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Scan_Doc0026 - 1.8 The speed limit on many highways in the...

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20 Chapter One Chemical Foundations Since the distance was originally given as 10.0 km, the result can have only three sig- nificant figures and should Derounded to 6.22 mi. Thus 10.0 km = 6.22 mi Alternatively, we can combine the steps: 1000 m l.094 yd 1mi 10.0 km X X X = 6.22 mi 1 k:m 1 rn 1760 yd SEE EXERCISES 1.41 AND 1.42 In using dimensional analysis, your verification that everything has been done cor- rectly is that you end up with the correct units. In doing chemistry problems, you should always include the units for the quantities used. Always check to see that the units can- cel to give the correct units for the final result. This provides a very valuable check, es- pecially for complicated problems. Study the procedures for unit conversions in the following Examples.
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Unformatted text preview: 1.8 The speed limit on many highways in the United States is 55 miIh. What number would be posted in kilometers per hour? Solution 55 mi 1760 yd--X X h lmi Result obtained by rounding only at the end of the calculation , I v l m 1km ~ l.094 yd X 1000 m = 88 km/h Note that all units cancel except the desired kilometers per hour. SEE EXERCISES 1.47 THROUGH 1.49 EXAMPLE 1.9 A Japanese car is advertised as having a gas mileage of 15 kmJL. Convert this rating to miles per gallon. Solution Result obtained by rounding only at the end of the calculation 15 k:m 1000 m l.094 yd 1 mi 1 ~ 4 qt t .-~-X 1 k:m X 1 m X 1760 yd X 1.06 qt X 1 gal = 35 mi/gal SEE EXERCISE 1.50...
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