Unit 1 Scientific Investigation, Lab Reports, Units, Conversions, Scientific Notation, Dimensional Analysis, Accuracy, Precision, Significant Digits Generate a hypothesis on the basis of credible, accurate, and relevant sources of scientific information. (PS-1.1) Use appropriate laboratory apparatuses, technology, and techniques safely and accurately when conducting a scientific experiment. (PS-1.2) Use scientific instruments to record measurement data in appropriate metric units that reflect the precision and accuracy of each particular instrument. (PS-1.3) Design a scientific investigation with appropriate methods of control to test a hypothesis (including independent and dependent variables). (PS-1.4) Organize and interpret the data from a controlled scientific investigation by using mathematics (including formulas and dimensional analysis), graphs, models, and/or technology. (PS-1.5) Evaluate the results of a controlled scientific investigation in terms of whether they refute or verify the hypothesis. (PS-1.6) Use appropriate safety procedures when conducting investigations. (PS-1.9) Apply established rules for significant digits, both in reading a scientific instrument and in calculating a derived quantity from measurement. (C-1.1)

Scientific Investigation & Parts of a Lab Report Statement of Problem Clearly testable Implies a specific experiment NOT a yes or no question Hypothesis Tentative explanation of observations (includes both independent and dependent variables) Either supported or not supported by experimental data

Variables Independent (IV): the variable that the experimenter changes Dependent (DV): the variable that changes as a result of a change in the IV Constants: factors held constant Control: used as a comparison for experimental data Scientific Investigation & Parts of a Lab Report

Materials Only list the materials you use Use proper names List quantities Procedure Numbered steps that anyone can follow to repeat the experiment Usually includes diagrams Scientific Investigation & Parts of a Lab Report

Observation v. Inference Observations: Performed by scientists during experiments Include only quantitative or qualitative measurements Inferences: Conclusions drawn based on prior knowledge (i.e., you knew that the white object was a candle…you cannot measure that with a tool or your senses…you had to be told what a candle is)

Qualitative Observations collected using 4 senses Data Tables Include quantitative data collected using scientific instruments numbers with units and significant digits Example Scientific Investigation & Parts of a Lab Report

Data Tables Always put title on data table Headings are name of variables (IV & DV) and units used for measurement Data tables include measured variables and calculated values Measurements for the Density of H 2 O Mass (g)Volume (mL) Density (g/mL)

Graphs Show the relationship between the IV and the DV Must have a title and axes labels (with units) IV on x-axis and DV on y-axis Different types of graphs but most common in science is a scatter plot Example Scientific Investigation & Parts of a Lab Report

Graphs

Statistics Measures of Central Tendency Mean Median Mode Measure of Variation (range) Line of best fit calculations Percent Error Scientific Investigation & Parts of a Lab Report

Analysis of Results All statements must be supported by data Discusses all of the data (even outliers) Discusses trends and what they mean Discusses statistics and what they mean Possible sources of experimental error Do not include math or other human errors Discuss how error may have affected data Scientific Investigation & Parts of a Lab Report

Conclusion Hypothesis is restated Hypothesis is evaluated according to the data Reasons for accepting or rejecting the hypothesis are given Statements are supported by the data Recommendations for future experiments Scientific Investigation & Parts of a Lab Report

Theory v. Law Theory: Explanation that has been supported by many, many experiments Can be modified Law: Relationship in nature that is supported by many experiments

Units SI System: international system of units Base units: Defined unit based on a standard 7 SI base units Second (s), meter (m), kilogram (kg), Kelvin (K), mole (mol), candela (cd), ampere (A) Derived units: Combination of base units Examples: volume (m 3 ), speed (m/s), density (g/mL)

Prefixes You need to know the metric prefixes below and how to convert from one to another… Giga (G) = 1, 000, 000, 000 base units Mega (M) = 1, 000, 000 base units Kilo (k) = 1,000 base units Deci (d) = 1/10 base unit Centi (c) = 1/100 base unit Milli (m) = 1/1000 base unit Micro (  ) = 1/1, 000, 000 base unit Nano (n) = 1/1, 000, 000, 000 base unit

Prefixes Some helpful conversions: 1 hour = 60 minutes = 3600 seconds 1 cm 3 = 1 mL and 1 dm 3 = 1 L

Dimensional Analysis Method of converting units Things to remember: When you add/subtract numbers, their units MUST match exactly When you multiply/divide numbers, the units do the same thing. 3 x 3 = 3 2 and s x s = s 2 9 / 2 = 9/2 and m / s = m/s 3 / 3 = 1 and s / s = 1 Practice with metric prefixes

Accuracy and Precision Accuracy How close a data point is to the accepted value Precision How close data points are to each other

Accuracy and Precision

Percent Error How far off your data is from the accepted value (a measure of accuracy) % error = accepted – experimental x 100 accepted Don’t forget to take absolute value… percent error CANNOT be negative!

Significant Figures Tells precision of instruments Include all known digits plus one estimated digit. Example: Know for sure: 52 mL Estimate last digit. Final volume = 52.9 mL

Significant Figures Read the instrument using the appropriate significant figures.

Significant Figures How do you know if a digit is significant? Rules for counting sig. figs: 1.All non-zero numbers are significant. 1.Ex. Any number 1 – 9 2.Zero-sandwich rule: 1.Zeros between non-zero numbers are significant. 2.Ex. 203 or Decimal Point Rule

Significant Figures Decimal Point: Start counting left to right with the 1 st non-zero number and keep counting Ex Or NO Decimal Point: Start counting right to left with the 1 st non-zero number and keep counting Ex Or 50030

Significant Figures x x x x ,456 How many sig. figs. are in the following?

Rounding for Sig. Figs 1.Decide how many digits you need. a)Hint: circle the last digit needed b)Ex. Round to 3 SF If following digit is: a)Less than 5  leave last digit alone b)More than 5  round last digit up one c)Equal to 5  you choose…

Rounding for Sig. Figs Examples: 1.Round to 2 SF 1.4 is less than 5 so  Round to 3 SF 1.8 is greater than 5 so  Round to 3 SF 1.It’s a 5 so  34.5 or Round to 2 SF 1.It’s a 5 so  4.6 or 4.7

Math with Sig. Figs Addition and Subtraction Answer should have the same number of digits behind the decimal as given number with fewest digits behind decimal point. Ex cm cm cm cm  77.2 cm 1 digit 3 digits 2 digits1 digit

Math with Sig. Figs Multiplication and Division Answer should have the fewest number of SFs in the given numbers Ex cm x 3.65 cm x 2.05 cm = cm 3 = 23.9 cm m / 51.2 s = 2 m/s = 2.00 m/s All have 3 SFs 3 SFs 4 SFs 3 SFs

Scientific Notation Some numbers are REALLY big or REALLY small Scientific notation is a way to write number without tons of zeros… 2 major parts: Number between 1 and raised to a power # greater than 1 – exponent is positive # less than 1 – exponent is negative

Scientific Notation Let’s look at some examples of writing numbers in scientific notation… Now, on your calculator, find the key that says “EE” or “EXP.” This replaces the “x 10” when you enter numbers in the calculator… Let’s practice…