Basics of Chemistry. manner so that the results can be duplicated and rational conclusions can be

Transcription

1 Basics of Chemistry Some initial definitions: Experiment - an observation of natural phenomenon carried out in a controlled manner so that the results can be duplicated and rational conclusions can be obtained. Hypothesis - a tentative explanation of some regularity of nature. Theory - a tested explanation of basic natural phenomenon. Law - a concise statement or math equation about a fundamental relationship or regularity of nature. Law of Conservation of Mass The total mass remains constant during a chemical change. Carbon + Oxygen Carbon monoxide "is changed to" Examples: You place 1.85 grams of wood in a vessel with 9.45 grams of air and seal the vessel. You heat the vessel strongly so that the wood burns. In burning the wood you produce ash and gases. After the experiment, you weigh the ash and the find that the mass is 0.28 grams. What is the mass of the gases in the vessel at the end of the experiment? A 15.9 g sample of sodium carbonate is added to a solution of acetic acid weighing 20.0 g. The 2 substances react, releasing carbon dioxide gas into the atmosphere. After reaction, the contents of the reaction vessel weighs 29.3 g What is the mass of the carbon dioxide given off during the reaction?

2 Matter 3 physical states 1. Solid 2. Liquid 3. Gas These 3 forms of matter comprise the states of matter. Physical changes - a change in the form of matter but not its chemical identity. Chemical changes - a change in which one or more kinds of matter are transformed into a new kind of matter or several new kinds of matter. Physical Property - characteristic that can be observed for a material with out changing its chemical identity Chemical property - characteristic of a material involving its chemical change. Substance - kind of matter that can't be separated into other kinds of matter by any physical processes. Elements - substance that can't be decomposed by any chemical reaction into simpler substances. Compounds - substances composed of 2 or more elements that are chemically combined. Mixtures - a material that can be separated by physical means into two or more substances. Heterogeneous vs Homogeneous

3 Qualitative vs Quantitative Extensive vs Intensive Measurements and Significant Figures Precision vs Accuracy Accuracy - an agreement of a measurement with the accepted value for the quantity. quantitative measure of accuracy = % error A determination of the density of copper is performed. The experimenter determines the density to be 8.82 g/ml. The accepted value is 8.94 g/ml. what is the % error of this determination. Precision - indicates how well several determinations of the same quantity agree. It indicates how well several determinations of the same quantity agree. What is the standard deviation for the following series of measurements carried out to determine the density of copper Run # Density (g/ml)

4 Significant Figures The number of digits reported for a value of a measured or calculated quantity indicating the precision of the value. Rules 1. All digits are significant except zeros at the beginning of the number and possibly terminal zeros. 2. Terminal zeros ending at the right of the decimal point are significant. 3. Terminal zeros in a number without an explicit decimal point may or may not be significant. Addition and Subtraction Rules When adding or subtracting measured quantities, give the same number of decimal places in the answer as there are in the measurement with the least number of decimal places. Multiplication and Division Rules When multiplying or dividing measured quantities, give as many significant figures in the answer as there are in the measurement with the least number of significant figures. Exact Numbers = counted numbers - has an infinite number of significant figures

5 SI Units Temperature - although SI unit is Kelvin the Celsius scale is generally used. Derived Units - units derived by combining SI base units Examples: Density - object's mass per unit volume d = m/v Dimensional analysis - method of calculation in which one carries along the units for quantities.