Presentation on theme: "Do Now: Create a conversion factor for minutes per hour"— Presentation transcript:
1 Do Now: Create a conversion factor for minutes per hour Create a conversion factor for milligrams per gramCreate a conversion factor for kilograms per gram
2 International System of Units (SI) Based on the metric system, units are based on multiples of 10.Once you understand the prefixes for one unit, you understand them for every unit.Unlike the English system, where it is seemingly random –teaspoons in a tablespoon, ounces in a pound, inches in a foot and feet in a yard, etc.
3 5 SI units most commonly used by chemists are: QuantitySI Base UnitSymbolLengthmetermMassKilogram (gram)kg (g)TimesecondsAmount of substancemolemolTemperaturekelvinK
4 Important Unit prefixes 1 Kilometer (km) = 1000 meters = 1 x 103 m100 Centimeters (cm) = 1 x 102 cm = 1 meter1000 Millimeters (mm) = 1 x 103 mm = 1 meter1,000,000,000 Nanometers (nm) = 1 x 109 nm = 1 meterTrick – Only Kilo is bigger than the basic unit of measurement. Everything else you need to remember is smaller.
5 Celsius and Kelvin What is the temperature water freezes in Celsius? What’s the temperature water boils in Celsius?This scale was setup by defining the freezing and boiling points of water at 0 and 100, and dividing up the distance between into 100 equal parts, degrees.
6 Celsius and KelvinLord Kelvin ran an experiment and calculated the temperature when particles completely stop moving, commonly referred to as absolute zero. The Kelvin temperature scale set absolute zero as 0 K.The freezing point of water is 273 K and the boiling point of water is 373 K. There are 100 degrees between water boiling and freezing in both scales.One degree Kelvin is the same amount of change as 1 degree Celsius. You can interconvert Kelvin and Celsius using the following equation:K = °C + 273
7 Practice Problems 150 °C is what temperature in Kelvin? 67 K is what temperature in Celsius?250 K is what temperature in Celsius?423 K196 K-206 °C-23 °C
8 Dimensional AnalysisUsing Dimensional Analysis to convert units. There is no one method that’s best for solving every problem. One of the most general ways to solve problems is through Dimensional AnalysisDimensional analysis is a way to analyze and solve problems using the units (dimensions) of the measurements.To see how to use dimensional analysis, let’s see it in action, solving a problem.
9 How would you use Dimensional Analysis to figure out how many seconds there are in one day? Step 1: Start by listing what we know. We know and what we do not know:Known:1 day = 24 hours1 hour = 60 minutes1 minute = 60 secondsUnknown:1 day = ?? secondsStep 2: Setup a dimensional analysis1 day x 24 hours x 60 minutes x 60 seconds1 day hour minute
10 Step 3: Cancel out units and do the math operations: 1 day x 24 hours x 60 minutes x 60 seconds =1 day hour minute86,400 seconds (8.64 x 104 sec)Step 4: Evaluate – Does the answer make sense?The answer is in seconds, and you’d expect a big number of seconds in a day. Double checking the math, all of the correct units were crossed out, and the conversion factors are all equal to each other.
11 Example 2: how many mg are there in 2. 2 kg Example 2: how many mg are there in 2.2 kg? Give the answer in scientific notation.Step 1: Listing Known and UnknownKnown:Quantity present = 2.2 kg1 kg = 1000 g1 g = 1000 mgUnknown:2.2 kg = ?? mgStep 2: Setup Dimensional Analysis2.2 kg x 1000 g x 1000 mg1 kg g
12 Step 3: Cancel Units and do the math 2.2 kg x 1000 g x 1000 mg = 2,200,000 mg = 2.2 x 106 mg1 kg gStep 4: Evaluate – Does the answer make sense?The answer is in mg and you’d expect a big number of mg in a kg. Double checking the math, all of the correct units were crossed out, and the conversion factors are all equal to each other.
14 Practice ProblemsExpress 3.7 mm in km. Give your answer in scientific notation.Express 77 cm3 in m3. Give your answer in scientific notation.The mass of Earth is 5.97 x 1024 kg. How many mg is the mass of Earth?3.7 x 10-6 km7.7 x 10-5 m35.97 x 1030 mg
15 Converting FractionsDimensional Analysis can be used to convert fractions, such as density. It just takes more than one conversion factor. Just follow the unit conversions with your conversion factors.Example - Convert 3.5 g/mL to mg/LStep 1 – List known and unknown:Known:Have 3.5 g/mL1000 mg = 1 g1 L =1000 mLUnknown:3.5g/mL = ?? kg/LStep 2 – Setup the Dimensional Analysis3.5 g x 1000 mg x 1000 mLmL g L
16 Step 3 – Cancel units and do the math 3.5 g x 1000 mg x 1000 mL = 3.5 x 106 mg/LmL g LStep 4 – EvaluateThe units cancel out correctlyThe answer has units labeledThe answer makes sense – mg are smaller so g->mg should increase and mL smaller than L so 1/mL -> 1/L should increase.
17 Practice ProblemA student measures that a cube weighs 2.9 kg and has a volume of1.7 L. Express the density in g/mL using scientific notation and with the correct number of significant figures.1.7 x 100 g/mL