Section 3.2 The International System of Units International System of Units (SI) –Revised version of metric system –We use mostly SI units in class Metric System –Based on.
Download ReportTranscript Section 3.2 The International System of Units International System of Units (SI) –Revised version of metric system –We use mostly SI units in class Metric System –Based on.
Section 3.2 The International System of Units International System of Units (SI) –Revised version of metric system –We use mostly SI units in class Metric System –Based on 10s –Internationally used –EASY! 7 base units in SI measurement –You need to know these 5 for now: Length: meter (m) Mass: kilogram (kg) Time: second (s) Quantity: mole (mol) (6.02 x 1023) Temperature: Kelvin (K) Other common units to know: –Volume: cubic meter (m3), liter (L), milliliter (mL) (derived unitcomes from other SI units.) –Temperature: Celcius (oC) –Energy: Joule (J) Metric Prefixes: many, many, many! –Memorize these: kilo-= 1000 centi-- = 1/100 or .01 milli-= 1/1000 or .001 Section 3.3 Conversion Problems Conversion Factor –A ratio of equivalent measurements. Examples: –Time… –Money… –Rulers… When using conversion factors, the number value changes, but the actual size of the measurement does not… –Change $1.00 into pennies = Same amount of money, but different number value. Equivalent measurement is… = Dimensional Analysis – An organized way to analyze and solve problems using conversion factors. – Carefully…AND NEATLY! Read problem. Set up problem with what you know and don’t know. Label EVERYTHING! Calculate the number value, cancel out units. Evaluate: Does your answer make sense? Write final answer with units. Practice Problem If you have Chemistry class for 85 minutes, how many seconds are you in class? Practice Problem If it took you 6 hours to drive to Chicago, how many seconds were you in the car? Practice Problem If your bus to Chicago drove at an average speed of 85 kilometers/hour, what was the average speed in meters/second? Section 3.4 Density Definition: Density is the ratio of the mass of an object to its volume. In other words: How much stuff is packed into a certain amount of space. High density Low density Formula: Density = Mass Volume Units: grams Density = mL Or: g/mL Or: any mass units/any volume units Density is an intensive property. –It does not depend on how much of a substance you have. Density is an identifying property. –It can be used to help identify a substance. Practice Problems A piece of metal has a mass of 3.5g and a volume of 0.18 cm3. What is its density? Practice Problems 1.2 L of an unknown gas has a mass of 1.6 g. What is its density? What do you think is the identity of this gas? (see chart on p. 90)