1 Chemistry Chapter 1 & 2 Scientific method and Data management Chemistry- Matter and Change Glencoe Last revision Fall 2006

2 The Scientific Method Is a systematic way of gathering evidence to support ideas and theories that help explain the natural world around us. Steps to the scientific method  State the Problem  Do some research and form a hypothesis A Hypothesis is a testable prediction based on research and observations. It is what you think the answer to the problem is. A good way of writing a hypothesis is: If…(a cause (independent variable) )…then…(an effect (dependent variable) ).

3 An experiment should have these three things to be a proper experiment  Variables are things that change. There are always two; The independent variable. Sometimes called the manipulated variable. The experimenter chooses one thing to do differently in the experiment. The dependent variable. Sometimes called the measured or responding variable. This is the data that is being gathered or recorded. 3.Design and conduct an experiment.

4 II.Constants are all other things in the experiment that are kept the same all the time. III.A control is a standard for comparison. It is like a base line or the data at time zero. You will compare the data you gathered to it to see how much the dependent variable changed.

5 4.Analyze the Data This includes making graphs and/or calculations. Look for trends in the data.  Parts of a proper graph: (more info to come) Use graph paper and a ruler Title: Dependent vs. Independent Labels including units: independent – x axis, dependent – y axis Appropriate scale: Data range/number of lines, round up to a counting number Smooth line or curve

6 5.Draw a conclusion A conclusion is a 5 sentence paragraph that summarizes your investigation.  Restates your hypothesis  Briefly describe your experiment.  What was the data you collected. Give examples of your data as evidence.  What was the trend you found in the data or what does the data mean.  Did the data trend support or reject your hypothesis.

7 Report your results You will want to put your research out for peer review and/or publish your findings for your peers to evaluate.

8 Data Table Format The proper format for a data table is:  Label your independent variable and unit in the first/left-most column  Label your dependent variable and unit in the next/right-most column  REVIEW: Independent Variable  The thing that is changed by the experimenter Dependent Variable  The thing that is measured in the experiment Organizing and Graphing Data

9 Titling a Graph A title for a graph should describe what the experiment was comparing For pie graphs:  Titles should name the quantity or thing being divided Student Hair Color For line and bar graphs:  Titles should list the dependent variable vs. the independent variable Temperature vs. Time All titles are placed at the TOP of the graph

10 Creating Line & Bar Graphs Line and bar graphs must: use graph paper if not constructed on a computer use even graduations or scale with even increasing or decreasing increments along the axis - to determine scale for x and y axis, divide range of data (data range is highest value – lowest value) by the number of lines on the axis. Then round the number up to a good counting number like.1,.2,.5, 1, 2, 5, 10, 20, 50… Start your scale near the lowest number.

11 Calculating the Scale on a Graph For example:  The left hand column is the independent variable. The data range should subtract the high data point from the low data point. Data range:  Then count the number of lines on the axis you will be putting the scale on.  For example: Speed (m/s) Water Temperatur e (°C) Then divide the range by the number of lines You need to round that number up to one that is easy to count by like 0.1, 0.2, 0.5, 1.0, 2.0, 5.0, 10.0 Start your scale near the lowest number. 17-5= = = 1.0

12 The Metric System This system is based on powers of 10. It consists of a base unit which is changed by powers of ten when a prefix is added Metric Conversion scale Great Mighty King Henry Died monday drinking chocolate milk maybe no one paid attention Giga __ __ Mega__ __ Kilo Hecto Deka base unit deci centi milli__ __micro__ __nano__ __pico (meter) G- M- K- H- D- or dk- m,g,L,s d- c- m- µ- n- p

13 SI System Because units are combined all the time in math equations they often become very large and complex. They are called derived units and consist of multiple base units. Scientists tend to abbreviate them. Example: The equation for potential energy is E P = mgh The unit for this using all base units is Kg m 2 /s 2 The abbreviated version of this unit is J for Joule Without standardizing the base units, scientists would never know which mass, distance and time unit was imbedded in the abbreviated unit Joule.

14 7 Standard Base Units QuantityBase unit TimeSeconds (s) Lengthmeter (m) MassKilogram (Kg) TemperatureKelvin (K) Amount of a specific substance mole (mol) Electric current ampere (A) Luminous intensity candela (cd)

15 Measurements and Significant Digits A measurement consists of three things.  A number: this is the value of the measurement.  The number of digits in the number or the resolution: this indicates the smallest increment the equipment scale read to.  The unit: this is a label that tells you how the measurement was made.

16 Determine the length of the red line. What is the value of the lines between the 2 cm and 3 cm marks? 0.1 cm So this line is at least 2.8 cm Is it exactly on the line? What would the imaginary lines between 0.8 and 0.9 be worth?.01 cm Since it is hard to estimate where it is between the lines just say it is half way if it is between the lines or.05 cm, if it is on the line, keep the decimal place but just report a zero or.00 cm. What is the length of the red line here? 2.85 cm

17 Significant digits The Atlantic/Pacific rule: If a decimal is absent, start on the Atlantic side of the number Go through all zeros until you hit a real number. All digits after that are significant. 5 significant digits If a decimal is present, start on the Pacific side of the number. Go through all zeros until you hit a real number. All digits after that are significant. 4 significant digits

Calculations with Significant digits Addition & Subtraction: report you answer in the least decimal places as your data This is the last digit but you must calculate the next one to see if you should round

19 Multiplication & Division: report your answer in the least number of significant digits as your data x digits6 digits = or 3.08 x10 3 You try: = / = Scientific notation can be used to report the correct number of significant digits Do not round your data until you are finished with all calculations.

20 This is used to make very large and very small numbers manageable. Ex. 4,763,000,000 = ? Report only one digit to the left of the decimal. Multiply by a power of 10 that you have removed from original number. If your number becomes smaller by moving the decimal- your exponent should be larger. Ex X 10 9  greater than 0. If your number becomes larger by moving the decimal- your exponent should be smaller (be careful of negative numbers). Ex = 7 X  smaller than 0. Scientific Notation

21 Errors in data There are numerous types of errors that can occur in the lab. 1.Equipment error: This happens when the equipment used for an experiment wasn’t calibrated or is faulty. The error tends to be consistent throughout the data. This usually results in data that is precise but not accurate. 2.Operator error: These are mistakes made by the experimenter. It may be technique problems or mistakes that result in regular errors occurring each time. These results are usually neither precise nor accurate.

22 Errors in data Errors can all average out to be an accurate value by coincidence. This would not be precise but accurate. The best is to strive for both precision and accuracy to achieve the best data possible, The best way to gather data is to take multiple measurements (minimum of three) of the same data and then taking an average of the data.

23 Calculating Percent Error The percent error calculation is used to see how far off your experimental data is from the theoretical, accepted, book or true value. An acceptable variance is within 5% of the true value. % Error = |True value – Experimental value| x100 True value

24 Mass: The amount of matter (atoms) an object has. Unit: grams or kilograms Volume: The amount of space an object takes up. Unit: milliliters or cm 3 Density : A relationship between the mass and volume of an object. Or; the amount of matter per volume.

25 A theory is an explanation that has been supported by many, many experiments. It is the most logical explanation of why things work they way they do based on evidence gathered by experimentation. Scientific Law is a relationship in nature that is supported by many experiments. It is a rule that describes, but doesn’t explain, a pattern in nature and predicts what will happen under special conditions. It is often described with a mathematical equation. Theory & Law