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Foundations Chemistry Lab Procedures and Safety Safety is the MOST important priority Safety features of the room Fire extinguishers Fire blanket Exits Googles Fume hoods Spills/Breakage Say “Code One” to alter the teacher We will facilitate what to do next Basic Lab Equipment Bunsen burner Graduated cylinder Crucible Clay triangle Buret Crucible tongs Evaporating dish Scoopula Wire gauze Mortar and Pestle Microwell plate Funnel Beaker Utility Clamp Transfer pipet Ring stand Test tube Test tube holder Erlenmeyer flask Test tube rack Thermometer Florence flask Hot hands Dropper pipet Watch glass Udiometer Hot plate Interactive MSDS Sheets Https://www.texasgateway.org/resource/material-safetydata-sheets Example ..\Helpful Teaching Pics\Sample Label - Ethyl Alcohol.pdf Example ..\Helpful Teaching Pics\MSDS.pdf Uncertainty in measurement A measurement has some degree of uncertainty Estimation Different people estimate differently When recording data Rerecord all certain number and include one estimated number Scientific Notation A system of writing big and small numbers 4.67 x 106 5.23 x10-3 Base Number (argument) – tells the value Times (X) and Exponent – tells the scale of the number If exponent is negative Number is smaller than one If exponent is positive Number is greater than one Significant Figures Counting Nonzero digits Nonzero digits always count as significant figures. For example, the number 1457 has four nonzero integers, all of which count as significant figures. Page 124 and 125 in text Significant Figures Counting Zeros1. Leading zeros are zeros that precede all of the nonzero digits. A. 2. They never count as sig. figs. Captive zeros fall between nonzero numbers. B. 3. Three classes They always count as sig. figs. Trailing zeros happen at the right end of a number. C. They are significant only if the number is written with a decimal point. i. EX. 100 vs 100. Exact Numbers Numbers that were not obtained using measuring but were determined by counting Examples of exact numbers: 10 experiments, 3 apples, 1910 students at SBHS, 8 molecules . They have an infinite number of significant digits. Exact numbers apply to conversion factors and definitions. EX. 1 inch = 2.54 cm. or 1 pound equals 454 grams. the 1 isn’t used to determine the significant figures because it is an exact number Rules for Handling Numbers Significant Figures https://www.khanacademy.org/math/arithmetichome/arith-review-decimals/arithmetic-significantfigures-tutorial/v/significant-figures Computations https://www.khanacademy.org/math/arithmetic-home/arith-reviewdecimals/arithmetic-significant-figures-tutorial/v/more-onsignificant-figures Rules for Rounding Numbers 1. If the digit to be removed A. is less than 5 i. B. the preceding digit stays the same. is equal to or greater than 5, i. the preceding digit is increased by 1. In a series of calculations, carry the extra digits through to the final result and then round off. ****This means you should carry all the digits in your calculator until you get the answer and then round off according to RULE #1. Conversion Factors Changing one unit into another or dimensional analysis • • Read problem carefully Check Units in the problem See if starting and ending units are in the same category • if not look for a relationship to relate them • • Steps to Solve 1. Begin with what you are given 2. put units you want to finish with after the = 3. Determine number of significant figures and round answer to meet this •______X 𝑵𝑬𝑾 𝑼𝑵𝑰𝑻 𝑨𝑳𝑾𝑨𝒀𝑺 𝑶𝑵 𝑻𝑶𝑷 𝑼𝑵𝑰𝑻 𝒀𝑶𝑼 𝑾𝑨𝑵𝑻 𝑻𝑶 𝑪𝑨𝑵𝑪𝑬𝑳 𝒐𝒏 𝑩𝑶𝑻𝑻𝑶𝑴 *Use things you know to connect what you know with what you want to find out. = _______ new unit you want to find Accuracy vs. Precision Accuracy-describes how close a measurement is to the correct or (accepted) value of the thing you are measuring Measured % Error = by Percent Error |𝒆𝒙𝒑𝒆𝒓𝒊𝒎𝒆𝒏𝒕𝒂𝒍 −𝒂𝒄𝒄𝒆𝒑𝒕𝒆𝒅| 𝑎𝑐𝑐𝑒𝑝𝑡𝑒𝑑 𝑣𝑎𝑙𝑢𝑒 Must be Memorized X 100 Precision-the degree of exactness of a measurement; how reproducible a measurement is Percent Error Example Example: a student measures the mass of an object to be 2.59 grams. The actual mass is usually 2.85 grams. What is the % error? % Error = |𝒆𝒙𝒑𝒆𝒓𝒊𝒎𝒆𝒏𝒕𝒂𝒍 −𝒂𝒄𝒄𝒆𝒑𝒕𝒆𝒅| 𝑎𝑐𝑐𝑒𝑝𝑡𝑒𝑑 𝑣𝑎𝑙𝑢𝑒 2.59 −2.85 X 100 2.85 (.0912) X 100 =9.12% error 3 sig.figs X 100 Density Density = Mass Volume Units: g/ cm3 Amount of matter per unit volume in a given substance This should be a review from previous science classes. sample problems from the Unit packet page 27.
