Mr. Walsh's Class



Name _____________________________Date __________________ Block _______Chemical Safety, Measurement, Conversions, and Sig Fig NotesNFPA Safety SymbolsThe NFPA symbol above is found on all chemical products used in the laboratory, be they liquid or solid. It is your responsibility as a scientist to research the safety of any chemicals you intend on using in the lab prior to experimentation.What safety risks do the following chemicals pose? Hydrochloric Acid Potassium NitrateAcetoneMSDS ReportsIf the compound you plan on using carries a danger indicator of 1 or higher, consult the Material Safety Data Sheet (MSDS) for specific health risks by searching for your specific chemical in the MSDS book or online. Reference the example MSDS report for Diethylenetriamine. Name three specific things you learned about the chemical that you didn’t know from the NFPA symbol.1)2)3)Regardless of the official health risks listed in the MSDS or warned on the NFPA symbol; remember to treat all chemicals in the lab as potentially hazardous. That means taking immediate action to wash areas of direct skin/eye contact and notifying Mr. Walsh in the event of any chemical spills.In your own words, explain why NFPA and MSDS reports should be used together.How to MeasureMost of you are probably familiar with how to take a general measurement with everyday instruments such as rulers and weight scales. However, when collecting scientific data, there are important rules that must be followed to gain and maintain accuracy during experimentation. Rule 1: The accuracy of your data collection (measurement) is limited by your equipment.Example: What is the accuracy of the digital scale below? (To what place can you read if the scale shows 0.00 g?)So for digital instruments, you are limited to the lowest _______________________ (whole number, tenths, hundredths, etc.) that the instrument can read. Most instrumentation is guaranteed out to the last digit it displays with minimal error. Therefore, always report as many digits as your instrument allows. For other instruments, you will have to do take the readings yourself. That brings us to our second rule…Rule 2: When taking manual measurements, always read once between the lines. In other words, your last digit should be your best estimate.Example: What temperatures/volumes are shown in the examples below?379476027940001828808890000Thermometer (°C)Graduated Cylinder (mL)Temperature ___________Volume ____________Pro tip: Where do you measure the level for a liquid?41033701968519050554990Volumetric glassware (pipettes and flasks) are made and guaranteed to be accurate to the tenths place as long as the volume is brought exactly to the graduated mark. If this is a 50mL volumetric flask and 25mL volumetric pipette, what volume would you document for each?Time to put this to practice, let’s go hone our laboratory skills with the Lab Skills Technique Activity.Significant FiguresWhen a measurement is taken and recorded as data, the number of digits you record reflect how accurate you can assure that value is.Example: Since volumetric glassware is guaranteed accurate to the tenths place, a 100mL volumetric flask would be recorded as a volume of ______________.Writing 100.0mL versus 100mL shows that you are certain of the accuracy of your measurement down to the tenths place, whereas 100mL could be a rounded estimate for all we know. (If the last zero was accurate, the author should put a decimal behind it to show its accuracy as 100. mL)Significant figures reflect the limitation of accuracy of the data you collect in lab. They are the digits that add to the accuracy of your data.General Rules for Counting Sig Figs:All numbers 1-9 are significant. Zeros are the only digits you will need to decide the significance of.How many sig figs?16b) .132c) 13.12Heading zeros never count because they provide no info on how accurate the measurement is.How many sig figs?0016b) 0.132c) 0.001312Trailing zeros before a decimal do not count because they could be the result of rounding. How many sig figs?160b) 13200c) 10Trailing zeros after the decimal do count because they add a digit of accuracy.How many sig figs?16.0b) .1320c) 13.1200Last, all digits in-between two significant digits are significant.How many sig figs?106b) .13002c) 10.00120The same rules apply for the use of scientific notation. Let’s review how to properly convert values into scientific notation while maintaining the correct number of sig figs.Put the following values in scientific notation. Remember to use the correct sig figs.105,000b) 0.0024c) 0.00003040d) 100Try It! There are examples of sig fig problems hidden through-out the room. Find a card, answer it, check your answer with me up front and re-hide the card! Once you have done 3, grab the Sig Fig Application in Chemistry handout.Measurement (Metric) ConversionsIn this course, we will focus on using standard (or SI) units in our measurements and calculations. Below, you will find a chart of the most common metric prefixes used in scientific notation. You will be responsible for memorizing the values for kilo (k), milli (m), centi (c), and nano (n).15678152127251 Gigameter (Gm) = 1, 000, 000, 000 meters1 Megameter (Mm) = 1, 000, 000 meters1 Kilometer (Km) = 1, 000 meters1 Decameter (Dm) = 10 meters1 meter (m)10 decimeters (dm) = 1 meter100 centimeters (cm) = 1 meter1000 millimeters (mm) = 1 meter 1,000,000 micrometers (m) =1 meter1,000,000,000 nanometers (nm) = 1 meter1,000,000,000,000 picometers (pm) = 1 meter001 Gigameter (Gm) = 1, 000, 000, 000 meters1 Megameter (Mm) = 1, 000, 000 meters1 Kilometer (Km) = 1, 000 meters1 Decameter (Dm) = 10 meters1 meter (m)10 decimeters (dm) = 1 meter100 centimeters (cm) = 1 meter1000 millimeters (mm) = 1 meter 1,000,000 micrometers (m) =1 meter1,000,000,000 nanometers (nm) = 1 meter1,000,000,000,000 picometers (pm) = 1 meterThe chart shows how many base units there are for every 1 of the prefix unit.Examples: 1 gigagram = grams (prefixed unit) (base unit)1 liter = centiliters (base unit) (prefixed unit)1 kilometer = meters (prefixed unit) (base unit)In order to convert between different prefixes and units, we will use the “Factor Label Method.” The fundamental principle at work here is “cancellation of units.” Just like in algebra, where multiplying a denominator by the same value accomplishes a cancellation:1291590214630x00xExample: 10 = 2We can multiply units together to get them to cancel.Example: 10 grams When staying in the same unit of measurement (liters, grams, meters), but changing prefixes (ex: milligrams to grams). There is a quick conversion method you can follow as long as you know the relationship between the prefix and the base unit.Example: Convert 113 mg to g113 mgStep 1: Set up your conversion factor, units only, so that you cancel out the units you are in (bottom) and convert into the desired units (top).Step 2: Add the numerical relationship between the units into the conversion factorStep 3: Complete the mathExample: Convert 2.2 L to cL2.2 LError CalculationsWhen working in lab, we will strive for perfection but it is very difficult to achieve due to human and lab error. Often, you will be able to calculate an anticipated (or theoretical) result from your experiment that would be achieved under ideal conditions. Your ability to obtain an experimental value near the theoretical result will reflect the accuracy of your lab technique. There are two error calculations you will need to be familiar with:Absolute Error: The amount of physical error in a measurement, or the difference between the measured value and the actual (theoretical) value. *note that units are retained when calculating absolute errorRelative Error: The relative size of the error of the measurement in relation to the measurement itself, or the ratio of the absolute error to the accepted (theoretical) measurement value. 360553050800(100)00(100)*note that no units are retained when calculating relative error (units cancel during division) and the value is expressed as a percentageTry It! Calculate how accurate your pipetting skills were for your first trial. The theoretical volume delivered by a 10 mL volumetric pipette is 10.0 mL. What was the absolute and relative error of this measurement? Glassware Refresher: We demo’d trying out different types of glassware to measure 10 mL of water in the Lab Technique Activity. Let’s compare the error associated with using each piece of glassware for measuring volume.Beaker:Graduated Cylinder:Volumetric Pipette: ................
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