Ch1 - CHAPTER 1 CHEMICAL FOUNDATIONS Questions 19 A law...

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1 CHAPTER 1 CHEMICAL FOUNDATIONS Questions 19. A law summarizes what happens, e.g., law of conservation of mass in a chemical reaction or the ideal gas law, PV = nRT. A theory (model) is an attempt to explain why something happens. Dalton’s atomic theory explains why mass is conserved in a chemical reaction. The kinetic molecular theory explains why pressure and volume are inversely related at constant temperature and moles of gas present, as well as explaining the other mathematical relationships summarized in PV = nRT. 20. A dynamic process is one that is active as opposed to static. In terms of the scientific method, scientists are always performing experiments to prove or disprove a hypothesis or a law or a theory. Scientists do not stop asking questions just because a given theory seems to account satisfactorily for some aspect of natural behavior. The key to the scientific method is to continually ask questions and perform experiments. Science is an active process, not a static one. 21. The fundamental steps are (1) making observations; (2) formulating hypotheses; (3) performing experiments to test the hypotheses. The key to the scientific method is performing experiments to test hypotheses. If after the test of time the hypotheses seem to account satisfactorily for some aspect of natural behavior, then the set of tested hypotheses turns into a theory (model). However, scientists continue to perform experiments to refine or replace existing theories. 22. A random error has equal probability of being too high or too low. This type of error occurs when estimating the value of the last digit of a measurement. A systematic error is one that always occurs in the same direction, either too high or too low. For example, this type of error would occur if the balance you were using weighed all objects 0.20 g too high, that is, if the balance wasn’t calibrated correctly. A random error is an indeterminate error, whereas a systematic error is a determinate error. 23. A qualitative observation expresses what makes something what it is; it does not involve a number; e.g., the air we breathe is a mixture of gases, ice is less dense than water, rotten milk stinks. The SI units are mass in kilograms, length in meters, and volume in the derived units of m 3 . The assumed uncertainty in a number is " 1 in the last significant figure of the number. The precision of an instrument is related to the number of significant figures associated with an experimental reading on that instrument. Different instruments for measuring mass, length, or volume have varying degrees of precision. Some instruments only give a few significant figures for a measurement, whereas others will give more significant figures.
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2 CHAPTER 1 CHEMICAL FOUNDATIONS 24. Precision: reproducibility; accuracy: the agreement of a measurement with the true value. a.
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This note was uploaded on 07/07/2010 for the course CHEM 11 taught by Professor Scholefield during the Summer '08 term at Santa Monica.

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Ch1 - CHAPTER 1 CHEMICAL FOUNDATIONS Questions 19 A law...

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