Scientific Method

Hypothesis: prediction concerning a phenomenon/educated guess which can be tested
Experiment: hypothesis is tested
Data: facts from the observation and measurements
Scientific Laws: summary of patterns in brief statements
Theory: explanation of the observations and the predications can be tested

Scientific Measurements

The metric system or SI (international system) is

a decimal system based on 10
used in most of the world
used everywhere by scientists

Units in the Metric System

Measurement Metric SI

Length meter(m) meter(m)
Volume liter(L) cubic meter(m^3)
Mass gram(g) kilogram(kg)
Time second(s) second(s)
Temperature Celsius(C) Kelvin(K)

Comprehension Check

A bag of tomatoes is 4.6kg

mass

A person is 2.0 m tall

length

A medication contains 0.50g of aspirin

mass

A bottle contains 1.5L of water

volume

Temperature Conversion

Tc= Tf - 32/1.8

Tf= 1.8Tc +32

K=C+273.15

Comprehension Check

85C------>F
-12.2C------>F
335F------->C
20.8F------->C

Uncertainty in Measurements

Exact: numbers with defined values
Inexact: numbers obtained from any other method other than counting

Inexact beacause of inaccurately calibrated instruments, human error etc.

There are two ways to gauge the quality of a set of measure numbers:

Precision: measure of how closely individual measurements agree with each other
Accuracy: how closely individually measured numbers agree with the correct or true value

Significant Figures

use to conveny uncertainty

non zero digits are always significant; 1 2 3 etc.
Zeros between nonzero digits are always significant; 1005
Zeros at the beginning of a number are NEVER significant. they are place holders; 0.02 1 sig fig
Zeros that fall at the end of a number and after the decimal point are always significant; 0.200g has 3 sig figs. 2.0 has 2 sig figs
When a number ends in zeros but contains no decimal point, the zeros are not significant; 130 2 sig figs 10300 3 sig figs

Comprehension Check

How many sig figs in the following numbers?

7.001

4

0.0107

3

Multiplication and Division

the same number of sig figs as the measurement with the fewest sig figs must be used
use rounding rules to obtain the correct number of sig figs

Addition and Subtraction

use the same number of decimal places as the measurement with the fewest decimal places
use rounding rules to adjust the number of digits in the answer

Conversion Factor Method

Equalities

use two different units to describe the same measured amount
are written for relationship between units of the metric system, US units, or between metric and US units

EX: 1m=1000mm

A conversion factor

a fraction obtained from an equality

1in=2.54cm

written as a ratio with numerator/denominator
can be inverted to give two conversion factors for every equality
may be obtained from information in a word problem

Problem Solving: Given and Needed Units

To solve a problem

Identify the GIVEN
Identify the NEEDED
write them down
write a unit plan to convert the given unit to the needed unit
write equalities and conversion factors that connect the units
use conversion factors to cancel the given unit and provide the needed unit

Density

compares the mass of an object to its volume
is the mass of a substance divided by its volume
Density=mass/volume g/ml

Volume by displacement

a solid completely submerged in water displaces its own volume of water
the volume of the solid is calculated from the volume difference

Density as a Conversion Factor

a substance of 3.8 g/ml equates to

3.8g=1ml

The Foundations of Chemistry: Matter,Energy, and Measurements