Ch1 Chemistry

The study of composition, structure,

properties, and reactions of matter.

Branches:

– General

– Organic

– Biochemistry

Describing Observations

Qualitative- observations using

words to describe something

Quantitative- measurements using

equations and mathematics to

describe something

Models- scientific tool for studying

large or small substances/systems

Ch 2.1 International System

CH. 2.3

Reliability of Measurements

Accuracy- the extent to which

a measurement approaches

the true value. (bull’s eye)

–Ex. Your results in an

experiment for the density of

water is 1 g/ml.

Reliability of Measurements

Precision – the degree of

exactness of a measurement.

-the consistency of results in

an experiment

Measuring Precision

Measuring Precision

More Precise

Measuring Precision

Significant Digits (figures)

–Determines the precision

of a measured number.

–Counting (exact) numbers

have indefinite amount of

sig. fig.

Sig Fig Rules

1. All digits 1-9 are significant.

Ex. 4567 has 4 sig figs

Ex. 34.989 has 5 sig figs

2. Any zeros between two

significant digits are significant

Ex. 45078 has 5 sig figs

Ex. 45.0387 has 6 sig figs

Sig Fig Rules 3. Any number bigger than “1” containing a decimal

point, all the numbers will be significant.

Ex. 2.00 has 3 sig figs

Ex. 34.900 has 5 sig figs

Ex. 7000. has 4 sig figs

4. Zeros used solely as plac holders, are NOT

significant.

Ex. 0.00783 has 3 sig figs

Ex. 7,000,000 has 1 sig fig

Sig Fig Review

Ch. 2.4 Calculating Rules • The product or quotient will be reported as having as

many significant digits as the number with the least

significant digits.

Ex. 12.65 cm x 42.1 cm = 532.565

=533 cm2

• The sum or difference must have the same number

of decimal places than the number with the least

number of decimal places.

Ex. 10.13 g + 20.5 g = 30.63

= 30.6 g

Where the Heck to Round?

Ch 2.2 SCIENTIFIC NOTATIONA way of expressing really big or small numbers.

N x 10A

N is the proper significant digit

A is the number of times you moved decimal

Positive = big, Negative = small

Page 30 and 31 review using calculator

Ch 2.5 The Metric SystemUniversal language of measurement

SI base units are used for consistency than the

imperial system

Scientist all over the world use, thus making it easy to

communicate.

The system uses a series of prefixes to identify large

and small measurements.

This makes the measurements easy to convert from

each other.

– Prefixes are based on a factor of 10

Countries that don’t use Metric System

Base Unit (1)

Ch. 2.6,7 Dimensional Analysis

(factor label)

A math skill of organizing and converting one unit to another

Conversion Factor: a fraction that always equals one.

Ex. 1 km = 1000 m, so 1km/1000 m = 1 or 1000m / 1km =1

Steps

12 m = ? cm

1. Write what they give you.

2. Find conversion factors.

3. Set up conversion factor by

placing unit to cancel on bottom

and unit to keep on top.

4. Do math: multiply then divide.

Ch 2.7 Derived Units

Units can be made into derived or

combined units

Units formed as result of a calculation

g/ml, mol/L, grams/mol, m/s, or cm3

Why do some things float while

others sink?

Ch. 2.7 Density

Measures how closely packed molecules

are in a given volume

Mass divided by volume

D=m/v

Rearrange to solve for m and v

Density Units

Density is the derived unit g/ml or g/cm3

Example

An unknown metal is measured to be 36 grams. What is it’s density if it has a volume of 15.5 cm3?

D=m/v d= 36 g/ 15.5 cm3

D = 2.322 g/cm3

Last point is sig. figs. 2.3 g/cm3

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