Problem Set 2 - Chem 105 PDF

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Problem(Set(02(–(Measurement,(Calculation! Chem!105! 1. (a) Define precision and accuracy (1 sentence each). Precision: Accuracy: (b) To test the precision and accuracy of a weight scale in the laboratory, you take a small metal block that is known to be exactly 1.000 g and weigh it three times on the scale. Three measurements are reported as follows: 0.843 g, 0.842 g, and 0.843 g. Is this scale precise, accurate, both, or neither? Explain your choice in 1 sentence. 2. If the real weight of an object is 100 grams, state whether the following measurements are precise, accurate, both, or neither, and explain why. a. 112 g, 118 g, 106 g b. 99.7 g, 100.1 g, 100.2 g c. 110 g, 111 g, 110.5 g d. 105 g, 93 g, 102 g e. 105 ± 2 g f. 100.5 ± 0.2 g 3. How many sig figs are in the following number? 0.0509200 4. Perform the following calculations for measured numbers. Give your answers in scientific notation with the correct units and number of significant figures. a. 124 mg + 316 mg b. 613 µL + 582 µL c. 4´10–3 mL – 2´10–5 mL d. 85 ng ´ 34 ng e. 6.31´104 pm ´ 3.536 ´105 pm f. 25.34 cm ÷ 1.55´10–4 cm 5. Perform the following calculations for measured numbers. Convert your answers to the SI unit for that quantity (m, kg, m3, kg/m3). Give your answers with the correct number of significant figures. a. 77.3 g + 41.7 g b. 123.4 Gm – 68.93 Gm c. 21.7 cm ´ 9300 cm2 d. (2.76´103)(7.4´102) nL e. 8.1´10–1 µm – 3.7´10–8 µm f. 387 pg ÷ 2´10–2!mL

6. Comfortable room temperature is about 72°F. Body temperature is about 98°F. Water freezes at 32°F and boils at 212°F. The lowest temperature ever recorded at sea level (by a human) was −128.6 °F at the Soviet Vostok Station in Antarctica, on July 21, 1983. Convert these temperatures to °C and K. 72°F 98°F 32°F 212°F −128.6 °F 7. The diameter of a US dime is 17.9 mm, and the diameter of a silver atom is 2.88 Å. How many silver atoms could be arranged side-by-side across the diameter of a dime? (10 Å = 1 nm).

8. Which of the following represents the largest amount of matter? a. 3.0 ´ 10–1 Mg b. 4.5 ´ 102 mg c. 1.0 ´ 107 µg d. 2.0 ´ 108 ng e. 2.5 ´ 1013 fg 9. Lead metal (11.3 x 109 ng/ml), tungsten (0.019 kg/ml), and liquid mercury (13.5 g/cm3) are all very dense. If chunks of lead and tungsten are placed in liquid mercury, will they sink or float? Does it matter what size the chunks are? Why or why not?

10. The price of gold in May was $1,228.40 per ounce (1 ounce = 28.35 g). A typical gold bar such as those shown here has a mass of 12.4 kg. a. How much would one of these bars of gold cost?

b. The density of gold is 19.3 g/cm3. Suppose a certain gold wedding ring displaced 0.55 mL of liquid when dropped in a glass of sparkling cider. How much did this wedding ring cost? (assuming you paid the market price of gold)

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