Experimental Design Unit Grade 10 Science Ms. Hayduk
Safety
Why is Safety Important? Why is safety important? Read the article. Discuss the following questions with the person next to you: What did the students and teacher do correctly? Whose fault is this accident? What could have been done to prevent this accident?
Safety Equipment in the Lab Eyewash used to flush out eyes if any chemical or abrasive substance gets in them First aid kit for minor cuts, scrapes and burns Fire extinguisher for small- to medium-sized fires that are uncontrolled (PASS) Spill kit to neutralize and clean up chemical spills Personal protective equipment - worn by everyone in the lab for the entire duration of the activity (goggles, aprons, gloves, etc.)
Safety Procedures - Fire For small- to medium-sized fires, use a fire extinguisher. Our fire extinguisher will work on all types of fires. PASS: pull out the pin, aim at the base of the fire, squeeze the trigger and sweep the spray. If the fire is large and cannot be controlled, leave the room immediately and pull the fire alarm. The last student from the room should close the door. If a fire alarm goes off during a lab, shut off
Safety Procedures - Spills If the spill is harmless (e.g. water, vinegar), clean it up with paper towel. If the spill is a more hazardous substance, inform an instructor. If possible, block the spill from spreading and remove books, bags and personal items from the area. If many chemicals spill in the same area, inform an instructor and evacuate the room immediately.
Safety Procedures - Injury For minor injuries, use the first aid kit. Be sure to thoroughly clean any cuts or scrapes to remove any chemical contamination before applying a bandage. For serious injuries (head injury, unconsciousness, major bleeding), call 911 immediately. Be sure to tell EMS if the injury was caused by contact with a chemical or equipment contaminated with a chemical.
General Safety Procedures Behave in a calm, professional, responsible manner at all times. No food in the lab at any time. Beverages are allowed provided they are in resealable containers. Never eat any materials being used for experiments. Use the appropriate personal protective equipment for the activity you (or others) are performing. Do not remove your PPE until you are instructed to do so by the teacher.
General Safety Procedures Keep yourself, your equipment and your workstation clean before, during and after the lab. Handle equipment with care. Wash glassware thoroughly with soap and water. After handling chemicals, wash hands thoroughly with soap and water. Keep aisles and table tops clear of bags and books.
General Safety Procedures Dispose of materials properly. Do not dump any chemicals down the drain unless instructed to by the teacher. Do not put any solid material in the drains. Sharp materials (e.g. dissection pins, broken glass) should be disposed of in the proper waste container never in the garbage can. Do not touch any chemicals or equipment you have not been instructed to handle. Do not smell or taste chemicals. Do not try any unauthorized experiments. Do not enter the science storage room.
General Safety Procedures Never leave your lab station unattended. Dress appropriately. Tie back long hair. Avoid wearing loose or dangling clothes or jewelry around chemicals or open flames. Wear closed-toed shoes. Report any accident or incident immediately, no matter how minor. Students who do not follow these safety procedures will be asked to leave the lab, and will be given an alternate written assignment to complete for that and subsequent labs.
Asking Questions
The Scientific Method The scientific method is a process of doing scientific experiments. It provides an order for how experiments should be done. In general, the order is: Purpose (ask a question) Research and hypothesis Experiment Analysis Conclusion
Creating a Purpose The purpose is the reason you are doing an experiment, or the question you want to answer. A purpose can be stated as a statement: To determine the effects of soil ph on plant growth Or as a question: How will the density of the liquid affect the buoyancy of the ball?
Why the Purpose is Important There are three purposes of a purpose (!): 1. It informs others why the experiment was conducted. 2. It keeps the experimenter focused on what they are trying to find out. 3. It gives a starting point for doing research and planning the experiment.
A Good Purpose The purpose should accurately describe what you want to know and why you are conducting the experiment. It should be specific (something you can make an experiment around). Generally it is not a yes-or-no question, but it can be. It should also include the variables being investigated (more on this later).
Examples What is the effect of temperature on plant growth? To determine how the level of inflation of tires on a vehicle will affect gas mileage.
The Hypothesis
Writing a Hypothesis A hypothesis is an educated guess. It is a prediction of what the outcome of an experiment will be. The hypothesis is based on previous knowledge and usually some research or new learning. Most importantly, although it is a guess, it should be written without saying I think.
Examples A good way to start writing hypotheses is to use the form If then because, or guess because : If the wings are larger, then the plane will fly further because there will be more lift on the plane. The powdered sugar will dissolve the fastest because it has the largest surface area.
Lab Equipment
General Procedures Keep everything clean. Wash glassware like you would wash dishes, with soap and hot water. Clean equipment as soon as possible. Handle hot items carefully. Use the correct type of tongs to hold hot glassware. Do not put very hot glass in cold water it can shatter.
General Procedures Use the right equipment for the right task! See handout
Designing an Experiment
Variables Variables are factors in an experiment that can be changed to get results. The condition that is modified is called the variable. The factors that are kept the same in all trials of an experiment are called controls or controlled variables.
Fair Tests For an experiment to give good results, it needs to be a fair test. This means that the data collected needs to be based on only one changed factor. Usually, a control experiment is set up. In the control, everything about the experiment is in a normal state, and in any other trials, only one thing is different.
Independent and Dependent Variables The independent variable is the variable that the experimenter is changing (on purpose). The dependent variable is the variable that is being measured or observed (changing as a result of the other variable). Controlled variables are variables that should not change, and are being kept the same on purpose.
Why Control Variables? If you are trying to figure out the effect of X on Y, it is really important that X is the only thing that changes. Otherwise, changes in Y might be due to the changes in variables A, B or C! Variables need to be controlled so that the observations made are directly as a result of the one variable we want to change.
Example You want to know if adding different amounts of salt to water makes it boil faster. What should your control set up be? What variable are you changing? What variables need to be the same in every trial?
Measurements: Scientific Notation
Scientific Notation Scientific notation is used for very large or very small numbers, which are common in science! It is written as a product of a number between 1 and 10 and a power of 10. 3.45 10 5 is a big number. 2.31 10-4 is a small number.
Convert to Scientific Notation 1. Place the decimal point so that there is one non-zero digit on the left of the decimal point. Get rid of any extra zeros. 2. Count the number of spaces the decimal moves to determine the exponent on the 10. If the decimal moves left, the exponent is positive. (original number greater than 1) If the decimal moves right, the exponent is negative. (original number less than 1)
Example 1 3 346 000 000 1. Write as a decimal with no extra zeros: 2. Find the exponent on the 10: 3. Write the number in S.N.:
Example 2 0.000 002 340 1. Write as a decimal with no extra zeros: 2. Find the exponent on the 10: 3. Write the number in S.N.:
Convert to Standard Form Multiply the two terms (the decimal between 1 and 10 and the power of 10) together. This can be used to check the original conversion.
Comparing Values Numbers with higher exponents on the 10 are greater: 10 > 3 4 > -1-2 > -5 For numbers with the same exponent, numbers with a larger decimal value are greater: 6.43 10 5 > 2.17 10 5 3 10-2 > 1 10-2
Measurements: Significant Digits
Importance of Significant Digits Significant digits are a method in science of indicating the precision of a measurement. There are specific rules about how to identify with digits are significant, and how to determine the number of significant digits in a measurement after doing a calculation. Significant digits are important because they tell how good the data is.
Significant Digit Rule 1 Any number that isn t zero, 1-9, is significant. 5424 = four sig. digs. 3.25 = three sig. digs.
Significant Digit Rule 2 Leading zeros, used to fix a decimal place, are not significant. 0.00342 = three sig. digs. 0.46 = two sig. digs.
Significant Digit Rule 3 Captive zeros, between two significant digits, are significant. 4032 = four sig. digs. 0.00401 = three sig. digs.
Significant Digit Rule 4a Trailing zeros, where there is no decimal place, are not significant. 500 = one sig. dig. 5 726 000 = four sig. digs.
Significant Digit Rule 4b Trailing zeros, where they are used to fix a decimal place, are significant. 500. = three sig. digs. 2110.00 = six sig. digs.
Significant Digit Rule 5 All numbers in scientific notation before the multiplication sign are significant. 4.0 10 3 = two sig. digs. 6.72 10-18 = three sig. digs.
Significant Digit Rule 6 All numbers in an exact number are significant. Exact numbers are not measured numbers, and are usually the result of a count or are a conversion factor. 760 people = three sig. digs. 5280 feet in a mile = four sig. digs.
Calculations with Significant Digits Use regular rounding rules (round up if the next number is 5 or greater; round down if the next number is 4 or less) when writing the answer with the correct number of significant digits.
Calculations with Significant Digits For multiplication and division, the answer should have the same number of significant digits as the piece of data with the least significant digits. 9.02 5.4 = 48.708 = 49 (2 SD)
Calculations with Significant Digits For addition and subtraction, the answer should have the same number of decimal places as the least precise piece of data (fewest decimal places). 1.234 + 8.2 = 9.434 = 9.4 (1 decimal place)
Calculations with Significant Digits 5.424 + 4.32 + 1.1 6.592 = 4.252 = 4.3 (1 decimal) 4.32 10 9 5.1 10-8 145 = 1.519448276 = 1.5 (2 S.D.)
Measurements: The Metric System
The Metric System In most of the world, the metric system is used for measurements of mass, volume and distance. The base unit for each type of measurement: Measurement Units Unit Symbol Mass Grams g Length Metres m Volume Litres L
Metric Unit Conversions
Converting Metric Units When going from a BIG unit to a smaller unit, MULTIPLY. When going from a SMALL unit to a bigger unit, DIVIDE. When you get your answer, ask yourself if it is reasonable!
Example 1 Convert 52 000 centimetres to kilometres.
Example 2 Convert 0.00245 g into mg.
Error in Science
What is Experimental Error? Experimental error is a term used to explain why measurements are not perfect, even when the experiment is done perfectly Experimental error DOES NOT mean: Making mistakes in the procedure or calculations Using the wrong equipment Being careless
Experimental Error Experimental error has to do with measurements. Even with very good tools, a measurement will always be a little off from the real value.
Sources of Error When asked for sources of error, remember that it has to be things that were UNAVOIDABLE. So, using dirty glassware is NOT a source of error, but contaminants left on the glass after thoroughly cleaning it IS.
Example Sources of Error Limited accuracy of measuring tools (how many decimal places the measurement can reasonably have) Contaminants on equipment or in chemicals Measuring tools not calibrated properly Impurities in chemicals Not enough trials or data Accidental spills or residue from pouring from one container to another Lots of measurements that increase uncertainty in calculations Not reading volumes and temperatures directly at eye-level Reaction does not go to completion Volumes are too small to read easily
Accuracy and Precision Accuracy is how close a measurement is to the real value. Precision is how close consecutive measurements are to each other.
Systematic and Random Errors Systematic errors affect the accuracy of a measurement precise but not accurate How good is the equipment? Random errors affect the precision of a measurement accurate but not precise How well was the measurement taken? How many times was the measurement taken?
Graphing
Checklists for Good Graphs Should be done on graph paper or on a computer Descriptive title: Good Title Rate of Cactus Growth Driving Distance of a Car from Campbell Collegiate Bacterial Culture Growth from the Girls Washroom Bad Title Height of Plant Distance versus Time Bacteria Population
Checklists for Good Graphs All lines should be drawn with a ruler Scale should be consistent on each axis (but each axis can have a different scale) Graph should fill the page and data should fill the graph Independent variable is on the x-axis (horizontal) and dependent is on the y-axis (vertical)
Checklists for Good Graphs Each axis should be labeled with the variable and units Data points need to be clear use a legend when needed Use the right type of graph for the data (you will rarely use a bar graph)
Bad Graph
Good Graph
Writing Conclusions
Analyzing Results After collecting observations and data during an experiment, you need to analyze your results while considering the purpose of your experiment. Basically, what did you find out? What does that mean?
Conclusions A conclusion should be two to five sentences that: Restates the purpose of the experiment Outlines any important data or results Nothing said in the conclusion should be something new it should be a summary of the things you have already said