Chapter 1 - Measurements in Chemistry

Science – a way of knowing and understanding the universe (from Latin scire, "to know")

Scientific Method - the process by which science operates

    1. Observation – facts gathered by experiments
    2. Hypothesis – a tentative explanation of related ideas. It can be used to predict result of more experiments.
    3. Experiment – Search for new information to help support hypothesis.

Scientific Laws - Large amounts of scientific data summarized in a brief statement.

Scientific Theories - Detailed explanations of the behavior of matter based on experiments; may be revised if new data warrants.

Measurement – determines the quantity, dimensions, or extent of something usually in comparison to a specific unit.

Unit – a definite quantity adopted as a standard of measurement.

Significant figures (digit) – a digit that is either reliably known or estimated.

Precision - relates to the degree of Reproducibility of the measurement.

Accuracy - refers to how close the measurement is to the true value.

Scientific Notation

in science are many very large or very small numbers, need a simple method to describe these numbers. The use of an exponent and the factors of 10 will be used.

100 = 1 10-1 = 0.1
101 = 10 10-2 = 0.01
102 = 10 x 10 = 100 10-3 = 0.001
103 = 10 x 10x10 = 1000 10-4 = 0.0001

What if number is not a factor of 10?

Need to move the decimal and multiply by the factor of 10.

Mass, Length and Volume

Use the Metric system of measurement, not English

SI Units - extremely precise standards

Volume - space that a give quantity of matter occupies:  SI unit = 1 liter = 1 L

Mass - the quantity of matter that a sample contains.  SI unit = 1 gram = 1 g

Length - SI unit = 1 meter = 1 m

Significant figures

Counting Significant figures.

  1. all integers 1-9 are significant
  2. zeros
    1. trailing zeros - only when decimal is present
    2. captive zeros - always
    3. leading zeros - never

What happens to the precision when we do calculations?

1. Addition/ Subtraction - lowest number to the right of the decimal

2. Multiplication/division - answer has lowest number of sig. figs. total.

Conversion factor - relationship between the units expressed as fractions.

 

Dimensional Analysis - The relationships above can be expressed in terms of fractions ( unit fraction)

1000 m = 1 km

divide each side by 1 km divide each side by 1000 m

To convert from one unit to another

(what's given) x (conversion factor) = (what's requested)

or

Temperature - a measure of the intensity of heat of a substance

For WATER

Temperature Conversions

T(K) = t(° C) + 273K