Chapter 2 Measurements and Calculations Integrated Chemistry Chapter 2 ...

Chapter 2

Measurements and Calculations

Chapter 2 Section 1

Section 2-1 Objectives Describe the purpose of the scientific method. Distinguish between qualitative and quantitative observations. Describe the differences between hypotheses, theories, and models.

Scientific Method: a logical approach to

understanding or solving problems that needs solved.

Integrated Chemistry

The goal is to solve a problem or to better understand an observed event.

The scientific method is a set of processes and scientists may repeat stages many times before there is sufficient evidence to formulate a theory. You can see in the diagram above that each stage represents a number of different activities.

? Aspects of the Scientific Method Observation is information that you obtain through your

senses. Repeatable observations become known as facts. Generalizing/ Hypothesis: A hypothesis is a testable statement that

serves as the basis for predictions and further experiments.

Your hypothesis addresses questions raised by your observations. Your hypothesis states that one variable causes a change in another variable. Testing / Experimenting ? Controlled Experiment: an experiment in which only one variable, the manipulated variable, is deliberately changed; the responding variable is observed for changes, all other variables are kept constant (controlled). Theorizing: A theory is a broad generalization that explains believed facts or phenomena.

Chapter 2

Measurements and Calculations

A scientific theory is a well-tested explanation for a set of

observations or experimental results, supported in repeated

experiments by scientists.

Theories are never proved; they become stronger if the

facts continue to support them. However, if an existing

theory fails to explain new facts and discoveries, the

theory must be revised or a new theory will replace it.

A scientific law is a statement that summarizes a pattern found in

nature.

A scientific law describes an observed pattern in nature without attempting to explain it.

Model: representation, of an object or event. Scientific models are used to make it easier to understand things that might be too difficult to observe directly.

Integrated Chemistry

HW: Section Review Page 31 #1-5; Chapter Review: Page 59 #1-3 SECTION REVIEW Page 31 1. What is the scientific method? 2. Which of the following are quantitative?

a. the liquid floats on water b. the metal is malleable c. the liquid has a temperature of 55.6?C 3. How do hypotheses and theories differ? 4. How are models related to theories and hypotheses? 5. What are the components of the system in the graduated cylinder shown on page 38?

FIGURE 2-7 (from page 38 in your text) Density is the ratio of mass to volume. Both water and copper shot float on mercury because mercury is more dense.

Chapter 2

Measurements and Calculations

Integrated Chemistry

Chapter 2 Section 2

Chapter 2-2 Objectives 1. Distinguish between a quantity, a unit, and a measurement

standard. 2. Name SI units for length, mass, time, volume, and density.

3. Distinguish between mass and weight. 4. Perform density calculations. 5. Transform a statement of equality to a conversion

factor.

Measurements are quantitative information.

Measurements represent quantities (how much, how big etc.).

However; they are not the same thing,

Measurements use specific units Quantity states what the unit means.

For example, the quantity represented by a teaspoon is volume. The teaspoon is a unit of measurement, while volume is a quantity.

Scientists have agreed on a single measurement system: The SI (Le Syst?me International d'Unit?s). SI units are defined in terms of standards of measurement. SI has seven base units; other units are derived from these seven.

Numbers are written in a form that is agreed upon internationally. The number seventy-five thousand is written 75 000, not 75,000, because the comma is used in other countries to represent a decimal point. In place of the comma a space is used to avoid confusion

Some non-SI units are still commonly used by chemists and are also used in this class.

The standards are objects or natural phenomena that are of constant value, easy to preserve and reproduce, and practical in size. In the United States, the National Institute of Standards and Technology plays the main role in maintaining standards and setting style conventions.

Select Base Units ? See Table 2-1 page 34 for the entire list

Quantity Unit

Quantity symbol Unit name

abbreviation

Length

l meter

m

Mass

m kilogram kg

Time

t second

s

Temperature

T Kelvin

K

Amount of matter n mole

mol

Chapter 2

Measurements and Calculations

Mass & Weight Mass is often confused with weight because people

often express the weight of an object in grams, this is incorrect ? weight is measured in newtons a derived unit.

Mass is determined by comparing the object to a set of standards that are part of the balance. Weight is a measure of the gravitational pull on mass, and depends on gravity. Mass is measured on instruments such as a balance and weight is typically measured on a spring scale.

Length: The standard unit for length is the meter.

To express long distances, the kilometer (km) is used. To express shorter

distances, the centimeter is often used.

Derived SI Units

Many SI units are combinations of the Base units

Combinations of SI base units form derived units.

See Table 2-3 page 36.

Volume is the amount of space occupied by an object. The derived SI unit of volume is cubic meters, m3.

Such a large unit is inconvenient for expressing the volume of materials in

a chemistry laboratory.

A smaller unit, the cubic centimeter, cm3, is used. There are one

hundred centimeters in a meter, so a cubic meter contains one million cm3. Here is the math:

1m3

X

100 1 m

cm

X

100 1 m

cm

X

100 cm 1 m

=1 000 000 cm3

Density is the ratio of mass to volume, or density equals

D =

m V

mass divided by volume.

Conversion Factors A conversion factor is a ratio derived from the

equality between two different units that can be used to convert from one

unit to the other. By multiplying by the conversion factor, you do not

change the overall meaning of the quantity. A conversion factor is a

ratio made from an equality ? which means the ratio is

equal to one. Example: 1 m = 100 cm which means

100 cm 1 m

= 1

and we can Substitute this in the equation for volume in 1 m3 . . . = ? cm3

After substituting into

1m3 X

100 cm 1 m

X

100 cm 1 m

X

100 cm 1 m

=1

000

000

cm3

you get 1m3 X 1 X 1 X 1 =1 000 000 cm3 = 106 cm3

Integrated Chemistry

Chapter 2

Measurements and Calculations

Then is

1 =

106 cm3 m3

=

now

conversion factor to use

1m3 106 cm3

your final answer 1m3 =106 cm3 and

we have a new

Integrated Chemistry

Note: quantity sought = quantity given multiplied by the conversion factor

Examples: page 39 sample problem (sp) 2-1; page 41 sp 2-2

HW: Practice Problems: Page 40 #1-3(AT THE TOP OF THE PAGE; page 42 #1-5 Chapter Review: Page 59 #12 -15; 27-29; 32-34

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