Lesson 1-5 Chemistry Problem Solving Metric and Unit Conversions “The Chemist’s Toolkit”

What is unique about Solving Chemistry Problems? Metrics System accepted by most of the world Simple – Units are multiples of 10 Scientific Notation Use the Factor – Label Method also called “dimensional analysis” or the “railroad track” method A procedure for keeping track of and converting units

Changing Metric Units To most easily change from one prefix to another in the metric system you move the decimal. grams meters liters

"Real Life" Science - Inquiry 5/10/2019 Changing Measurement Units The Factor-Label Method the most important mathematical process in chemistry!

The Factor-Label Process As you know, numbers in science almost always have some measurement units: 300 g, 0.62 Km, 0°C The numbers are factors, and units are labels: 300 is a factor and grams is the label 0.62 is a factor and Kilometer is the label 0 is a factor and degrees Celsius is the label With the factor-label process we consider both the “factor” and the “label” when we calculate answers. The factors and labels are equally important - they are a team - and when multiplying a factor (number), we must also consider the label (units).

The general form of a factor-label problem is shown below The general form of a factor-label problem is shown below. The factor-label method is a tool that allows us to write down the calculations that are in our brain, and to keep track of the relationship between quantities with different “labels”. The critical step in the factor-label method is using conversion factors Quantity - Label 1 Quantity - Label 2 Answer - Label 2 Quantity - Label 1 A “Conversion Factor” When we use factor label it’s important to understand that each space in the chart represents a multiplication or a division when using our calculator

Problem #1: Convert 1000 grams to pounds. Sample Problem Explanation Write what is given. Draw the horizontal and vertical lines. It is known that 454 grams = 1 pound. This becomes our conversion factor. The problem is solved when the label of “pounds” is in the numerator and all other units are canceled. The fraction is turned to put grams on bottom so it will cancel the “grams” labels. Use your calculator to do the math - 1000 times 1 divide by 454. 1000 g 1 pound 454 g 454,000 g2 / lb 2.2 pounds 454 g 1 pound Wrong Way – Units Don’t Cancel Correct Way – Finish with Desired Units

Problem #2: Convert 65 miles/hour to meters/second.

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