Metric system / Concentrations

this lab is intended to provide an introduction to the use of standard measuring tools and skills that will be used throughout the semester. Experimentation in the field of cell and molecular biology requires extremely accurate measurements. The most common reason for failure to collect accurate data is inaccurate measurements. In this lab you will learn which units of measurement are used in science and how to convert between units. You will also learn how to prepare accurate concentrations of solutions. Finally you will familiarize yourself with journal articles in preparation for the research article that you will write later this semester. Part 1: The metric system The metric system is the most common measuring system used throughout the world. In the United States the metric system is mostly used by the scientific community; the general population uses the English system of measurement which includes inches feet and miles for distance; pints quarts and gallons for volume; and ounces pounds and tons for weight. The basic unit of length in the metric system is the meter (m). The meter is a relatively large unit slightly shorter than a yard. Shorter objects are measured in centimeters or millimeters. There are 100 centimeters in one meter and 1000 millimeters in one meter. Cells are measured in micrometers and viruses are measured in nanometers. Some conversions are shown below. 1 kilometer (km) 1000 m 1 hectometer (hm) 100 m 1 dekameter (dkm) 10 m 1 meter (m) 1 m 1 decimeter (dm) 0.1 m 1centimeter (cm) 0.01 m 1 millimeter (mm) 0.001 m 1 micrometer (m) 0.000001 μm 1 nanometer (nm) 0.000000001 m The units for the metric system are easy to remember and convert. For example if you need to convert 5 m to cm you multiply by the conversion factor: 5 m x (100 cm/1 m) = 500 cm. Note that the m in the numerator cancels out the m in the denominator. A shortcut to multiplying and dividing by 10 is to move the decimal to the right or left. For example since there are 102 cm in one m you move the decimal two places to the right in to go from a larger unit to a smaller unit: 5.0 m = 500.0 cm. To divide by 10 you move the decimal to the left. The basic unit of volume is the liter. Because one liter is a lot of liquid (about a quart) we usually measure liquids in milliliters. Just like a millimeter is 1000th of a meter a milliliter is 1000th of a liter. Theoretically we could measure volume in centiliters etc but most volume-measuring equipment such as graduated cylinders and pipettes are labeled in milliliters. The basic unit of weight or mass is one gram. One gram is very light about the weight of a paper clip so your weight is measured in kilograms. Just like there are 1000 meters in 1 kilometer there are 1000 grams in 1 kilogram. Another common unit of weight is the milligram used to measure the active ingredient of a medicine. Finally the metric system uses the Celsius scale to measure temperature instead of Fahrenheit. The Celsius scale was developed using notable temperatures of water; thus the freezing point of water is 0oC and the boiling point of water is 100oC. Room temperature is approximately 25oC and body temperature is 37oC. Object Length in cm Length in mm Length in m Paper clip Cell phone Pen or pencil 2. Conversion problem: convert your height in feet and inches to meters and centimeters. Note that there are 12 inches in a foot. Height in feet and inches Height in m Height in cm Part 2: Concentrations In a homogenous solution solutes are dissolved in a solvent. The solvent is the substance that is found in much larger quantities than the solute. For example brine solution consists of salt as the solute dissolved in water as the solvent. Concentration measures the amount of solutes in a solution. Concentration is measured in two ways:

a) by mass % and b) by molarity. For example the salinity of seawater is approximately 3%. That means there is 3 g of NaCl for every 100 g of seawater. A mole is the number of atoms or molecules. For any molecule or compound the mass of one mole in grams is equal to the mass of the molecule in atomic units. For example the mass of one mole of water is equal to 18 g (mass of H is 1 mass of O is 16 therefore mass of H2O is 18 a.u.). Here is the link to a video that explains the mole conversion in detail. A salt solution with a concentration of 2M would consist of 117 g NaCl in a liter of solution.

3. a) Explain how you would prepare a 15% sugar (sucrose) solution.

b) Explain how you would prepare a 4 M solution of salt. Another way of preparing different concentrations of solutions is to start with a stock solution and dilute it serially as shown in the diagram below.

4. You have a stock sugar solution with a concentration of 12 M. To dilute the stock solution you take 5 ml of the stock and mix it with 5 ml of water. You repeat the process until you reach a concentration of 1.5 M. How many dilutions have you done? Part 3 Journal articles Scientific articles are usually the result of experimentation although some articles are the result of observations or modeling. Articles also review or summarize a collection of articles. Authors submit their articles to journals for publication. Most journal articles are peer reviewed meaning the articles are selected or rejected by other researchers. Because each article is written by scientists who have a narrow focus for the experiment the vocabulary is usually specific and difficult. Most experts suggest that you first read enough to get the point of the article then go back for details.

5. For this lab assignment you will read the journal article Efficacy of masks and face coverings in controlling outward aerosol particle emission from expiratory activities and answer the following questions.

Requirements: answer all the Questions | .doc file

Directions: Measure the length of 3 different objects in centimeters. If you do not have a centimeter ruler google one and measure your pen against the actual-sized one that appears on your screen. Then convert the units and fill out the table below. % concentration = mass of solute/(mass of solute + mass of solvent) x 100 Molarity = mol/L What is the journal name and date of publication? What kind of information is given in the Abstract? What is the purpose of the Abstract? How many references are cited in the Introduction? What level of information is given in the Introduction? For example does it provide details about the virus? The respiratory tract? What is a hypothesis of the experiment? Do the authors explicitly state “My hypothesis is…”? Who is the audience of the article (eg. general public virologist)? What is the control of the experiment? How many references are listed at the end of the article? How is the information in the Results section different from that in the Discussion section? Briefly summarize Figure 2. What did the authors suggest as the reason for why particle emissions increased with homemade paper or cloth masks? What is the overall writing style of the article? Does it have a cute attention-grabbing title and hook? Based on this article would you wear surgical masks? Why or why not? Directions: Measure the length of 3 different objects in centimeters. If you do not have a centimeter ruler google one and measure your pen against the actual-sized one that appears on your screen. Then convert the units and fill out the table below. What is the journal name and date of publication?What kind of information is given in the Abstract? What is the purpose of the Abstract?How many references are cited in the Introduction?What level of information is given in the Introduction? For example does it provide details about the virus? The respiratory tract?What is a hypothesis of the experiment? Do the authors explicitly state “My hypothesis is…”?Who is the audience of the article (eg. general public virologist)?What is the control of the experiment?How many references are listed at the end of the article?How is the information in the Results section different from that in the Discussion section?Briefly summarize Figure 2.What did the authors suggest as the reason for why particle emissions increased with homemade paper or cloth masks?What is the overall writing style of the article? Does it have a cute attention-grabbing title and hook?Based on this article would you wear surgical masks? Why or why not?