Understanding the International System of Units (SI) in Chemistry

1. Chapter 3 Section 3.2 & 3.3

2. The International System of Units • Known as SI (from the French name) • It is the revised form of the metric system • There are five base units commonly used by chemists…the meter, the kilogram, the kelvin, second and the mole

3. Metric Measure of Length • The meter is the base unit in the SI for length. • Common length measurements include the centimeter (cm), the meter (m) and the kilometer (km) • cm = width of a shirt button • m = height of a doorknob from the floor • km = length of 5 city blocks 5 x

4. Metric Measure of Volume • The space occupied by matter is called its volume. • The SI base unit of volume is the liter (L) • 1 L = 1000 cm3 so…1 mL = 1 cm3 • Common metric units of volume include: the liter (L), milliliter (mL), cubic centimeter (cm3), and the microliter (uL) • The formula for finding volume is: • V = L x W x H

5. Prefix Chart

6. 10 x 10 x 10 = 1,000 cm3 = 1 L

7. Believe it or not....1000 of those little cubes can fit into a cube which is a liter big. Since 1000 cubic centimeters can fit into a liter, it is given the special name of a milliliter.   Remember that the prefix -milli means 1/1000 or one thousandth. So, a milliliter is one thousandth of a liter.

8. Metric Measure of Mass • The mass of an object is measured in comparison to a standard mass of 1 kilogram (kg) • A kilogram was originally defined as the mass of 1 L of liquid water at 40C • Common metric units of mass include: the kilogram (kg), gram (g), milligram (mg) and the microgram (ug)

9. Mass vs Weight • How are mass and weight different? • Mass never changes…it is the amount of matter in an object. • Mass is a measure of quantity of matter (how much) • Weight can change depending on the gravitational pull. • Weight is a measure of force (of gravity) • We can weigh a little more or a little less at the ocean or on a mountain because the gravitational pull is less or more. • Objects can become weightless but never massless.

10. How many kilograms would an average teenager weigh?? • One kilogram = 2.2 pounds • So…if a young lady weighs 100 lbs how could we find her weight in kilograms? • We would divide: • 100 lbs / 2.2kg/lb = 45.5 kg

11. Metric Measure of Temperature • Temperature is a measure of how cold or hot an object is. • An object’s temperature determines the direction of heat transfer. • Most substances expand in higher temps and contract in lower temps. • Scientists commonly use two equivalent units of temperature, the degree Celsius and the kelvin.

12. Celsius Boiling Point 1000C Freezing Point 00C Named after the Swedish astronomer Anders Celsius. Kelvin Boiling Point 373.150K Freezing Point 273.150K Named after the Scottish physicist and mathematician Lord Kelvin. Absolute Zero is a number = -273.150K Celsius vs Kelvin For Chemistry class..we round off and use the whole number 273. K = 0C + 273 or 0C = K - 273

13. Metric Measure of Energy • Energy is the capacity to do work or to produce heat. • Common units of energy include: the joule (J) and the calorie (cal) • One calorie is the quantity of heat that raises the temperature of 1 g of pure water by 10C • Conversions between J and cal follow these formulas: • 1 J = 0.2390 cal • 1 cal = 4.184 J

14. Class Activity • Mass of a Penny • Purpose: To provide practice in weighing groups of objects • Materials: balance with at least precision of 0.01g, sets of 15 pennies each separated according to minting dates between pre 1960’s and present • Procedure: 1. Each student will weigh 3 sets of 5 same year pennies (for example…Student A will have 15 pennies from 1972…she will weigh them 5 at a time…3 groups…and record her measurements) 2. We will make a class graph to compare the mass of the pennies to the year they were minted.

15. Who weighs what?Find 15 of each of your years. • – 1970-1974 • – 1975-1979 • – 1980-1984 • – 1985-1989 • – 1990-1994 • – 1995-1999 – 2000-2004

16. 1979 – 1980 – 1981 – 1982 – 1983 – 1984 – 1985 – 1986 – 1987 – 1988 – 1989 – 1990 – 1991 – 1992 – 1993 – 1994 – 1995 – 1996 – 1997 – 1960 – 1961 – 1962 – 1963 – 1964 – 1965 – 1966 – 1967 – 1968 – 1969 – 1970 – 1971 – 1972 – 1973 – 1974 – 1975 – 1976 – 1977 – 1978 – 1998 – 1999 – 2000 – 2001 – 2002 – 2003 – 2004 – 2005 – 2006 – 2007 – 2008- 2009 – 2010 – 2011

17. Quick Lab – Accuracy and Precision • Pre-read the Quick Lab on page 72 in your book. • Read carefully, and follow the directions exactly. • You will need to briefly summarize the lab in writing in your notebook. • After we look at the data on the board, then you need to answer the Analyze and Conclude questions in your lab notebook.

18. Conversion Problems • There are expressions that help us convert from one unit to another unit. • For example 1 dollar = 4 quarters = 10 dimes = 20 nickels = 100 pennies • A conversion factor is a ratio of equivalent measurements. • For example 100cm/1m and 1m/100cm (hint…smaller number is with larger unit and larger number is with smaller unit)

19. Conversion Factors • When a measurement is multiplied by a conversion factor, the numerical value is generally changed, but the actual size of the quantity measured remains the same. • 100 cm = 1 m  both are equal to the same amount or quantity

20. Group Activity • We will work as a group to solve the following dilemma. • I need help…I don’t want to measure out each item on my recipe 6 times so…using what you learned about conversion factors and the information I will give you…rewrite this recipe so I have one “batch” of cookies to give each of my 6 friends.

21. Chocolate Chip Cookies Recipe: 1 cup unsalted butter, room temperature ¾ cup granulated white sugar ¾ cup firmly packed light brown sugar 2 large eggs 2 teaspoons pure vanilla extract 3 cups all-purpose flour 1 teaspoon baking soda ¼ teaspoon salt 1 ½ cups semisweet chocolate chips Note:  Can add 1 cup of toasted and chopped nuts (pecans or walnuts).

22. Conversion Factors you may need… 1 ½ teaspoons = ½ tablespoon 3 teaspoons = 1 tablespoon 2 tablespoons = 1 ounce = 1/8 cup 8 ounces (16 tablespoons) = 1 cup 2 cups = 1 pint = 16 ounces 2 pints = 1 quart = 4 cups = 32 ounces 4 quarts = 1 gallon = 16 cups = 128 ounces

23. DimensionalAnalysis • Is a way to analyze and solve problems using the units, or dimensions, of the measurement • Dimensional analysis provides an alternative approach to problem solving • Look at the examples in your book on page 82 and 83. Working with the person to your left, see if you can solve problems 28-31.

24. Practice Problems • How many minutes in 1 week? • How many seconds are in exactly a 40 hr work week?

25. Practice Problems • An experiment requires that each student use an 8.5 cm length of Mg ribbon. How many students can do the experiment if there is a 570 cm length of Mg ribbon? • A 1.00 degree increase on the Celsius scale is equivalent to a 1.80 degree increase on the Fahrenheit scale. If a temperature increases by 48.00C, what is the corresponding temperature increase on the Fahrenheit scale?

26. Converting Between Units • Problems in which a measurement with one unit is converted to an equivalent measurement with another unit are easily solved using dimensional analysis. • Sometimes multi-step problems are necessary to find the solution. • Many measurements are expressed with 2 units. You need to convert both using dimensional analysis. • Look at the sample problems in your book on pages 84, 85 & 86. Working with the person to your right, see if you can solve problems 32-37 using the examples given.

27. Practice Problems • Using tables from this chapter, convert the following… • 0.044km to m • 4.6mg to g • 0.107g to cg • Convert the following… • 15cm3 to L • 7.38g to kg • 6.7sec to ms • 94.5g to micrograms

28. Class Work/Homework • Book page 79 (18-27) • Book page 87 (38-45) • WS 3.2 • WS 3.3