6th grade Experimental Design
Name: UTeach Outreach Date of Lesson: Week of September 19th, 2011 Description of Class: 6th grade after school STEM clubs Length of the Lesson: 75 – 90 minutes Source of the Lesson: UTeach Outreach Resources Used: http://chem4kids.com/files/react_acidbase.html http://sciencefairproject.virtualave.net/scientific_method.htm http://misterguch.brinkster.net/acidtutorial.html http://www.nyu.edu/pages/mathmol/textbook/compounds.html http://www.definitions.net/definition/element TEKS Addressed: 6th grade 6.(2) Scientific investigation and reasoning. The student uses scientific inquiry methods during laboratory and field investigations. The student is expected to: (B) Design and implement experimental investigations by making observations, asking well-­‐defined questions, formulating testable hypotheses, and using appropriate equipment and technology; (D) Construct tables and graphs, using repeated trials and means, to organize data and identify patterns; and (E) Analyze data to formulate reasonable explanations, communicate valid conclusions supported by data, and predict trends. I. Overview The purpose of this series of lessons is to allow students to design and carry out their own experiment rooted in the larger scientific concept of acids and bases (pH). Emphasis will be placed on the use of proper data collection techniques as well as interpretation of trends. Students will be expected to prepare a report summarizing their experiment’s hypothesis, variables, materials, and procedure along with qualitative observations and applicable results. They will also be responsible for formulating a conclusion based on an analysis of their collected data. II. Performance Objectives 1. Students will learn about the pH scale and use it to properly identify solutions as either acidic or basic. 2. Students will become more familiar with the steps of the scientific method and practice communicating these steps through the completion of a written report. 3. Students will perform data collection techniques through the process of making detailed observations and taking accurate measurements. III. Resources, materials, and supplies Page 1 of 33
Whole class/per teacher: Cabbage juice demo – (a) Two beakers, each filled with 150 mL cabbage juice (b) 100 mL of dilute 10% ammonia solution (c) 100 mL of vinegar Chart paper (for pH scale notes; alternatively, doc cam can be used) Tube of curdled milk (add vinegar to whole milk to achieve effect) Straw demo (a) One clear bag filled with normal straws (b) One clear bag filled with bent straws; some tied together in knots To share per group of 4 students (see images under Section IV): (a) Test tube rack with four test tubes with lids containing the following (one liquid per tube): • Lemon juice (pH 2-­‐3) • Vinegar (pH 2-­‐3) • Baking soda solution (pH 8) • Dilute 10% Ammonia solution (pH 11) (b) Dixie cup with water (for waste/cleaning pipettes) (c) Test tube containing whole milk (d) Forceps Per pair: Testing the pH of a mystery solution – (a) Unknown solution (tap water, slightly basic) (b) pH indicator key (c) 2 pH indicator strips (d) Paper towels (e) Goggles Testing the pH at which milk curdles – (a) 4 plastic pipettes (b) Paper towels (c) 4 empty, flat bottomed containers with lids (d) pH indicator key (e) 8 pH indicator strips (f) Goggles ***Pack extra pH indicator strips in the event students use all of them. IV. Advanced Preparation (see images below) • Make enough cabbage juice for the whole class demonstration that occurs during the Engage. • Perform a pH test for each solution you plan on using for this lesson prior to implementation. Creating a pH key beforehand will make it easier to identify when student groups make errors in reading the pH (through interpretation of the pH indicator strips). Page 2 of 33
V. Supplemental Worksheets, materials and handouts • pH Scale Handout • Experimental Design Student Worksheet • Experimental Design Requirements • Question of the Day • Safety Instructions • Job Cards • Cards to post on pH scale (if using chart paper vs. doc cam) VI. Background Information College level Following correct experimental design is crucial for reliable data. Data, both quantitative and qualitative, must be recorded in great detail during an experiment. Materials and methods should be recorded so that an experiment can be replicated in order to corroborate results. During this lesson, students will design and conduct an experiment stemming from the larger scientific concept of acids and bases. Svante Arrhenius was the first person to define acids and bases. He said an acid was anything that increased the concentration of protons (H+ ions) in water, and a base was anything that increased the concentration of hydroxide ions (OH–). These definitions are independent of one another, but Bronsted and Lowry realized that acids and bases are related, and offered a broader definition: an acid is a compound that gives up a proton, and a base is a compound that accepts a proton. Under the Bronsted-­‐Lowry definition, acids and bases are related to one another, and whenever an acid gives up an H+, there must always be a base there to accept it. Some compounds, such as water, can act as both a proton donor and a proton acceptor. When you dissolve an acid in water, water acts as a base and accepts the proton. When you dissolve a base in water, the water acts as an acid and donates a proton. Acids and bases are often identifiable by their chemical formulas. The chemical formulas for acids, such as hydrochloric (HCl) and sulfuric (H2SO4) begin with H. Strong bases such as sodium hydroxide (NaOH) and barium hydroxide (Ba(OH)2) end with OH. The chemical formula for ammonia (NH3) is often combined with that of a water molecule (H2O) to result in NH4OH in order to make it more apparent that ammonia is a base. There are two important distinctions that must be made when talking about acids and bases: Page 3 of 33
1) Acid and base versus acidic and basic solutions, and 2) Strong acid or base versus concentrated acid or base. The designations "acid" and "base" refer to specific chemical compounds, such as those mentioned earlier. The terms "acidic" or "basic" refer to solutions. A solution can go from acidic to basic and back again by adding sufficient base or acid, but an acid cannot be turned into a base, nor a base turned into an acid without changing the molecule itself. The greater misunderstanding is confusion between a strong acid and a concentrated acid. Some acids, when added to water, dissociate completely, which means that each acid molecule in the solution gives up a proton. There are only seven acids that do this, and you've heard of some of them. The best known of the seven are hydrochloric acid (HCl), nitric acid (HNO3), and sulfuric acid (H2SO4). Similar to hydrochloric acid but less common are hydrobromic acid (HBr) and hydroiodic acid (HI). The last two strong acids are chloric acid and perchloric acid, HClO3 and HClO4 respectively. When any of these are dissolved in water, each acid molecule loses a proton. All other acids are weak acids, meaning that when they are dissolved in water, some of the acid molecules give up a proton but others do not. We say that these acids only partially dissociate. There is actually a constant flux occurring in the solution, where some acid molecules are giving up H+ ions, and others which have already lost theirs up are picking up H+ ions from the solution, but at any given time, only a fraction of weak acid molecules in the solution have let go of their H+ ion. A strong acid is strong no matter what its concentration might be, and a weak acid is still weak no matter what its concentration is. The designation "strong" and "weak" refers to the acid itself, not to the solution. Concentration is a measure of how much acid or base is in the solution. Because strong acids dissociate completely and weak acids do not, if you have a solution of a strong acid and a strong base at equal concentrations, the strong acid solution will always be more acidic than the weak acid solution. But a highly concentrated solution of a weak acid can be more acidic than a low concentration solution of a strong acid. The same holds true for bases: a strong base is one in which each base unit breaks off one (or more) hydroxide ions (OH–). In a solution of a weak base such as ammonia, some of the ammonia molecules will pull an H+ from a water molecule and thereby create OH– in solution, but not all of them do. In the case of a strong base such as NaOH, each one of the base "molecules" (strong bases are actually ionic, not molecular) releases an OH– into solution. Page 4 of 33
The concentration of H+ or OH– in solution is measured using a unit called pH. The “p” in pH is a mathematical function that means take the –log10 of the next quantity. The H is the hydrogen ion concentration in moles per liter (molarity, or M). pH is a log function, similar to the Richter scale used in measuring earthquake strength. In the Richter scale, each step up of 1 indicates an earthquake that is ten times more powerful than the one before. So a 7 on the Richter scale is 10 times more powerful than a 6, and 100 times more powerful than a 5. pH works the same way, except that because it is a negative log, each step down on the pH scale is a solution that is 10 times more concentrated than the one before. So a solution that has a pH of 3 has ten times the H+ concentration of a solution that is pH 4, and 100 times the concentration of a pH 5 solution. The lower the pH, the more acidic the solution is, and the higher the pH, the more basic. The concentration of H+ in a solution is typically a very small number. In most real world situations the H+ concentration ranges from about 0.1 M to 1×10-­‐14 M. If you take the –log10 of these values, this results in a pH range of 1 to 14, where 1 is the most concentrated (most acidic) solution, and 14 is the most basic. Concentrated reagents of strong acid or strong base will exceed this range, but pH 1 to 14 is generally regarded as the usual working range. There are substances which have the property of changing their color when they come in contact with an acidic or basic environment. These substances are called pH indicators. Usually, they are used as dissolved substances, such as phenolphthalein or bromothymol blue. Often, to measure the pH, special papers which have been soaked with indicators are used. These papers change color when they are immersed in acidic or basic solutions (this is the case of the well-­‐known litmus paper). It is also possible to measure the pH with electrical instruments like a pH meter. In the experimental design lesson, students will be denaturing the protein casein (most commonly found in milk). This denaturing occurs at a very specific pH. Proteins have a shape or three-­‐dimensional structure that they maintain through hydrogen bonding. Changing the pH of a protein will often cause the protein to lose its shape (denature) through removing or adding hydrogen ions to the structure. When the protein loses its natural shape, it can become tangled with other proteins and form visible clumps. 6th grade level The ability to design a good experiment is an important skill for any scientist. A good experimental design will include carefully controlling the independent variable (the one you change) and measuring the dependent variable (what we measure). Experimental design is usually guided by a hypothesis, and observations and data should be recorded during the experiment so that if someone else were to repeat your experiment they could easily compare their results to yours. We will keep all of this in mind during this lesson as we design and carry out an experiment related to the scientific concepts of acids, bases, and the pH scale. Scientists use something called the pH scale to measure how acidic or basic a solution is. It typically goes from 0 to 14. Acidic solutions have a pH at the lower values (around Page 5 of 33
0 to 6). Basic solutions have pH values from around 8 to 14. The middle, pH 7, is neutral. Pure water is neutral, but household solutions can have a wide range of pH values. Normally we think of acids as being dangerous, but strongly basic solutions such as drain cleaners can also be very hazardous. The pH scale is based on multiples of ten and it works like the Richter scale used in measuring earthquake strength. In the Richter scale, each step up of 1 indicates an earthquake that is ten times more powerful than the one before. So a 7 on the Richter scale is 10 times more powerful than a 6, and 100 times more powerful than a 5. pH works the same way, except that each step down on the pH scale is a solution that is 10 times more concentrated than the one before. So a solution that has a pH of 3 has ten times the concentration of a solution that is pH 4, and 100 times the concentration of a pH 5 solution. There are substances which have the property of changing color when they come in contact with an acidic or basic environment. These substances are called pH indicators. Usually, they are used in liquid form, such as red cabbage juice. Often, to measure the pH, special papers which have been soaked with indicators are used. These papers change color when they come in contact with an acidic or basic solution. It is also possible to measure pH with electrical instruments like a pH meter. All of the new knowledge you gain related to acids, bases, and the pH scale will be used to design an experiment involving the proteins found in milk. Milk typically has a pH of about 6.5; we consider it to be a neutral solution, since it has a pH very close to 7. If the milk becomes acidic, it will start to go bad. The experiment you design will try to figure out at which pH milk starts to curdle, or clump together. This change in milk’s pH is what is responsible for milk going bad or sour after its expiration date passes. VII. Possible Misconceptions 1. All experimental questions can be answered with simple yes or no responses. The students’ statement of problem for their experiment should not have a yes or a no answer. Their statement needs to be specific and unique to the experiment being conducted. 2. A pH of 0 indicates a neutral substance. A 7 on the pH scale corresponds to a neutral substance, such as pure water. Zero indicates a very strong acid. 3. All bodily fluids have the same pH. Spit has a pH of 7.4 (normally neutral), whereas vomit is considered to be an acidic solution with a pH of 2. This is because vomit contains stomach acid, which is used in the digestive process to break down foods completely. 4. A solution can be considered an acid or base, depending on its pH. The designations "acid" and "base" refer to specific chemical compounds. The terms "acidic" or "basic" refer to solutions. A solution can go from acidic to basic and back again by adding sufficient base or acid, but an acid cannot be turned into a base, nor a base turned into an acid without changing the molecule itself. Page 6 of 33
5. A strong acid or base, in diluted form, is more acidic than a weak acid or base that is highly concentrated. A highly concentrated solution of a weak acid can be more acidic than a low concentration solution of a strong acid. VIII. Vocabulary and Definitions College level 1. Acid -­‐ A proton donor, or a compound that when added to water, increases the concentration of H+ ions in solution; comes from the Latin word acidus that means "sharp" or "sour." 2. Base -­‐ A proton acceptor, or a compound that when added to water, decreases the concentration of H+ ions in solution. 3. Aqueous -­‐ A solution in which water is the solvent. 4. Strong Acid -­‐ An acid that dissociates completely in water. 5. Strong Base -­‐ A base that dissociates completely in water. 6. Weak Acid -­‐ An acid that only partially ionizes in an aqueous solution (i.e. not every molecule breaks apart). 7. Weak Base -­‐ A base that only partially ionizes in an aqueous solution (i.e. not every molecule contributes an OH– ion to the solution). 8. Neutral -­‐ A solution that has a pH of 7; it is neither acidic nor basic. 9. Denature – To cause a protein to lose its natural shape. 10. pH – A measure of the acidity or alkalinity of an aqueous solution. 11. Compound – a substance formed by the chemical union of two or more elements 12. Element – one of a class of substances that cannot be separated into simpler substances by chemical means 6th grade level 1. Acidic solution (solución ácida) -­‐ A solution that when added to water decreases the pH. 2. Basic solution (solución básica) -­‐ A solution that when added to water increases the pH. 3. Neutral (neutral) -­‐ A solution that has a pH of 7; it is neither acidic nor basic. 4. Indicator (indicador) – A substance that changes color depending on the properties of a solution. 5. pH –A measure of how acidic or basic a solution is. 6. Compound – a substance formed when two or more elements are chemically joined 7. Element – substance that cannot be separated a simpler substance IX. Safety Considerations No tasting of the solutions. Safety goggles must be worn by both students and teachers. Teachers must witness all students washing their hands immediately following the experiment or in the event of any spills. Wipe down tables after experiment. X. Question of the Day At what pH does milk curdle? Five-­‐E Organization ENGAGEMENT Time: 2-­‐3 minutes Page 7 of 33
What the Teacher Will Do Probing Questions Expected Student Responses Potential Misconceptions Hi everyone! Just in case you don’t remember, my name is ______ and this is _________. We are excited to get club started this week. Before we begin, let’s go over the Hook ‘Em sign. Make horns. When we say Hook’Em and make the horns sign, we want you to say Horns and make the horns sign, and focus all your attention on us at the front of the room. Review with class. Great job! Now we are ready to start. Show students cabbage juice. I found some of this liquid in the lab and I wanted to test it out with you to see what it actually does. 1. What color is the liquid in 1. Purple. the beakers (before anything is added)? It comes from a vegetable you may already be familiar with. 2. What vegetable do you 2. Red cabbage. think this liquid comes from? It’s made from red cabbage. Let’s see what happens when I add different solutions to this liquid…Put safety goggles on. 3. What do you think will 3. Nothing. It will have more happen when I add this liquid. Color change will clear liquid to the cabbage occur. juice? Let’s count down together…3,2,1! Pour some Page 8 of 33
ENGAGEMENT What the Teacher Will Do Probing Questions Time: 2-­‐3 minutes Expected Student Responses Potential Misconceptions base into beaker (dilute ammonia). Let’s count down together again…3,2,1! Pour some acid into a second beaker containing cabbage juice (vinegar). Great predictions! EXPLORATION What the Teacher Will Do 4. What just happened? 5. And what do you think will happen when I add another clear liquid to this second beaker of cabbage juice? 4. There was a color change! 5. It will turn a darker shade of that color. Nothing will happen. Hold up both beakers. One partner should pass out the pH scale worksheet while the other explains and writes definitions on the board. There was a chemical reaction! The pH of the cabbage juice changed when each solution was added. The color change was caused because cabbage juice is known as an indicator. Write the word indicator on the board or under doc cam. Have students fill out the following definition on their vocabulary sheet: A substance that changes color depending on the properties 1. Why could this be happening? Probing Questions Time: 60 minutes Student Responses Potential Misconceptions 1. A chemical reaction occurred. Page 9 of 33
EXPLORATION What the Teacher Will Do of a solution. We can use this color change to indicate a certain property of a solution. In this case, the chemical property we just observed changing was pH. Write pH and the definition underneath it (or use doc cam and fill in handout along with students). Note: This is a new vocab so they probably haven’t heard this word before. pH scale: A measure of how basic or acidic a solution is Notice that the “p” is lowercase and the “H” is uppercase. Great! pH is a measure of how acidic or basic a solution is. While talking, fill out the handout with the students. Acidic solutions are present between pH values of 0 and about 6. Neutral substances are between pH values of 6 and 8. Basic solutions have pH values from around 8 to 14. Probing Questions 2. What does pH measure again? 3. Looking at your worksheet, what should be at the bottom of my pH scale? 4. At the top? 5. Looking at our number line, what number would be in the middle or between 0 and 14? 6. What does the pH scale remind you of that you’ve seen in science before? Time: 60 minutes Student Responses Potential Misconceptions 2. How acidic or basic a solution is. 3. Zero. 4. Fourteen. 5. Seven. 6. Thermometer, ruler. Page 10 of 33
EXPLORATION What the Teacher Will Do Probing Questions Time: 60 minutes Student Responses Potential Misconceptions 7. What does a thermometer 7. Temperature. measure? 8. What does the pH scale 8. Whether a solution is Scientists use the pH scale to measure? acidic or basic. measure how acidic or basic a solution is. So I woke up this morning and I felt like having a big glass of milk with my breakfast. 9. What does milk normally 9. It is white and looks look like? smooth. When I poured my milk out of the carton, I noticed it was all clumpy! 10. Has that ever happened to 10. Yes. No. The milk smells you? What is this called? bad! It’s called curdling! Milk gets all clumpy, or curdles, when it gets past the expiration date listed on the container. It smells really bad and I heard it tastes pretty sour. Write curdle on the board with definition: To clump up. Have students copy on their worksheets. I brought the milk in with me to show you what it looks like when it’s curdled. Pass around tube containing curdled milk. 11. What does the curdled 11. It is sticking to the sides milk look like? of the tube. It looks clumpy. 12. Could you identify curdled 12. Yes! I can compare what I milk if you saw it? think is curdled milk to the tube you passed out. Great! Now I need you to help me answer the question of the day: At what pH does milk curdle? Post on doc cam. Page 11 of 33
EXPLORATION What the Teacher Will Do Before we do anything, I need to go over some important safety instructions with you. We are going to read these together. Post safety instructions under doc cam. Emphasize that we need to be safe so that we don’t accidentally get any solution in our eyes or irritate our skin. Safety Instructions: 1. Wear goggles at all times. 2. Do not taste, touch or smell the substances. Ammonia, Vinegar and lemon juice can irritate eyes. Ammonia can irritate skin. 3. Wash hands after the experiment with hand soap. 4. Notify a teacher of spills immediately. Pass out goggles. Goggles are very important for our experiment today. You must wear your goggles at all times. If I see you without your goggles on or not following any of these safety rules, you will have to sit out for the rest of the experiment—remember, we are all wearing goggles together! Pass out goggles and paper towels. Make sure that both partner teachers are wearing goggles at all times to set the Probing Questions Time: 60 minutes Student Responses Potential Misconceptions Page 12 of 33
EXPLORATION What the Teacher Will Do example. I am also passing out job cards. We need to work as a team today! Pass out job cards. We will use these for most of the experiments we do in afterschool club. Don’t worry if you don’t get the job you want this time—you’ll have a chance to do every job by the end of club! Take turns reading your job to your group. Be sure to pay attention because you may have that job next week. Give students a few minutes. Recorders raise your hands. Please come up and get enough data collection worksheets for your group—
one per person! Allow these students to come up and get worksheets. Make sure everyone in your group records the data as the experiment occurs. To test a solution’s pH, all we need to do is dip a pH indicator strip into the solution. Make sure all the boxes touch the solution—dip it in for five seconds to be sure! Demonstrate. Once the indicator gets wet it changes color to correspond to the pH of that solution. Then, we just need to compare the strip to the pH Probing Questions 13. What do we do with the pH strip? Time: 60 minutes Student Responses Potential Misconceptions 13. Dip it into the solution and wait five seconds before we take it out. Page 13 of 33
EXPLORATION What the Teacher Will Do key and figure out what range the solution falls into. Pass out keys to each pair of students. Remember! When you read the pH strip you want to make sure you align it with the key. Demonstrate on doc-­‐cam proper alignment of key to read pH. Walk around room and make sure pairs are doing this correctly. Probing Questions 14. Once our strip changes color, what do we do? 15. What was the question of the day? What problem are we trying to investigate? 16. What should the milk look like in the test tube when it curdles? When milk curdles, you should be able to see it stick to the sides of the test tube. Remember I have this test tube up here of curdled milk for comparison! In pairs, you will perform an experiment to test and reach a conclusion regarding the question of the day. The first thing you need to do when designing an experiment is to write down your hypothesis. Before you begin the actual experiment, you need to write a detailed procedure of the steps you plan to take to answer the question of the Time: 60 minutes Student Responses Potential Misconceptions 14. Compare it to the key. 15. At what pH does milk curdle? 16. It should stick to the sides of the tube. Page 14 of 33
EXPLORATION What the Teacher Will Do day. Someone else should be able to read your procedure and replicate the steps you took. Be sure to include proper scientific terminology. An example would be to write the word “pipette” instead of “dropper.” You must also include a data table to record your results. Probing Questions 17. How did we test the pH of the mystery solutions earlier? 18.
Do y
ou think you should test the pH of all of the substances you use? Why or why not? Show materials list on the doc cam while the other holds them up so entire class can see them. You must have a detailed procedure and it must be checked before you are given any milk. You must also have 19. What does your group a data table! need to write before you get any milk? We have prepared a sheet that you can reference if you are having trouble writing your procedure. Pass out “What to think about when you are writing your experiment” sheet. Go ahead and begin brainstorming! If groups have trouble starting: Circulate and check 1. What are you trying to procedures. Assist students study? that are having difficulties by Time: 60 minutes Student Responses Potential Misconceptions 17. We used pH indicator paper. We dipped it into the solution for five seconds and then we compared it to a key. 18. Yes so we know what pH they are. 19. A detailed procedure and a data table. Page 15 of 33
EXPLORATION What the Teacher Will Do Probing Questions Time: 60 minutes Student Responses Potential Misconceptions redirecting with questions. 2. What can you vary? 3. What Allow students to begin materials/supplies can experiment once procedures you use? and data table have been approved. Initial their If g
roups have trouble creating procedures and put a smiley a data table: face for positive feedback! 1. What do you need to (This will help you keep track know to answer the of whose work has been question of the day? checked). 2.
What are you changing? (Note: If students ask for 3. How many different more materials, tell them solutions have you they need to edit their been given? materials list and procedure first.) Questions to ask after students have finished collecting their data (also look at experimental design handout): 1. Did your experiment provide you with enough data? 2. What conclusions can you make about pH’s effect on the curdling of milk? 3. Were there any sources of error? 4. What would you change about this experiment to make it better? 5. If you had time to do a second experiment, what would you do? 6. Look at your neighbor’s procedure. Could you carry out their experiment? Were the directions clear enough? What would Page 16 of 33
EXPLORATION What the Teacher Will Do Probing Questions EXPLANATION What the Teacher Will Do We need to know the pH of solutions in order to figure out whether or not they are dangerous. Also, changes in pH in the environment can be used as indicators of pollution. Even doctors run tests on the pH of blood to see if it is more acidic than normal. We also need to check the pH of swimming pools on a regular basis—if not, your eyes may start to burn when you get in the pool! Not only is water a neutral solution, but it is also an example of a compound. A compound is a substance formed when two or more elements are chemically joined. Time: 60 minutes Student Responses Potential Misconceptions you have improved? Probing Questions 1.
2.
3.
4.
5.
Time: 15 minutes Student Responses Potential Misconceptions Why is pH important 1. To see if something is an anyway? acid or base. To see if something is safe. Vomit is an example of a 2. It’s an acid! solution with a pH of 2. Is it considered acidic, basic, or neutral? Why? Think about the acid in your stomach! What is a common neutral 3. Water! substance we tested earlier? Blood is an example of a 4. It’s neutral! Because it’s solution with a pH of 7.4. part of our body. Is it considered acidic, basic, or neutral? Why? Think about your body! Hand soap has a pH of 10. 5. Basic because it needs to Page 17 of 33
Acid rain is another thing scientists watch out for because it is harmful to the environment. It is rain that becomes very acidic due to atmospheric pollution. Is it considered acidic, basic, or neutral? What is left? Why? neutralize anything we have on us when we are using it. Let’s discuss our results. 6. What was the pH of milk 6. Around 6.5. before we added any solutions to it? 7.
Does t
hat m
ake m
ilk a
n 7. Neutral. acidic, basic, or neutral solution? 8. At what pH did the milk 8. Around 4.6. curdle? How did you find that? Right, so milk curdled at a pH of 4.6. 9. Is that within the acid or 9. Acids range. base r
ange? 10. Which solution(s) made 10. The lemon juice or the milk curdle? vinegar. 11.
Are t
hose a
cidic o
r b
asic? 11.
Both are acidic. 12. What type of pH 12. Acidic. environment caused the milk to curdle? That’s an important finding! It didn’t matter which acidic solution was used. All that mattered was that the acidic solution being added was strong enough to make a new solution that went below a pH 13.
Whenever m
ilk g
oes b
ad, 13. Sour. of 4.6 what do most people say? Does milk go sour or bitter? 14. What does that tell you 14. Acidic solutions are sour. about the properties of an acidic solution? This is just an interesting side note, so I don’t recommend that you taste the milk when it goes bad! You could get Page 18 of 33
sick! Because milk curdled at 4.6, we can conclude that an acidic environment was necessary. As scientists, it’s important to continue collecting data even if you have found what you were looking for so you have more data and can draw broader conclusions. 15. What other acidic solutions have we worked with today that are sour? 16. Once you found that the milk curdled, did you stop or did you continuing testing with the other solutions? 17. Why might it be important to continue to test even though you already found an answer? 15. Lemon juice. 16. Continued testing/skipped to conclusion questions. 17. To finish the experiment, collect more data to make broader conclusions. ELABORATION What the Teacher Will Do Let’s continue our discussion about spoiled milk. Within milk there are many proteins as well as lactic acid. Over time, lactic acid builds up, and the pH begins to change until the proteins lose their shape and clump together. Hold up two bags of straws-­‐-­‐ one with straws laying flat and the other with bent straws. Probing Questions Time: 5 minutes Student Responses Potential Misconceptions 1. What observations can you 1. The bent straws are make about each bag of clumped together and in straws? the other bag the straws lay flat. 2. Which bag models how the 2. The one with the flat Page 19 of 33
Right, so the proteins before the milk went bad looked like this. Hold up bag with unbent straws. It comes out easily, and doesn’t pull out any other straws. They are able to flow easily, like when you are pouring milk into your cereal. Now let’s examine the other bag. Hold up bag with bent straws. Exactly, one straw may be attached to other straws; if I pulled one out, I could easily pull out several more because they would be stuck together. When milk goes bad, proteins begin to fold up like these straws. These folds cause clumps, just like what we saw during our experiment today. Thanks to your experiments, we were able to demonstrate that milk curdles in an acidic pH. Now you can tell your parents and friends the science behind why milk goes bad! EVALUATION proteins looked before we straws. added lemon juice or vinegar to the milk? 3. What do you think will 3. Just one straw will come happen if I take out one out. straw from this bag? 4. What do you think will 4. Some other straws may happen if I take one straw come with it. out of this bag? 5. What effect does shape 5. The more bent the have on the volume that straws, the more space the straws take up? More they take up. specifically, if you look at the bags sideways, what do you notice? Time: 5 minutes Page 20 of 33
What the Teacher Will Do Probing Questions Now that you have designed and completed an experiment and learned the “why” behind milk curdling, it is time to reflect and analyze your work once again. We will do so by answering some questions and then going over them as a class. Student Responses Potential Misconceptions Give students about five minutes to finish the Show Off What You Know worksheet, and then go over the answers as a class. If time permits, continue with the journal prompt. Brainstorm an answer to this journal prompt, and write it down in your science journals: What revisions to the experimental design can you make that will lead to more accurate findings and reduce errors? Page 21 of 33
Name: ______________________________ Date: _________________________ Vocabulary words Indicator – a substance that ___________ ____________ depending on the properties of a solution pH – a measure of how _______________ or ______________ a solution is Curdle – to _________________________ pH Scale 14
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Question of the Day: At what pH does milk curdle? 1.
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SAFETY INSTRUCTIONS Wear goggles at all times. Do not taste, touch or smell the substances. Wash hands after the experiment. Notify a teacher of spills immediately. Page 23 of 33
What to Think About When Writing Up Your Experiment Experimental Design Requirements Research Question: The research question is the single most important part of the scientific method. Every part of your project is done to answer this question. The research question is sometimes formed as a statement and is called the "Problem" or "Problem Statement." For this experiment, your research question will be the question of the day. Hypothesis: The hypothesis is an "educated guess" or prediction, formed as a statement, which you propose to be the answer to the research question. An educated guess is based on some prior knowledge. Experimental Design: Plan an experiment in which you can test your hypothesis. •
Variables: The independent variable is what we change in an experiment and the dependent variable is what we measure. •
Control: The control is a particular sample that is treated the same as all the rest of the samples except that it is not exposed to manipulated variables. •
Observation: When you interact with your experiment, you are using your senses to observe. Does it have a smell, make a noise, have color, etc.? •
Collect Data: As you observe your experiment, you will need to record the progress of your experiment. Data can be whatever you observe about your experiment that may or may not change during the time of the experimentation. Examples of data are values in pH, temperature, a measurement of growth, color, distance, etc. Data can be both qualitative (written observations) and quantitative (measurements or graphs). Data: The data are the values written down as the experiment progresses. Examples of data entry on measuring plant growth à Plant # Measurement • Charts & Graphs: When at all possible, (mm) illustrations of data are advisable. They can Control 7.4 convey a great deal of information. Examples Plant 1 15.6 include: Bar Graph, Pie Chart, X & Y axis Graph, Plant 2 20.9 Histogram, etc. Plant 3 32.1 Control 7.8 Materials: List all supplies and equipment. Example list: Plant 1 16.7 1. 250 ml. glass beaker Plant 2 25.2 2. 1 straw Plant 3 32.1 3. 150 m. Lime Water 4. 10 g Baking Soda •
Procedure: The procedure is a detailed, step -­‐ by -­‐ step description of how you conducted your experiment. Example: "After 1 minute, I stirred in the baking soda and timed the reaction to be 45 seconds." Page 24 of 33
Results: The results are usually in the form of a statement that describes the data. You do not go into any detail or explanations here. You simply say in words what your data is telling you. Example: "Test Plant 3 showed little difference in growth rate as compared to the Control Plant." In this section, you would reference the data you collected during your experiment. Conclusion: The conclusion is a summary of the research and the results of the experiment. This is where you answer your research question. You make a statement of whether your data supported your hypothesis or not. You may have data that supported only part of your hypothesis. You may also have data that did not support your hypothesis at all. In this case, you may explain why the results were different. Possible Experimental Errors: A statement indicating any sources of errors and this includes reporting any human errors Ø Random Error/Indeterminate Error: introduced because of limited precision of instruments, also known as, an indeterminate error. Ø Mess-­‐up Error/Determinate Error: introduced because of a known mistake Ø Systematic Error: introduced because of equipment failure Recommendations for Further Experimentation Based on Your Data and Practical Applications: Give at least one suggestion to improve the experiment and list another possible experiment that could examine your same hypothesis. Page 25 of 33
Name: _________________________________ Date: __________________________ Experimental Design Worksheet Problem: At what pH does milk curdle? Testing the Liquids: Liquid pH Acidic, Basic or Neutral? Lemon Juice Ammonia Vinegar Baking Soda Solution Hypothesis (what do you think will happen and why?): _________________________ _______________________________________________________________________ _______________________________________________________________________ Materials (what will you use to do your experiment?): Page 26 of 33
Procedure (what steps must be followed in your experiment?): Data/Results (record what you see, but also use a data chart to organize your data!): Page 27 of 33
Conclusion (answer the questions below): 1. What is your answer to the question of the day? _______________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 2. How does your data support your conclusion? ________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 3. What revisions to the experimental design can you make that will lead to more accurate findings and reduce errors? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ Page 28 of 33
Hand Soap
Blood
Water
Lemon Juice
Milk
Vomit
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Ammonia
Vinegar
Baking Soda
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Milk Lemon Juice Vinegar Ammonia Baking Soda Solution Pipettes Test Tubes pH Indicator Strips pH indicator Key Forceps Paper Towel Cups Vials Page 31 of 33
Name: ________________________ Show Off What You Know: 1. What kind of an environment causes milk to become curdled? a. Basic b. Acidic c. Neutral d. Indicator 2. The pH of Coke was measured and determined to be 2.5. This is a. More acidic than vomit. b. More basic than blood. c. Less acidic than lemon juice. d. Neutral like water. 3. Based on the image of the pH scale, what would happen if you mixed baking soda with lemon juice? a. It would form a basic solution b. It would form an acidic solution c. It would form a neutral solution d. Nothing would happen 4. Rob is performing an acid/base reaction by mixing Diet Coke and baking soda together. He wants to know if the Diet Coke will become more acidic or more basic after adding the baking soda. What are the steps he needs to follow in order to reach a conclusion? a. Procedure à Hypothesis à Conclusion à Materials à Data/ Results b. Conclusion à Data/Results à Procedure à Materials à Hypothesis c. Hypothesis à Materials à Procedure à Conclusion à Data/Results d. Hypothesis à Materials à Procedure à Data/Results à Conclusion Page 32 of 33
Journal Prompt: What revisions to the experimental design can you make that will lead to more accurate findings and reduce errors? Page 33 of 33