Marie Purvis - Virginia Commonwealth University



Making a Graph Using Melting and Freezing Point[1]

8th Grade Physical Science

Purpose/Rationale: The purpose of this lab is to compare two unknown substances’ freezing and melting points. The data that the students collect will be used to teach the students how to plot a line graph. The students will be able to take what they learned and apply it to make graphs for any lab done through out the year.

Safety Issues: Students will be working with an open flame, weak acids and breakable glassware. Students must follow laboratory safety guidelines and rules set forth at the beginning of the year. These include tying back long hair, wearing safely goggles and apron at all times, no playing with the open flame, and no horseplay.

Relevant Standards of Learning:

PS.1 The student will plan and conduct investigations in which

a) chemicals and equipment are used safely;

d) triple beam and electronic balances, thermometers, metric rulers, graduated cylinders, and spring scales are used to gather data;

g) independent and dependent variables, constants, controls, and repeated trials are identified;

h) data tables showing the independent and dependent variables, derived quantities, and the

number of trials are constructed and interpreted;

j) frequency distributions, scattergrams, line plots, and histograms are constructed and interpreted;

k) valid conclusions are made after analyzing data;

l) research methods are used to investigate practical problems and questions.

PS.2 The student will investigate and understand the basic nature of matter. Key concepts include:

e) physical properties (shape, density, solubility, odor, melting point, boiling point, color)

PS.7 The student will investigate and understand temperature scales, heat, and heat transfer. Key concepts include:

b) phase change, freezing point, melting point, boiling point, vaporization, and condensation

Materials:

• Ring stand

• Ring clamp

• Wire screen

• Alcohol burner

• Buret clamp

• Water bath

• Test tube

• Thermometer

• Stop watch

• Unknown substances (Lauric and Patmitic Acid)

• Safety Goggles

• Apron

• Matches

• Stir rod

• Graph paper

• Colored pencils

Resources:

• PowerPoint Program

• Laptop Computer

• Overhead Projector

Procedures for Teaching:

Before class starts prepare the unknown substance in a test tube. Insert a thermometer and let freeze. Place the test tube in the test tube rack at each station.

1. Engagement: 5 minutes:

Ask the students to recall what they learned about melting point and freezing point this week. Ask them if they have ever seen ice melt or freeze. Ask them if they think everything freezes at 0ºC. Tell them today we are going to look at two unknown substances and determine their melting point and freezing point by observing the test tube and temperature over time. Tell them that the melting point and freezing point can be determined also by graphing! Ask them how many people have ever seen a line graph. How many people have ever drawn one? Today, after carrying out the lab they are going to learn how to draw a line graph with the data they collected and determine the melting and freezing point.

[2] Prepared by Marie Purvis, Virginia Commonwealth University, TEDU 540 Fall 2006

2. Exploration 40 minutes:

Lab partners will be assigned an unknown #1 or #2, which are Lauric Acid and Palmitic Acid. (They went over the lab procedure and set-up yesterday) See Lab Handout. Basically, the students will heat their solid unknown and record the temperature every .5 minutes starting at 0 continuing until 5 minutes after the solid had completely melted. They record their data in the data chart and place a star next to the temperature as the solid first begins to melt. They then extinguish their alcohol burner and record the temperature at 0 and every .5 minutes until 5 minutes after their substances had completely frozen. Have them construct a graph and graph their data.

3. Explanation: 40 minutes:

Discuss the graph they made. Ask questions about uniformity, scaling of the axis, (information on page 60 of Rezba text) etc and present in PowerPoint. I will explain what a line graph and a coordinate plane are using my PowerPoint presentation. I will also explain how to construct a line graph based on the data that they collected in lab. I will use examples from lab and ask them questions about their data. This will also be the student’s opportunity to construct their own graph of their melting and freezing point data. They need to determine a scale for their individual results as well as plot their points, label their graph, and sketch a line of best fit. They will turn this in when finished.

4. Elaboration: 15 minutes:

I will give the class a new data table to use to construct another line graph. See Attached.

This will enable them to independently apply the skills that they just leaned to create a new line graph.

5. Evaluation 100 pts:

Part of the student’s assessment is their participation and proper lab behavior. (25 pts) Students should have completed their melting and freezing point graph in class and turned it in. (25 pts)

They will also answer the post lab questions included on the back of their lab handout for homework. (25 pts)

Students will also finish the independent practice graph for homework and turn in if not finished in class. (25 points)

[3] Prepared by Marie Purvis, Virginia Commonwealth University, TEDU 540 Fall 2006

A Comparison of Two Similar Substances’ Freezing and Melting Points

Background Information:

Matter can exist in one of three physical states – solid, liquid, or gas. In a crystalline solid, the particles are arranged in an orderly, repeating, three-dimensional pattern. As the solid is heated, the kinetic energy of the particles increases. Eventually, at some temperature, which is called the melting point, the molecules overcome the forces of attraction holding the particles together, and the substance changes to a liquid. When a liquid is cooled, the reverse process occurs. The temperature of the liquid decreases until the freezing point is reached. Only after the liquid is completely changed to a solid will the temperature begin to decrease again. In this investigation, you will compare the melting and freezing point of two substances 1 & 2.

Purpose:

Hypothesis:

Materials:

Diagram:

Procedure:

____1. Put on safety goggles and apron.

____2. Set up the equipment as diagramed above.

____3. Record the temperature of the substance at 0.0 minutes in the melting point data chart. (Estimate thermometer readings to 0.1 ºC)

____4. Light the alcohol burner and begin recording the temperature readings every 0.5 minutes.

____5. Stir the water in the beaker continuously.

____6. Continue recording temperatures every 0.5 minutes until 5 minutes after you are confident the substance has completely melted. (Put a star beside the temperature of the substance as it first begins to melt.)

____7. Put out your burner flame and record the temperature of the substance at 0.0 minutes in the freezing point data chart.

____8. Continue recording temperatures every 0.5 every 0.5 minutes until 5 minutes after you are confident the substance has completely frozen. (Put a star beside the temperature of the substance as it first begins to freeze.)

[4] Prepared by Marie Purvis, Virginia Commonwealth University, TEDU 540 Fall 2006

Data Chart I: Temperature Recordings Used to Determine Melting Point for Substance _____

|Time (min) |Temp (ºC) |Time (min) |Temp (ºC) |

|0.0 | |16.5 | |

|0.5 | |17.0 | |

|1.0 | |17.5 | |

|1.5 | |18.0 | |

|2.0 | |18.5 | |

|2.5 | |19.0 | |

|3.0 | |19.5 | |

|3.5 | |20.0 | |

|4.0 | |20.5 | |

|4.5 | |21.0 | |

|5.0 | |21.5 | |

|5.5 | |22.0 | |

|6.0 | |22.5 | |

|6.5 | |23.0 | |

|7.0 | |23.5 | |

|7.5 | |24.0 | |

|8.0 | |24.5 | |

|8.5 | |25.0 | |

|9.0 | |25.5 | |

|9.5 | |26.0 | |

|10.0 | |26.5 | |

|10.5 | |27.0 | |

|11.0 | |27.5 | |

|11.5 | |28.0 | |

|12.0 | |28.5 | |

|12.5 | |29.0 | |

|13.0 | |29.5 | |

|13.5 | |30.0 | |

|14.0 | |30.5 | |

|14.5 | |31.0 | |

|15.0 | |31.5 | |

|15.5 | |32.0 | |

|16.0 | |32.5 | |

[5] Prepared by Marie Purvis, Virginia Commonwealth University, TEDU 540 Fall 2006

Data Chart II: Temperature Recordings Used to Determine Freezing Point for Substance _____

|Time (min) |Temp (ºC) |Time (min) |Temp (ºC) |

|0.0 | |16.5 | |

|0.5 | |17.0 | |

|1.0 | |17.5 | |

|1.5 | |18.0 | |

|2.0 | |18.5 | |

|2.5 | |19.0 | |

|3.0 | |19.5 | |

|3.5 | |20.0 | |

|4.0 | |20.5 | |

|4.5 | |21.0 | |

|5.0 | |21.5 | |

|5.5 | |22.0 | |

|6.0 | |22.5 | |

|6.5 | |23.0 | |

|7.0 | |23.5 | |

|7.5 | |24.0 | |

|8.0 | |24.5 | |

|8.5 | |25.0 | |

|9.0 | |25.5 | |

|9.5 | |26.0 | |

|10.0 | |26.5 | |

|10.5 | |27.0 | |

|11.0 | |27.5 | |

|11.5 | |28.0 | |

|12.0 | |28.5 | |

|12.5 | |29.0 | |

|13.0 | |29.5 | |

|13.5 | |30.0 | |

|14.0 | |30.5 | |

|14.5 | |31.0 | |

|15.0 | |31.5 | |

|15.5 | |32.0 | |

|16.0 | |32.5 | |

[6] Prepared by Marie Purvis, Virginia Commonwealth University, TEDU 540 Fall 2006

Freezing and Melting Point Post-lab Questions

1. What is freezing point?

2. What is melting point?

3. What substance did you experiment with in this lab?

a. Look at the chart of data you recorded during heating and determine the substance’s approximate melting point.

b. Look at the chart of data you recorded during heating and determine the substance’s approximate freezing point.

4. Using class data, determine the freezing point and melting point of:

a. Substance 1: Melting point :_____ Freezing point:______

b. Substance 2: Melting point :_____ Freezing point:______

c. Using your line graph, explain how you determined the temperature of the melting and freezing?

d. How does a substance’s melting point and freezing point compare?

5. Explain what is happening to the bonds between molecules….

a. when a substance melts.

b. when a substance freezes

[7] Prepared by Marie Purvis, Virginia Commonwealth University, TEDU 540 Fall 2006

6. Why should the water in the bath be stirred when determining the melting and freezing point?

7. Do you think the temperature at which the substance melts/freezes depends on the mass of the substance? Explain

8. Do you think time it takes for a substance melts/freezes depends on the mass of the substance? Explain

9. In viewing a line graph of a substance freezing, what happens at a substance’s freezing point?

10. What happens when a substance undergoes sublimation?

11. How is molecular motion measured?

12. A characteristic property is one that can be used to identify a substance or tell a difference between two or more substances.

a. Is melting point a characteristic property? Explain

b. Is freezing point a characteristic property? Explain

13. Describe what happens to the particles of a sold at its melting point.

14. Describe what happens to the particles of a sold at its freezing point.

[8] Prepared by Marie Purvis, Virginia Commonwealth University, TEDU 540 Fall 2006

Independent Practice: Constructing a Line Graph

Using the data table, below construct a line graph. Remember to apply what you learned today! I will be looking for the following things:

• Title

• Correctly labeled x axis, including units

• Correctly labeled y axis, including units

• x axis correctly subdivided into scale

• y axis correctly subdivided into scale

• Data pairs correctly plotted

• Data trend summarized with line of best fit

|Independent Variable |Dependent Variable |

|Time Paper Towel Submerged (sec) |Mean Height (mm) |

|10 |11 |

|15 |14 |

|20 |14 |

|25 |15 |

|30 |16 |

|35 |17 |

|40 |19 |

[9] Prepared by Marie Purvis, Virginia Commonwealth University, TEDU 540 Fall 2006

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[1] Prepared by Marie Purvis, Virginia Commonwealth University, TEDU 540 Fall 2006

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