Chapter 1 Outline Prentice Hall Chemistry Connections to Our Changing World
...nit The English measurement system is called the metric system A) The International System of Measurements 1) Abbreviated as SI 2) Length (a) The meter (m) is the basic SI unit of length (b) A meter is defined as the distance that light travels in a vacuum during a time interval of 1/299,792,458 (c) A meter is 3.3 feet 3) Mass and Weight (a) The amount of material in an object is called its mass. (b) The united of mass is called the kilogram (kg). (c) Weight is equal to the amount of force or gravity pulling on the object 4) Volume (a) The SI unit of volume is the cubic meter (m3) (b) Volume is the amount of space that an object occupies B) The Units Used in This Textbook 1) Science is based on Rules although there are some exceptions 2) The liter(L) is a non-SI unit used to measure volume 3) There are exactly 1000L in 1 cubic meter 4) Celsius, used for measuring temperature is also a non-SI unit C) Metric Prefixes 1) Prefixes that make the unit larger (a) Mega- (M) = 1,000,000 (b) Kilo- (k) =1,000 2) Prefixes that make the unit smaller (a) Deci- (d) =0.1 (b) Centi- (c) =0.01 (c) Milli (m) =0.001 (d) Micro- ( ) =0.000001 (e) Nano- (n) =0.000000001 (f) Pico- (p) =0.000000000001 V) Uncertainty in Measurement A) Making Measurements 1) Measurements are never completely accurate for two reasons: (a) Measuring instruments are never free of flaws (b) Measuring always involves some estimation 2) Estimating with a Digital Display (a) Digital displays automatically estimate the uncertain digit (b) When the instrument flickers two readings, chose the dominant (c) Always write down the number and the unit 3) Estimating with a scale (a) A graduated cylinder is a type of scale (b) To make a better reading, you must estimate (c) Imagine extra divisions where needed 4) The Uncertainty of a Measurement (a) The uncertainty of a graduated cylinder’s measurement is approx. 0.1millimeters (b) Make measurements as accurate as possible despite the fact that all measurements are uncertain (c) Keep all equipment is the best working order possible B) Reliability in Measurement 1) Precision (a) Precision is achieved by achieving the same, or very similar, results each time an experiment is performed. 2) Accuracy (a) Accuracy can be tested by checking against a standard (b) The correct answer is called the accepted value 3) A Dartboard Analogy (a) Darts grouped together away from the bull’s-eye represents high precision and low accuracy (b) Darts spread out all over the dartboard show low precision and low accuracy (c) Darts grouped together at the bull’s-eye represent high accuracy and high precision VI) Working with Numbers A) Significant Digits 1) The certain digits and the estimated digit of a measurement are the significant digits of a measurement. 2) The uncertainty of separate measurements must be recorded correctly when combing measurements 3) When a Zero is Not Significant (a) A zero that is a place keeper is not a significant digit (b) Zeros that are used to show the placement of the decimal point are not significant (c) The Atlantic-Pacific Rule (a) When a decimal point is present, count from the Pacific Side. When a decimal point is absent, count from the Atlantic Side (b) All digits from the first non-zero digit, including any zeros following it, are significant (d) Placing a decimal point after numbers like 250 and 100 allows the zeros to remain significant B) Significant Digits in Calculations 1) Exact numbers do not effect the number of significant digits in a calculation 2) In multiplication and division, the measurement(s) with the smallest number of significant digits determines the number of digits in the final answer 3) In addition and subtraction, the measurement is rounded off to the uncertainty of the least certain digit because the calculation can not be more accurate the least accurate measurement C) Scientific Notation 1) Numbers written in scientific notation are separated into two parts (a) Number between 1 and 10 (b) Power of ten 2) Exponents (a) Show how many times the base is multiplied by itself (b) Writing very small numbers requires the use of reciprocals 3) Converting Numbers to Scientific Notation (a) The exponent can be found by counting how many spaces the decimal point must be moved to bring the number between 1 and 10 4) Percents and Percent Error (a) Percent error can be used to compare a measurement to its accepted value (b) Percent errors can be either positive or negative 5) Ratios (a) Density is a ratio frequently used in chemistry (b) Density is calculated by dividing the mass of an ...