g
Mass of syringe +
urine (g)
5.954
8.050 6.100 8.157
Mass of urine (g)
2.033
4.129 2.179 4.2365
Volume of urine (mL)
2.00 mL
4.10 mL 2.10 mL 4.10 mL
Density of urine (g/mL)
Measured Specific Gravity of urine sample (use hydrometer): _______1.020__________________
Post Lab Questions: Complete only questions 2 – 4.
1. DO NOT complete question 1, it requires hands on experience measuring flow rate from an IV.
2. In part 1B which measurement do you trust more: a single trial measuring the flow rate, or the average flow rate that you calculated? Why?
3. In Part 2A the density of a metal rod was measured in two ways:
1) by measuring the length, width, and height of the rod with a ruler and calculating the volume.
2) by displacing water to measure the volume.
Explain which method was the most accurate, use your data to support your answer.
4. Diagnose your patient: Normal urine has a specific gravity range of 1.010 to 1.030, compare your unknown patient urine sample to this range of values. Identify your patient from the three choices below. Then provide an explanation using your data to support your diagnosis.
Patient A: A patient being treated for a benign brain tumor that complains of extreme thirst. They are drinking excessive amounts of ice water and urinating extremely frequently. A urinalysis shows low potassium levels, the doctor suspects Diabetes Insipidus caused by the brain tumor the patient is being treated for.
Patient B: A patient diagnosed with type 2 diabetes reports that in the past six months they have quit smoking, jogged 3-4 times a week, and followed the nutrition plan their health team created. The urinalysis does not detect excess glucose in the urine. The doctor congratulates the patient, these interventions have adequately managed their diabetes.
Patient C: A pregnant patient is emitted to the ER with abdominal pain and continued vomiting. A urinalysis indicates glucose is present in the urine. The doctor suspects the patient has developed gestational diabetes mellitus.
Student Name:
Experiment 1: Laboratory Techniques & Density: Student Worksheet
Part A
Q1. Images of different instruments used in a chemistry lab are provided in the procedure. For Each instrument in the image: 1) record the physical property that is being measured in the type of measurement column; 2) record the measurement reading with correct significant figures; and 3) report the number of significant figures in the recorded value (ex: for a measurement of 2 mL you would report the number of signficant figures as 1).
Table A: Reporting measurements with the correct number of significant figures.
Instrument Type of
Measurement Actual Reading Significant Figures in
Reading
200 mL Beaker
100 mL Graduated
Cylinder
10 mL Graduated
Cylinder
Mass Balance
50 mL Buret
Thermometer
Q2. Which instrument in table A is the most precise? <type answer here>
Part B
Q3. While following the instructions outlined in the procedure, record your measurements of the dimension of 10 pennies in Tables B below. Be sure to report values with the correct number of significant figures.
Complete the calculations and show your work below the table.
Table B1: Diameter of 3 pennies.
Penny 1 Penny 2 Penny 3
Diameter of Each Penny
(mm)
Calculate the average diameter of a penny from your measurements in table 1B. Show your work and be sure to report your answer with correct significant figures.
<type or embed a picture of handwritten work here>
Table B2: Density of a penny by measuring the dimensions of 10 pennies.
1 Average Diameter of a penny (mm)
2 Average Radius of a penny (mm)
3 Average Radius of a penny (cm)
4 Length of 10 pennies (mm)
5 Length of 10 pennies (cm)
6 Volume of 10 pennies (mL) using row 3 & 6
volume = πr2l
7 Mass of 10 pennies (g) 25.068 g
8 Density of a penny
Show your work for the calculation of the Volume of 10 pennies and the density of a penny below.
<type or embed a picture of handwritten work here>
Part C
Q4. While following the instructions outlined in the procedure, record your measurements of the volume of 10 pennies determined by displacing water in Table C below. Be sure to report values with the correct number of significant figures. Complete the calculations and show your work below the table.
Table C: Density and Volume of 10 pennies by water displacement.
Mass of 10 pennies (g) 25.068 g
Initial volume of water in graduated cylinder (mL)
Final volume of water in graduated cylinder with pennies (mL)
Volume of 10 pennies (mL)
Density of a penny
