Department of Chemistry CHEM1010 General Chemistry *********************************************** Instructor: Dr. Hong Zhang Foster Hall, Room 221 Tel:

CHEM1010/General Chemistry _________________________________________ Chapter 1. (L3)-Introduction Today’s Outline..Review: How to distinguish between things in a scientific way?..How to measure matter -the units for measuring the properties -scientific expression of numbers -measurement of some basic commonly used physical properties (mass, length, area, volume, density, etc.)

Chapter 1. (L3)-Introduction How to distinguish between things in a scientific way? L ast time, we discussed about how to distinguish between things in a scientific way, i.e., distinguish between things accurately The approach: using various properties of matter to characterize things and thus distinguish between them. Two basic categories of properties of matter: -Physical properties, no change of chemical composition (e.g., mass, size, temperature, color, hardness, density, etc.) -Chemical properties, involving chemical changes

Chapter 1. (L3)-Introduction The units for measuring the physical properties Why we need units? Let’s do a pop quiz first. Quiz Time 1. Which book is more expensive, the one with the cost of: (a)5 cent; (b) 15 cents; (c) 0.45 dollar; (d) 4 dimes 2. Which pencil is longer, the one with the length of: (a) 4 inch; (b) 0.5 feet; (c) 8 cm; (d) 60 mm

Chapter 1. (L3)-Introduction The units for measuring the physical properties The previous quizzes illustrate the following observation: The numerical value of a property depends on the unit. The measurement is based on the unit used. In other words, the value of a property is meaningless without a unit. For example: “The pencil’s length is 2” is meaningless. “The book costs 5” is meaningless. You have to give a unit to the value.

Chapter 1. (L3)-Introduction The units for measuring the physical properties There are various units for a certain property. For example, length has the units of inch, feet, and meter. The US money has the units of cent and dollar. To have a good communication among scientists as well as the people who use science, there is a need to use a unified unit system in science. Now, we ask this question, what is the unit system used in science?

Chapter 1. (L3)-Introduction The units for measuring the physical properties The unit system used in science is the International System of Units or SI Unit System. This system is based on the metric system, rather than the English system. The metric system is based on the decimal system (i.e., based on 10, rather than 12, or 16).

Chapter 1. (L3)-Introduction The units for measuring the physical properties Several most commonly used SI units: PropertyUnit SymbolUnit Name Mass kg kilogram Length mmeter Timessecond TemperatureKkelvin

Chapter 1. (L3)-Introduction Scientific expression of numbers - In science, because the universe is so large and matter can be so small, we deal with very large or small numbers, such as 1,000,000 or These very large or small numbers are awkward to handle. -We now ask this question, can we have some handy way to handle these very large or small numbers?

Chapter 1. (L3)-Introduction Scientific expression of numbers The answer is yes. The trick is to express these numbers using exponential numbers of powers of 10. What is power of 10? See the following examples: 10 2 = 100, 10 4 = 10, = 0.01, =

Chapter 1. (L3)-Introduction Scientific expression of numbers For convenience, we give various exponential expressions of power of 10 different prefix, such as the following commonly used: PowerDecimal ExpressionEquivalentPrefixSymbol ,000,000,000,000teraT ,000,000,000gigaG ,000,000megaM ,000kilok

Chapter 1. (L3)-Introduction Scientific expression of numbers PowerDecimal ExpressionEquivalentPrefixSymbol decid centic milim microµ nanon picop femtof

Chapter 1. (L3)-Introduction Scientific expression of numbers Converting powers of 10 to prefixes Example: 1.23  g = 1.23 mili g = 1.23 mg (Note: = mili = m) 3.21  10 3 g = 3.21 kilo g = 3.21 kg (Note: 10 3 = kilo = k) This a new language. You have to remember these prefixes.

Chapter 1. (L3)-Introduction Scientific expression of numbers Converting prefixes to powers of 10 Example: 1.23 micro g = 1.23 µg =1.23  g (Note: micro = µ = ) 3.21 mega g = 3.21 Mg = 3.21  10 6 g (Note: mega = M = 10 6 ) This a new language. You have to remember these prefixes.

Chapter 1. (L3)-Introduction Scientific expression of numbers Converting decimal numbers to the exponential expression of powers of 10 Examples: = 1.23  (Tip: 3 zeros before the first non-zero number;so the power is raised to –3 for the number small than 1) 1,230 = 1.23  10 3 (Tip: 3 digits after the first number; so the power is raised to 3 for the number large than 1)

Chapter 1. (L3)-Introduction Scientific expression of numbers Converting decimal numbers to the exponential expression of powers of 10 More examples: = 1.23  ; (Tip: 6 zeros before the first non-zero number;so the power is raised to –6 for the number small than 1) 1,230,000 = 1.23  10 6 (Tip: 6 digits after the first number; so the power is raised to 6 for the number large than 1)

Chapter 1. (L3)-Introduction Scientific expression of numbers Quiz Time (1)  is equivalent to: (a) ; (b) ; (c) ; (d) (2) 12,000 is equivalent to: (a) 1.2  10 5 ; (b) 1.2  10 4 ; (c) 1.2  10 3 ; (d) 1.2  10 2

Chapter 1. (L3)-Introduction Scientific expression of numbers Quiz Time (1) is equivalent to: (a)1.23  ; (b)1.23  ; (c)1.23  ; (d)1.23  (2) 1.2  10 5 is equivalent to: (a)1200; (b) ; (c) 12000; (d)

Chapter 1. (L3)-Introduction Measurement of some basic commonly used physical properties Common physical properties and units: -Mass: kg or g -Length: km, m, dm, cm, mm, µm -Area: m 2, dm 2, cm 2, mm 2, etc. -Volume: m 3, dm 3, cm 3, mm 3, etc. L, mL (1 L = 1000 mL, 1 L = 1000 cm 3 )

Chapter 1. (L3)-Introduction Measurement of some basic commonly used physical properties Time: 1 hour = 60 minute, 1 minute = 60 second, or 1 h = 60 min; 1 min = 60 s Quiz Time How many minutes you will spend in CHEM1010, given that you will spend 42 class periods and each period is 55 minutes: (a) 1230 min; (b) 2000 min; (c) 1000; (d) 2310 min

Chapter 1. (L3)-Introduction Measurement of some basic commonly used physical properties Quiz Time How many hours you will spend in CHEM1010, given that you will spend 42 class periods and each period is 55 minutes: (a) 55 h; (b) 38.5 h; (c) 30 h; (d) 8.5 h

Chapter 1. (L3)-Introduction Measurement of some basic commonly used physical properties Density Definition: d = m/V where d is density, m is mass, and V is volume Calculation of density Example: m = 156 g, V = 20.0 cm 3 d = 156 g/20 cm 3 = 156 g divided by 20 cm 3 = 7.80 g/cm 3 = 7.80 g cm -3

Chapter 1. (L3)-Introduction Measurement of some basic commonly used physical properties The Densities of some substances: SubstancesDensityT (ºC) Copper8.94 g/cm 3 25 Gold19.3 g/cm 3 25 Mercury13.5 g/cm 3 25 Water~1.0 g/cm 3 25 Ethyl alcohol 0.79 g/cm 3 20 Analogy: a box of same volume would hold ~9 copper balls, and ~19 gold balls, supposing 1 ball is 1 g. Obviously, the copper balls are larger than the gold balls. Right?

Chapter 1. (L3)-Introduction Measurement of some basic commonly used physical properties The Densities of some substances: SubstancesDensityT (ºC) Copper8.94 g/cm 3 25 Gold19.3 g/cm 3 25 Mercury13.5 g/cm 3 25 Water~1.0 g/cm 3 25 Ethyl alcohol 0.79 g/cm 3 20 Anything which has a density less the density of water will float in the water, but anything with a density higher than that of water will sink in water.

Chapter 1. (L3)-Introduction Measurement of some basic commonly used physical properties Quiz Time 1. Which substance will sink in water, the one with the density of: (a) 0.94 g/cm 3 ; (b) 0.79 g/cm 3 ; (c) 0.89 g/cm 3 ; (d) 19.3 g/cm 3 2. Which substance will float in water, the one with the density of: (a) 8.94 g/cm 3 ; (b) 13.5 g/cm 3 ; (c) 0.79 g/cm 3 ; (d) 19.3 g/cm 3 ;