Unit 2 Chapters 3 & 4

Review Qualitative measurement Qualitative measurement Uses descriptive wordsUses descriptive words Quantitative measurement Quantitative measurement Uses numbersUses numbers

Exact vs. Measured Numbers Exact numbers - counting numbers Exact numbers - counting numbers Not measurementsNot measurements A stated value that is certainA stated value that is certain Example: 100 years = 1 century Example: 100 years = 1 century Measured numbers- have uncertainty because of the equipment/device used and the observer Measured numbers- have uncertainty because of the equipment/device used and the observer

Scientific Notation Expresses numbers as a multiple of two factors Expresses numbers as a multiple of two factors 1.A number between 1 and raised to a power (X) or exponent # times 10 x

How can you tell if the power is negative or positive?  If the number you are converting is… LESS than 1, the exponent will be NEGATIVELESS than 1, the exponent will be NEGATIVE Example: = 2.5 x MORE than 1, the exponent will be POSITIVEMORE than 1, the exponent will be POSITIVE Example: 7300 = 7.3 x 10 3 Example: 7300 = 7.3 x 10 3

Converting to Scientific Notation # x 10 x How? 4 steps: How? 4 steps: 1.Move the decimal so that the front number is a single digit. (between 1 and 10) 2.Count how many places the decimal moves. That number represents x in. 2.Count how many places the decimal moves. That number represents x in 10 x. 3.If you move the decimal to the left, then x is positive. 4.If you move the decimal to the right, then x is negative. Remember your vocabulary: Remember your vocabulary: The x in is called the exponent. The x in 10 x is called the exponent.

Converting to Scientific Notation # x 10 x Common Sense Double Check: 1.If your answer has a negative exponent, then your original number must be less than zero. Example: 1.0 x = If your answer has a positive exponent, then your original number must be more than zero. Example: 1.0 x 10 2 = 100

Scientific Notation Do the practice problems Do the practice problems

Precision vs. Accuracy What’s the difference? Accuracy refers to the closeness of a measurement/measured value to the accepted or known value. Accuracy refers to the closeness of a measurement/measured value to the accepted or known value. Accuracy = CorrectAccuracy = Correct Precision refers to the agreement among several measurements/ measured values Precision refers to the agreement among several measurements/ measured values Precision = ConsistencyPrecision = Consistency

Precision vs. Accuracy Can an instrument be precise and not be accurate?

Bull’s Eye When is it precise but NOT accurate? When is it precise but NOT accurate? Hits the same spot over and over but not near the Bull’s eyeHits the same spot over and over but not near the Bull’s eye When it is accurate but NOT precise? When it is accurate but NOT precise? Hit Bull’s eye once, and then not ever hit it againHit Bull’s eye once, and then not ever hit it again When is it accurate AND precise? When is it accurate AND precise? Hit the Bull’s eye over and over again!!Hit the Bull’s eye over and over again!!

Example 1: Accuracy vs Precision

Example 2: Accuracy vs Precision

Quantity A quantity includes both a number and a standard unit A quantity includes both a number and a standard unit Examples: 14.5 g 12 mi Examples: 14.5 g 12 mi A quantitative measurement!!!! A quantitative measurement!!!!

Units of Measurements Units used by scientists (everywhere) and people (outside of the US) Units used by scientists (everywhere) and people (outside of the US) Système Internationale d’ Unités or SI units Système Internationale d’ Unités or SI units

Seven Base Units in SI Quantity Base Unit Time Second (s) Length Meter (m) Mass Kilogram (Kg) Temperature Kelvin (K) Amount of a substance Mole (mol) Electric current Ampere (A) Luminous intensity Candela (cd)

Derived Units A combination of base units A combination of base units Examples: Examples: Speed: meters/s or miles/hoursSpeed: meters/s or miles/hours Density: g/cm 3 or g/mLDensity: g/cm 3 or g/mL

Metric Prefixes Powers of 10 Powers of 10 Know the Metric Prefix to Power of 10 Know the Metric Prefix to Power of 10 Mega (10 6 ) to pico ( ) Mega (10 6 ) to pico ( ) Show chart and Practice Examples on board Show chart and Practice Examples on board

Conversions The middle “man” The middle “man” Grams (g)Grams (g) Liters (L)Liters (L) Meters (m)Meters (m) Set the bigger prefix as 1 when determining the conversion factors you need Set the bigger prefix as 1 when determining the conversion factors you need Example 1: how many kilograms are in 25 grams?Example 1: how many kilograms are in 25 grams? Conversion factor: 1 kilogram = 1x10 3 grams Example 2: how many micrograms are in 25 grams?Example 2: how many micrograms are in 25 grams? Conversion factor: 1 gram = 1x10 6 micrograms

Density A ratio that compares the mass of an object to its volume or A ratio that compares the mass of an object to its volume or How much mass takes up a certain amount of volume How much mass takes up a certain amount of volume Density of an substance will NOT change Density of an substance will NOT change If the mass changes, then the volume will change alsoIf the mass changes, then the volume will change also What kind of property is density?What kind of property is density?

Common Units of Density grams/ cm 3 grams/ cm 3 grams/ mL grams/ mL Important Conversion to Know: Important Conversion to Know: 1 mL = 1 cm 3

The Standard for All Density Water!! Water!! The density of water is 1.0 g/mL The density of water is 1.0 g/mL

The End!! Work on the Scientific and Standard Notation Handout Work on the Scientific and Standard Notation Handout HW: HW: Complete Handout – scientific and standard notation only, not sig figs yetComplete Handout – scientific and standard notation only, not sig figs yet Read Chapter 5.1 and complete problems on page 164 #9-34; Some are difficult. Don’t give up. Try every problem.Read Chapter 5.1 and complete problems on page 164 #9-34; Some are difficult. Don’t give up. Try every problem.

Error  The difference between an accepted value and an experimental value is ERROR The difference between an accepted value and an experimental value is ERROR Take the absolute valueTake the absolute value No negative values No negative values | experimental – accepted | = error Accepted- what you are “suppose” to getAccepted- what you are “suppose” to get Experimental- what you “actually” getExperimental- what you “actually” get

% Percent Error % Percent error- the ratio of an error to an accepted value Percent error- the ratio of an error to an accepted value Equation: Equation:

Practice Problem Suppose you calculate your semester grade in chemistry as 90.1, but you receive a grade of What is your percent error?What is your percent error?Error = 0.7 Percent error 0.7/ 90.1 times 100 = 0.78%

Significant Figures The # of digits reported in a measurement indicates how precise the measurement is The # of digits reported in a measurement indicates how precise the measurement is The more digits reported, the more precise the measurement The more digits reported, the more precise the measurement The digits reported are called SIG FIGS The digits reported are called SIG FIGS

Sig Fig’s cont’d The accuracy of the final answer to a problem depends upon the accuracy of the numbers used to express each measurement used The accuracy of the final answer to a problem depends upon the accuracy of the numbers used to express each measurement used Digits in answers that are more accurate than the measurements justify are NOT significant and must be dropped Digits in answers that are more accurate than the measurements justify are NOT significant and must be dropped

Significant Figures If no decimal Start from the right until you hit the 1st non-zero number Start from the right until you hit the 1st non-zero numberExamples: If decimal is present Start from the left until you hit the 1st non-zero number Examples:

When are numbers significant? ALL NONZERO numbers are significant!!

When are ZEROS significant? 1. All zeros between NONZERO numbers are significant 1. All zeros between NONZERO numbers are significant 2. If a decimal is NOT present, the zero at the end of the number is NOT significant 2. If a decimal is NOT present, the zero at the end of the number is NOT significant 3. Zero that act as place holders are NOT significant 3. Zero that act as place holders are NOT significant 4. If a decimal is present, zeros following NONZERO numbers are significant 4. If a decimal is present, zeros following NONZERO numbers are significant 5. All digits to the LEFT of the 10 x (in scientific notation) are Significant!! 5. All digits to the LEFT of the 10 x (in scientific notation) are Significant!!

Sig Fig Measurement Example

Significant Digits in Calculations When adding or subtracting, the answer may ONLY contain the LEAST accurate decimal place When adding or subtracting, the answer may ONLY contain the LEAST accurate decimal place Let’s do the example problems Let’s do the example problems

Significant Digits in Calculations When multiply or dividing, the answer will have the LEAST amount of significant digits When multiply or dividing, the answer will have the LEAST amount of significant digits Let’s do the practice problems Let’s do the practice problems

Specific Gravity Specific gravity is a comparison of the density of a substance with the density of a reference substance, usually at the same temperature. Specific gravity is a comparison of the density of a substance with the density of a reference substance, usually at the same temperature. Water is the reference or standard = 1 (no units) Water is the reference or standard = 1 (no units)

Specific Gravity A hydrometer is the device that measures specific gravity. A hydrometer is the device that measures specific gravity. Applications: urinalysis tests & antifreeze tests Applications: urinalysis tests & antifreeze tests

Temperature Used to describe how hot or cold an object feels Used to describe how hot or cold an object feels 2 scales commonly used: Celsius and Kelvin 2 scales commonly used: Celsius and Kelvin One Kelvin is equal to one degree on the Celsius One Kelvin is equal to one degree on the Celsius

Conversions To convert from Celsius to Kelvin To convert from Celsius to Kelvin # °C = _____ Kelvin To convert from Kelvin to Celsius To convert from Kelvin to Celsius # Kelvin – 273 = _____ Celsius

Practice Problems 0 degrees Celsius = ______ Kelvin 0 degrees Celsius = ______ Kelvin 500 Kelvin = ________ Celsius 500 Kelvin = ________ Celsius