Introduction To Chemistry Unit 2 Introduction To Chemistry

Topic Units Of Measurements

Measurements Measurements are quantitative information. Measurement = a number + a unit

The Metric System Also Known As… Le Systeme International d’Unites The SI system The decimal system The scientific community’s agreed upon single measurement system. Based multiples of 10’s Seven base SI units Length, mass, time, temperature, amount of substance, electric current and luminous intensity.

QUANTITY SYMBOL BASE NAME UNIT ABBREVIATION LENGTH MASS TIME TEMPERATURE AMOUNT OF SUBSTANCE

l QUANTITY SYMBOL BASE NAME UNIT ABBREVIATION LENGTH meter m MASS TIME TEMPERATURE AMOUNT OF SUBSTANCE

l QUANTITY SYMBOL BASE NAME UNIT ABBREVIATION LENGTH meter m MASS kilogram kg TIME TEMPERATURE AMOUNT OF SUBSTANCE

l QUANTITY SYMBOL BASE NAME UNIT ABBREVIATION LENGTH meter m MASS kilogram kg TIME t second sec TEMPERATURE AMOUNT OF SUBSTANCE

l QUANTITY SYMBOL BASE NAME UNIT ABBREVIATION LENGTH meter m MASS kilogram kg TIME t second sec TEMPERATURE T degree Celsius kelvin ºC K AMOUNT OF SUBSTANCE

l QUANTITY SYMBOL BASE NAME UNIT ABBREVIATION LENGTH meter m MASS kilogram kg TIME t second sec TEMPERATURE T degree Celsius kelvin ºC K AMOUNT OF SUBSTANCE n mole mol

Mass vs. Weight Mass is a measure of matter, measured by a balance. Weight is a measure of gravitational pull, measured by a scale. http://www.onlineconversion.com/weight_on_ot her_planets.htm On Earth, mass equals weight.

SI PREFIXES` Prefix Unit Abbreviation Exponential Factor Meaning Tera T 1012 1 000 000 000 000 Giga G 109 1 000 000 000 Mega M 106 1 000 000 Kilo k 103 1000 Hecto h 102 100 Deka da 101 10 Base Unit (g, L, m)  1 Deci d 10-1 1/10 Centi c 10-2 1/100 Milli m 10-3 1/1000 Micro μ 10-6 1/1 000 000 Nano n 10-9 1/1 000 000 000 Pico p 10-12 1/1 000 000 000 000

QUANTITY SYMBOL BASE NAME UNIT ABBREVIATION Volume (SI) (Common) Density

QUANTITY SYMBOL BASE NAME UNIT ABBREVIATION Volume (SI) V cubic meter m3 (Common) Density

QUANTITY SYMBOL BASE NAME UNIT ABBREVIATION Volume (SI) V cubic meter m3 (Common) liter L Density

kilogram per cubic meter QUANTITY SYMBOL BASE NAME UNIT ABBREVIATION Volume (SI) V cubic meter m3 (Common) liter L Density D kilogram per cubic meter kg/m3

QUANTITY SYMBOL BASE NAME UNIT ABBREVIATION Volume (SI) V cubic meter m3 (Common) liter L Density D kilogram per cubic meter kg/m3 grams per cubic centimeter grams per milliliter g/cm3 g/mL

Remembering the Important Ones King Henry Died By Drinking Chocolate Milk Kilo-, Hecto-, Deka-, BASE, Deci-, Centi-, Milli-

Conversions Converting a measurement from one unit to another unit.

Metric-Metric Measurement Conversions Slide The Decimal Method Slide the decimal the number of steps there are between the given and desired unit. Remember that meters, liters, and grams are base units. When you move from large to smaller units (), move the decimal to the right. When you move from small to larger units (), move the decimal to the left. Example Problems

English-Metric & Metric-English Measurement Conversions Factor Label Method (Fence Post) Identify the needed conversion factor for the given units and desired units. A conversion factor is a ratio that relates two measurements. Set up your problem according to the factor label method. Make sure the conversion factor is set up to cancel out given units. Multiple across and divide below to solve the problem.

Temperature Measures the amount of kinetic energy associated with the motion of atoms or molecules Quantitative observation Physical property Measured with a thermometer

Temperature Scale Fahrenheit (°F) is only used by the public in the U.S. Celsius (°C) is used by the public in the rest of the world and in most scientific experiments Kelvin (K) is used in scientific experiments involving gases Each temperature scale is defined by its boiling point of water, its freezing of water and its lowest possible temperature.

Temperature Scales

Temperature Conversions °C = (°F – 32) × (5/9) °F = (°C × (9/5)0 + 32 K = °C – 273 °C = K - 273

Density The ratio of mass to volume Mathematically, density = mass ÷ volume Physical property – unique to each pure substance Quantitative observation Value (g/cm3) Qualitative observation Sink or float

Water Displacement

Solving Density Problems Familiar Units g/mL g/cm3

Solving Density Problems Identify given and unknown variables Decide what equation is needed Plug in given quantities Solve equation

Using Scientific Measurement

Uncertainty Of Measurements Due to 1. Human Error – Skill and carefulness 2. Limitation of measuring device. Example – use of metric ruler. To measure the length of book – YES To measure the thickness of a page – NO

Accuracy how close a measurement is to the accepted value accuracy is measured with percent error accurate = correct

Precision how close a series of measurements are to each other precision is measured with significant digits precise = consistent

High Precision High Precision Low Precision High Accuracy Low Accuracy Low Accuracy

Percent Error Measurement Measurement of the accuracy of an experimental value compared to an accepted value. Percent error value under 5% is considered acceptable Percent Error = Accepted – Experimental X 100 Accepted Experimental  calculated, measured or found value Accepted  correct, known, actual or given value

Significant Figures (AKA…Sig Fig) A measurement consisting of all the digits known with certainty plus one final digit, which is somewhat uncertain or estimated. An answer can never be any better than the least accurate piece of data.

Rules For Significant Figures Rule 1 - All nonzero numbers are significant 5379 789 Rule 2 - All zeros between non-zero digits are significant. 4008 20603 Rule 3 - Leading zeros are never significant. 0098 0.0043 Rule 4 - Trailing zeros with a decimal are significant. 1.230 72400.

Examples: 0.02400  55500  1.0330  4.4033  083009  760. 

Why Bother With Significant Figures? Sig figs help us determine how many places your answer needs. Answers cannot have more sig figs than the measurement with the least number of sig figs.

Multiplication/Division The answer can have no more significant figures than are in the measurement with the fewest number of significant figures.

Practice Problems: 4.3 × 5.09 = 562 ÷ 8.7 = 1.05 × 321 = 43.2 ÷ 7.55 = 0.125 × 0.75 = 2.334 ÷ 0.888 =