Physical Properties - Freezing & Melting Points

No technology Setup

Teacher Notes:

Chm.2.1.1 Explain the energetic nature of phase changes.
Chm.2.1.2 Explain heating and cooling curves, heat of fusion, heat of vaporization, heat, melting point, and boiling point).

Chm.2.1.3 Interpret the data presented in phase diagrams. 

In this lab, students will analyze data from graphs made using independent and dependent variables. They will find the relation between the melting point and boiling point of water.

This lab will not include heat of vaporization but can be shown later in this explanation or in another lab.

Helping Students Learn How to Make a Data Table

The data analysis in this lab is a double line graph.  There are no mathmatical calculations in this lab unless you change the lab.

To teach students to make a data table, they must read the lab.  In the first lab, I teach them how to pick out what must be part of the data table.  This probably will not be the first lab.  Some may still need help in making the data table.  If they ask, I ask them what they think are the dependent (controlled)  and independent manipulated) variables.  This would be a good lab in which to discuss variables.  In this lab the variables will be time and temperature.

If a mini lecture on graphing has not been given to the student, the following overhead can be helpful for a quick review. Use the info on an overhead projector or project the information on a smart board.  (Never assume that all students know this information from previous classes. If all do, move on.) Discuss what is included in a well-constructed graph, such as labeled x-axis and y-axis (including units), an appropriate title, neatness and readability.  Students always need to know what is expectedl

This lab will help most students understand that there is a correlation between freezing and melting point.  This lab can be done using technology or no technology.  Both methods will be explained.  Students need help in understanding that there are many experimental errors in this lab but the teacher does not need to state these nor tell the correlation between freezing and melting points.  This needs to be discovered by the student.  The teacher can answer any questions but not tell the expected data to collect.  The students always record data that they truly observe, not what they think they should observe.  The teacher should observe all setups and "might" make recommendations if necessary.

The thermometer should not be used as a stirring instrument.  Remind the students as often as necessary.  Provide plastic spoons for stirring.

Conclusion

In many labs, I added conclusion questions that they might see on a test.  I feel that it makes a connection with what was discussed in class. Also, it can be an aid when studying and reviewing for a test.  Yes, I asked the students to write the questions in the lab book so that they would know what the question was when reviewing for a test.

Experimental Errors
See lab "The Law of Conservation of Energy" to read explanation of experimental errors.

Helping Students To Think       (Important for every Lab)

During a lab, I rarely give additional instructions (beyond the written lab instructions) or give  answers to an experiment, but will answer any questions that will help them.  Yes, it causes frustration, but they learn that I am teaching them how to think.  Sometimes I will answer a question with a question, to again, help them with a thinking process.  I think it is important for students to use a marbled lab book. The Purpose (or Question), Hypothesis, Materials, Procedure and Data Table must be written in the lab book before a student may begin the lab.  (My signature proves that it was done). Every teacher can form their own opinion about this technique but I found that students take more ownership of their lab work.  It also is a good way to organized their lab work.

Technology
In this lab, a temperature probe will replace the thermometer.  This lab can be completed using a CBL or LabPro with a temperature probe and TI calculator.  The computer can be used also if available.  This lab has been completed successfully with all three Vernier products.  Pasco has great science sensors, also. Then, there are probes for classrooms having iPads.  These companies include instructions on the use of the temperature probe, including a temperature lab  such as the CBL temperature lab for Vernier .  Students of all ages love using technology in the science classroom, but in order for it to work smoothly as possible, the teacher needs to have completed the lab with the technology prior to instructing students. It also takes time to set up the technology but becomes easier each time -  well, most of the time. I have found that there will be some students very savvy in the use of the equipment and can help other frustrated students.  Student lab assistants can become helpful with this task also. But again, the teacher needs to know the problems and can help students work through problems encountered during the lab.

Freezing and Melting Points Lab

Question:  What is the freezing point and melting point of water?

Hypothesis:  ?  (Some students will need help.)

Materials: alcohol thermometer, ring stand, utility clamp, test tube, 400-mL beaker, water, 10-mL graduated cylinder, ice, rock salt, plastic spoon, stop watch

Procedure:  

1. Fill the 400-ml beaker 1/2 full of ice and add enough water to fill the beaker to 3/4 full of ice and water.
2. Put 5 mol of water into a test tube and use a test tube clamp to fasten the test tube to a ring stand. (Be careful not to break the test tube by clamping too tight too.)  Clamp the test tube above the water bath.  Place the thermometer into the water inside the test tube. Record the temperature.
3. When the equipment is ready, lower the test tube into the ice-water bath.  Begin the stop watch and record the temperature of the thermometer every 30 seconds for 15 minutes.
4. As soon as the test tube is lowered into the beaker, add 5 spoons of salt to the beaker and stir with a plastic spoon.  Do not use the thermometer to stir!  
5. Add more ice to the ice-water bath as the ice in the beaker begins to melt. Remember to keep recording the temperature every 30 seconds.
6. When 15 minutes have passed, stop collecting data but keep the test tube submered in the ice-water bath.  Using the data collected, determine the freezing temperature of the water in the test tube.
7. Begin a new data list.  Raise the test tube and clamp it above the ice-water bath.  Do not move the thermometer.
8. Remove the ice water from under the test tube.  Start stop watch and begin collecting temperature data every 30 seconds.  Pour the ice-water in a disposal bucket provided by your teacher.  Rinse the beaker and put 250 mL warm water in the beaker.  When 12 minutes have passed, lower the test tube and thermometer into the warm-water bath.
9. When 15 minutes have passed, stop collecting temperature and time data. Using the data collected during the melting, determine the melting temperature of the water in the test tube.
10. Graph the data with time as the independent variable and temperature as the dependent variable.  Graph the temperatures in the first 15 minutes and the second 15 minutes on the same x and y axes(total of 30 minutes).  The difference in the two line graphs can be supported with a line and broken line, or different colors.  Label where phase changes occur and the heat of fusion. Be sure to make a key for your graph.

Data Table:  (Includes the dependent and independent variables)

Data Analysis:  (This would include the graph on graph paper)

Conclusion:  

Questions:  Write the question and answer in complete questions.

1. What does phase change mean ans where do they occur in this lab.
2. What is the dependent variable and independent variable in this experiment?
3. Describe what happens to the water temperature as it freezes.  Describe  what happens to the water temperature as it melts.  
4. Why are there flat lines on the graph?
5. Using the data from the graph, what was the freezing temperature of the water? What was the melting temperature of the water?
6.  Using the independent and dependent variables, describe the relation between the melting point and boiling point of water.

Remember that there has to be a paragraph about the experimental errors and what changes would be made if the lab was repeated.

The Law of Conservation of Matter Lab

Teacher Notes:

Chm.2.2.3 Analyze the law of conservation of matter and how it applies to various types of chemical equations (synthesis, decomposition, single replacement, double replacement, and combustion).              

This is a double replacement reaction.  Within the reaction is a decompostion reaction.  The specific kind of double replacement is a neutralization reaction.  The NaHCO₃ is the base and the CH₃COOH is the acid.

The first reaction is  NaHCO₃   +       CH₃COOH    →   H₂CO₃    +     CH₃COONa     

The products are called sodium acetate and carbonic acid.

The second reaction      H₂CO₃   →    CO₂   +   H₂O      which is a decompostion reaction

The Overall equation reaction is:

NaHCO₃   +       CH₃COOH     →     CH₃COONa  +   CO₂   +   H₂O

Students will find the molar mass on each side of the yield sign to be the same.



Helping Students Explain Experimental Errors
Some chemistry students will state that the Law of Conservation of Matter is not supported in this lab.  When teaching with a lab, the teacher must be careful in not telling or even hinting the expected data the student should collect during a lab.  The student collects the data that happens during a lab, whether it supports or does not support a theory or law.  It should be the teachers job to get the students to ask questions on why the data supported or did not support the theory or law.  That is part of the data analysis and is very important in teaching about experimental errors. Many students do not understand experimental error.  Many will state human error.  There may be human error but humans can make many kinds of errors during an experiment.  Where and how do humans make these errors? Are there other incidents that cause errors that are not human?  Did the lab equipment raise concerns for the errors?  These statements must be very specific for the student to understand why or why not laws or theories are supported or not supported.

Teaching Students About Being a Scientist
Before this lab, it is important that the students know the parts of a scientific investigation and can eventually formulate this themselves.  It could be taught during this lab.  Many educators believe that students should devise all this themselves but many other educators believe that this is done gradually.  In the first lab, I told the Purpose (question), hypothesis, materials, procedure, data table and conclusion in the first lab and gradually left off more information each time for the students to complete themselves.  For example,  students in the beginning of chemistry find it difficult to make a hypothesis about what they think will happen.  Discussions about the definintion of hypothesis and that alone helps them become better at making a hypothesis. In the first lab, I modeled the scientific investigation so that they knew exactly what was expected.  In the last few labs, the students are given a purpose.  In groups, or with a partner, the students develop their own hypothesis, list the materials needed, write the procedure, develop the data table, complete the experiment, do the data analysis, and write their conclusion which should discuss the experimental errors and what changes would be done if the lab were done again.  In the semester project, students complete the parts of the scientific investigation by themselves, including the purpose (or question).

Conclusion

In many labs, I added conclusion questions that they might see on a test.  I feel that it made a connection with what was discussed in class. Also, it is a help when studying and reviewing for a test.  Yes, I asked the students to write the questions in the lab book so that they would know what the question was.


Helping Students To Think 
During a lab, I rarely give additional instructions (beyond the written lab instructions) or give  answers to an experiment, but will answer any questions that will help them.  Yes, it causes frustration, but they learn that I am teaching them how to think.  Sometimes I will answer a question with a question, to again, help them with a thinking process.  I think it is important for students to use a marbled lab book.  Every teacher can form their own opinion about this technique but I found that students take more ownership of their lab work.  It also is a good way to organized their lab work.

Helping Students Learn How to Make a Data Table
To teach students to make a data table, read the lab.  In the first lab, I teach them how to pick out what must be part of the data table.  In this lab you will notice that the data to record are the following:
* mass of the sodium bicarbonate (this is only to make sure that a reasonable amount is used)  If you
   don't want them to mass it, show them how much to use)
* mass of the set-up before the reaction
* mass of the set-up after the reaction
* observation of the reaction (smell, temperature, sight, sounds)

Helping Students with Data Analysis
Data analysis includes graphs and/or equations and math related to the experiment. It is important to teach them how to organize this.  Without help, some will include data analysis in the procedure or the data table. (Some simple labs will not have data analysis but all need to talk about the conclusion. This lab has no data analysis unless you change the procedure)

Safety
Lab safety is of upmost important in chemistry.  That topic should be covered before any lab experimenting is done. Lab techniques can be taught and demonstrated as a lab calls for it.

Now for the lab.  This lab is usually the first chapter or unit in chemisty or physical science.

The Law of Conservation of Matter Lab            

Safety: Safety googles, apron (if using HCl), closed toed shoes (if using HCl)

Purpose: (or Title of Lab)  To demonstrate that the mass of the reactants is equal to the mass of the product after a chemical reaction has occurred.

Hypothesis:  ?  (The student may need help in the first attempt to hypothesize.)

Materials:  Balance, 250mL beaker, ballon, spatual (or spoon), test tube, 100 mL beaker, disposibleregular stem pipette, acetic acid or vinegar (CH₃COOH),  baking soda or sodium bicarbonate (NaHCO₃),  safety goggles,

Procedure:
1.  Tare the balance.
2.  Obtain 100mL beaker that is 1/2 full of acetic acid.  (Dilute HCl can also be used but care must be
      used when handling it.  It can bleach clothing.  If using HCl, using an apron is advised.)
3.  Fill the test tube 1/2 full of acid.  Place the test tube in the 250 mL beaker.
4.  Obtain a balloon and sodium bicarbonate, NaHCO₃.
5.  Place a scoop (3-4 grams) of  NaHCO₃ in the balloon.
6.   Stretch the opening of the balloon over the open end of the test tube.  Be careful not to let any of the sodium bicarbonate spill into the test tube.
7.  Place the test tube/balloon in the beaker.  Make sure the balance is tared and determine the total mass of the balloon, test tube and beaker.  Record the data in the data table.  This would be the "before the reaction" data.
8.  Empty the contents of the balloon into the test tube.  Record the observations.
9.  After the reaction is complete do not remove the balloon yet.  Record the mass of the test tub, balloon and beaker.  The balloon can be removed after the set-up has been massed and recorded.

Data Table:

Data Analysis: (Students need to include the part of the lab but state that there is no data analysis)

Conclusion:

Questions:  Write the question and answer in complete questions.
1.  How do you know that a chemical reaction occurred?
2.  What filled the balloon?
3.  What would have happened if the balloon was not attached to the test tube?
4.  What does the Law of Conservation of Matter state?
5.  Did this experiment support the Law of Conservation of Matter?  Why or why not?

Remember that there has to be a paragraph about the experimental errors and what changes would be made if the lab were done again.

Life Happens

I loved my career as a science teacher, though I didn't start as a science teacher.  I started my career as a Family and Consumer Science teacher.  When I started teaching, the position was called a home economics teacher.  In the late 80's, I returned to school and spent the equivelent of 4 more years taking science and math courses to become a science teacher.  It was a good choice for me.  My completely right brain became more left brained.  My last twenty-five years of teaching were spent teaching chemistry, physics, physical science and earth science.

When I begin thinking about retiring, I wanted to teach part-time.  So, I prepared myself to begin teaching science online courses for -- and that is as far as I got.  My mother became ill and needed 24/7 care. Since retirement, I have spent most of my time at the coast of NC taking care of my mother.

I have several other interests besides teaching.  I like to read for fun.  That was almost impossible while I was teaching.  I was serious about keeping those papers graded and tutoring students who needed help to understand the science courses I was teaching.  But now, I have started making dolls for ragdolls2love.com.  I also enjoy making blankets for the Project Linus.  I knit, crochet, or quilt the blankets for all ages.  I have been able to work on these projects and also take care of my mother.  I crochet and knit hats for the Coats for the Children project.  For now, these projects give me a since of helping others.  In the process, I am also using up my mother's fabrics and yarn in her sewing room.  My mother had to have a no to low sodium diet.  To help with this diet, I learned how to use many spices

In this new adventure, I thought that I might find a way to share the ideas and lesson plans and science activities.