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Chemical Foundations

Chemical Foundations. AP Chemistry. Scientific Method. Observation. Hypothesis. If hypothesis is false, propose new hypothesis. Experiment. Theory. Law. Must repeat several times. SI Units & Prefixes. SI Unit (from le Systeme International , in French):

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Chemical Foundations

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  1. Chemical Foundations AP Chemistry

  2. Scientific Method Observation Hypothesis If hypothesis is false, propose new hypothesis. Experiment Theory Law Must repeat several times.

  3. SI Units & Prefixes SI Unit (from le Systeme International, in French): •Based on metric system •measurements must have a unit unless they cancel out •use prefixes for small or large numbers

  4. More on Units 1. Volume -derived from length, l x l x l -liquids are measured in L, 1L = 1000mL = 1000cm3 (1cm3 = 1mL) • Mass vs weight -mass: measure of the resistance of an object to a change in its state of motion -weight: mass under the force of gravity

  5. Uncertainty in Measurement All measurements have some degree of uncertainty, which affects the precision of the measuring device. -we record all certain digits plus one uncertain (estimated) digit -use significant figures -remember your Pacific/Atlantic Rules

  6. Accuracy & Precision accuracy: the agreement of a particular value to the true value precision: degree of agreement among several measurements of the same quantity *diagram taken from www.mathisfun.com

  7. Accuracy & Precision random error: measurement that has an equal probability of being either high and/or low -aka intermediate error -2nd picture systematic error: occurs in the same direction every time -aka determinate error -1st picture

  8. Dimensional Analysis dimensional analysis: way to convert from one unit to another -aka unit factor method -set up so units cancel conversion factor: equivalent values with different units -1 dozen = 12 donuts -2.54 cm = 1 in -set up as a ratio

  9. Temperature 3 units: Celcius, Kelvin, Farenheit TK = TC + 273.15 (K oC or oC  K) TC = (TF -32oF)5oC or TF = TC 9oF + 32oF 9oF 5oC There is no direct relationship between K and oF.

  10. Density density: mass of substance per unit volume of substance density = mass or D = m volume V -often the identification tag of a substance

  11. Classification of Matter Three states of matter: • solid: definite shape and volume • liquid: definite volume and indefinite shape -assumes the shape of its container • gas: indefinite shape and indefinite volume -highly compressible Image from http://antoine.frostburg.edu/chem/senese/101/matter/slides/sld002.htm

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