Unit 2: Measuring and Calculating Chapter 2 “1000 grams...well it sounded like a lot when i orderd it. ah well, I cant make hide nor hair of these metric boobytraps” My car gets fourty rods to the hogshead and that's the way I like it

Objectives By the end of this unit, you will be able to: Distinguish between qualitative and quantitative characteristics List three requirements for making a measurement List and define the seven basic SI units with their categories of measurement Define the commonly used SI prefixes Define mass, weight, balance, and state the difference between mass and weight Define temperature and give the basis for the Celsius temperature scale Distinguish accuracy and precision

Objectives cont. Define significant digits and counting numbers and determine the number of significant digits in a given measurement Express results of math equations in significant digits Convert numbers from decimal to scientific notation Combine SI units to form derived units Demonstrate use of logic to solve problems Use the factor-label method to solve problems Define density and perform calculations using density, mass, and volume

The International System (SI) Qualitative measurement – a description with no measurement Color Smell Quantitative measurement- a description with numerical information Length Mass

SI System continued… Three requirements for quantitative measurement We must know exactly what property we are trying to measure We must have some standard with which to compare whatever we are measuring We must have some method of making this comparison

SI System continued… The SI system is the standard measuring system used in science SI is a modified version of the metric system Most countries use SI or are converting to it The SI system is very simple and consistent The SI system has seven basic units…

Seven Basic Units of SI Quantity Unit Unit Symbol Length Meter m Mass Kilogram kg Time Second s Electric Current Ampere A Temperature Kelvin K Amount of substance Mole Mol Luminous intensity Candela cd

SI prefixes In SI, prefixes are added to the base units to obtain different units of a convenient size for measuring larger or smaller quantities Kilometer = 1000 meters Millimeter = 1/1000 of a meter You will need to memorize the metric prefixes and the values which they stand for Next, a table of the metric prefixes…

SI Prefixes Prefix Symbol Meaning Multiplier Mega M Million 1,000,000 Kilo K Thousand 1,000 Deci d Tenth 0.1 Centi c Hundredth 0.01 Milli m Thousandth 0.001 Micro µ Millionth 0.000001 Nano n Billionth 0.000000001 Pico p Trillionth 0.000000000001

Homework Worth a possible 5 points Due:

Mass and Weight What's the difference? Weight is a measure of the force of gravity between two objects On objects weight on Earth can change when the distance between the object and the center of the Earth changes Mass is a measure of the amount of matter an object has Mass never changes

Mass The SI unit for mass is the kilogram The Balance In the lab, we usually use the gram (g), because a kilogram is too large The mass of a paperclip is about 1.5 g The Balance The balance is the tool used to measure mass Using the balance

Length Length is the distance covered by a line segment connecting two points The SI unit for length is the meter (m) Length is usually measured with a ruler or similar device Examples A nickel has a diameter of ~2 cm A notebook is about 25 cm long

Time Time is the interval between two occurrences The SI unit for time is the second (s) Time is usually measured with a clock or watch The atomic clock is the most accurate tool for measuring time

Temperature The temperature of a sample of matter is a measure of the average kinetic energy of the particles that make up the sample The greater the kinetic energy, the higher the temperature Temperature is usually measured with a thermometer The SI unit for temperature is the Kelvin (k) The Celsius scale is also often used The Celsius scale is based on the boiling point and freezing point of water It is related to the Kelvin scale. More later…

Accuracy Vs. Precision Accuracy refers to how close a measurement is to the true or correct value for the quantity Precision refers to how close a set of measurements for a quantity are to one another, regardless of whether the measurements are correct Usually measurements that have precision are also accurate, but not always

Assignment Complete Exercises 1-2 on page 19 of your text This assignment is worth 10 points Due: By the end of class

Significant Digits (Sig Fig’s) All digits that occupy places for which actual measurement was made are referred to as significant digits The places actually measured include one uncertain, or estimated digit See Figure 2-7 in your text

Sig Fig’s cont. The exactness of measurements is very important This is determined by the number of significant digits in the measurement There are a few rules for determining the number of significant digits in a recorded measurement Counting numbers (an exception) When something is counted (not measured) it is considered to have an infinite amount of significant figures (more on that later)

Sig Fig Rules Digits other than zero are always significant 96 g 2 sig figs 61.4 3 sig figs 0.52 2 sig figs One or more final zeros used after the decimal point are always significant 4.7200 km 5 sig figs 8.0 2 sig figs Zeros between two other significant digits are always significant 5.029 m 4 sig figs Zeros used solely for spacing the decimal point are not significant 7000 g 1 sig fig 0.00783 kg 3 sig figs

Practice How many significant digits in each of the following? 30.4 2700 5.10 0.023 7.0200 0.04010 3.00 2.700 0.0304 51.0

Assignment Complete Exercise 5 on page 24 of your text This assignment is worth 5 points Due: Tomorrow

Pop Quiz!!! Write the correct number of sig figs for the following: 1. 320 g 11. 1234 meters 2. 32.0 m 12. 100,000 cd 3. 0.0045 kg 13. 504.0032 g 4. 50,000.0 L 14. 9.8 km 5. 2.340 cm 15. 100.0001 pm 6. 756 dm 16. 300 g 7. 100 g 17. 5.34 ML 8. 0.000500 L 18. 34 L 9. 1.096 mL 19. 0.001 g 10. 11.506 cg 20. 50 pencils

Scientific Notation Scientific Notation makes it easier to work with large numbers In Scientific Notation all numbers are expressed as the product of a number between 1 and 10 and a whole-number power of 10 M x 10n 1,000 = 1 x 103 Using Scientific Notation also makes counting sig figs easier 8000 = 8 x 103 1 sig fig 8000.0 = 8.0000 x 103 5 sig figs

Scientific Notation Practice Convert the following to scientific notation 30,000 1,567 0.000000340 5.67 7,500,000

Scientific Notation Rules To determine the number of digits that should appear in the answer to a calculation, we use two rules In addition and subtraction, the answer may contain only as many decimal places as the measurement having the least number of decimal places 5.44 + 3.1 = 8.5 This answer should then be rounded off to the nearest tenth, so the answer would be 8.5 In Multiplication and division, the answer may contain only as many significant digits as the measurement with the least number of significant digits 1.1 x 2.000 = 2.200 You can only have 2 significant digits, so your answer would be 2.2

Assignment Complete Exercises 6-12 on page 27 of your text This will be worth a possible 10 points Due: Tomorrow

Derived Units By combining SI units, we can obtain measurement units to express other quantities Distance divided by time = speed Length x Length = area Unit of area is the square meter (m2) Area x Length = volume Unit of volume is the cubic meter (m3) Most often in lab we use the milliliter (mL) for volume 1000 cm3 = 1000 mL = 1 L = 1 (dm3)

Problem Solving 3 part method for solving problems Decide what information is given Decide what information is needed Find a “bridge” that can help you use the information that you have to obtain the information that you need The “bridge” is the information that you will learn studying chemistry

Conversion Factors A conversion factor is a ratio equivalent to one Convert 72 cm to meters 100 cm = 1 meter 100 cm/100cm = 1m/100cm; therefore 1m/100cm is your conversion factor 72cm x 1 = 72cm x (1m/100cm) So, 72cm = 72m/100 = 0.72 m Convert 5.5 L to ml

Conversion Factors Cont. Vertical bar To make conversions easier, we can set off each factor by a vertical bar Convert 5 dm3 to cm3

Factor Label Method In the factor label method, units are treated as factors, and as such, can be divided out Example on board

Density Density is mass per unit of volume Density = mass/volume D=m/v Unit is g/ml

Assignment Complete Exercises 13-24 on pages 30-31 Exercises 29, 32, 38, and 39 on page 32 of the text Exercises 44, 45,46 on page 35 of your text Worth 20 points Due: Monday

Chapter Review Complete chapter review questions 48 all, 49a, 50 all, 51 all, 54, 55, 57, 59, 60, 61, 62, 64, 65, 66 all, 68 all, 69 all, 70, 71 all, 73 all, 83, 85, 86, 94, and 95 on pages 36-38 of your text Remember, these questions will be very similar to those found on the unit test, so do them all This will be collected for a possible 25 points