Ksp Lab
Introduction: Connecting Your Learning
Barium is toxic to humans, yet patients are given a barium sulfate “cocktail” to drink before certain gastrointestinal x-rays. Since BaSO4 is opaque to x-rays, ingesting it enables medical professionals to find evidence of blockage or leakage throughout the gastrointestinal tract as well as other abnormalities without having to cut a patient open. The solubility product constant (Ksp) of BaSO4 is 1.1×10-11 , which indicates the amount that actually ionizes, is well below the toxicity threshold for humans.
Also in the human body, when levels of uric acid (a nitrogenous waste product from protein metabolism in the blood) exceeds the Ksp, the uric acid can precipitate out, especially in the joints, leading to a painful arthritic condition known as gout.
In streams and rivers, as water moves through soil and rock, it dissolves small amounts of minerals and holds them in solution. Calcium and magnesium dissolved in water are the two most common minerals that make water “hard.” In many places where water is “hard,” people have water softeners. What the water softener does is replace the calcium ions in the water with sodium (or potassium) ions. This ion exchange is done to take out the ions whose Ksp is large enough to precipitate out of solution and cause scale or lime deposits. The ions that are replaced in the solution have a Ksp small enough that they will not precipitate out.
Ksp is just a simplification of Keq. For the ionization equation below:
Since the concentration of a solid ([Ax By]) does not appreciably change, you simplify the Keq of an ionization or dissociation equation to:
For example, Ksp (CaCO3 )=[Ca2 +][CO32-]=4.5×10-9. In this lab, you will determine experimentally the Ksp for sodium chloride (NaCl) as well as potassium chloride (KCl).
Resources and Assignments
Multimedia Resources None
Required Assignments Lab 9 Report
Materials (Lab Kit) • 3 Premassed samples of each:
o (KCl) Water softener salt
o (NaCl) Rock salt
• Mortar and pestle
• 2-50 ml Beakers
• 10.0 ml Graduated cylinder
• 2 Styrofoam cups
• Thermometer
Materials (Student supplied) • Stirring spoon
• Distilled water
• Crushed ice
Focusing Your Learning
Lab Objectives
By the end of this lesson, you should be able to:
1. Determine the molarity of saturated salt solutions.
2. Calculate Ksp and percent error.
Procedures
Preparation
1. You will have to calibrate your dropper pipette to determine the volume of a drop of water. Fill the dropper with distilled water. Add the water drop-by-drop to the 10.0 ml graduated cylinder, and count how many drops it takes to fill the graduated cylinder to a volume of exactly 1.00 ml. (Since this graduated cylinder is calibrated to tenths of a milliliter, you should be able to accurately measure the volume and estimate to hundredths.) Record the number of drops of distilled water it takes to fill a volume of 1.00 ml in the data table. (Hint: It may help to move the tip of the dropper as far into the graduated cylinder as possible to avoid getting drops on the side of the cylinder. This is also a good time to practice your skills in forming consistent drops and avoiding air bubbles.)
2. Repeat this process (Step 1 above) for calibrating the number of drops in 1.00 ml for the distilled water two more times. Average the three values. Record the average value on the data table.
3. Print out your data table.
4. Prepare two (2) ice water baths, by crushing enough ice to fill the Styrofoam cup and adding just enough water to cover the ice.
5. Into one of the ice water baths, place a 50 ml beaker about three-fourths full of distilled water. You use this solvent during experimentation. You will want your solvent to be as close to 0°C as possible.
6. Into the second ice water bath, place the other empty 50 ml beaker, which will be your reaction vessel during experimentation.
Experimentation
1. Place one (1) entire sample of the solid, premassed KCl in your mortar and pestle. Record the mass of KCl used in your data table. Grind the entire sample to the consistency of a fine powder, and pour the entire sample into the 50 ml beaker.
2. Using the 10.0 ml graduated cylinder and the dropper pipette, measure out exactly 2.0 ml of the chilled distilled water and add to the mortar. Swirl the water inside the mortar to dissolve any remaining salt. Pour this salt solution into the beaker that contains the ground up sample of salt. Record the volume of water added.
3. Add drops of the chilled distilled water in two-drop increments. Stir/swirl the solution to dissolve.
4. Continue to add these two-drop increments of chilled distilled water until the entire solid is dissolved. It is important to keep track of the total amount of chilled distilled water added in order to determine the point of saturation. Record this amount of water added in your data table.
5. Repeat Steps 1- 4 for three trials for the KCl.
6. Repeat Steps 1 – 4 using the NaCl, and perform three trials for this salt.
Assessing Your Learning
Calculations
1. Convert concentration of salt at the end of each of the six trials into molarities of KCl and NaCl, and record in your data table for each trial.
2. Write the dissociation reactions for both salts.
3. Determine the molarity of ions in the solution.
4. Write the formula for the Ksp of each salt.
5. Calculate the Ksp for each salt.
Discussion
1. The theoretical value for the Ksp of KCl at 0°C is 12, and, at the same temperature, the Ksp for NaCl is 32. Determine the percent error between these theoretical values and your experimental values.
Percent error = theoretical value – experimental value
________________________________________theoretical value X 100
2. Reference the graph (figure 13.18) on page 525 of your textbook. Why do you think the instructions for this lab included using chilled distilled water? In other words, why didn’t you simply use room temperature water?
3. Predict how the Ksp values of both salts would change if this experiment were done at temperatures above 90°C. Explain how the values would change when comparing both salts to each other.
Lab Report
Make sure to complete a full lab report and submit it via email by the due date.
Submission
Important information: Please follow the procedure below in the completion of your assignments.
Compose your responses to the questions in a word processing program. Run spell check. Review your work to make sure that you have completely answered all questions.
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Select the following link to upload: Lab 9.https://www.riolearn.org/_layouts/qmlink/perception.aspx?SESSION=4429490450216914
Title: Ksp Lab
Introduction
Barium is toxic to humans, yet patients are given a barium sulfate “cocktail” to drink before certain gastrointestinal x-rays. Since BaSO4 is opaque to x-rays, ingesting it enables medical professionals to find evidence of blockage or leakage throughout the gastrointestinal tract as well as other abnormalities without having to cut a patient open. The solubility product constant (Ksp) of BaSO4 is 1.1×10-11 , which indicates the amount that actually ionizes, is well below the toxicity threshold for humans.
Also in the human body, when levels of uric acid (a nitrogenous waste product from protein metabolism in the blood) exceeds the Ksp, the uric acid can precipitate out, especially in the joints, leading to a painful arthritic condition known as gout.
In streams and rivers, as water moves through soil and rock, it dissolves small amounts of minerals and holds them in solution. Calcium and magnesium dissolved in water are the two most common minerals that make water “hard.” In many places where water is “hard,” people have water softeners. What the water softener does is replace the calcium ions in the water with sodium (or potassium) ions. This ion exchange is done to take out the ions whose Ksp is large enough to precipitate out of solution and cause scale or lime deposits. The ions that are replaced in the solution have a Ksp small enough that they will not precipitate out.
Ksp is just a simplification of Keq. For the ionization equation below:
Since the concentration of a solid ([Ax By]) does not appreciably change, you simplify the Keq of an ionization or dissociation equation to:
Objectives
Determine the molarity of saturated salt solutions.
Calculate Ksp and percent error.
(a) Materials
The following materials were used in the laboratory experiment
• 3 Premassed samples of each:
(KCl) Water softener salt
(NaCl) Rock salt
• Mortar and pestle
• 2-50 ml Beakers
• 10.0 ml Graduated cylinder
• 2 Styrofoam cups
• Thermometer
• Stirring spoon
• Distilled water
• Crushed ice
(b)Procedures
1. You will have to calibrate your dropper pipette to determine the volume of a drop of water. Fill the dropper with distilled water. Add the water drop-by-drop to the 10.0 ml graduated cylinder, and count how many drops it takes to fill the graduated cylinder to a volume of exactly 1.00 ml. (Since this graduated cylinder is calibrated to tenths of a milliliter, you should be able to accurately measure the volume and estimate to hundredths.) Record the number of drops of distilled water it takes to fill a volume of 1.00 ml in the data table. (Hint: It may help to move the tip of the dropper as far into the graduated cylinder as possible to avoid getting drops on the side of the cylinder. This is also a good time to practice your skills in forming consistent drops and avoiding air bubbles.)
2. Repeat this process (Step 1 above) for calibrating the number of drops in 1.00 ml for the distilled water two more times. Average the three values. Record the average value on the data table.
3. Print out your data table.
4. Prepare two (2) ice water baths, by crushing enough ice to fill the Styrofoam cup and adding just enough water to cover the ice.
5. Into one of the ice water baths, place a 50 ml beaker about three-fourths full of distilled water. You use this solvent during experimentation. You will want your solvent to be as close to 0°C as possible.
6. Into the second ice water bath, place the other empty 50 ml beaker, which will be your reaction vessel during experimentation.
Experimentation
1. Place one (1) entire sample of the solid, premassed KCl in your mortar and pestle. Record the mass of KCl used in your data table. Grind the entire sample to the consistency of a fine powder, and pour the entire sample into the 50 ml beaker.
2. Using the 10.0 ml graduated cylinder and the dropper pipette, measure out exactly 2.0 ml of the chilled distilled water and add to the mortar. Swirl the water inside the mortar to dissolve any remaining salt. Pour this salt solution into the beaker that contains the ground up sample of salt. Record the volume of water added.
3. Add drops of the chilled distilled water in two-drop increments. Stir/swirl the solution to dissolve.
4. Continue to add these two-drop increments of chilled distilled water until the entire solid is dissolved. It is important to keep track of the total amount of chilled distilled water added in order to determine the point of saturation. Record this amount of water added in your data table.
5. Repeat Steps 1- 4 for three trials for the KCl.
6. Repeat Steps 1 – 4 using the NaCl, and perform three trials for this salt.
Data Table(s) for Ksp Lab
Standardization of Dropper Pipette
Trial Number Number of drops = 1.0 mL
1 5 drops
2 6 drops
3 6 drops
Average number of drops = 1.0 mL 5.7 drpos
Experimentation and Calculation Summary
Trial
Number Original
mass of sample (g) Volume of
water (mL) added to rinse salt Number of
drops of water added to saturation Total
volume (mL) water added Moles of
salt added Molarity
(M) of salt solution
NaCl – 1 2.5 2 12 2
NaCl – 2 2.5 2 12 2
NaCl – 3 2.5 2 12 2
KCl – 4 2.5 2 12 2
KCl – 5 2.5 2 12 2
KCl – 6 2.5 2 12 2
Sample calculations: Choose one trial and show all calculations. Include formulas used, and round molar masses to tenths. Ensure that your reporting of measured values are both precise and accurate, and calculated values include a consideration of significant digits.
Total volume of water added:
Moles of salt added:
Molarity of salt solution:
Calculations
1. Convert concentration of salt at the end of each of the six trials into molarities of KCl and NaCl, and record in your data table for each trial.
2. Write the dissociation reactions for both salts.
3. Determine the molarity of ions in the solution.
4. Write the formula for the Ksp of each salt.
5. Calculate the Ksp for each salt.
Discussion
1. The theoretical value for the Ksp of KCl at 0°C is 12, and, at the same temperature, the Ksp for NaCl is 32. Determine the percent error between these theoretical values and your experimental values.
Percent error = theoretical value – experimental value
________________________________________theoretical value X 100
2. Reference the graph (figure 13.18) on page 525 of your textbook. Why do you think the instructions for this lab included using chilled distilled water? In other words, why didn’t you simply use room temperature water?
3. Predict how the Ksp values of both salts would change if this experiment were done at temperatures above 90°C. Explain how the values would change when comparing both salts to each other.
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