BEHS Chemistry

Assignment directions for a project using freezing various salt water solutions

Chem Projects Research Team

CheMystery Labs

380 South Buzz Blvd

Bee Hive, UT 84302

 

Dear Team:

 

The Director of CheMystery Inc. wants your research team to discover how the amount of salt affects the freezing point of water.  The company has a budget of $50,000 to answer this question.

 

 Before you begin your work, I will need the following information from you so that I can approve your work.  The planning space for these items is found in your project packet.

 

Ø       a detailed summary of your hypothesis, experimental

      design table, a plan for the procedures along with all

       necessary data tables

Ø       a description of necessary calculations

Ø       an itemized list of equipment with costs and chemical with

      their costs, include labor costs of $80 / hour and cost for

      laboratory space $10,000/day, and a standard disposal

      fee of $2000 / gram of material. 

 

After you complete the analysis, prepare a report for the Director and Officers of CheMystery Inc.  Remember that this report will be seen by a variety of people, so be certain it projects the image we want to present.  The items that should be included in the report are found in your project packet.

 

Good luck with the project.  Please keep in close contact me as you proceed with the project.  You will need a data verification signature, by having me observe one of the trials in the experiment.

 

Sincerely

 

Your teacher

 

President and CEO

CheMystery Labs Inc.

 

 

 

Freezing Various Salt Water Solutions
 

        Background Information

                    Solutions are homogenous mixtures that contain two or more substances.  The major component is called
              the solvent, and the minor component is called the solute.  Since the solution is primarily composed of solvent,
              physical properties of a solution resemble those of the solvent.  Some of these physical properties, called
              colligative properties, are independent of the nature of the soluteand depend only upon the solute concentration.
              The colligative properties include vapor-pressure lowering, boiling-point elevation, freezing-point lowering,
              and osmotic pressure.  It has been found experimentally that the dissolution of a nonvolatile solute (one with very
              low vapor pressure) in a solvent lowers the vapor pressure of the solvent, which in turn raises the boiling point
              and lowers the freezing point.

                    You are probably familiar with some common uses of these effects: Antifreeze is used to lower the freezing
              point and raise the boiling point of coolant (water) in an automobile radiator; and salt is used to melt ice.  These
              effects are expressed quantitatively by the colligative-property law, which states that the freezing point and boiling
              point of a solution differ from those of the pure solvent by amounts that are directly proportional to the molar
              concentration of the solute.  This relationship is expressed by the equation for the freezing-point lowering and
              boiling-point elevation:
 

 

 ∆ T (the change in temperature)  =  Kf  m



                    where change in the temperature (∆ T) is the freezing-point lowering or boiling-point elevation, K is a constant
              that is specific for each solvent, and m is the molarity of the solute (number of moles solute per/ 1000 g solvent).


              The freezing point constant of water is (1.86 oC/m).  In the case of a non-electrolyte, the molality of the non-electrolyte

               and the molality of particles in solution is the same.  For electrolytes, the molality of particles is equal to the molality

               of the electrolyte times the number of ions in the chemical formula of the compound.

         Procedures:

Caution:  THE THERMOMETERS ARE FRAGILE.  DO NOT USE THE THERMOMETER AS A STIRRING ROD.  USE ONLY A PLASTIC BEAKER OR BUCKET TO CONDUCT THIS EXPERIMENT.




              1.    Half fill a 600-mL plastic beaker or bucket with ice and cover it with about 20 grams of sodium chloride (rock salt).  Stir
              this ice-salt mixture with a stirring rod until it reaches a constant temperature at or below -10oC.  Cover the
              outside of the beaker with aluminum foil with the reflective side in.

              2.    Half fill a test tube with distilled water and place it in the ice bath.  Rinse the stirring rod and use it to stir
              the water gently until ice crystals first appear and starts getting slushy.  Use a thermometer to measure the freezing
              point and record it in the Data Table.

              3.    Mix up the various concentrations of salt solutions

  4.   Test using steps 1 and 2.

 

     CALCULATIONS:

 

            Calculate the correct freezing point using the formula below.

 

                        CORRECT FREEZING POINT   =   0oC  minus   ( 1.86 oC/M  *  Molarity of the solution  * 2 )

 

                        Calculate the percent error using the formula inside the periodic table handout.


 

Other Ideas for Freezing Point Research Projects
 

 
 All the solutions and apparatus required for Freezing Point studies and analysis will be provided, except that you must provide the ice and rock salt to lower the temperature of the solution.  Here are some general suggestions for the types of projects that you might consider.

                              What effect does the type of salt have on the freezing point?

 

                              What is more effective at lowering the freezing point of water salt or a commercial de-icer?

 

                              At what temperature does the windshield washer fluid freeze?

Contact: Tom Davidson, Box Elder High School 380 So. 600 w. (435-734-4840) Email: tom.davidson@besd.net