Introduction to Science

Lab 1 Introduction to Science

Introduction to Science

Concepts to Explore

• The Scientific Method

• Observations

• Variables

• Controls

• Data Analysis

• Calculations

• Data Collection

• Scientific Reasoning

• Writing a Lab Report

Introduction

What is science? You have likely taken several classes throughout your career as a student, and know that it is more than just chapters in a book. Science is a process. It uses evidence to understand the history of the natural world and how it works. Scientific knowledge is constantly evolving as we understand more about the natural world. Science begins with observations that can be measured in some way, and often concludes with observations from analyzed data.

Following the scientific method helps to minimize bias when testing a theory. It helps scientists collect and organize information in a useful way so that patterns and data can be analyzed in a meaningful way. As a scientist, you should use the scientific method as you conduct the experiments throughout this manual.

Figure 1: The scientific method process.

11

Introduction to Science

The process of the scientific method begins with an observation. For example, suppose you observe a plant growing towards a window. This observation could be the first step in designing an experiment. Remember that observations are used to begin the scientific method, but they may also be used to help analyze data.

Observations can be quantitative (measurable), or qualitative (immeasurable; observational). Quantitative observations allow us to record findings as data, and leave little room for subjective error. Qualitative obser- vations cannot be measured. They rely on sensory perceptions. The nature of these observations makes them more subjective and susceptible to human error.

Let’s review this with an example. Suppose you have a handful of pennies. You can make quantitative obser- vations that there are 15 pennies, and each is 1.9 cm in diameter. Both the quantity, and the diameter, can be precisely measured. You can also make qualitative observations that they are brown, shiny, or smooth. The color and texture are not numerically measured, and may vary based on the individual’s perception or background.

Quantitative observations are generally preferred in science because they involve "hard" data. Because of this, many scientific instruments, such as microscopes and scales, have been developed to alleviate the need for qualitative observations. Rather than observing that an object is large, we can now identify specific mass, shapes, structures, etc.

There are still many situations, as you will encounter throughout this lab manual, in which qualitative obser- vations provide useful data. Noticing the color change of a leaf or the change in smell of a compound, for ex- ample, are important observations and can provide a great deal of practical information.

Once an observation has been made, the next step is to develop a hy- pothesis. A hypothesis is a statement describing what the scientist thinks will happen in the experiment. In other words, it is a proposed ex- planation for an event based on previous observation(s). Hypotheses are typically written in an if/then format. To construct an if/then hypothe- sis, first determine an explanation for an occurrence. The “if” precedes the explanation, and the “then” precedes the occurrence. For example:

Hypothesis

If plants are grown in soil with added nutrients, then they will grow faster than plants grown without added nutrients.

Figure 2: What affects plant growth?

12

Introduction to Science

In this example, the explanation is “plants are grown in soil with added nutrients” and the occurrence is “plants will grow faster than plants without added nutrients”.

A null hypothesis is a testable statement that if proven true, means the hypothesis was incorrect. For exam- ple:

Null hypothesis

If plants are grown in soil with added nutrients, then they will grow at the same rate as plants grown in soil without nutrients.

If plants grow quicker when nutrients are added, then the hypothesis is accepted

and the null hypothesis is rejected.

Both a hypothesis and a null hypothesis statement must be testable, but only one can be true.

There are often many ways to test a hypothesis. However, three rules must always be followed for results to be valid.

• The experiment must be replicable.

• Only test one variable at a time.

• Always include a control.

Experiments must be replicable to create valid theories. In other words, an experi- ment must provide precise results over multiple trials Precise results are those which have very similar values (e.g., 85, 86, and 86.5) over multiple trials. By con- trast, accurate results are those which demonstrate what you expected to happen (e.g., you expect the test results of three students tests to be 80%, 67%, and 100%). The following example demonstrates the significance of experimental re-

peatability. Suppose you conduct an experiment and con- clude that ice melts in 30 seconds when placed on a burn- er, but you do not record your procedure or define the pre- cise variables included. The conclusion that you draw will not be recognized in the scientific community because

Precise results may not hit the bulls-eye, but they all hit the same region.

Accurate results all hit the bulls-eye on a target.

other scientists cannot repeat your experiment and find the same results. What if another scientist tries to repeat your ice experiment, but does not turn on the burner; or, uses a larger ice chunk. The results will not be the same, because the experi- ment was not repeated using the same procedure. This makes the results invalid, and demonstrates why it is important for an experiment to be replicable.

13

Introduction to Science

Variables are defined, measurable components of an experiment. Controlling variables in an experiment al- lows the scientist to quantify changes that occur. This allows for focused results to be measured; and, for re- fined conclusions to be drawn. There are two types of variables, independent variables and dependent varia- bles.

Independent variables are variables that scientists select to change. For example, the time of day, amount of substrate, etc. Independent variables are used by scientists to test hypotheses. There can only be one in- dependent variable in each experiment. This is because if a change occurs, scientists need to be able to pin- point the cause of the change. Independent variables are always placed on the x-axis of a chart or graph.

Dependent variables are variables that scientists observe in relationship to the independent variable. Com- mon examples of this are rate of reaction, color change, etc. Any changes observed in the dependent variable are caused by the changes in the independent variable. In other words, they depend on the independent vari- able. There can be more than one dependent variable in an experiment. Dependent variables are placed on the y-axis of a chart or graph.

A control is a sample of data collected in an experiment that is not exposed to the independent variable. The control sample reflects the factors that could influence the results of the experiment, but do not reflect the planned changes that might result from manipulating the independent variable. Controls must be identified to eliminate compounding changes that could influence results. Often, the hardest part of designing an experi- ment is determining how to isolate the independent variable and control all other possible variables. Scientists must be careful not to eliminate or create a factor that could skew the results. For this reason, taking notes to account for unidentified variables is important. This might include factors such as temperature, humidity, time of day, or other environmental conditions that may impact results.

There are two types of controls, positive and negative. Negative controls are data samples in which you ex- pect no change to occur. They help scientists determine that the experimental results are due to the inde- pendent variable, rather than an unidentified or unaccounted variable. For example, suppose you need to cul- ture bacteria and want to include a negative control. You could create this by streaking a sterile loop across an agar plate. Sterile loops should not create any microbial growth; therefore, you expect no change to occur on the agar plate. If no growth occurs, you can assume the equipment used was sterile. However, if microbial growth does occur, you must assume that the equipment was contaminated prior to the experiment and must redo the experiment with new materials.

Alternatively, positive controls are data samples in which you do expect a change. Let’s return to the growth example, but now you need to create a positive control. To do this, you now use a loop to streak a plate with a

14

Introduction to Science

sample that you know grows well on agar (such as E. coli). If the bacteria grow, you can assume that the bac- teria sample and agar are both suitable for the experiment. However, if the bacteria do not grow, you must assume that the agar or bacteria has been compromised and you must re-do the experiment with new materi- als.

The scientific method also requires data collection. This may reflect what occurred before, during, or after an experiment. Collected data help reveal experimental results. Data should include all relevant observations, both quantitative and qualitative. After results are collected, they can be analyzed. Data analysis often in- volves a variety of calculations, conversions, graphs, tables, etc.

Scientific notation is a common method used to transform a number. Scientific data is often very large (e.g., the speed of light) or very small (e.g., the diameter of a cell). Scientific notation provides an abbreviated ex- pression of a number, so that scientists don’t get caught up counting a long series of zeroes.

There are three parts to scientific notation: the base, the coefficient and the exponent. Base 10 is almost al- ways used and makes the notation easy to translate. The coefficient is always a number between 1 and 10, and uses the significant digits of the original number. The exponent tells us whether the number is greater or less than 1, and can be used to “count” the number of digits the decimal must be moved to translate the num- ber to regular notation. A negative exponent tells you to move the decimal to the left, while a positive one tells you to move it to the right.

For example, the number 5,600,000 can be written as 5.6 x 106. If you multiply 5.6 by 10 six times, you will arrive at 5,600,000. Note the exponent, six, is positive because the number is larger than one. Alternative, the number 0.00045 must be written using a negative exponent. To write this number in scientific notation, deter- mine the coefficient. Remember that the coefficient must be between 1 and 10. The significant digits are 4 and 5. Therefore, 4.5 is the coefficient. To determine the exponent, count how many places you must move the decimal over to create the original number. Moving to the left, we have 0.45, 0.045, 0.0045, and finally 0.00045. Since we move the decimal four places to the left, the exponent is -4. Written in scientific notation, we have 4.5 x 10-4

Although these calculations may feel laborious, a well-calculated presentation can transform data into a for- mat that scientists can more easily understand and learn from. Some of the most common methods of data presentation are:

Table: A well-organized summary of data collected. Tables should display any information relevant to the hy- pothesis. Always include a clearly stated title, labeled columns and rows, and measurement units.

15

Introduction to Science

H ei

g h

t (m

m )

Table 2: Plant Growth With and Without Added Nutrients

Variable Height Wk. 1 (mm) Height Wk. 2 (mm) Height Wk. 3 (mm) Height Wk. 4 (mm)

Control (without nutrients)

3.4

3.6

3.7

4.0

Independent

(with nutrients)

3.5

3.7

4.1

4.6

Graph: A visual representation of the relationship between the independent and dependent variable. They are typically created by using data from a table. Graphs are useful in identifying trends and illustrating find- ings. When constructing a graph, it is important to use appropriate, consistent numerical intervals. Titles and axes labels should also reflect the data table information. There are several different types of graphs, and each type serves a different purpose. Examples include line graphs or bar graphs. Line graphs show the rela- tionship between variables using plotted points that are connected with a line. There must be a direct rela- tionship and dependence between each point connected. More than one set of data can be presented on a line graph. By comparison, bar graphs compare results that are independent from each other, as opposed to a continuous series.

Figure 3: Sample line graph. Plant growth, with and without nutrients, over time.

16

Introduction to Science

S p

ee d

( kp

h )

Figure 4: Sample bar graph. Top speed for Cars A, B, C, and D. Note, since there is no relationship between each car, each result is independent and a bar graph is appropriate.

After compiling the data, scientists analyze the data to determine if the experiment supports or refutes the hypothesis. If the hypothesis is supported, you may want to consider additional variables that should be ex- amined. If your data does not provide clear results, you may want to consider running additional trials or revising the procedure to create a more precise outcome.

The scientific method gives us a great foundation to conduct scientific reason- ing. The more data and observations we are able to make, the more we are able to accurately reason through the natural phenomena which occur in our daily lives. Scientific reasoning does not always include a structured lab report, but it always helps society to think through difficult concepts and determine so- lutions. For example, scientific reasoning can be used to create a response to the changing global climate, develop medical solutions to health concerns, or even learn about subatomic particles and tendencies.

Although the scientific method and scientific reasoning can guide society through critical or abstract thinking, the scientific industry typically promotes lab reports as a universal method of data analysis and presentation. In gen-

Figure 5: Lab reports are an important part of science, providing a way to report conclusions and ideas.

17

Introduction to Science

eral terms, a lab report is a scientific paper describing the premise of an experiment, the procedures taken, and the results of the study. They provide a written record of what took place to help others learn and expe- dite future experimental processes. Though most lab reports go unpublished, it is important to write a report that accurately characterizes the experiment performed. Table 3 summarizes the components of a typical lab report.

Table 3: Lab Report Components

Part of the Lab Report

Purpose

Title

A short statement summarizing the topic

Abstract

A brief summary of the methods, results and conclusions. It should not ex- ceed 200 words and should be the last part written.

Introduction

An overview of why the experiment was conducted. It should include: • Background - Provide an overview of what is already known and what

questions remain unresolved. Be sure the reader is given enough infor- mation to know why and how the experiment was performed.

• Objective - Explain the purpose of the experiment (i.e. "I want to deter- mine if taking baby aspirin every day prevents second heart attacks.")

• Hypothesis - This is your "guess" as to what will happen when you do the experiment.

Materials and Methods

A detailed description of what was used to conduct the experiment, what was actually done (step by step) and how it was done. The description should be exact enough that someone reading the report can replicate the experiment.

Results

Data and observations obtained during the experiment. This section should be clear and concise. Tables and graphs are often appropriate in this section. Interpretations should not be included here.

Discussion

Data interpretations and experimental conclusions. • Discuss the meaning of your findings. Look for common themes, relation-

ships and points that perhaps generate more questions. • When appropriate, discuss outside factors (i.e. temperature, time of day,

etc.) that may have played a role in the experiment. • Identify what could be done to control for these factors in future experi-

ments.

Conclusion A short, concise summary that states what has been learned.

References

Any articles, books, magazines, interviews, newspapers, etc. that were used to support your background, experimental protocols, discussions and con- clusions.

18

Introduction to Science

Exercise 1: Data Interpretation

Download the Week 1 Lab Reporting Form and answer the Exercise 1 Questions based on the information

found in these readings.

19

Weather and Climate Change

Appendix Good Lab Techniques

20

Good Lab Techniques

Good Laboratory Techniques

Science labs, whether at universities or in your home, are places of adventure and discovery. One of the first things scientists learn is how exciting experiments can be. However, they must also realize science can be dangerous without some instruction on good laboratory practices.

• Read the protocol thoroughly before starting any new experiment. You should be familiar with the action required every step of the way.

• Keep all work spaces free from clutter and dirty dishes.

• Read the labels on all chemicals, and note the chemical safety rating on each container. Read all Material Safety Data Sheets (provided on www.eScienceLabs.com).

• Thoroughly rinse lab ware (test tubes, beakers, etc.) between experi- ments. To do so, wash with a soap and hot water solution using a bottle brush to scrub. Rinse completely at least four times. Let air dry

• Use a new pipet for each chemical dispensed.

• Wipe up any chemical spills immediately. Check MSDSs for special handling instructions (provided on www.eScienceLabs.com).

• Use test tube caps or stoppers to cover test tubes when shaking or mixing – not your finger!

A B C

Figure 1: A underpad will prevent any spilled liquids from contaminating the sur- face you work on.

Figure 2: Special measuring tools in make experimentation easier and more accu- rate in the lab. A shows a beaker, B graduated cylinders, and C test tubes in a test tube rack.

67

Good Lab Techniques

• When preparing a solution, refer to a protocol for any specific instructions on preparation. Weigh out the desired amount of chemicals, and transfer to a beaker or graduated cylinder. Add LESS than the required amount of water. Swirl or stir to dissolve the chemical (you can also pour the solution back and forth between two test tubes), and once dissolved, trans- fer to a graduated cylinder and add the required amount of liquid to achieve the final volume.

• A molar solution is one in which one liter (1L) of solution con- tains the number of grams equal to its molecular weight.

For example:

1M = 110 g CaCl x 110 g CaCl/mol CaCl

(The formula weight of CaCl is 110 g/mol)

Figure 3: Disposable pipettes aid in ac- curate measuring of small volumes of liquids. It is important to use a new pi- pette for each chemical to avoid con- tamination.

• A percent solution can be prepared by percentage of weight of chemical to 100ml of solvent (w/v) , or volume of chemical in 100ml of solvent (v/v).

For example:

20 g NaCl + 80 mL H2O = 20% w/v NaCl solution

• Concentrated solutions, such as 10X, or ten times the normal strength, are diluted such that the final concentration of the solution is 1X.

For example:

To make a 100 mL solution of 1X TBE from a 10X solution:

10 mL 10X TBE + 90 mL water = 100ml 1X TBE

• Always read the MSDS before disposing of a chemical to insure it does not require extra measures. (provided on www.eScienceLabs.com)

• Avoid prolonged exposure of chemicals to direct sunlight and extreme temperatures. Immediately se- cure the lid of a chemical after use.

• Prepare a dilution using the following equation:

c1v1 = c2v2

Where c1 is the concentration of the original solution, v1 is the volume of the original solution, and c2 and v2 are the corresponding concentration and volume of the final solution. Since you know c1,

68

Good Lab Techniques

c2, and v2, you solve for v1 to figure out how much of the original solution is needed to make a cer- tain volume of a diluted concentration.

• If you are ever required to smell a chemical, always waft a gas toward you, as shown in the figure below.. This means to wave your hand over the chemical towards you. Never directly smell a chemical. Never smell a gas that is toxic or otherwise dangerous.

• Use only the chemicals needed for the activity.

• Keep lids closed when a chemical is not being used.

• When diluting an acid, always slowly pour the acid into the water. Never pour water into an acid, as this could cause both splashing and/or an explosion.

• Never return excess chemical back to the original bottle. This can contaminate the chemical sup- ply.

• Be careful not to interchange lids between different chemical bottles.

• When pouring a chemical, always hold the lid of the chemical bottle between your fingers. Never lay the lid down on a surface. This can contaminate the chemical supply.

• When using knives or blades, always cut away from yourself.

69

© 2012 eScience Labs, LLC - All rights reserve -

68