Chapter 1 Questions in Class PDF

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Dr. Rita Upmaics lecture material...

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Law of Conservation of Mass Example: Aluminum powder burns in oxygen to produce a substance called aluminum oxide. A sample of 2.00 grams of aluminum is burned in oxygen and produces 3.78 grams of aluminum oxide. How many grams of oxygen were used in this reaction? (a)  1.78 g oxygen (b)  2.00 g oxygen (c)  3.78 g oxygen aluminum

+ oxygen

= aluminum oxide

2.00 g aluminum + x g oxygen = 3.78 g aluminum oxide x

= 1.78 g oxygen

(Answer a)

An example of Physical versus Chemical Properties

Potassium is a soft, silvery-colored metal that melts at 64°C. It reacts vigorously with water, with oxygen, and with chlorine. Which are physical properties? (a)  It is a soft metal (b)  It melts at 64°C (c)  Both of the above

Physical Property

Chemical Property

Soft

Reacts with water

Silvery-colored

Reacts with oxygen

Melting point (64°C)

Reacts with chlorine

SI Prefixes and Conversions What is 1.0 ng when expressed in g? (a) 1.0 x 109 g (b) 1.0 x 10-9 g

1 nano unit is 10-9 units 1 nanogram is 10-9 grams 1.0 ng x

10-9 g = 1.0 x 10-9 g 1 ng

1.0 ng x

1 g = 1.0 x 10-9 g 9 10 ng

SI Prefixes and Conversions What is 4.851 x 10-9 g when expressed in ng? (a) 4,851 ng (b) 4.851 ng (c) 0.4851 ng

4.851 x 10-9 g

4.851 x

10-9

g

1 ng 10-9 g

= 4.851 ng

109 ng x 1 g

= 4.851 ng

x

109 is the conversion factor for g to ng

SI Prefixes and Conversions What is 8.93 x 10-9 s when expressed in ps? (a)  8.93 ps (b)  8930 ps (c)  0.0893 ps

8.93 x 10-9 s

8.93 x

10-9

s

1 ps 10-12 s

= 8.93 x 103 ps = 8930 ps

1012 ps x 1 s

= 8.93 x 103 ps = 8930 ps

x

1012 is the conversion factor for s to ps

SI Prefixes and Conversions What is 25.4 cm when expressed in m? (a)  2.54 x 10-2 m (b)  2.54 x 10-1 m (c) 

2.54 x 101 m

25.4 cm x

10-2 m = 25.4 x 10-2 m = 2.54 x 10-1 m 1 cm

25.4 cm x

1 m = 25.4 x 10-2 m = 2.54 x 10-1 m 2 10 cm 10-2 is the conversion factor for cm to m

A Density Example A sample of the mineral galena (lead sulfide) weighs 12.4 g and has a volume of 1.64 cm3. What is the density of galena? (a)  0.132 g/cm3 (b)  20.3 g/cm3 (c)  7.56 g/cm3

mass

12.4 g =

Density = volume

1.64 cm3

= 7.5609 = 7.56 g/cm3

Oil and Water Substance

Density (g/mL)

octane water

0.70 1.00

• The densities of hydrocarbons (e.g. octane) are less than that of water and so oil floats on water.

salad dressing

BP oil spill

Densities of Common Substances Substance

Density (g/mL)

zinc copper mercury

7.13 8.96 13.53

• Mercury is the densest liquid under normal conditions and otherwise dense objects will float on it.

A cent floats on mercury because it is copper-plated zinc and both elements are less dense than mercury

A man floating on mercury (don't try this at home!)

Densities of Common Substances Substance

Density (g/mL)

mercury gold

13.53 19.28

Question: Will gold float on mercury? (a)  Yes (b) No

Mercury dissolves gold (and many other metals) forming amalgams. Don’t break a mercury thermometer on a gold wedding ring!

don't try it!

Dental amalgams are ≈ 50% mercury, 30% silver, and smaller amounts of tin, copper and zinc.

Densities of Common Substances Substance

Density (g/mL)

potassium water

0.89 1.00

Question: Will potassium float on water? (a)  Yes …but, be careful (b) No

Potassium does float on water... but it reacts violently!...