Week 2 Worksheet Key - practice problems answer key PDF

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General Chemistry Week Two (Chapter 2-3) Worksheet Course checklist: MC2 (due 8/29), IQ4-6 Chapter 3 should be READ for discussion. Coming up: MC3 (due 9/5), no class on Labor Day (9/3) Exam #1 is 9/17 (3 weeks!)

Scientific Notation 1) Write the following numbers using scientific notation. a.) 1000 1 x 103

b.) 978100000 9.781 x 108

c.) 0.8470 8.470 x 10-1

2) Write the following numbers using decimal notation. a.) 8 x 105 800000

b.) 3.94 x 103 3940

c.) 5.4 x 10-3 .0054

Significant Figures 3) How many sig figs are in the following numbers? a.) 4050 Three

b.) 12000000 Two

c.) 12000000. Eight

d.) 0.000482 Three

e.) 0.002500 Four

f.) 1.2 x 107 Two

Significant figures in calculations 4) Perform the following calculations reporting your answers with the appropriate number of sig figs.

3.20

a.) 1000 x 22

b.) 2147 x 82

c.)

20000

180000

64

d.) 800 + 900 1700

e.) 1380 – 10.7 1370

f.) 0.0055 – 0.00250 0.0030

g.) (3.50 x 103 + 2.84 x 103) x 0.020

h.)

130

0.18

0.0024+5.003

0.050

i.) 7.5 x 10-2 + 8 x 10-2 x 3.5

100−72

0.4

Units of Measurement 5) Perform the following unit conversions and report the correct number of significant figures. b.) 3.5 x 107 μs to s 35 seconds

a.) 3.5 kJ to J 3500 Joules

c.) 6 L to mL 6000 milliliters

d.) 4 g/mL to kg/kL e.) 2 m3 to mm3 4 g/mL * (1000 mL / 1 L) * (1000 L / 1kL ) * (1 kg / 1000 g) = 4000 kg/kL 2 m3 ∗ (

1000 mm 3 1m

) = 2 ∗ 109 mm3 OR 2 m3 ∗

1000 mm 1m

∗

1000 mm 1m

∗

1000 mm 1m

6) Silver’s density is 10.49 grams per cubic centimeter. a.) What is the volume of a block of silver that is 30.0 grams? 30.0 g ∗

1 cm3 Ag

10.49 g Ag

= 2.86 cm3

b.) What is the mass of a cube of silver that is 10. cm on a side? 10.3 cm3 ∗

10.49 g Ag 1 cm3 Ag

= 10490 g Ag, has to be 1.0 x 10^4 for reporting two sig figs.

Mixtures 7) Provide examples of a homogenous or heterogeneous mixture at your table and explain your reasoning.

Physical and Chemical changes 8) Classify each change as a physical or chemical change P or C . a) Gasoline exhibiting gasoline odor-physical change. Liquid to gas. b) The burning of gasoline in an engine-chemical change --combustion c) Copper turning green when exposed to air-chemical change—rust/oxidizing d) Melting of a sugar cube-physical change—solid to liquid e) Sugar dissolving into coffee—physical change—solid to aqueous, dissolved.

9) Perform the following conversions: a. 22.5 kilowatt-hours (kWh) to Calories (Cal) 22.5 kWh

3.60 x 106J

1 cal

I Cal

1 kWh

4.184 J

1000 cal

c. 277 Kelvin (K) to °C 277 K -273.15 = 4°C

b. 67.13 Joules (J) to calories (cal)

1.94 x 104 Cal

67.13 J

d. 53.0 °F to K (53F – 32) x (5/9) + 273.15 = 285K

1 cal

16.04 cal

4.184 J

e. 19.0 °C to °F 19.0 °C x (9/5) + 32 = 66.2 F

Specific Heat capacity 10) Specific heat capacity is the amount of energy input that it takes to raise 1 gram of a substance 1 degree Celsius which is expressed in the units J/(g*C). I have a pot that contains 1.0 L water at room temperature (22 degrees Celsius) and 169.66 kJ of energy is added on the stovetop. Its temperature raises by 40.5 degrees Celsius. What is the specific heat capacity of the water? (Hint: we need the density of water for this problem!)

Convert 1 liter of water to grams using the density of pure water. Convert kilojoules to joules I would suggest being able to see how the units guide your math here, and an understanding of the fact that room temperature water is not ice (this is why you plug 40.5 C for delta Temp rather than 62.5).

Answer is 4.2 J/(g*C) which is close to the specific heat of water on your exam information sheet. The final temp of water would be 60.5 or -18.5 degrees Celsius. NOTE: this ignores a key idea we will learn later and is not the correct answer....