This lesson connects with students' prior knowledge that the ocean is salty to develop a lab where students compare how salt and fresh water are different.
I hope to add to their schema of salt and fresh water properties and density. I will access this learning when students look at river mouths and when we discuss reasons for salty oceans.
This lesson provides an opportunity to review aspects of the scientific investigation process and to reinforce what scientific writing looks and sounds like.
Planning and Carrying Out Investigations - SP3
Students start their lab to compare how objects float in fresh and salt water.
Students unpack the science question, write their hypothesis, review the procedure and begin their lab, making observations on how objects float in fresh water.
Analyzing and Interpreting Data - SP4
Students record and review data to compare how objects float in fresh vs. salt water.
Using Mathematics and Computational Thinking - SP5
Students use quantitative descriptors to indicate how much of an object was above or below the water surface.
- make 12 teams; 2 students / team
- make a chart to record class data to make it easier for students to see trends, especially if fresh water and salt water will be tested over 2 days.
- Consider having 6 teams test for salt water and 6 for fresh, then teams can compare with their buddy team that is testing the 'other' water. This will help students make visual observations on how the objects float in both types of water and allow more time to develop their conclusions on day 2.
- copy h2o vs nacl h2o lab booklet for student observations
I chose to copy one booklet / student to encourage all students to participate with writing their observations, results and conclusion.
The booklet is set up so that the paper can be cut in half to create two booklets. Each aspect of the lab, i.e. question, hypothesis ...is written on its own page so that I can direct the discussion and focus of the scientific process.
- gather small objects made out of plastic, wood, metal that can be placed in the fresh and salty water (grapes and soap work well)
- test these objects to be sure that some sink in the fresh water but float or float noticeably higher in salty water
- mark the fresh water line on each object with a sharpee (see reflection on reference to water line and object line)
Be sure to test objects for how they float, for example my blocks of wood did not float level and the horizontal line I used for the ball did not line up with the water line.
- 12 clear containers; 1 / team (test fresh water on day 1 and salt water on day 2)
- 6 larger water containers; one per table (so students can access water to set up the lab)
Material for Each Lab Team
Placed in a baggie:
- measuring spoons and cups
- 1 container for testing objects in fresh (next time will test in salt water)
- small objects to test in the water
- lab pages for each person
- paper towels
- salt (for day 2)
http://www.onr.navy.mil/focus/ocean/water/salinity1.htm - information about ocean salinity
KLEWS Chart Check-in
I have established the norm for science class that after science folders are placed on desks, students meet me on the rug to discuss the question of the day.
This helps to standardize transitions which allows for a better use of time. Students know the expectations for moving to the rug.
Before the students and I discuss the question for the day, we review the KLEWS chart. I ask if they have any webquest water observations that they want to add to the chart.
The KLEWS chart provides a an interactive component to connect student learning across disciplines and over time.
Since students will be working on the webquest outside of science time, I want to be sure that time is set aside to summarize what they are learning from the webquest. Asking student's about their webquest learning validates their research and sets the expectation that I want to hear about what they are observing and learning.
Question for the Day - How is ocean water different than fresh water?
I use a 'question of the day' to direct student's attention on the lesson topic and to model that the science process is about asking questions.
After students share information on the KLEWS chart, students read the 'question of the day' with me: How is ocean water different than fresh water?
"Since we are going to look at surface waters oceans and fresh water systems, I want us to explore how these 2 types of water are different."
"Please turn to your neighbor and discuss the question." After moving around the group to listen in on conversations, I signal for students' attention and call on students to share what their partner said.
Students are familiar with the protocol that I will ask what their neighbor said, which helps set the expectation that I expect them to listen carefully to each other and to ask clarifying questions if they do not understand their neighbor's answer.
I write student answers on the board.
Because we live close to the ocean, I expect that students will be able to tell me that the ocean is salty. That they know this by how it tastes and that they cannot drink ocean water.
"Today you will do a lab with your partner to learn if small objects float differently in salt and fresh water. Please return to your seats so that we set up our lab page and work area."
Lab Booklet - Page by Page
Page One - Question:
I project lab booklet page 1 on the board and direct students to read and discuss their answer to the question. Meanwhile, I pass out lab booklets to each student.
After everyone has their lab booklets, students and I read the question: Do objects float/sink differently in salt water and fresh water? ( p. 1)
"Let's unpack that question, just like we do in math. What is the question asking us? There is a comparison word in the question, what is it? Think of the comparison chart we made with the aphotic and rocky shore animals. We compared how the animals were the same and .....
"Right, differently," I underline the word in the question. "What 2 things are being compared? Right fresh water and salt water"
So our hypothesis should have the words different, fresh water and salt water.
I am building students' schema on how to take apart a question and compose an answer that would specifically answer the question.
"O.K. so let's look at the question again, since we do not need to answer about whether or not each of these objects float, our hypothesis may start like this,
I model how the hypothesis statement could start; 'I think objects placed in fresh water will .... ....and objects placed in salt water will ....or ' I think objects will/will not float/sink differently because ..."
I write the sentence frames on the board.
The sentence frames are printed in the students' lab booklets because I want students to spend their time working our their reasons rather than using time to copy the sentence frame.
Next I scaffold possible reasons why there may or may not be a difference. "Hmm, what do you know about salt water and fresh water? What is the difference between the 2 waters? Yes salt water is salty. Your knowledge about the difference between the 2 waters could be your reason why objects float differently or not."
"So when you fill in the rest of this sentence; ' I think objects will float/sink differently because ... you can write how fresh water and salt water are different!"
"You will write your hypothesis on page 2."
Page Two - Hypothesis
"Let's look at page 2. This is where you will write your hypothesis, your best guess based on your experiences and knowledge."
Before your write your hypothesis, you may want to examine the objects and discuss with your team partner about what you may write. Scientists always collaborate and share ideas."
At this point I pass out the bag of objects that students will test.
You will have 5 minutes to discuss, examine and write your hypothesis.
I walk around the room to encourage students to complete their hypothesis and return objects to the bag when they are finished looking at them.
When the 5 minutes are up, I signal for student's attention.
"We have a question we will investigate, so what could we do to find out how an object may float differently in salt water vs fresh water? Right! We will place things in fresh water and salt water and make observations! Let's look at page 3.
Page Three - Procedure
Just like in a recipe, we need to have specific steps to set up our lab experiment. Why is this important to a scientist or engineer?
I keep this discussion short, but I want to develop a schema for lab protocol.
"We will read the procedure steps and set up the lab for the fresh water today."
"Next week you will test the same objects in salt water and write up your summary. If we use the same objects in the salt water today, the objects will not be the same. Why not? Right, the objects are wet and some may have absorbed water, making them different. So we would not be testing the exact same object."
If you want to test for both salt water and fresh water on the same day, use fewer items and have duplicate objects for fresh and salt water.
After the lab is set up, I call students to the rug to discuss page 4, observations. "You are almost ready to do your experiment! There is only one more step we need to discuss. How you will take accurate precise observations?"
Page Four - Observations
On page 4 we discuss how their data/observations will be recorded.
"It is important that we make careful observations and record as much detail as we can. It may not be enough to say that the object floated. What if the object floated higher in one water than it did in the other water? It floated in both solutions but not the same. How could you capture that observation?"
"Are there any observation words we could write on the board that could help us describe how the object floated?"
I write their suggestions on the board, under the title: 'Observation Word Bank'
I involve students on how to record their data so that they are thinking critically about how to write specific, exact observations.
"Raise your hand if you noticed the lines drawn around your objects? Those lines show where the middle of the object is. How will this line help you make specific observations about how the objects float?"
"Right, for example you may observe that the water line was above the mid line on your object. You could write the water was above the mid line. What other words could you use to describe where the water line is in reference to the mid line?"
I add these suggestions to the 'Observation Word Bank'.
"Today you will only be testing objects in fresh water. If there are no more questions, you may begin your lab."
I walk around the room to check that students are taking accurate observations and to ask questions about what they notice or if they observed anything surprising.
When there is 15 mins left for science. I give students a 5 minute notice.
This helps the kiddos transition to the next phase of the science lesson.
When the 5 minutes are up, students dry off objects and place them in the bags, pour the fresh water in the plant containers, and bring their lab booklets to the rug.
"Look at your observations, page 4, what did you notice about how the objects floated in the fresh water? Please turn to a neighbor and share. Remember your observations explain where the fresh water line was compared to the line drawn on the object."
I name one of the objects tested and ask students to silently read the observation they wrote for this object. After show me with a thumbs that they have found the object observation, I read one of the headings for our class data table and ask students to raise their hand if this was their observation for this object. I write the object and number of students who raised their hand for this quantitative observation.
I realized that I would need to write the number of students who had a particular observation because not all the teams got the same results.
Hopefully by drawing the fresh water line on the objects vs the mid line on the objects, the next time I do this lab, will help have more consistent results. If not, by totaling the number of students who got a specific quantitative observation, will help to establish a pattern/trend for how most of the objects floated.
The students were very tentative about sharing their observations. I had to remind them they were just sharing their observations, and to look at what they wrote. I think some students may have thought their observations were incorrect if they were in the minority.
If there are disagreements about the sort, we have a discussion and reasons are noted on the board to be reviewed at our next class.
I save the class's compiled observations. This will be used when we compare and summarize how objects floated in both fresh and salt water in 'Day 2'.
I thank everyone for their participation and remind them to place their lab booklet in their science folder.