Destroying Water: A Classic Lab Rejuvenated for NGSS
Posted: Monday, June 20th, 2016
by Rich Hedman and Lisa Hegdahl
After nearly 15 years teaching the 1998 CA Science Standards, many science educators have file cabinets and hard drives full of activities. The activities themselves are valuable in that they clearly illustrate scientific concepts and phenomena. However, in the past, they were often used only to verify information already presented in class. One of the many challenges of implementing the Next Generation of Science Standards (NGSS) is to move towards three dimensional learning and still utilize activities from the past. How can teachers modify labs that used to be just recipes for verification and turn them into experiences that engage students in the process of scientific discovery?
Electrolysis of water is a classic chemistry lab used as a way to confirm that water is made of 2-parts hydrogen to 1-part oxygen— in other words, that the chemical formula, H2O, is actually based on the proportion of atoms in a water molecule. Teachers tell students that the chemical formula of water is H2O, and that during the experiment, they will be breaking water into hydrogen and oxygen gases. Ion-rich water is electrified with direct current (DC), and gas bubbles form at the positive and negative terminals in the solution. The gases are collected in tubes, and the volume of gas present in each tube is compared. It turns out that twice as much of one gas is collected compared to the other gas. Teachers frequently use a splint and flame test (very carefully; following all safety protocols) to identify which gas is which (oxygen relights a splint, hydrogen pops loudly) and to verify that the elements that make up water have different properties than the water itself. Students see that there is twice as much hydrogen as oxygen, which verifies the chemical formula of water, and the lesson is completed in one class period.
How does this lesson align with the performance expectations (PEs) of NGSS? Where did students use the 3-dimensions of NGSS (science and engineering practices, crosscutting concepts, and disciplinary core ideas) to make sense of phenomenon? We asked ourselves these questions and then set out to “NGSS-ize” the activity. We began by examining the performance expectations and disciplinary core ideas (DCIs) related to this lesson.
The most closely aligned performance expectation is:
- MS-PS1-5 – Develop and use a model to describe how the total number of atoms does not change in a chemical reaction and thus mass is conserved.
The disciplinary core idea connected to this PE is –
- PS1.B Chemical Reactions: the total number of each type of atom is conserved* and thus mass does not change.
(*Note: we focus on conservation of the particles in this lesson, not on the mass.)
So, the underlying science ideas were indeed connected to an NGSS PE and DCI. How about the science and engineering practices (SEPs) and the crosscutting concepts (CCCs)? From the description of the classic electrolysis activity above, it is clear that students are not engaged in science and engineering practices. The teacher is asking the questions, the teacher is designing the investigation, the teacher is constructing the explanations, and the teacher is communicating the information. So, the lesson, as described, completely fails the SEP test. Regarding the CCCs, from the description above, it is difficult to determine whether or not the teacher would draw attention to the related crosscutting concepts, such as patterns, systems and system models, or energy and matter in systems. An NGSS lesson plan would need to explicitly include those connections.
The first step in ‘NGSS-izing’ the classic electrolysis lesson was to figure out a way for student groups to engage in sense-making during the investigation. Instead of telling students the answer (that water is H2O and the number of particles is conserved before and after the reaction), we wanted the students to figure that out for themselves, based on the patterns (CCC-patterns) they detect in their data. What follows is a brief description of what we came up with after much thoughtful collaboration. We tried to focus our description here on the NGSS shifts in the lesson and not so much on detailed procedures, which you can access by contacting either one of us.
Students obtain a condiment cup that contains ionized water and record their observations of its properties in their science notebooks. Students place a 3-ounce condiment cup over a 9 volt battery and mark the location of the battery terminals. At the terminal marks, students insert metal tacks into the condiment cup so that the tacks stick up into the cup and place the condiment cup on top of a battery with the tack heads touching the battery terminals. In their science notebooks, students write observations of what they see. Students should see bubbles coming up from both tacks, with the (-) terminal producing more bubbles. Students write an initial explanation (SEP – constructing explanations) for what they observe. As a class, they discuss the groups’ observations and their explanations for the phenomenon. Students are then directed to think about how they might capture the gases. Eventually the teacher will guide students to the possibility of placing test tubes over the tacks.
Students fill 2 labeled (+ and -) test tubes up to the top with the ionized water. Placing their thumb over the top of the test tube, they turn the test tube upside down over the tack making sure not to take their thumb off the test tube until it is under water. This is to prevent air from getting into the test tube. The (+) test tube should be over the tack that is in contact with the (+) terminal and the (-) test tube should be over the tack that is in contact with the (-) terminal. Each of the test tubes should begin to fill with gas. The class discusses what kind of quantitative data they can take to illustrate what is happening in the test tubes. Through thoughtful questioning, the teacher leads this discussion to the realization that the amount of gas can be approximated by measuring the height of the gas in each test tube. After running the reaction for 20 minutes, the student groups record their data on a class data table.
Students share with the class what they think is inside the test tubes above the liquid. Typical student answers include the following: “nothing”, “air”, “water vapor”, “hydrogen”, and “oxygen”. The teacher records the student answers and asks students if they can think of ways that any of these possibilities can be tested (SEP – planning and carrying out investigations). The teacher will probably need to discuss with students how a splint flame test can be used to test two of their ideas; for example, oxygen will relight a splint, and hydrogen will pop loudly when exposed to the splint. The teacher works with a group of students to conduct these tests in front of the class. The results are that the lit splint held over the (-) test tube will ‘pop’, and a glowing flint held over the (+) test tube will reignite. At this point you may want individual students to construct claim, evidence, reasoning statements for what they observed and how they identified the gases (SEP – Engaging in Argument from Evidence).
Now that the students have identified the gases in each test tube, students are tasked with analyzing the class data table and discussing with their table groups the patterns (CCC-Patterns) they see. The goal is for students to realize that just about every group obtained a 2:1 ratio of hydrogen to oxygen. This is not as easy as it might seem, as students have to identify the 2:1 ratio from measurements that are not always exactly 2:1. If some groups have data that does not fit the pattern, discuss possibilities for why that might be true. Once the students identify that electrolysis of water is producing twice as much hydrogen as oxygen, the teacher should ask the students: “WHY? What causes this pattern?” Student groups should develop answers to this question, and then share their ideas (SEP-Obtaining, Evaluating, and Communicating Information). Usually several groups will have an “aha” moment and say that there is twice as much hydrogen as oxygen produced because a water molecule itself is composed of 2 hydrogen atoms for every 1 oxygen atom. Students have figured it out for themselves!
To wrap things up, we provide students with a handout summarizing the particle model of matter (SEP- Developing and Using Models). We then ask students to apply the particle model to explain (in words and pictures) what was happening before and after the electrolysis reaction. Our goal is for students to draw water molecules as the reactants, and separate hydrogen and oxygen atoms as the products, in such a way that the number of particles is conserved. This task allows us to assess students related to Performance Expectation MS-PS1-5.
Our modifications have turned a typical lab, which was designed to confirm something students were told, into an experience where students figure out a concept on their own. In the process, students are engaged in several of the NGSS science and engineering practices and crosscutting concepts and are able to make progress towards mastering a performance expectation. Modifying classic experiments to align with NGSS is not an easy task, but it will provide students with valuable experiences in making sense of the world around them.
Please don’t hesitate to contact either one of us for the handouts and other useful information about this revamped activity.
Rich Hedman – Director, Sacramento Area Science Project (SASP) and CSTA member, email@example.com
Lisa Hegdahl – 8th grade science teacher, McCaffrey Middle School in Galt, CA NGSS Early Implementer, President of CSTA, firstname.lastname@example.org
Posted: Wednesday, October 12th, 2016
by Jessica Sawko
In June 2016 California submitted a waiver application to discontinue using the old CST (based on 1998 standards) and conduct two years of pilot and field tests (in spring 2017 and 2018, respectively) of the new science assessment designed to support our state’s current science standards (California Next Generation Science Standards (CA-NGSS) adopted in 2013). The waiver was requested because no student scores will be provided as a part of the pilot and field tests. The CDE received a response from the U.S. Department of Education (ED) on September 30, 2016, which provides the CDE the opportunity to resubmit a revised waiver request within 60 days. The CDE will be revising the waiver request and resubmitting as ED suggested.
At its October 2016 North/South Assessment meetings CDE confirmed that there will be no administration of the old CST in the spring of 2017. (An archive of the meeting is available at http://www.cde.ca.gov/ta/tg/ai/infomeeting.asp.) Learn More…
Posted: Thursday, September 22nd, 2016
by Carol Peterson
1) To celebrate the 100th anniversary of the National Park Service, Google has put together a collection of virtual tours combining 360-degree video, panoramic photos and expert narration. It’s called “The Hidden Worlds of the National Parks” and is accessible right from the browser. You can choose from one of five different locales, including the Kenai Fjords in Alaska and Bryce Canyon in Utah, and get a guided “tour” from a local park ranger. Each one has a few virtual vistas to explore, with documentary-style voiceovers and extra media hidden behind clickable thumbnails. Ideas are included for use in classrooms. https://www.engadget.com/2016/08/25/google-offers-360-degree-tours-of-us-national-parks/. Learn More…
Posted: Thursday, September 22nd, 2016
CSTA is pleased to announce the winners of the 2016 CSTA Awards for Distinguished Contributions, Margaret Nicholson Distinguished Service Award, 2014 and 2015 PAEMST-Science recipients from California, and the 2016 California PAEMST Finalists. The following individuals and organizations will be honored during the 2016 California Science Education Conference on October 21- 23 in Palm Springs. This year’s group of awardees are truly outstanding. Please join us in congratulating them!
Margaret Nicholson Distinguished Service Award
The Margaret Nicholson Distinguished Service Award honors an individual who has made a significant contribution to science education in the state and who, through years of leadership and service, has truly made a positive impact on the quality of science teaching. This year’s recipient is John Keller, Ph.D. Dr. Keller is Associate Professor, Cal Poly San Luis Obispo and Co-Director, Center for Engineering, Science, and Mathematics Education, Cal Poly San Luis Obispo. In her letter of recommendation, SDSU science education faculty and former CSTA board member Donna Ross wrote: “He brings people together who share the desire to make a difference in the development and implementation of programs for science teaching. Examples of these projects include the Math and Science Teaching Initiative (MSTI), Noyce Scholars Program, Western Regional Noyce Initiative, and the Science Teacher and Researcher (STAR) program.” Through his work, he has had a dramatic impact on science teacher education, both preservice and in-service, in California, the region, and the country. He developed and implemented the STEM Teacher and Researcher Program which aims to produce excellent K-12 STEM teachers by providing aspiring teachers with opportunities to do authentic research while helping them translate their research experience into classroom practice. SFSU faculty member Larry Horvath said it best in his letter:“John Keller exemplifies the best aspects of a scientist, science educator, and mentor. His contributions to science education in the state of California are varied, significant, and I am sure will continue well into the future.” Learn More…
Posted: Tuesday, September 20th, 2016
by Peter A’hearn
NGSS is a big shift. Teachers need to learn new content, figure out how this whole engineering thing relates to science, and develop new unit and lesson plans. How could NGSS possibly make life easier?
The idea that NGSS could make our lives easier came to me during the California State NGSS Rollout #1 Classroom Example lesson on chromatography. I have since done this lesson with high school chemistry students and it made me think back to having my own students do chromatography. I spent lots of time preparing to make sure the experiment went well and achieved the “correct” result. I pre-prepared the solutions and organized and prepped the materials. I re-wrote and re-wrote again the procedure so there was no way a kid could get it wrong. I spent 20 minutes before the lab modeling all of the steps in class, so there was no way to do it wrong. Except that it turns out there were many. Learn More…
Posted: Tuesday, September 20th, 2016
by Robert C. Victor. Twilight sky maps by Robert D. Miller. Graph of evening planet setting times by Dr. Jeffrey L. Hunt
Our evening twilight chart for September, depicting the sky about 40 minutes after sunset from SoCal, shows brilliant Venus remaining low, creeping from W to WSW and gaining a little altitude as the month progresses. Its close encounter within 2.5° N of Spica on Sept. 18 is best seen with binoculars to catch the star low in bright twilight. The brightest stars in the evening sky are golden Arcturus descending in the west, and blue-white Vega passing just north of overhead. Look for Altair and Deneb completing the Summer Triangle with Vega. The triangle of Mars-Saturn-Antares expands as Mars seems to hold nearly stationary in SSW as the month progresses, while Saturn and Antares slink off to the SW. Learn More…