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To protect ferrous base metals from corrosion, cathodic protection is commonly used. Companies specialize in manufacturing items that have a coating of zinc. The coating of zinc protects the base metal from corrosion. Your company sells electrolytic formulations. These formulations are used by electroplating companies to plate zinc on a variety of metal parts used in the automobile industry. Your company's technical sales representative reports to technical support that one of his international customers with plants in six countries is having trouble with our product, Zink Koat 345. Zink Koat 345 has the following specifications. 
Ingredients Molarity   Grams per liter 
Zinc Sulfate Heptahydrate  3.4  240 
Ammonium chloride  0.3    15
Ammonium sulfate octadecahydrate  0.25  30 
Biocide     1
Suggested parameters:  pH: 3 to 4.5
Bath temperature 24 - 30oC 
Current Density: 2 to 10 amps per dm2 
Agitated bath 
The problem appears during certain parts of the year. On long term storage, the formulation tends to give unacceptable plated finishes. The technical sales rep has observed crystalline solids in the carboys used to store the Zink Koat 345. The sales representative wants to present solubility data for Zink Koat 345 to his customer. The sales representative request technical support to obtain data on the ingredients solubility as a function of temperature.

The tech support group gives you the responsibility of collecting this necessary data for the solubility of each electrolyte as a function of temperature. You agree to do a literature search and find three possible techniques for determining solubility. You report to the group that you have found three procedures to determine solubility. It's agreed that it would be best to run preliminary experiments in order to determine which of the three procedures technical support will use. As you leave the meeting, the group leader says, "Next week at our tech support group meeting, make recommendations on the method of choice and be prepared to justify the method." 

You go to the library computer center and find considerable information. The solubility of a substance is defined as the maximum amount of the substance, which can be dissolved in a definite amount of solvent at a certain temperature. The concentration of a saturated solution is often expressed in grams of solute per 100 grams of solvent. There are a number of methods to determine the concentration of a saturated solution. In this experiment we will utilize the following methods and compare their efficiency and accuracy. 
The three methods you select can be briefly summarized: 
1. Prepare a saturated solution at a desired temperature by stirring an excess amount of solute with the solvent until equilibrium is reached.  Once equilibrium is established find the salts concentration.
2.Prepare a solution at a high temperature. Cool the saturated solution to the desired temperature, filter, then find its concentration
3. Prepare a solution of known concentration at a high temperature, then cool to find the desired temperature at which the solution becomes saturated (marked by the incipient appearance of the crystalline solute). 

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I. Equilibration Method
Preparation of a Saturated Solution at Room Temperature and Determination of Its Concentration.       
Obtain 5 grams of potassium nitrate and pulverize, if necessary, the solute in a clean mortar. Place the potassium nitrate with 10 ml of distilled water in a small beaker. Stir vigorously, or preferably stir for half an hour using a magnetic stirrer. If the solid dissolves completely under these conditions, add more solid in order to ensure a saturated solution. When saturation has been achieved, filter this solution into a pre-weighed evaporating dish. Measure the temperature and determine the mass of the solution to the nearest 0.01-gram.

Cautiously evaporate the water using a low flame. A pre-weighed watch glass may be used to cover the dish in case of splattering. Stop heating when residue is dry. Let cool, and determine the mass of the solid residue.

Find the mass of water by difference, and calculate the solubility of potassium nitrate in units of g KNO3 / 100 g H2O. 

II. Super Saturated Method
Preparation of a Warm Saturated Solution and Determination of Its Concentration.
Obtain 5 grams of potassium nitrate and place it with 10 ml of water in a small beaker. Warm over a low flame with stirring, until the solid completely dissolves. Remove the heat source and let the solution cool to room temperature. Crystals of potassium nitrate should appear. Filter the solution into a pre-weighed evaporating dish. Measure the temperature and determine the mass of the solution to the nearest 0.01-gram.

Evaporate the water and determine the solubility of potassium nitrate as in Part I above. 

III. Determination of Saturation Temperature Method
Preparation of Solutions of Known Concentrations 
Conducting Part III Using LabWorks II
Now we must complete four tasks.

First, we must calibrate the thermistor. This will require using LabWorks II. Be prepared to perform this calibration. Read the instructions below.

Second, place 10.00 grams of potassium nitrate in a 1 inch diameter by 6 inch long test tube. Mount the test tube vertically with a clamp on a ring stand. Shape a copper wire into a stirrer that will freely fit around the thermistor. Adjust the glassware and equipment as shown in Figure 1. Using a volumetric pipette, add 6.00 ml of distilled water to the solid in the test tube.

Third, heat while stirring until a clear solution is obtained. Do not let the solution boil because evaporation of water will change the concentration. After the salt has dissolved remove the heat source.

Fourth, suspend the thermistor into the test tube using a buret clamp and a #4 rubber stopper that has a hole and a slit side as illustrated in Figure 2. Place the thermistor so that it extends into the test tube without it touching the hot glass and about one cm from the bottom. With the thermistor in the solution, allow the solution to cool with constant stirring. Note the temperature at which the first crystal is observed.

Immediately, repeat steps three and four that is the warming process and confirm the crystallization temperature as was done in the previous in tasks three and four. The formation of crystals represents a saturated solution and the noted temperature is that at which 10.00 g of potassium nitrate dissolves in 6.0-mL water to form saturated solution.

Apparatus setup for dissolving the potassium nitrate in water.
Figure 1.

Heating the mixture of water and potassium nitrate to form a solution.

The apparatus setup for measuring the temperature when the first crystal of salt are observed.
Figure 2.

Measuring the temperature as the saturated solution cools. Record the temperature when the first crystal of potassium nitrate is observed.

Add an additional 4.0-ml of water with the pipette to the contents already in the test tube and warm until KNO3 again dissolves. Again after removing the heat source, allow the solution to cool with stirring, measuring and recording the temperature at which crystallization occurs. Repeat to confirm the crystallization temperature. This is the temperature at which 10.00-g of potassium nitrate dissolves to form a saturated solution in 10.0 g or water.

Repeat with two 5.0-ml portions of water and determine the crystallization temperature. The last dilution may require cooling the test tube with an ice-water bath.

Instructions for the use of LabWorks II

Computer-based measurements (must be completed during the laboratory period)

i. Opening LabWorks II .
To open the LabWorks II program:

either Click on the Microsoft start button in the lower left corner of the screen. When a pop-up screen appears, click PROGRAMS, and then drag the cursor over to LabWorks II 4. Another pop-up window will appear; then click on LabWorks.exe. The LabWorks II program is then activated.
or open LabWorks II 4 by clicking on the ICON found on the Desktop Window.

A view of LabWorks II Main Menu window should appear on your screen.
In the Main Menu screen on the Tool bar , open the Calibrate window by clicking on the button labeled Calibrate.

ii. Calibration Set-up

Thermistor Calibration:
In order to obtain the temperature using thermistors, these sensors must be calibrated. The procedure for calibration is given below and must be completed before the actual experiment is performed. To calibrate a sensor, we place the thermistor in a known temperature and record the current produced, milliamperage. By repeating this at another known temperature , we can create a graph that relates the thermistors output, milliamperes, to the measured temperature. Since the temperature-current is a linear relationship, the computer can develop an equation that relates sensor output to the measured temperature. By solving this equation, the computer can calculate the value that corresponds to the measured voltage or current. The computer can then display this value.

In this experiment we are using a thermistor as our sensor. A thermistor is a semiconductor in which almost all of the electrons are bound closely to their parent atoms and will not move. However, application of heat to the thermistor material promotes some electrons to a conduction band. In this way the number of mobile electrons increase as the temperature of the semiconductor increases. The
LABWORKS laboratory interface can determine a value to one part in about 8000; therefore it is possible to use a thermistor to see 0.01o C in the room temperature range.

The Calibration window appears showing numerous probes which can be utilized in LabWorks II. In this experiment, we will use only thermistor as a probe:
We will complete three tasks to use the themistor for temperature measurements:

1st    Connect the probe to the LabWorks II interface
2nd  Edit the Sensor so that the data is collected as we choose
3rd  Calibrate the sensor using the Calibration Wizard. The sensor will be calibrated by recording a lwo temperature (ice water) and warm water (hot tap water) using a therometer.

iii. Design Set-up
The next step involves the design of the experiment. At this time you give the computer instructions to obtain temperature measurements at some regular time interval.

iv. Acquire Set-up
The next step involves collecting the experimental data using the probe and parameters previously defined.

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