# Chem 208 Notes

Slide 1

Lesson 1.1 : Scientific Method

1. Steps of the Scientific Method

The scientific method (performing a study in organized steps) consists of:

For example, applying the scientific method ultimately led to the enunciation of the Law of Conservation of Mass and Matter. Slide 2

1. Steps of the Scientific Method

Step 1: Performing Experiments

An experiment is a set of steps (procedures) that are performed under controlled conditions to propose or test a hypothesis. Step 2: Making Observations

Observations (a key factor in scientific studies as well as in everyday life) can be classified as: Qualitative| Quantitative|

Qualitative observation does not use numbers. Examples: * The flower is purple. * Bubbles are produced when lemon juice is added to baking soda.| Quantitative observation is a measurement. It has two components: * A measured quantity (numerical value) with an appropriate unit. Example:Observed temperature (measured using a thermometer) for the liquid was found to be 33°C. In this case, the measured quantity is temperature and the appropriate unit is °C.| | |

Step 3: Proposing a Hypothesis

A hypothesis is a tentative explanation to account for the observations of an experiment. A hypothesis is valid provided that one's assumptions to explain the observations of an experiment can be tested. Step 4: Confirming the Hypothesis

The validity of the hypothesis needs to be confirmed via repeated and controlled experiments. In order to accept a hypothesis, there must be no inconsistencies between the hypothesis and the experimental observations. In the event of any inconsistencies, steps 1 through 4 must be repeated. Step 5: Proposing a Scientific Law

By repeatedly performing experiments and modifying the hypothesis to account for the observations from these experiments, one is able to propose a scientific law.

Slide 4

Expression of Numerical Value

Certain rules apply to the expression of the numerical value and the system of units used in scientific measurements. These include:

* Scientific notation

* Significant figures

* SI system of units

Slide 5

2. Scientific Notation

Scientific notation is a very convenient way of expressing very large or very small numbers and at the same time provides a method of increasing efficiency in scientific calculations. It is a mathematical expression in which a number is expressed as: N x 10 ±n where N contains only one nonzero digit to the left of the decimal and n is an integer. Examples:

Measurement | Scientific Notation |

1.23 g | 1.23 x 10 0 g |

1000.4 mL| 1.0004 x 10 3 mL|

0.0012 mg| 1.2 x 10 -3 mg|

28.32 x 10 15 L | 2.832 x 10 16 L |

21.0 million kg| 2.10 x 10 7kg|

Slide 6

3. Significant Figures (Digits)

Every measurement and thus all of the calculations performed by using such measurements always have some uncertainty (a characteristic of any meaurement). This is due to experimental error. In the case of measuring devices, the last digit of the measurement is uncertain. Significant figures (sig.fig.) in a measured number include all certain digits and one uncertain digit. The concept of significant figures is:

• used to indicate the precision [reproducibility (closeness) of measurements] of a measurement or that of a calculated result using such measurements; • does not apply to counted items such as exact numbers (e.g., 5 cars, 3 houses) and defined conversion factors (e.g.,1 inch = 2.54 cm, 1 cal = 4.184 J). These have an infinite number of significant figures.

Slide 7

3. Significant Figures (Digits)

Rules for Determining Significant Figures (Digits) (1/3)

Rule #1: All nonzero digits are significant figures.

Examples:

Measurement | No. of sig. fig. |

135.62 g | 5|

23.6 cm | 3|

17.9871 kg | 6|

Rule #2: Counting begins from the left with the first nonzero number (thus leading zeros are not significant). Examples:...

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