Measurement and Significant Figures

Steps in the Scientific Method 1. Observations -quantitative - qualitative 2.Formulating hypotheses - possible explanation for the observation 3.Performing experiments - gathering new information to decide whether the hypothesis is valid whether the hypothesis is valid

Outcomes Over the Long-Term Theory (Model) - A set of tested hypotheses that give an overall explanation of some natural phenomenon. Natural Law - The same observation applies to many different systems

Law vs. Theory A law summarizes what happens A theory (model) is an attempt to explain why it happens. Einstein's theory of gravity describes gravitational forces in terms of the curvature of spacetime caused by the presence of mass

Nature of Measurement Part 1 - number Part 1 - number Part 2 - scale (unit) Examples: 20 grams 6.63 x Joule·seconds A measurement is a quantitative observation consisting of 2 parts:

The Fundamental SI Units (le Système International, SI)

Celsius & Kelvin

SI Prefixes Common to Chemistry

Uncertainty in Measurement A digit that must be estimated is called uncertain. A measurement always has some degree of uncertainty.  Measurements are performed with instruments  No instrument can read to an infinite number of decimal places

Precision and Accuracy Accuracy refers to the agreement of a particular value with the true value. Precision refers to the degree of agreement among several measurements made in the same manner. Neither accurate nor precise Precise but not accurate Precise AND accurate

Types of Error Random Error (Indeterminate Error) - measurement has an equal probability of being high or low. Systematic Error (Determinate Error) - Occurs in the same direction each time (high or low), often resulting from poor technique or incorrect calibration. This can result in measurements that are precise, but not accurate.

Rules for Counting Significant Figures - Details Nonzero integers always count as significant figures has 4 sig figs.

Rules for Counting Significant Figures - Details Zeros -Leading zeros do not count as significant figures has 3 sig figs.

Rules for Counting Significant Figures - Details Zeros -Captive zeros always count as significant figures has 4 sig figs.

Rules for Counting Significant Figures - Details Zeros Trailing zeros are significant only if the number contains a decimal point has 4 sig figs.

Rules for Counting Significant Figures - Details Exact numbers have an infinite number of significant figures. 1 inch = 2.54 cm, exactly

Sig Fig Practice #1 How many significant figures in each of the following? m  5 sig figs kg  4 sig figs 100,890 L  5 sig figs 3.29 x 10 3 s  3 sig figs cm  2 sig figs 3,200,000  2 sig figs

Rules for Significant Figures in Mathematical Operations Multiplication and Division: # sig figs in the result equals the number in the least precise measurement used in the calculation. # sig figs in the result equals the number in the least precise measurement used in the calculation x 2.0 =  13 (2 sig figs)

Sig Fig Practice # m x 7.0 m Calculation Calculator says: Answer m 2 23 m g ÷ 23.7 cm g/cm g/cm cm x cm cm cm m ÷ 3.0 s m/s 240 m/s lb x 3.23 ft lb·ft 5870 lb·ft g ÷ 2.87 mL g/mL 2.96 g/mL

Rules for Significant Figures in Mathematical Operations Addition and Subtraction: The number of decimal places in the result equals the number of decimal places in the least precise measurement =  18.7 (3 sig figs)

Sig Fig Practice # m m Calculation Calculator says: Answer m 10.2 m g g g 76.3 g 0.02 cm cm cm 2.39 cm L L L L lb lb lb lb mL mL 0.16 mL mL

The Organization of Matter Matter Matter Mixtures: a) Homogeneous (Solutions) b) Heterogeneous Pure Substances Compounds Elements Elements Atoms NucleusElectrons ProtonsNeutrons Quarks Quarks

Phase Differences Solid Solid – definite volume and shape; particles packed in fixed positions. Liquid Liquid – definite volume but indefinite shape; particles close together but not in fixed positions Gas Gas – neither definite volume nor definite shape; particles are at great distances from one another Plasma Plasma – high temperature, ionized phase of matter as found on the sun.

Properties of Matter Volume Mass Energy Content (think Calories!) Extensive properties Extensive properties depend on the amount of matter that is present. Intensive properties Intensive properties do not depend on the amount of matter present. Melting point Boiling point Density

Separation of a Mixture The constituents of the mixture retain their identity and may be separated by physical means.

Separation of a Mixture The components of dyes such as ink may be separated by paper chromatography.

Separation of a Mixture by Distillation

Separation of a Compound Separation of a Compound The Electrolysis of water Water  Hydrogen + Oxygen 2 H 2 O  2 H 2 + O 2 Reactant  Products chemical Compounds must be separated by chemical means. With the application of electricity, water can be separated into its elements