Chapter 2 Measurements in Chemistry Chemistry 2A

Data Qualitative –Data obtained from one ’ s opinion –Does not involve numbers Quantitative –Data obtained from measurements –Involves numbers

U.S. Customary System Also called: –American System –English System Inch Gallon Pound Teaspoon

Metric System Système International (SI) International decimalized system of measurement First adopted by France in 1791 Meter Gram Liter

Length How long something is, DUH! SI unit = meter (m)

Mass Measure of the quantity of matter (stuff) in an object SI unit = Kilogram (kg)

Volume The amount of space that an object or substance occupies. SI unit = Cubic meter (m 3 ) 1 L = m 3 1 L = 1000 mL 1 mL = 1 cm 3 = 1 cc

Time Duration of event SI unit = Second (s)

French Revolutionary Clock

System International (SI) Units

PrefixSymbolMultipleExample GigaG10 9 Gigabyte = Gbyte MegaM10 6 Kilok10 3 = 1000Kilogram = kg Hectoh10 2 = 100 Dekada10 1 = 10 No prefix (Unity) 10 0 Meter, liter, gram = m, L, g Decid10 -1 = 0.1 Centic10 -2 = 0.01 Millim10 -3 = 0.001Milliliter = mL Microμ10 -6 Nanon10 -9 Nanometer = nm Picop10 -12

Common Units and Their Equivalents Length 1 kilometer (km)= mile (mi) 1 meter (m)=39.37 inches (in.) 1 meter (m)=1.094 yards (yd) 1 foot (ft)=30.48 centimeters (cm) 1 inch (in.)=2.54 centimeters (cm) exactly

Common Units and Their Equivalents Volume 1 liter (L)=1000 milliliters (mL) 1 liter (L)=1000 cubic centimeters (cm 3 ) 1 liter (L)=1.057 quarts (qt) 1 U.S. gallon (gal)=3.785 liters (L) Mass 1 kilogram (km)=2.205 pounds (lb) 1 pound (lb)= grams (g) 1 ounce (oz)=28.35 grams (g)

Problems 1)Green light has a wavelength of approximately 550 nm. What is this value in meters? Picometers? Kilometers? 2)Your neighbor lost 50 pounds after having a baby. How many kg did she lose? How many micrograms? 3)How many milliseconds in a year?

Dimensional Analysis Using units as a guide to problem solving is called dimensional analysis Figure out which unit you want to start with and which one you want to get to Use conversion factors to get there –Relationship between two units –May be exact or measured –Generated from equivalence statements Always include units in your calculations!

12 eggs = 1 dozen

Temperature A measure of the average kinetic energy of the particles in a sample of matter, expressed in terms of units or degrees designated on a standard scale. A physical property that determines the direction of heat flow in an object upon contact with another object. Fahrenheit (°F), Celsius (°C), Kelvin (K)

Fahrenheit (ºF), Celsius (ºC), Kelvin (K) ºF = ºC(1.8) + 32 ºC = (ºF – 32)/1.8 K = ºC ºC = K – 273

Lord William Thomas Kelvin

Problems 1)If it’s 35ºC in London, would you say that it ’ s probably winter or summer? What is this temperature in Kelvin? 2)You are feeling sick and decide to take your temperature. Your thermometer, which only reads temps in Kelvin, says that you are at approximately 312 K. Do you have a fever?

Density The ratio of the mass of an object to its volume Mercury 13.6 g/cm g/cc Water 1.0 g/mL

Problems 1)Calculate the density of the rock in the picture to the right. The rock has a mass of 29.5g. 2)What is the mass of 5.5mL of mercury if Hg has a density of g/mL? 3)Calculate the height of the piece of wood to the right. Oregon Pine d = 0.53 g/mL

Scientific Notation 1)Locate the decimal point 2)Move the decimal so that there is only one number to the left of it 3)Write “ x 10 ” behind you new number 4)Count the number of places you ’ ve moved your decimal point and make this number the exponent on your 10 5)Assign a + or – sign to your exponent a)If your original # is larger than your SN #, the exponent is + b)If your original # is smaller than your SN #, the exponent is –

Problems 1)252 2) ) ) )3.33 x )4 x )35000 Write the following standard numbers in scientific notation and write the numbers in scientific notation in standard form.

Significant Figures

Scientific measurements are reported so that every digit is certain except the last, which is estimated CertainUncertain

Rules for Significant Figures 1)Numbers up to and including the “ uncertain ” number are significant 2)All non-zero numbers are significant 3)Zeros may or may not be significant 4)Zeros are significant if a)They are between two non-zero digits b)They are at the end of a decimal number

5)Zeros are not significant if a)They are used as place holders in large numbers without a decimal point b)They are at the beginning of decimal numbers 6)All numbers displayed in a number written in scientific notation are significant

Problems 1)45 2)45.0 3)405 4)4050 5) ) ) ) )4.0 x )3 x 10 8 Identify the correct number of significant digits in the figures below.

Mt. Everest ft, x 10 4 ft., or ft?

Calculation With Significant Digits Multiplication and Division –The final answer has the same number of sig figs as the measurement with the fewest sig figs –Example 1: 22.2 cm x cm = ? –Example 2: mm / mm = ?

Addition and Subtraction –The final answer is written so that it has the same number of decimal places as the measurement having the fewest decimal places –Example 1: 44.4 L L L = ? –Example 2: 4107 in – in = ?

Problems 1) ) / 4.4 x ) – – 2.2 4)

Precision and Accuracy Precision: how well several determinations of the same measurement agree –Reproducibility/repeatability Accuracy: agreement of a measurement with the accepted value

Determine whether the following students exhibit good or poor accuracy and precision Exam 1Exam 2 Accuracy & Precision Student A99%100% Student B100%89% Student C59% Student D25%49%