CHEMICAL FOUNDATIONS

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CHAPTER 1

CHEMICAL FOUNDATIONS

Review Questions

• Law versus theory: A law is a concise statement or equation that summarizes observed

behavior. A theory is a set of hypotheses that gives an overall explanation of some phenomenon. A law summarizes what happens; a theory (or model) attempts to explain why it happens.b.Theory versus experiment: A theory is an explanation of why things behave the way they do, while an experiment is the process of observing that behavior. Theories attempt to explain the results of experiments and are, in turn, tested by further experiments.c.Qualitative versus quantitative: A qualitative observation only describes a quality while a quantitative observation attaches a number to the observation. Some qualitative observations would be: The water was hot to the touch. Mercury was found in the drinking water. Some quantitative observations would be: The temperature of the water was 62˚C.The concentration of mercury in the drinking water was 1.5 ppm.d.Hypothesis versus theory: Both are explanations of experimental observation. A theory is a set of hypotheses that has been tested over time and found to still be valid, with (perhaps) some modifications.

• The fundamental steps are

(1)making observations; (2)formulating hypotheses; (3)performing experiments to test the hypotheses.The key to the scientific method is performing experiments to test hypotheses. If after the test of time the hypotheses seem to account satisfactorily for some aspect of natural behavior, then the set of tested hypotheses turns into a theory (model). However, scientists continue to perform experiments to refine or replace existing theories.

• A qualitative observation expresses what makes something what it is; it does not involve a

number; e.g., the air we breathe is a mixture of gases, ice is less dense than water, rotten milk stinks.The SI units are mass in kilograms, length in meters, and volume in the derived units of m 3 .The assumed uncertainty in a number is 1 in the last significant figure of the number.

• Volume readings are estimated to one decimal place past the markings on the glassware. The

assumed uncertainty is ±1 in the estimated digit. For glassware a, the volume would be Chemistry, 11e Steven Zumdahl, Susan Zumdahl, Donald DeCoste (Solutions Manual All Chapters.100% Original Verified, A+ Grade) 1 / 4

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estimated to the tenths place since the markings are to the ones place. A sample reading would be 4.2 with an uncertainty of ±0.1. This reading has two significant figures. For glassware b, 10.52 ±0.01 would be a sample reading and the uncertainty; this reading has four significant figures. For glassware c, 18 ±1 would be a sample reading and the uncertainty, with the reading having two significant figures.

• Precision: reproducibility; accuracy: the agreement of a measurement with the true value.

a. Imprecise and inaccurate data: 12.32 cm, 9.63 cm, 11.98 cm, 13.34 cm

b. Precise but inaccurate data: 8.76 cm, 8.79 cm, 8.72 cm, 8.75 cm

c. Precise and accurate data: 10.60 cm, 10.65 cm, 10.63 cm, 10.64 cm

• Significant figures are the digits we associate with a number. They contain all the certain digits

and the first uncertain digit (the first estimated digit). What follows is one thousand indicated

to varying numbers of significant figures: 1000 or 1 × 10

3

(1 S.F.); 1.0 × 10

3

(2 S.F.); 1.00 ×

10 3 (3 S.F.); 1000. or 1.000 × 10 3

(4 S.F.).

• In both sets of rules, the lease precise number determines the number of significant figures in

the final result. For multiplication/division, the number of significant figures in the result is the same as the number of significant figures in the least precise number used in the calculation.For addition/subtraction, the result has the same number of decimal places as the least precise number used in the calculation (not necessarily the number with the fewest significant figures).

To perform the calculation, the addition/subtraction significant figure rule is applied to 1.5 −

1.0. The result of this is the one significant figure answer of 0.5. Even though both numbers in

the calculation had two significant figures, they both showed uncertainty to the tenths place.Any addition or subtraction of these numbers can at best be known to the tenths place. Next, the multiplication/division rule is applied to 0.50/0.5. A two significant figure number divided by a one significant figure number yields an answer with one significant figure (answer = 1).

• The two scales have different zero points and different degree sizes. In converting from one

to the other, one must account for both differences. The Fahrenheit scale has the smallest change in temperature per degree, while the Celsius and Kelvin scales have the largest change in temperature per degree.

• Consider gold with a density of 19.32 g/cm

3 . The two possible ways to express this density as

a conversion factor are:

3 cm1 g32.19 or g32.19 cm1 3

Use the first conversion factor form when converting from the volume of gold in cm 3 to the mass of gold and use the second form when converting from mass of gold to volume of gold.When using conversion factors, concentrate on the units canceling each other.

• Solid: a state of matter that has fixed volume and shape; a solid is rigid.

Liquid: a state of matter that has definite volume but no specific shape; it assumes the shape of the container. 2 / 4

CHAPTER 1 CHEMICAL FOUNDATIONS 3

Gas: a state of matter that has no fixed volume or shape; it takes on the shape and volume of the container. Unlike the solid and liquid state where the molecules/atoms are very close together, a gas is mostly empty space. Gases are easily compressed.

Pure substance: a substance with constant composition

Element: a substance that cannot be decomposed into simpler substances by chemical or physical means.

Compound: a substance with constant composition that can be broken down into elements by chemical processes.

Homogeneous mixture: a mixture having visibly indistinguishing parts.

Heterogeneous mixture: a mixture having visibly distinguishable parts.

Solution: another name for a homogeneous mixture

Chemical change: a change of substances into other substances through a reorganization of the atoms; a chemical reaction.

Physical change: a change in the form of a substance (solid, liquid, or gas), but not in its

chemical composition: chemical bonds are not broken in a physical change.

Active Learning Questions

• 1 month × 1 yr 365 days 24 hr 60 min

12 months yr day hr

   = 4.38 × 10

4 min

• 1 month × 4 wk 7 days 24 hr 60 min

month wk day hr

   = 4.03 × 10

4 min

• The 4.38 × 10

4 min answer is best. In each calculation, one of the conversion factors is not exact. In the first calculation, 365 days per year is fine for most months except for leap year where there are 366 days per year. In the second calculation, 4 weeks per month is an inexact conversion. There are 52 months per year, which comes out to 4.33 weeks per year.There is a larger percent error in the weeks to month conversion factor than in the days to year conversion factor. Hence, the first calculation gives the better estimate of minutes in a month.

• The best explanation is c. The marble sinks because it is denser that water. Statement c says

that given equal volumes of water and a marble, the same volume of the marble has a greater mass (it is denser). For statement a, surface tension is the resistance of a liquid to increase its surface area. Water can support a paper clip because the denser metal is spread out over a large volume. However, once the paper clip breaks through the surface, it sinks. For statement b, the mass per unit volume of marble is greater than the water, but the overall mass of water in a beaker is more than likely larger than the mass of the marble. For statement d, surface tension can support more dense items on the surface for a certain period of time, but the real reason substances sink in water is that they are denser than water. And for statement e, if the marble 3 / 4

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has a greater mass and a greater volume, then the marble may be less dense than water and it would float. This is an ambiguous statement that does explain why the marble sinks.

• The mass of the sugar and water combined will be 280.0 g (statement iii). No chemical

reaction takes place, so no gases are lost when the sugar dissolves. Because everything is present before mixing as compared to after mixing, mass is conserved.

• The volume should be significantly less than 200.0 mL (statement v). Dry sugar in the

beaker has a lot of empty space between the sugar molecules. When the sugar is dissolved in water, each sugar molecule is surrounded by water molecules. This eliminates the empty space that was present in the dry sugar. Therefore, the volume will be significantly less than 200.0 mL. However, since students probably don’t realize the significant amount of empty space in a dry sugar, answer d is also a reasonable choice for students.

• When a gas boils, water is converted from the liquid phase to the gaseous phase. So water

molecules in the vapor phase are present in the bubbles.

• A physical change is the change of the form of a substance (solid or liquid or gas), but not

in its chemical composition. Chemical bonds are not broken in a physical change. The boiling of water is a physical change; liquid water is converted to gaseous water. In a chemical change, a substance is converted into a different substance by breaking and making new chemical bonds.

• Pudding takes the shape of the container, but the pudding molecules are close together so

there is not a lot of empty space in the pudding. This defines a liquid. However, pouring pudding can be problematic. So, from this observation, a solid designation is also applicable.

• Sand takes the shape of the bucket and it can be poured, so a liquid designation can apply.

However, sand is generally considered a solid made up of silicon and oxygen atoms bonded together in an extended structure. The structure of each sand particle is very ordered, hence the solid designation. A bucketful of sand can pour because there are significant amounts of air in between the sand particles in the bucket and this allows the sand to pour.

• There is no single correct answer. Any drawing showing 2 different compounds, but having

visibly distinguishable parts is correct. For example, a beaker of water (H2O) with an insoluble compound like AgCl(s) at the bottom.

• Any drawing of an element and a compound have the same composition throughout is

correct. The easiest drawings would be two different gases in a container. For example, a container with CO2(g) and N2(g) would be fine. The gases would be equally distributed throughout the container.

• Yes, this is consistent with the scientific method. Paracelsus is instructing his students to learn

by observation. Observation of facts along with experimentation of potential remedies to heal a patient are key parts of the scientific method.

• Experimental results are the facts we deal with. Theories are our attempt to rationalize the facts.

If the experiment is done correctly and the theory can’t account for the facts, then the theory is wrong.

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