CHEMISTRY NOW: Using Salt to Melt Ice Cubes (Grades 9-12)

Objective:


Students will design an experiment to quantify effectiveness of different salts in melting ice at different temperatures. Students will draw conclusions from their experiment, conduct research that supports their experimental results, and submit an essay that discusses the chemical nature of each salt when reacting with ice.


Introduction Notes:


CHEMISTRY NOW: Using Salt to Melt Ice Cubes

 

 

Title:

 

 

Using Salt to Melt Ice Cubes

 

Subject/Topic:

 

 

Chemistry

 

Grades:

 

 

9–12

 

Standards

Alignment:

 

 

Science as Inquiry

 

 

Time Allowance:

 

 

50 minutes

 

 

Overview and Purpose/Objective(s)

(information, concepts to be learned):

 

Students will design an experiment to quantify effectiveness of different salts in melting ice at different temperatures

 

Students will draw conclusions from their experiment, conduct research that supports their experimental results, and submit an essay that discusses the chemical nature of each salt when reacting with ice.

 

 

VOCABULARY

 

Melting point—the temperature at which solid and liquid coexist in equilibrium.

 

Normal boiling point—the temperature at which boiling occurs when there is exactly    1 atm of external pressure.

 

Materials (per group of 2–3 students)

-          ice cubes made from tap water

-          ice cube trays

-          3 beakers

-          graduated cylinder

-          sodium chloride (table salt)

-          calcium chloride (road salt)

-          magnesium sulfate (Epsom salt)

-          access to a freezer

-          thermometer

 

 

 

ACTIVITY/ENGAGEMENT

(reinforcing lesson, making real-world connection)

 

Organize the students into groups of 2–3. Engage students in the following questions and concepts:

 

How does ice melt? When you add salt to water, you introduce dissolved foreign particles into the water. The freezing point of water becomes lower as more particles are added until the point where the salt stops dissolving.

 

What happens to a salt when it is added to water?

 

What hypothesis can we make about some salts used to melt ice? Look at the following formulas for salts with the class and solicit inferences as to how these molecules are structured.

-        calcium chloride CaCl2 (type of road salt)

-        sodium chloride NaCl (table salt)

-        magnesium sulfate MgSO4 (Epsom salt)

 

Have students begin to formulate a hypothesis for an experimental design. Organize students into groups of 2-3 and have them design an experiment that accurately quantifies the ability of each salt to melt or not to melt ice. Students will be awarded credit based on how many variables they can test for, and for conclusions that demonstrate thorough investigations into the properties of each salt and its effect on ice.

 

Have students fill in a hypothesis or, if appropriate, write down a guiding question in place of a hypothesis.

 

Encourage each group to work on a method for testing the salts. While each group deliberates be sure students include variables such as temperature and mass, and use a control group. All methods, regardless of the type of experiment conducted, will most likely have to include these variables as part of a good experimental design.

 

Experimental designs will vary. Discuss with students some methods that they have decided to employ in their experiments. Be sure to pay close attention to methods that lack a good methodology. Some general questions for places where students may need help may include the following:

 

     How can students account for the amount of ice melted?

     Will students make the ice first and then melt it?

     Can the students make specific solutions and attempt to freeze them?

     How will students measure the ingredients and account for them?

 

 

Concluding discussion/activities

 

Have each student group report to the class to discuss what their data show. Can the class create a class conclusion? If so, what is it?

 

Once all the students have completed an effective experiment have them prepare a group presentation to the class about their results. Their main conclusion should explain their methods and why they consider it to be a well-designed method.

 

Once all the results are in from each completed experiment, engage in a class discussion to decide and vote on which method performed best, and why.

 


 

 

Student Worksheet for Using Salt to Melt Ice Cubes

 

Name: _____________________________________  Date: ______________

 

Materials available:

-          ice

-          ice trays

-          water

-          thermometer

-          100 ml graduated cylinder

-          classroom balance (optional)

-          calcium chloride CaCl2 (type of road salt)

-          sodium chloride NaCl (table salt)

-          magnesium sulfate MgSo4 (Epsom salt)

 

Procedure:

 

Lab safety equipment should be used, and safety protocols followed.

Group hypothesis or guiding question:

_________________________________________________________

 

_________________________________________________________

 

_________________________________________________________

 

 

Group Procedure:

_________________________________________________________

 

_________________________________________________________

 

_________________________________________________________

 

_________________________________________________________

 

_________________________________________________________

 

_________________________________________________________

 

_________________________________________________________

 

 

 

 


Data Table(s):

 

Object

Measurement

Mass of

 

Mass of

 

Mass of

 

Volume of water

 

Temperature of water

 

Temperature of ice

0.0˚C

Temperature of freezer

 

Time to melt

 

 

 

 

 

 

Additional Data Table (can be used for repeated trials or to experiment with other variables):

Object

Measurement

Mass of

 

Mass of

 

Mass of

 

Volume of water

 

Temperature of water

 

Temperature of ice

0.0˚C

Temperature of freezer

 

Time to melt

 

 

 

 

 

 

Data and Observations 

 

___________________________________________________________________

 

___________________________________________________________________

 

___________________________________________________________________

 

___________________________________________________________________

 

___________________________________________________________________

 

___________________________________________________________________

 

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