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Data Analysis in Chemistry Quantitative v. Qualitative Measurements Standard Measurements --SI System (Système Internationale d’Unités SI Base Units Length Mass Time Temperature meter (m) kilogram (kg) second (s) Kelvin (K) Amount of Substance Luminous Intensity Current mole (mol) candela (cd) Ampere (A) The above units are considered to be base units. Things that are smaller than the base units use Latin prefixes; things that are larger use Greek prefixes. Prefixes in the SI System gigamegakilodecicentimillimicronanopico- G M k d c m n p 1000000000 1,000,000 1000 0.1 0.01 0.001 0.000001 0.000000001 0.000000000001 109 106 103 10-1 10-2 10-3 10-6 10-9 10-12 Scientific Notation Review: Very large and very small numbers should be expressed in scientific notation. 65000000 m becomes 6.5 x 107 m 0.000045 g becomes 4.5 x 10-5 g When using your calculator use the “EE” key that appears above the comma. Use conversions factors to solve the following: 345 mm =_____ m 678 kg = _____ g Significant Figures Include all known digits plus one estimate digit. All non-zero numbers are significant. Captive zeros are significant. Trailing zeros are only significant when there is a decimal point. Trailing zeros are NOT significant when there is no decimal point. Atlantic - the "A" stands for decimal absent. This means that they start on the atlantic ocean side of the number, find the first non-zero number and count everything after. Pacific - "P" stands for decimal present. Start on the pacific side of the number at the first non-zero number and then count everything after. http://science.widener.edu/svb/tutorial/sigfigures.html Derived Units A derived unit is one that is a combination of base units. Examples are volume (the space occupied by an object) 1 mL = 1 cm3 1 L = 1 dm3 and density (the ratio of the mass to the volume of an object) D = mass volume Accuracy and Precision Accuracy refers to how close a value is to the accepted value. Precision refers to how close measurements are to each other. Percent Error is used to determine the accuracy of your experimental results. Use the following formula to calculate percent error: Percent Error = Experimental – Accepted Value x 100 Accepted Value Determine the percent error when a student calculates the density of copper to be 7.65 g/cm3. The true value for the density of copper is 8.92 g/cm3.