DATA ANALYSIS Measurement; Units; Calculations; Significant Figures; Prefixes; Dimensional Analysis Neely's Chemistry

MEASUREMENT Used to measure properties SI System based on the Metric System “Systeme International” Base Units & Derived Units Adopted by scientists in 1960 Neely's Chemistry

BASE UNITS Property Do not depend on other units to describe them Name Unit Symbol Property meter m length kilogram kg mass second s time ampere A electric current kelvin K temperature candela cd luminous intensity mole mol amount of substance Neely's Chemistry

TEMPERATURE Measures average kinetic energy in a substance Heat flows from higher to lower temp. Kelvin Temperature T = oC + 273 Ex. 25oC is taken as “room temperature” ………………... What is this in kelvin? T = 25 + 273 = 298 K (not 298oK) Neely's Chemistry

An experiment is performed at 378 K. What is this temperature in oC? Ans. 105oC Neely's Chemistry

DERIVED UNITS Defined by combination of base units EXAMPLE: Length is used to define Area & Volume Area = length2 Volume = length3 The area of a 10 cm by 8 cm rectangle is 10 cm x 8 cm = 80 cm2 The volume of a 2 cm x 4 cm x 6 cm rectangular solid is 48 cm3 Note: When working math problems always do the same thing with the units that you do with the numbers. It will always give you correct units, etc. Neely's Chemistry

10 cm x 10 cm x 10 cm is a volume of 1 liter Liter and cm3 or mL are convenient laboratory volume units 1 cm3 = 1 mL 1 Liter 10 cm x 10 cm x 10 cm Neely's Chemistry

DENSITY an important derived unit Defining Equation mass D = volume Neely's Chemistry

“I Luv Density” D = Can u see “m over v” Neely's Chemistry

A block of wood with a density of 0. 95 g/cm3 is cut exactly in half A block of wood with a density of 0.95 g/cm3 is cut exactly in half. What is the resulting density of each half ? Density will be 0.95 g/cc for each piece. Density is an intensive property. It does not depend on the size of the sample. Neely's Chemistry

Liquid Hg has a density of 13. 5 g/mL. What is the mass of 20 Liquid Hg has a density of 13.5 g/mL. What is the mass of 20.0 mL of Hg? Neely's Chemistry

SIGNIFICANT FIGURES and MEASUREMENTS quantities or numbers go with units to have a meaningful measurement. Each measured digit is a “Significant Figure” Ex. 13 cm has __ sig figs 13.1 cm has ___ sig figs. How many sig figs in 9.07 cm? Neely's Chemistry

How Many Sig Figs in: 10.8 m ___ 3 sig figs 120. m ___ 130 g ___ 2 sig figs (the last zero implies but does not give a decimal) Neely's Chemistry

How many sig figs? 0.59 L 2 sig figs (0 merely there to “hold place”) 2 sig figs (all the zero’s “hold place”) 0.0340 3 sig figs (only the 1st 2 zero’s “hold place”. The last zero is a measured zero.) Neely's Chemistry

Counting Significant Figures when a decimal is present Count from left to right  Start counting sig fig digits when you get to the first non-zero Any zeros that occur after the first non-zero digit must count as significant Ex. Sig figs in? a) 100.0 ___ b) 0.09140 ___ Neely's Chemistry

Counting Significant Figures when a decimal is not present Count from right to left  Start counting sig fig digits when you get to the first non-zero Any zeros that occur after the first non-zero digit do not count unless they are “sandwich zero’s” Ex. Sig figs in? a) 1060 ___ b) 240,000 ___ Neely's Chemistry

Complete the Significant Figure WorkSheet Neely's Chemistry