Part of Unit: Chemistry of Life
Lesson Plan Overview / Details
The Curds and Whey Lab is a great lab to teach pH. During this lab, students will observe what happens when different substances are added to milk. Milk curdles when it reaches a certain pH. The students will be able to use their knowledge of pH to predict which substance will cause the milk to curdle.
- Instructional Time
- 55 Minutes
California Career and Technical Education Standards
- ANR.C.C13.1 Understand the steps of the scientific method.
- ANR.C.C13.3 Use the scientific method to conduct agricultural experiments.
- ANR.FS.11.0 Demonstration and Application
- ANR.FS.9.6 Understand leadership, cooperation, collaboration, and effective decision-making...
California Academic Content Standards (Reinforced)
- ELA.8.R.VCD.1.3 Use word meanings within the appropriate context and show ability to verify thos...5
- ELA.9-10.R.CAGT.2.5 Extend ideas presented in primary or secondary sources through original analysis...3
- ELA.9-10.R.CAGT.2.6 Demonstrate use of sophisticated learning tools by following technical direction...2
- ELA.9-10.W.2.3a Write expository compositions, including analytical essays and research reports ...
- ELA.9-10.W.2.3f Write expository compositions, including analytical essays and research reports ...
- S.9-12.IE.1.l Analyze situations and solve problems that require combining and applying concep...
- S.9-12.LS.1.b Students know enzymes are proteins that catalyze biochemical reactions without a...1
Objectives and Goals
- Students will be able to conduct an experiment to determine the name of substances that cause milk to curdle.
- Students will be able to identify given substances as acidic or basic using pH paper.
- Students will be able to identify sources of experimental error.
- pH Paper [ View Image ] [ Download Original ]
- Vinegar [ View Image ] [ Download Original ]
- Lemon Juice [ View Image ] [ Download Original ]
- Tea [ View Image ] [ Download Original ]
- Diluted Chocolate Syrup [ View Image ] [ Download Original ]
- Milk [ View Image ] [ Download Original ]
- Graduated Cylinder [ View Image ] [ Download Original ]
- Plastic Cups [ View Image ] [ Download Original ]
- Stirring Rods [ View Image ] [ Download Original ]
Activities in this Lesson
- Cereal Eating Contest - Hooks / Set
Working with teenagers, you quickly learn that food motivates them. To start this lesson off, I tell my students that we will be having a cereal eating contest and that I need two volunteers to participate in the contest. I have two pre-poured bowls of cereal, complete with milk. Just as I sit the two volunteers down in front of the bowls of cereal, I tell them there is one hitch, one bowl of cereal contains fresh milk and the other contains old curdled milk. I proceed to tell the students I am not going to tell them which bowl contains the bad milk until after the contest. As expected, I get a huge reaction from the students. I excused both students back to their seats and preceed to have a class discussions about curdled or bad milk. I tell a story about one time when I accidentally drank curdled milk and I let the students tell a few stories as well. At this point most of the students are grossed out and I ask them why they think milk curdles? This leads right into our lab and discovering that milk curdles because of pH.
- Background Information - Lecture
The pH scale is a measure of how acidic or basic a substance is. The pH value can determine whether a chemical reaction will occur. For example, the pH of milk determines whether curds will form, as in the production of cottage cheese.The pH of a substance can be measured with pH paper. This method can determine whether a solution is acidic or basic. Acids have a pH of less than 7, and bases have a pH of more than 7. Pure water is neutral and has a pH of 7. Milk curdles when the pH approaches 4.6. The remaining liquid is called whey. This is a great time to talk to the students about the process of cheese making and the use of whey as a agricultural byproduct. This lesson could be followed by a cheese making activity. I have attached three pictures of the pH scale. I use my LDC projector in my classroom to show the students the scales and example substances' pH value.
- Safety - Other
Use care when handling vinegar and lemon juice. Don’t get it in your eyes!! Goggles/lab glasses recommended. Do not eat or drink any of the materials. Wash your hands as necessary.
- Using pH Paper - Demo / Modeling
Before, I start the lab activity, I do a simple demonstration on how to use pH paper to determine acidity. I use the attached pH paper guide on my LCD projector. I then test the pH of water and show the students what color the pH paper turns. I then proceed to show the students how to read the pH paper by matching the color to the guide.
- pH Paper Guide [ Download ]
- Stating the Problem / Forming the Hypothesis - Lab / Shop
Problem:Which of the following substances will cause milk to curdle: lemon juice, tea, vinegar, and/or chocolate syrup?
Students will then write a hypothesis based on which substance they think will cause the milk to curdle.
- Lab Procedures - Lab / Shop
1) Gather your supplies from the front of the classroom.
2) Using the pH paper, determine pH of the vinegar, lemon juice, tea and diluted chocolate syrup.
3) Record the results in the Data table.
4) Add the vinegar (2 tablespoons, tbs) to one cup of milk and stir.
5) Observe and record your observations.
6) Add the lemon juice (2 tbs) to another cup of milk and stir.
7) Observe and record your observations.
8) Add the tea (2 tbs) to another cup of milk and stir.
9) Observe and record your observations.
10) Add the diluted chocolate syrup (2 tbs) to the last cup of milk and stir.
11) Observe and record your observations.
12) Answer the questions below.
- Curds and Whey Lab- Student Lab Sheet [ Download ]
- Data and Results - Lab / Shop
During the lab, students will be recording the pH of each substance and write observations base what happened when the substance was added to the milk. Refer to "Curds and Whey- Student Lab Sheet"
- Analysis and Conclusion - Closure
At the end of the lab, the students will be answering two questions in the analysis to make them go back and exam their results. The students will then draw conclusions by answering four conclusion questions, include a question requiring them to identify source of experiment error.
- Assessment Types:
- Journals, Writing Samples, Observations,
Students will be assessed by their completion of the attached student lab sheet. I also have a system in place that is part of my daily routine that holds students accountable for their own learning. My students fill out a student learning log every day. I have attached this document below. At the beginning of class my students write down the posted daily objective and at the end of the day the students log their response to the daily objective by writing how they individualy met the objective in class that day. I use this as an assessment tool. I can open up a students binder and read their student learning log to evaluate their comprehension of the lesson. Through the lesson, I remind my students that they will be responding to the objective at the end of the period and it encourages them to make sure the have the content so they will have something to write about in their log.
- Student Learning Log [ Download ]