Chapter 2.1 thru 2.12

2.1Mass and Weight 

   Mass is the amount of matter in amaterial.

The mass of a body does not vary no matter

where in the universe the object is located.

The mass can be measured by comparing

it to other known masses on a balance.

    Weight is the force that results from the

mutual attraction of a body with the earth.

The weight of an object can vary due to it's

location. An astronaut can be weightless in

orbit around the earth but he is not massless.

2.2 Measurement and Significant

Figures

   Numbers obtained from a measurement are

never exact. They always have some degree of

error associated with them, even the most

precise. Obtained numbers have a certain

number of significant figures associated with

them. The significant figure has all the digits

that are known plus one that is uncertain or

estimated. Exact numbers such as those found

in counting operations(1,2,3ect...) or defined

numbers(12inches in 1ft.) have no uncertainty.

Know these rules

• zeros between nonzero digits are

significant. exp.:

                     306 has three

• zeros that proceed (locate a decimal point)

a nonzero digit are not significant.  exp.:                         

                    0.0035 has two

• zeros that are at the end of the number

that has a decimal point are significant. exp.:

                     0.600 has three

• zeros at the end of a number without a

decimal point are not significant. exp.:

                     1200 has two

Here's an idea! If uncertain of

number of significant figures, try to

change it into scientific notation.

Exp.: 12459 is 1.2459 x 10⁴ and there are 5 of them

Exp.: 450 is 4.5 x 10² and there are 2 of them

2.3 Rounding off Numbers

   If the digit after the one to be retained is 4

or less then this digit and all the others to the

right are dropped and the last digit to be kept

is not changed.

      Exp.: 45.784 to four places = 45.78

If the first digit after the one to be dropped

is 5 or greater, then that digit and all others

to the right are dropped and the last digit

remaining is increased by one.

        Exp.: 23.785 to four places = 23.79

2.4 Scientific Notation of Numbers

   Very long distances are often

so far that scientific notation offers to simplify

the numbers.

    Microscopic measurements are so

small that scientific notation is beneficial as

well.

This method is simply writing numbers as a

power of ten. The scientific notation is a

decimal number between 1 and 10 multiplied

by 10 raised to a power.

                    2431     =     2.431 x 10³

        standard notation                     scientific notation

2.5 Significant Figures in

Calculations

   The results of a calculation based upon

measurements cannot be more precise

than the least precise measurement.

Multiplication or Division

The answer in any multiplication or division

cannot contain any more significant figures

than that measurement which contains the

least number of significant figures.

Examples:12.1 x 6.5 = 6.3 x 10² not 630.36

Try this

Addition and Subtraction

The value must be rounded to the same number

of decimal places as that number with the

least digits to the right of the decimal place.

Examples:       Try this

2.6 The Metric System

The metric system is summarized in the following

table.

The following are some common units that you

will find in the study of chemistry.

*Density: a measure of the ratio of mass to volume

mass/volume              

grams/liter (often used for gases)

grams/milliliter (often used for solids and liquids)

*Sometimes the term specific gravity is used. This is

the ratio of the density of a substance to the density

of water at 40°C. Since the density of water at 40°C

is 1.00 g/ml, specific gravity is the same value

numerically as the density of a substance(but without

dimensions) since the ratios of density of one

material dived by the density of another cancel out.

2.7Measurement of length

   The meter is the standard unit of length

in the metric system which is equal to

39.37 inches. The meter is currently

measured as a derived unit of time. It is

the distance that light travels in

1/299,792,458 of a second.

2.8Problem Solving

   Some basic steps in problem solving:

1. Read the problem and determine what is to be solved.
2. List and label all the data with the proper units.
3. Decide what principles are involved and what mathematical relationships are needed.
4. Set up the problem in a clear and logical fashion.
5. Carry out the mathematical operations making sure to keep the proper number of significant figures.
6. Review the results for reasonableness.

*Dimensional analysis will be stressed

throughout this course.

It should be noted at this point that the measurement of

mass and the measurement of weight although closely

related are two different properties.

The mass of an object is the amount of matter in the object.

This does not change.

The weight of an object is the force of attraction between

that object and typically the earth. The weight of an object

depends upon its place. The force of gravity varies over

the surface and of the earth and of course if the object

leaves the earth it is possible for the object to be

weightless. It is not possible for the object to be massless.

A balance is used to compare the mass of an object that

is known to that of an unknown mass.

Conversion factors; The mass of 1 kg exerts a force

of 2.205lbs therefore:

2.9 Measurement of Mass

   The standard for mass is the kilogram(kg).

One of the most common units that you will

encounter in this course is the gram(g).

which is 1/1000 x kg.

This is a convenient unit of mass measurement

for many laboratory projects.

Metric Units of Mass Table

2.10Measurement of Volume

*Volume is the amount of space required by

a certain amount of matter.

2.11Measurement of Temperature

Temperature is a measure of the kinetic energy

of a system.

There are three commonly used temperature scales:

Celsius  C° = F°-32 
                        1.8

Fahrenheit F° = ( 1.8 x C° ) + 32

Kelvin = C° + 273.15

*Note that there is no degree sign with Kelvin units.

Heat is a form of energy and refers to the amount

of energy in a system.

2.12Density

Density is the ratio of mass of a material to its

volume.

d = mass     =      g               or           d =   g 
      volume           mL                                  cm³

Specific gravity is a term that is   refers to the ratio

of the densities of two substances. Typically it

refers to the ratio of the densities of one material

to that of liquid water at 4 C° at which point the

water has a density of 1.00g/mL.