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: Tuesday, March 14th, 2017
The pre-publication version of the new California Science Curriculum Framework is now available for download. This publication incorporates all the edits that were approved by the State Board of Education in November 2016 and was many months in the making. Our sincere thanks to the dozens of CSTA members were involved in its development. Our appreciation is also extended to the California Department of Education, the State Board of Education, the Instructional Quality Commission, and the Science Curriculum Framework and Evaluation Criteria Committee and their staff for their hard work and dedication to produce this document and for their commitment to the public input process. To the many writers and contributors to the Framework CSTA thanks you for your many hours of work to produce a world-class document.
For tips on how to approach this document see our article from December 2016: California Has Adopted a New Science Curriculum Framework – Now What …? If you would like to learn more about the Framework, consider participating in one of the Framework Launch events (a.k.a. Rollout #4) scheduled throughout 2017.
The final publication version (formatted for printing) will be available in July 2017. This document will not be available in printed format, only electronically.
Posted: Monday, March 13th, 2017
The 2017 Award Season is now open! One of the benefits of being a CSTA member is your eligibility for awards as well as your eligibility to nominate someone for an award. CSTA offers several awards and members may nominate individuals and organizations for the Future Science Teacher Award, the prestigious Margaret Nicholson Distinguished Service Award, and the CSTA Distinguished Contributions Award (organizational award). May 9, 2017 is the deadline for nominations for these awards. CSTA believes that the importance of science education cannot be overstated. Given the essential presence of the sciences in understanding the past and planning for the future, science education remains, and will increasingly be one of the most important disciplines in education. CSTA is committed to recognizing and encouraging excellence in science teaching through the presentation of awards to science educators and organizations who have made outstanding contributions in science education in the state and who are poised to continue the momentum of providing high quality, relevant science education into the future. Learn More…
Posted: Monday, March 13th, 2017
CSTA is now accepting applications from regular, preservice, and retired members to serve on our volunteer committees! CSTA’s all-volunteer board of directors invites you to consider maximizing your member experience by volunteering for CSTA. CSTA committee service offers you the opportunity to share your expertise, learn a new skill, or do something you love to do but never have the opportunity to do in your regular day. CSTA committee volunteers do some pretty amazing things: Learn More…
Posted: Monday, March 13th, 2017
by Marian Murphy-Shaw
If you attended an NGSS Rollout phase 1-3 or CDE workshops at CSTA’s annual conference you may recall hearing from Chris Breazeale when he was working with the CDE. Chris has relocated professionally, with his passion for science education, and is now the Executive Director at the Explorit Science Center, a hands-on exploration museum featuring interactive STEM exhibits located at the beautiful Mace Ranch, 3141 5th St. in Davis, CA. Visitors can “think it, try it, and explorit” with a variety of displays that allow visitors to “do science.” To preview the museum, or schedule a classroom visit, see www.explorit.org. Learn More…
Posted: Monday, March 13th, 2017
by Joseph Calmer
Probably like you, NGSS has been at the forefront of many department meetings, lunch conversations, and solitary lesson planning sessions. Despite reading the original NRC Framework, the Ca Draft Frameworks, and many CSTA writings, I am still left with the question: “what does it actually mean for my classroom?”
I had an eye-opening experience that helped me with that question. It came out of a conversation that I had with a student teacher. It turns out that I’ve found the secret to learning how to teach with NGSS: I need to engage in dialogue about teaching with novice teachers. I’ve had the pleasure of teaching science in some capacity for 12 years. During that time pedagogy and student learning become sort of a “hidden curriculum.” It is difficult to plan a lesson for the hidden curriculum; the best way is to just have two or more professionals talk and see what emerges. I was surprised it took me so long to realize this epiphany. Learn More…