Ch. 2 “Scientific Measurement & Problem Solving” SAVE PAPER AND INK!!! If you print out the notes on PowerPoint, print "Handouts" instead of "Slides“ in the print setup. Also, turn off the backgrounds (Tools>Options>Print>UNcheck "Background Printing")!
Types of Observations and Measurements • We makeQUALITATIVEobservations of reactions — Describes using words Ex. Odor, color, texture, and physical state. • We also makeQUANTITATIVE observations, using numbers- measurements • Ex. 25.3 mL, 4.239 g
Standards of Measurement When we measure, we use a measuring tool to compare some dimension of an object to a standard. For example, at one time the standard for length was the king’s foot. What are some problems with this standard?
Our measurements must be both Accurate & precise! Accuracy – how close a measurement comes to the true value of what is measured Precision – is concerned with the reproducibility of the measurement
Can you hit the bull's-eye? Three targets with three arrows each to shoot. How do they compare? Both accurate and precise Precise but not accurate Neither accurate nor precise
Stating a Measurement In every measurement there is a • Number followed by a • Unit from a measuring device The number should also be as precise as the measurement!
SI Measurement • Le Systeme International d’Unites : SI Metrics • System of measurement agreed on all over the world in 1960 • Contains 7 base units • units are defined in terms of standards of measurement that are objects or natural occurrence that are of constant value or are easily reproducible • We still use some non-SI units!
Le Système international d'unités • SI units— based on the metric system • The only countries that have not officially adopted SI are Liberia (in western Africa) and Myanmar (a.k.a. Burma, in SE Asia), but now these are reportedly using metric regularly • Among countries with non-metric usage, the U.S. is the only country significantly holding out.The U.S. officially adopted SI in 1966. Information from U.S. Metric Association
Derived Unitsmade by combining Base Units! • Volume length cubed m3 cm3 • Density mass/volume g/mL kg/L g/ cm3 g/L • Speed length /time mi/hr m/s km/hr • Area length squared m2 cm2
kilo k 103 deci d 10-1 centi c 10-2 milli m 10-3 micro m 10-6 nano n 10-9
Metric System • These prefixes are based on powers of 10. • From each prefix every “step” is either: • 10 times larger or • 10 times smaller • For example • Centimeters are 10 times larger than millimeters • 1 centimeter = 10 millimeters
Metric System • An easy way to move within the metric system is by moving the decimal point one place for each “step” desired Example: change meters to centimeters 1.00 meter = 10.0 decimeters = 100. centimeters
A 1 kg bar will weigh 1 kg on earth 0.1 kg on moon • mass – measure of the quantity of matter • SI unit of mass is the kilogram (kg) • 1 kg = 1000 g = 1 x 103 g Not to be confused with - weight– mass + gravity force that gravity exerts on an object Mass does not vary from place to place! A 1 kg bar has a mass of 1 kg on earth and on the moon
Volume – Amount of space occupied by matter SI derived unit for volume is cubic meter (m3) m3 = m x m x m We often use the Liter (L) when working with liquid volumes! 1 L = 1000 mL= 1000 cm3 = 1 dm3 1 mL = 1 cm3 1 dm3 = 1 L
Anders Celsius 1701-1744 Lord Kelvin (William Thomson) 1824-1907 Temperature Scales • Fahrenheit • Celsius • Kelvin
TEMPERATURE SCALES In Chemistry, the terms heat and temperature are often used to describe specific properties of a sample. HEAT is the most common form of energy in nature and is directly related to the motion of particles of matter. The faster the motion of particles in a sample the greater its heat content.
TEMPERATURE is associated only with the intensity of heat and is not affected by the size of the sample. A forest fire and a lit match may both be at the same temperature, but there is a large difference in the amount of heat each possess. Heat always spontaneously flows from a hotter system (higher temp.) to a colder system (lower temp.).
212 ˚F 100 ˚C 373 K 100 K 180˚F 100˚C 32 ˚F 0 ˚C 273 K Temperature Scales Fahrenheit Celsius Kelvin Boiling point of water Freezing point of water Notice that 1 Kelvin = 1 degree Celsius
Temperature Scientists do not know of any limit on how high a temperature may be. The temperature at the center of the sun is about 15,000,000 °C. However, nothing can have a temperature lower than –273°C. This temperature is called absolute zero. It forms the basis of the Kelvin scale. Because the Kelvin scale begins at absolute zero, 0 K equals –273°C, and 273 K equals 0 °C.
Calculations Using Temperature • Many chemistry equations require temp’s to be in Kelvin • K = ˚C + 273 • Body temp = 37 ˚C + 273 = 310 K • Liquid nitrogen = 273 -77 K = -196 ˚C ˚C = K - 273
Platinum Mercury Aluminum DENSITY – an important and useful physical property (Derived Unit)ratio of mass per unit of volume platinum mercury 13.6 g/cm3 21.5 g/cm3 2.7 g/cm3
DENSITY Brick Styrofoam • Density is anINTENSIVEproperty of matter. • Since it is a ratio of mass to volume -does NOT depend on quantity of matter. The density of 1 g of gold = The density of 5 kg of gold!
Get out those calculators! ProblemA piece of copper has a mass of 57.54 g. It is 9.36 cm long, 7.23 cm wide, and 0.095 cm thick. Calculate density (g/cm3). Copper ore Pure copper metal
SOLUTION 1. Make sure dimensions are in common units. (all are in cm’s) 2. Calculate volume in cubic centimeters. L x W x H = volume 3. Calculate the density. (9.36 cm)(7.23 cm)(0.095 cm) = 6.4 cm3
Learning Check Which diagram represents the liquid layers in the cylinder? (K) Karo syrup (1.4 g/mL), (V) vegetable oil (0.91 g/mL,) (W) water (1.0 g/mL) 1) 2) 3) V W K V W K W V K
Solution (K) Karo syrup (1.4 g/mL), (V) vegetable oil (0.91 g/mL,) (W) water (1.0 g/mL) 1) WATER!! Denser materials ‘sink’ in less dense materials! V W Most solids sink in their liquid form. Can you think of an exception to this?! K
Finding Volume of an IrregularSolid byWater Displacement A solid displaces a matching volume of water when the solid is placed in water. Volume of solid is 8 mL 33 mL 25 mL
Calculator Time! What is the density (g/cm3) of 48 g of a metal if the metal raises the level of water in a graduated cylinder from 25 mL to 33 mL? a) 0.2 g/ cm3 b) 6.0 g/cm3 c) 252 g/cm3 33 mL 25 mL
Percent Error • Percent Error: • Measures the inaccuracy of experimental data • Can have + or – value • Accepted value : correct value based on reliable references • Experimental value: value you measured in the lab
The number of atoms in 12 g of carbon: 602,200,000,000,000,000,000,000 The mass of a single carbon atom in grams: 0.0000000000000000000000199 Scientific Notation 6.022 x 1023 1.99 x 10-23 N x 10n N is a number between 1 and 10 (1 non-zero digit to left of dec. pt.) n is a positive or negative integer
To change standard form to scientific notation… • Place the decimal point so that there is one non-zero digit to the left of the decimal point. • Count the number of decimal places the decimal point has “moved” from the original number. This will be the exponent on the 10. • If the original number was less than 1, then the exponent is negative. If the original number was greater than 1, then the exponent is positive.
Examples • Given: 289,800,000 • Use: 2.898 (moved 8 places) • Answer:2.898 x 108 • Given: 0.000567 • Use: 5.67 (moved 4 places) • Answer:5.67 x 10-4
To change scientific notation to standard form… • Simply move the decimal point to the right for positive exponent 10. • Move the decimal point to the left for negative exponent 10. (Use zeros to fill in places.)
Example • Given: 5.093 x 106 • Answer: 5,093,000 (moved 6 places to the right) • Given: 1.976 x 10-4 • Answer: 0.0001976 (moved 4 places to the left)
Learning Check • Express these numbers in Scientific Notation: • 405789 • 0.003872 • 3000000000 • 2 • 0.478260
move decimal left move decimal right Scientific Notation 568.762 0.00000772 n > 0 n < 0 568.762 = 5.68762 x 102 0.00000772 = 7.72 x 10-6 Addition or Subtraction • Write each quantity with the same exponent n • Combine N1 and N2 • The exponent, n, remains the same 4.31 x 104 + 3.9 x 103 = 4.31 x 104 + 0.39 x 104 = 4.70 x 104
Scientific Notation Calculations Multiplication (4.0 x 10-5) x (7.0 x 103) = (4.0 x 7.0) x (10-5+3) = 28 x 10-2 = 2.8 x 10-1 • Multiply N1 and N2 • Add exponentsn1and n2 • Put in proper format, if necessary Division 8.5 x 104÷ 5.0 x 109 = (8.5 ÷ 5.0) x 104-9 = 1.7 x 10-5 • Divide N1 and N2 • Subtract exponentsn1and n2 • Put in proper format, if necessary
Significant Figures • The numbers reported in a measurement are limited by the measuring tool • Significant Figures in a measurement include all certain digits plus one estimated digit