Unit 1

Matter and Measurement

Classifications of Matter

Matter is typically characterized by:

  1. Its physical state (gas, liquid, or solid)
  2. Its composition (element, compound, or mixture)

States of Matter

Gas — no fixed volume or shape, and can be compressed or expanded as there is space between the molecules.

Liquid — distinct volume but no distinct shape, cannot be compressed.

Solid — definite volume and shape, cannot be compressed.

Composition

A pure substance (or substance) is matter that has distinct properties and a composition that does not vary sample to sample.

Two types of substances: elements and compounds.

  • Elements are substances that cannot be decomposed into simpler substances.
  • Compounds are substances composed of two or more elements (e.g. water).

Most elements can interact with other elements to form compounds. The elemental composition of a compound is always the same; this is called the law of constant composition.

In a mixture, each substance retains its chemical identity and properties. The composition of a mixture may vary in quantities.

Homogenous mixtures are also called solutions, even if they're not liquid.

Properties of Matter

  • Physical properties — can be observed without changing the identity and composition of the substance.
  • Chemical properties — describe the way a substance may change to form other substances.
    • For example, flammability.
  • Intensive properties — do not depend on the amount of sample.
    • These can be used to identify substances.
  • Extensive properties — depend on the amount of sample.
    • For example, mass and volume.

Uncertainty in Measurement

Definitions

  • Exact numbers — numbers whose values are known exactly.
  • Inexact numbers — numbers whose value have some uncertainty.
    • All numbers obtained from measurement are inexact because of equipment or human errors.
  • Precision — how closely individual measurements agree with one another.
  • Accuracy — how closely individual measurements agree with the true value.

Significant Figures

All digits of a measured quantity, including the uncertain (last) digit, are called significant figures.

Determine significant figures by reading a number left to right and counting digits, starting with the first non-zero digit.

The zeroes in a number that ends with zeroes but contains no decimal point are assumed to be not significant.

However, this can be more clearly expressed with scientific notation: 1.03 * 10^4 (three significant digits) 1.0300 * 10^4 (five significant digits)

Significant Figures in Calculations

The final answer should be reported with only one uncertain digit.

Addition and Subtraction

The result has the same number of decimal places as the measurement with the fewest decimal places.

Example: 20.42 + 83.1 = 103.52 ⇒ 103.5

83.1 only has one decimal place, so the answer must be rounded to one decimal place.

Multiplication and Division

The result contains the same number of significant figures as the measurement with the fewest significant figures.

Example: 6.221 * 5.2 = 32.3492 ⇒ 32

5.2 only has two significant figures, so the answer must be rounded to two significant figures.

Dimensional Analysis

Dimensional analysis is the practice of multiplying or dividing units along with the numbers.

The key is using conversion factors, such as this one:

2.54 cm1 in.\frac{2.54 \, \text{cm}}{1 \, \text{in.}}

To calculate the units like this:

(8.50 in.)∗2.54 cm1 in.=21.6 cm(8.50 \, \text{in.}) * \frac{2.54 \, \text{cm}}{1 \, \text{in.}} = 21.6 \, \text{cm}

The inches cancel out on top and bottom leaving just centimeters.