Measurements and Calculations Chapter 2 – Modern Chemistry

2.1 Scientific Method 5 Steps Observing and collecting data Collecting data, measuring, communicating Formulating a hypothesis Organizing data, classifying, inferring, predicting Testing Experimenting, collecting new data, communicating Theorizing Constructing models, predicting, communicating Publish Results Communicating

2.2 Units of Measurement Systems of Measurement SI System (International System) Standardized for Science Metric System Used in most parts of the world English System Used in the United States

Measurements Quantity Units This is what is being measured Examples: length, mass, temperature, ect Units Expression of the quantity Examples: meter, grams, Kelvin, ect

SI Measurements Quantity Quantity symbol Unit Unit symbol Length l meter m Mass kilogram kg Time t second s Temperature T kelvin K Amount of Substance n mole mol Electric Current I ampere A Luminous Intensity Iv candela cd

SI Prefixes Prefixes are attached to base units Base units are grams, meters, liters, and seconds Prefixes are factors of the base unit Normally a factor of “x 10” Largest to smallest with symbols Tera (T), Giga (G), Mega (M), kilo (k), hecto (h), Deka (da), base unit, deci (d), centi (c ), milli (m), micro ( ), nano (n), pico (p)

Derived Units Quantity Quantity Symbol Unit Unit Symbol Area A Square meter m2 Volume V Cubic meter m3 Density D Kilograms per kg/m3 Molar Mass M Kilograms per mole kg/mol Molar Volume Vm Cubic meters per mole m3 /mol Energy E joule J

Conversion Factor Dimensional Analysis Conversion Factor Mathematical technique that allows you to use units to solve problems involving measurements Conversion Factor A fraction that use two different units of the same quantity in equal amounts to convert the units Example: Units of money are dollars and cents If 100 cents = 1 dollar, then 600 cents would equal x dollars? 600 cents x (1 dollar/100 cents) = 6 dollars

2.3 Using Scientific measurements Accuracy and Precision Accuracy is the closeness of a measurement Related back to a true or accepted value Precision is how close a group of measurements are to each other Relates back to the other measurements

Percent Error Calculation relating the experimental value to the accepted value as a percentage of difference Can be greater than or less than 100% Percent error = (experimental value/accepted value) x 100

Significant Figures Rules for significant figures Zeros between nonzero numbers are significant Zeros appearing in front of nonzero numbers are not significant Zeros at the end of a number and to the right of decimal point are significant Zeros at the end of a number and to the left may vary. If exact measurement, then they are significant. If not an exact measurement, then they are not significant All nonzero numbers are significant

Rounding We will simplify the rounding of digits to the same number of significant figures as the least amount from the problem Round any number 5 or greater up and any number 4 or less down

Scientific notation Method of writing values that are either really large or really small in order to simplify the value Coefficient x 10 ^positive or negative whole number Coefficient must be less than 10 but greater than or equal to 1 Exponent is positive if the number large and gets smaller Exponent is negative if the number is small and gets larger Example: 0.000000005 5.0 x 10-9

Scientific Notation Adding and Subtracting Multiplication Division In order to add or subtract in scientific notation, the exponents must be the same Multiplication Multiply the coefficients and add the exponents Division Divide the coefficients and subtract the exponents