Science and Measurement

OpenStax Chemistry, 2nd edition

Chapter 1: Essential Ideas

Learning Objectives

1.1 Chemistry in Context

            ·  Outline the historical development of chemistry

·  Provide examples of the importance of chemistry in everyday life

·  Describe the scientific method

·  Differentiate among hypotheses, theories, and laws

·  Provide examples illustrating macroscopic, microscopic, and symbolic domains

1.2 Phases and Classification of Matter

·  Describe the basic properties of each physical state of matter: solid, liquid, and gas

·  Distinguish between mass and weight

·  Apply the law of conservation of matter

·  Classify matter as an element, compound, homogeneous mixture, or heterogeneous mixture

 with regard to its physical state and composition

·  Define and give examples of atoms and molecules

1.3 Physical and Chemical Properties

            ·  Identify properties of and changes in matter as physical or chemical

·  Identify properties of matter as extensive or intensive

1.4 Measurements

            ·  Explain the process of measurement

·  Identify the three basic parts of a quantity

·  Describe the properties and units of length, mass, volume, density, temperature, and time

·  Perform basic unit calculations and conversions in the metric and other unit systems

1.5 Measurement Uncertainty, Accuracy, and Precision

            ·  Define accuracy and precision

·  Distinguish exact and uncertain numbers

·  Correctly represent uncertainty in quantities using significant figures

·  Apply proper rounding rules to computed quantities

1.6 Mathematical Treatment of Measurement Results

·  Explain the dimensional analysis (factor label) approach to mathematical calculations involving quantities

·  Use dimensional analysis to carry out unit conversions for a given property and computations

 involving two or more properties

Resources

1.1 Chemistry in Context 

Chemistry is the central science.

The scientific method:

•Chemistry is a science based on observation and experimentation.

•Chemists often formulate a hypothesis: a tentative explanation of observations. 

•The laws of science summarize a vast number of experimental observations, 

and describe or predict some facet of the natural world.

•Theory: A well-substantiated, comprehensive, testable explanation of a particular aspect of nature.

The macroscopic, microscopic, and symbolic domains:

Chemists study and describe the behavior of matter and energy in three different domains.

1) The macroscopic domain is familiar to us: It is the realm of everyday things that are

 large enough to be sensed directly by human sight or touch.

2)  The microscopic domain of chemistry is almost always visited in the imagination. 

Micro also comes from Greek and means “small.” Some aspects of the microscopic domains

 are visible through a microscope. 

3) The symbolic domain contains the specialized language used to represent components of the

 macroscopic and microscopic domains, such as chemical symbols. 

1.2 Phases and Classification of Matter

The three common phases of matter are solid, liquid, and gas.

Classification of matter as a pure substance or a mixture:

Compounds: Pure substance that can be broken down into simpler substances by chemical change.

1.3 Physical and Chemical Properties

A physical property is a characteristic of matter that is not associated with a change in its chemical composition. 

Examples: density, color, hardness, melting and boiling points, and electrical conductivity

A physical change is a change in the state or properties of matter without any accompanying change in its chemical composition. 

The change of one type of matter into another type (or the inability to change) is a chemical property.

        Examples: flammability, toxicity, acidity, reactivity, and heat of combustion.

     Extensive property

•Depends on the amount of matter present. 

•Examples: mass, volume, heat

   Intensive property

•Does not depend on the amount of matter present. 

•Examples: density, temperatureIdentify properties of matter as extensive or intensive

1.4 Measurements

            Every measurement provides three kinds of information:

1) The size or magnitude of the measurement: a number

2) A standard of comparison for the measurement: a unit

3) An indication of the uncertainty of the measurement.

1.5 Measurement Uncertainty, Accuracy, and Precision

Accuracy and precision:

A measurement is said to be precise if it yields very similar results when repeated in the same manner.

A measurement is considered accurate if it yields a result that is very close to the true or accepted value.

Counting are exact numbers all other measurements have uncertainty associated with the measurement.

Rules for Significant Figures in Calculations: Results calculated from measured numbers are at least as

 uncertain as the measurement itself. 

1) When we add or subtract numbers, we should round the result to the same number of decimal

 places as the number with the least number of decimal places (the least precise value in terms of

 addition and subtraction).

2) When we multiply or divide numbers, we should round the result to the same number of digits

 as the number with the least number of significant figures (the least precise value in terms of 

multiplication and division).

3) If the digit to be dropped (the one immediately to the right of the digit to be retained) is less

 than 5, we “round down” and leave the retained digit unchanged; if it is more than 5, we

 “round up” and increase the retained digit by 1; if the dropped digit is 5, we round up or down,

 whichever yields an even value for the retained digit.

1.6 Mathematical Treatment of Measurement Results

Each equivalence statement provides two unit conversion factors.

For example, 2.54 cm = 1 in. gives,