A Systematic Approach The experimental design is a systematic approach used in scientific study, whether it is chemistry, physics, biology, or another science. It is an organized process used by scientists to do research, and provides methods for scientists to verify the work of others. )

A Systematic Approach (cont.) The steps in a scientific method are repeated until a hypothesis is supported or discarded.

An observation is the act of gathering information. –Qualitative data is obtained through observations that describe color, smell, shape, or some other physical characteristic that is related to the five senses.Qualitative data –Quantitative data is obtained from numerical observations that describe how much, how little, how big or how fast.Quantitative data A Systematic Approach (cont.)

A hypothesis is a tentative explanation for what has been observed.hypothesis An experiment is a set of controlled observations that test the hypothesis.experiment A Systematic Approach (cont.)

A variable is a quantity or condition that can have more than one value. –An independent variable is the variable you plan to change.independent variable –The dependent variable is the variable that changes in value in response to a change in the independent variable.dependent variable A Systematic Approach (cont.)

A theory is an explanation that has been repeatedly supported by many experiments.theory –A theory states a broad principle of nature that has been supported over time by repeated testing. –Theories are successful if they can be used to make predictions that are true. Theory and Scientific Law

A scientific law is a relationship in nature that is supported by many experiments, and no exceptions to these relationships are found.scientific law Theory and Scientific Law (cont.)

Assessment Quantitative data describes observations that are _____. A.numerical B.conditions C.independent D.hypotheses

Assessment Scientific methods are _____ approaches to solving problems. A.dependent B.independent C.hypothetical D.systematic

Units and Measurements Scientific Notation and Dimensional Analysis Uncertainty in Data Representing Data

Units Système Internationale d'Unités (SI) is an internationally agreed upon system of measurements. A base unit is a defined unit in a system of measurement that is based on an object or event in the physical world, and is independent of other units.base unit

Units and Measurements base unit second meter kilogram Chemists use an internationally recognized system of units to communicate their findings. kelvin derived unit liter density

Metric chart  prefix.htm prefix.htm

Metric Line  Used to aid in prefix conversions:  k H D Base unit d c m  “Kiss Him/Her Dummy But Don’t Catch Mono g m L s Pa

Prefix Conversions  k H D Base unit d c m  Place one finger on the given prefix  Place 2 nd finger on new prefix  Count the number of spaces to get to new prefix  Move decimal point that many places toward the 2 nd finger Add zeros as needed to hold place Cannot change the magnitude (size) of the number!!

Practice!! L to mL mg to g ks to s kPa to cPa mm to Hm 7500 mL g s cPa Hm k H D Base unit d c m

Units (cont.) The SI base unit of time is the second (s), based on the frequency of radiation given off by a cesium-133 atom.second The SI base unit for length is the meter (m), the distance light travels in a vacuum in 1/299,792,458th of a second.meter The SI base unit of mass is the kilogram (kg), about 2.2 poundskilogram

Units and Measurements Scientific Notation and Dimensional Analysis Uncertainty in Data Representing Data

Units Système Internationale d'Unités (SI) is an internationally agreed upon system of measurements. A base unit is a defined unit in a system of measurement that is based on an object or event in the physical world, and is independent of other units.base unit

Units and Measurements base unit second meter kilogram Chemists use an internationally recognized system of units to communicate their findings. kelvin derived unit liter density

Metric chart  prefix.htm prefix.htm

Metric Line  Used to aid in prefix conversions:  k H D Base unit d c m  “Kiss Him/Her Dummy But Don’t Catch Mono g m L s Pa

Prefix Conversions  k H D Base unit d c m  Place one finger on the given prefix  Place 2 nd finger on new prefix  Count the number of spaces to get to new prefix  Move decimal point that many places toward the 2 nd finger Add zeros as needed to hold place Cannot change the magnitude (size) of the number!!

Practice!! L to mL mg to g ks to s kPa to cPa mm to Hm 7500 mL g s cPa Hm k H D Base unit d c m

Units (cont.) The SI base unit of time is the second (s), based on the frequency of radiation given off by a cesium-133 atom.second The SI base unit for length is the meter (m), the distance light travels in a vacuum in 1/299,792,458th of a second.meter The SI base unit of mass is the kilogram (kg), about 2.2 poundskilogram

Scientific Notation Scientific notation can be used to express any number as a number between 1 and 10 (the coefficient) multiplied by 10 raised to a power (the exponent).Scientific notation For example instead of writing 345,000,000,000,000,000. you would write it like this 3.45 x 10 17

Scientific Notation (cont.) 800 = 8.0  = 3.43  10 –5 The number of places moved equals the value of the exponent. The exponent is positive when the decimal moves to the left and negative when the decimal moves to the right. Count the number of places the decimal point must be moved to give a coefficient between 1 and 10.

Write these measurements in scientific notation.  The length of a football field, 91.4 m  The diameter of a carbon atom, m  The radius of the earth, 6,378,000 m  The diameter of a human hair, m HW –

Scientific Notation (cont.) Addition and subtraction –Exponents must be the same. –Rewrite values with the same exponent. –Add or subtract coefficients. (5.4 x 10 3 ) + (6.0 x 10 2 ) = cannot work (5.4 x 10 3 ) + (0.60 x 10 3 ) = 6.0 x 10 3 HW –

Scientific Notation (cont.) Multiplication and Division –To multiply, multiply the coefficients, then add the exponents. –To divide, divide the coefficients, then subtract the exponent of the divisor from the exponent of the dividend. (3 x 10 4 ) x (2 x 10 2 ) = (3 x 2) x 10 (4+2) = 6 x 10 6 HW –

Dimensional Analysis Dimensional analysis is a systematic approach to problem solving that uses conversion factors to move, or convert, from one unit to another.Dimensional analysis A conversion factor is a ratio of equivalent values having different units.conversion factor

Dimensional Analysis (cont.) Writing conversion factors –Conversion factors are derived from equality relationships, such as 1 in = 2.54 cm. –Percentages can also be used as conversion factors. They relate the number of parts of one component to 100 total parts. –75% by mass= 75 g/100 g

Dimensional Analysis (cont.) Using conversion factors –A conversion factor must cancel one unit and introduce a new one. Practice 1.You have 15 inches of rope. How many centimeters is this? Circle the conversion factor. 2.The directions to making a coat require you to cut 54 cm of a fabric. How many inches is this? Circle the conversion factor.

Assessment What is a systematic approach to problem solving that converts from one unit to another? A.conversion ratio B.conversion factor C.scientific notation D.dimensional analysis

Accuracy and Precision (cont.) Error is defined as the difference between an experimental value and an accepted value.Error

Accuracy and Precision (cont.) The error equation is error = experimental value – accepted value. Percent error expresses error as a percentage of the accepted value.Percent error

Practice Calculate the percent error for each trial. Trial g/cm 3 Trial g/cm 3 Trial g/cm 3 Actual/ Accepted 1.59 g/cm 3 HW –

Measurement Uncertainty Measurements always have some degree of uncertainty (doubt) Estimation is needed when using measurement devices  Last number is a visual estimate (read between the lines!)  Different people will estimate differently Amount of uncertainty depends on the precision measurement device

Uncertainty in Measurements No measurement is perfect  No instrument is perfect  Human error (an estimate) exists Reliability:  Precision: All measurements are close to each other  Accuracy: Closeness to the accepted value

Accuracy and Precision Precise; not accurate Accurate; not precise Precise and accurate

Significant Figures Shows the precision of a measurement  The more digits reported, the more precise the measurement All known digits (certain numbers) Plus a last estimated digit  “Read Between the Lines”  Uncertain number

Example: 3.0 cm3.5 cm 3.00 cm3.52 cm

What is the Volume? 8.6 mL

Significant Figures (cont.) Rules for significant figures Rule 1: Nonzero numbers are always significant. Rule 2: Zeros between nonzero numbers are always significant. Rule 3: All final zeros to the right of the decimal are significant.

Rule 4: Placeholder zeros are not significant. To remove placeholder zeros, rewrite the number in scientific notation. (zeros in front of nonzero numbers) Rule 5: Counting numbers and defined constants have an infinite number of significant figures. Significant Figures (cont.)

Examples: Measurement # of Sig Figs 405 g mL  s m 5

Atlantic-Pacific Rule Pacific Atlantic Decimal p resent, count from the P acific side 2. First nonzero digit 3. This & all other digits are significant

Atlantic-Pacific Rule Pacific Atlantic Decimal p resent, count from the P acific side 2. First nonzero digit 3. This & all other digits are significant

Atlantic-Pacific Rule Pacific Atlantic 2,501,600 1)Decimal point a bsent, count from A tlantic side 2) First nonzero digit 3) This & all other digits are significant

Examples a) b) c) d) 3014 e) f) MeasurementSignificant Digits

Atlantic-Pacific Decimal point present  Count from Pacific side  Starting with first nonzero digit  All other digits are significant Decimal point absent  Count from the Atlantic side  Starting with first nonzero digit  All other digits are significant

Significant Figures Sig Figs are the # of digits in a measurement that certain and estimated. An answer cannot be more accurate than the data that was used to obtain the answer. If an answer has more digits than are significant, it implies that the answer is more accurate. It is not and is therefore wrong. HW –

Significant Digits in Calculations Multiplication and Division  Find measurement with smallest # of significant figures  Round answer to this # of sig. figs  Example: Volume = length  width  height = 2.04 m  4.10 m  0.60 m = m 3 = 5.0 m 3

Addition and Subtraction Look for the measurement with the least number of decimal places. Round answer to the same number of decimal places. Example: s hoes g clothing 1545 g jewelry g glasses g total g 2619 g (proper number of sig. figs.)

Mixed Math Operator Perform all calculations without rounding Determine the last math operator used Round answer according to the last math operation performed HW –

Review Why do measurements always have some degree of uncertainty?  Because of the visual estimation of the last digit The amount of uncertainty depends on?  The measurement device What do significant figures show?  The degree of certainty for a measurement  All the certain numbers plus the first uncertain (or estimated) number

Rounding Numbers Calculators are not aware of significant figures. Answers should not have more significant figures than the original data with the fewest figures, and should be rounded. Ex. Calculator reads But in your calculation the lowest amount of significant figures was 3 Correct answer = 0.453

Rounding Numbers (cont.) Rules for rounding –Rule 1: If the digit to the right of the last significant figure is less than 5, do not change the last significant figure. –Rule 2: If the digit to the right of the last significant figure is 5 or greater than 5, round up to the last significant figure.

Rounding Numbers (cont.) Addition and subtraction –Round numbers so all numbers have the same number of digits to the right of the decimal. Multiplication and division –Round the answer to the same number of significant figures as the original measurement with the fewest significant figures.

Assessment Determine the number of significant figures in the following: 8,200, 723.0, and A.4, 4, and 3 B.4, 3, and 3 C.2, 3, and 1 D.2, 4, and 1

Assessment A substance has an accepted density of 2.00 g/L. You measured the density as 1.80 g/L. What is the percent error? A.20 % B.10 g/L C.10 % D.90 %

Density Chemistry

Density Density= Mass Volume D= m V

Mass Mass: Amount of matter in a substance. Don’t confuse with weight. Weight: the force with which the earth pulls on the substance.

Question Which weighs more? 50 kilograms of iron Or 50 kilograms of feathers

Question Which has a greater density? iron Or feathers

Common Units of Density Density= Mass Volume g/mL = g/cm 3 kg/m 3 1 cm 3 =1 mL 1 dm 3 =1L

Densities of Common Substances

Density as a Function of Temperature For most substances, as temperature increases the volume increases and as a result the density decreases.

Density of Water At 4 o C water has its maximum density of 1g/cm 3 Convert to kg/m 3 : 1000kg/m 3

Note Density is an intensive physical property. (Does not depend on amount of matter in the sample)

Density Column

Galilean Thermometer