1 / 22

Chapter 1 Chemistry and Measurements

Chapter 1 Chemistry and Measurements. 1.9 Problem Solving. Given and Needed Units. To solve a problem, identify the given unit identify the needed unit Example : A person has a height of 2.0 meters. What is that height in inches?

zwilling
Download Presentation

Chapter 1 Chemistry and Measurements

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 1 Chemistry and Measurements 1.9 Problem Solving

  2. Given and Needed Units To solve a problem, • identify the given unit • identify the needed unit Example: A person has a height of 2.0 meters. What is that height in inches? The given unitis the initial unit of height. given unit = meters (m) The needed unitis the unit for the answer. needed unit = inches (in.)

  3. Study Tip: Problem Solving Using GPS The steps in the Guide to Problem Solving (GPS) are useful in setting up a problem with conversion factors.

  4. Setting Up a Problem How many minutes are in 2.5 hours? Solution: Step 1 State the given and needed quantities. Given unit: 2.5 hours Needed unit: min Step 2Write a unit plan. Plan: hours min

  5. Solving a Problem How many minutes are in 2.5 hours? Step 3State equalities and conversion factors to cancel units. 60 min = 1 h 60 min and 1 h 1 h 60 min Step 4 Set up problem to cancel units. Given Conversion Needed unit unit factor 2.5 h x 60 min = 150 min (2 SF) 1 h

  6. Learning Check A rattlesnake is 2.44 m long. How many centimeters long is the snake?

  7. Solution A rattlesnake is 2.44 m long. How many centimeters long is the snake? Step 1 State the given and needed quantities. Given unit: 2.44 m Needed unit: cm Step 2Write a unit plan. Plan: meters centimeters

  8. Solution A rattlesnake is 2.44 m long. How many centimeters long is the snake? Step 3State equalities and conversion factors to cancel units. 1 m = 102 cm 102 cm and 1 m 1 m 102 cm Step 4 Set up problem to cancel units. Given Conversion Needed unit unit factor 2.44 m x 102 cm = 244 cm (3 SF) 1 m

  9. Learning Check How many minutes are in 1.4 days?

  10. Solution How many minutes are in 1.4 days? Step 1 State the given and needed quantities. Given unit: 1.4 days Needed unit: minutes Step 2Write a unit plan. Factor 1 Factor 2 Plan: days h min

  11. Solution How many minutes are in 1.4 days? Step 3State equalities and conversion factors to cancel units. 1 day = 24 hours 24 hours and 1 day 1 day 24 hours 1 hour = 60 minutes 60 min and 1 h 1 h 60 min

  12. Solution How many minutes are in 1.4 days? Step 4 Set up problem to cancel units. Given Conversion Conversion Needed unit unit factor factor 1.4 days x 24 h x 60 min = 2.0 x 103 min 1 day 1 h (rounded) 2 SF Exact Exact =2 SF

  13. Study Tip: Check Unit Cancellation • Be sure to check the unit cancellation in the setup. • The units in the conversion factors must cancel to give the correct unit for the answer. What is wrong with the following setup? 1.4 day x 1 day x 1 h 24 h 60 min = day2/min is not the unit needed. Units don’t cancel properly.

  14. Learning Check If your pace on a treadmill is 65 meters per minute, how many minutes will it take for you to walk a distance of 7.5 kilometers?

  15. Solution If your pace on a treadmill is 65 meters per minute, how many minutes will it take for you to walk a distance of 7.5 kilometers? Step 1 State the given and needed quantities. Given units: 7.5 km, 65 meters per minute Needed unit: minutes Step 2Write a unit plan. Factor 1 Factor 2 Plan: kilometers meters min

  16. Solution If your pace on a treadmill is 65 meters per minute, how many minutes will it take for you to walk a distance of 7.5 kilometers? Step 3State equalities and conversion factors to cancel units. 1 kilometer = 103 meters 103 meters and 1 kilometer 1 kilometer 103 meters 65 meters = 1 minute 65 meters and 1 minute 1 minute 65 meters

  17. Solution If your pace on a treadmill is 65 meters per minute, how many minutes will it take for you to walk a distance of 7.5 kilometers? Step 4 Set up problem to cancel units. Given Conversion Conversion Needed unit unit factor factor 7.5 kilometers x 103 meters x 1 minute = 120 minutes 1 kilometer 65 meters (rounded) 2 SF Exact 2 SF =2 SF

  18. Percent Factor in a Problem If the thickness of the skin fold at the waist indicates 11% body fat, how much fat is in a person with a mass of 86 kg? Percent factor: 11 kg fat 100 kg mass percent factor 86 kg mass x 11 kg fat 100 kg mass = 9.5 kg of fat

  19. Learning Check How many pounds of sugar are in 120 g of candy if the candy is 25% (by mass) sugar?

  20. Solution How many pounds of sugar are in 120 g of candy if the candy is 25% (by mass) sugar? Step 1 State the given and needed quantities. Given units: 120 g of candy 25% by mass sugar Needed unit: pounds sugar Step 2Write a unit plan. Conversion Percent factor factor Plan: grams pounds candy pounds sugar

  21. Solution How many pounds of sugar are in 120 g of candy if the candy is 25% (by mass) sugar? Step 3State equalities and conversion factors to cancel units. 1 pound = 454 grams 454 g and 1 lb 1 lb 454 g 25 pounds of sugar = 100 pounds of candy 25 lb sugar and 100 lb candy 100 lb candy 25 lb sugar

  22. Solution How many pounds of sugar are in 120 g of candy if the candy is 25% (by mass) sugar? Step 4 Set up problem to cancel units. Given Conversion Percent unit factor factor 120 g candy x 1 lb candy x 25 lb sugar 454 g candy 100 lb candy = 0.066 lb of sugar

More Related