Section 1: Units and Measurements Chemists use an internationally recognized system of units to communicate their findings. K What I Know W What I Want to Find Out L What I Learned

Essential Questions What are the SI base units for time, length, mass, and temperature? How does adding a prefix change a unit? How are the derived units different for volume and density? Copyright © McGraw-Hill Education Units and Measurements

Vocabulary Review New mass base unit second meter kilogram kelvin derived unit liter density Units and Measurements Copyright © McGraw-Hill Education

Units Système Internationale d'Unités (SI) is an internationally agreed upon system of measurements. A base unit is a defined unit in a system of measurement that is based on an object or event in the physical world, and is independent of other units. To better describe the range of possible measurements, scientists add prefixes to the base units. Copyright © McGraw-Hill Education Units and Measurements

Add link to concepts in motion interactive table from page 33 here. Interactive Table – SI Prefixes Concepts in Motion FPO Add link to concepts in motion interactive table from page 33 here. Copyright © McGraw-Hill Education Units and Measurements

Base Units and SI Prefixes The SI base unit of time is the second (s), based on the frequency of radiation given off by a cesium-133 atom. The SI base unit for length is the meter (m), the distance light travels in a vacuum in 1/299,792,458th of a second. The SI base unit of mass is the kilogram (kg), about 2.2 pounds. Copyright © McGraw-Hill Education Units and Measurements

Base Units and SI Prefixes The SI base unit of temperature is the kelvin (K). Zero kelvin is the point where there is virtually no particle motion or kinetic energy, also known as absolute zero. Two other temperature scales are Celsius and Fahrenheit. Copyright © McGraw-Hill Education Units and Measurements

Derived Units Not all quantities can be measured with SI base units. A unit that is defined by a combination of base units is called a derived unit. Example: The SI unit for speed is meters per second (m/s). Copyright © McGraw-Hill Education Units and Measurements

Derived Units Another quantity that is measured in derived units is volume (cm3), measured in cubic meters. The three cubes show volume relationships between cubic meters (m3), cubic decimeters (dm3), cubic centimeters (cm3), and cubic millimeters (mm3). Copyright © McGraw-Hill Education Units and Measurements

Derived Units Volume is measured in cubic meters (m3), but this is very large. A liter (L) is equal to one cubic decimeter (dm3), that is, 1 L equals 1 dm3. Density is a derived unit, g/cm3, the amount of mass per unit volume. The density of a substance usually cannot be measured directly. You can calculate density using the following equation: density = mass/volume Copyright © McGraw-Hill Education Units and Measurements

USING DENSITY AND VOLUME TO FIND MASS KNOWN UNKNOWN density = 2.7 g/mL mass = ? g initial volume = 10.5 mL final volume = 13.5 mL Use with Example Problem 1. Problem When a piece of aluminum is placed in a 25-mL graduated cylinder that contains 10.5 mL of water, the water level rises to 13.5 mL. What is the mass of the aluminum? SOLVE FOR THE UNKNOWN State the equation for volume. volume of sample = final volume - initial volume Substitute final volume = 13.5 mL and initial volume = 10.5 mL. volume of sample = 13.5 mL - 10.5 mL volume of sample = 3.0 mL State the equation for density. Response ANALYZE THE PROBLEM The mass of aluminum is unknown. The known values include the initial and final volumes and the density of aluminum. The volume of the sample equals the volume of water displaced in the graduated cylinder. The density of aluminum is 2.7 g/mL. Use the density equation to solve for the mass of the aluminum sample. Units and Measurements Copyright © McGraw-Hill Education

USING DENSITY AND VOLUME TO FIND MASS EVALUATE THE ANSWER Check your answer by using it to calculate the density of aluminum. Because the calculated density for aluminum is correct, the mass value must also be correct. SOLVE FOR THE UNKNOWN Solve the equation for mass. mass = volume × density Substitute volume = 3.0 mL and density = 2.7 g/mL. mass = 3.0 mL × 2.7 g/mL Multiple, and cancel units. mass = 3.0 mL × 2.7 g/mL = 8.1 g Units and Measurements Copyright © McGraw-Hill Education

Review Essential Questions Vocabulary What are the SI base units for time, length, mass, and temperature? How does adding a prefix change a unit? How are the derived units different for volume and density? Vocabulary base unit second meter kilogram kelvin derived unit liter density Copyright © McGraw-Hill Education Units and Measurements