1. What Makes Hard Water Hard?
A gravimetric analysis with a purpose

2. Design an experiment to use a separation experiment based on relative strengths of interactions between and among the components of a mixture
Interpret data from an experiment that uses gravimetric analysis to determine the concentration of an ion in solution
Translate an observed chemical change into a balanced equation and justify the type of chemical equation based on the circumstances
Use stoichiometry to predict the results of performing a reaction in the laboratory and/or deviations from expected results
Lab Objectives

3. Lab period 1 objectives (pre lab)
Explain how the solubility of a salt affects its ability to dissolve in water
Define hard water and describe some of its properties
Calculate the amount of a salt in solution based on the mass of the recovered precipitate
Use solubility product constant information to determine how to remove a cation from solution
Identify potential health risks and first aid measures for selected reagents
Lab period 1 objectives (pre lab)

4. Hard Water Who lives in a house that has it? What is it?
What is done to treat it?
Hard Water

5. Pre Lab Questions 7 questions Outside resources
Question 5:Select an ion: Mg+2 , Ca+2 , Fe +2
Pre Lab Questions

6. Pre lab question 1 Soluble salts break apart into ions
Some salts are more soluble than others
A lower number of dissolved ions
Collection through filtration
Pre lab question 1

7. Pre lab question 2 Metallic ions Causes soaps to lather poorly
Formation of soap scum
Pre lab question 2

8. Insoluble precipitate that forms because of the presence of metal ions
Example:
Ca+2 (aq) + 2C17H35COONa(aq)  Ca(C17H35COO)2(s) + 2Na+ (aq)
Pre lab question 3

9. Ion exchange
Magnetic
Salt-free
Pre lab question 4

10. Mole ratio
Molarity = mol/L
Remove impurities
Pre lab question 5

11. A small Ksp value indicates a salt that is not very soluble
Easier to precipitate out of solution
Pre lab question 6

12. Pre lab question 7 Hazards and safety concerns Treatments:
Skin and eyes: flush with water
Nasal irritant: fresh air
Ingestion: drink 2-4 cups of milk (We’ll contact the nurse first)
Pre lab question 7

13. Review of Lab period 1 objectives
Explain how the solubility of a salt affects its ability to dissolve in water
Define hard water and describe some of its properties
Calculate the amount of a salt in solution based on the mass of the recovered precipitate
Use solubility product constant information to determine how to remove a cation from solution
Identify potential health risks and first aid measures for selected reagents
Review of Lab period 1 objectives

14. Analyze samples of water to quantify them for water hardness
Use this information to help an individual purchase a house in an area where a water softener is not needed
What’s the Purpose?

15. Preview Practice with Instrumentation and Procedure
Obtaining a precipitate
Metathesis
Solubility
What determines if a cation is soluble?
Complete precipitation of analyte
What is the role of the analyte (ion to be analyzed) in the reaction?
Removing the precipitate
What method(s) have been used previously?
Analyzing the precipitate
What do you think is going to be most important to do with your precipitate to get accurate, reasonable results from the reaction?
Preview

16. Instrumentation and procedure
Mix solutions
Collect precipitate
Vacuum filtration
Allow to dry over night
Weigh precipitate and filter paper tomorrow
Answer the Practice with I and P Questions (finish for homework)
Note: Difference between successive weighings of the dry precipitate and filter paper should not differ by more than g
Instrumentation and procedure

17. Procedure Development
Step by step procedure
Think about Pre Lab and I & P:
Factors affecting solubility
Limiting and excess reactants
The role of the analyte
Washing the precipitate
List of materials needed (quantities)
You have solutions of 0.5M Na2CO3 and CaCl2 (the water sample (20.0 mL)) available to you and any other hardware/glassware you need
Test 2 water samples (concentrated: the volume of the water samples have been reduced by 200 times)
Please use no more than 40 mL of each solution (conserve the lab materials)
Stoichiometry will help you figure this out (and allow you to determine the amount of precipitate to expect)
You must use vacuum filtration
Data table
Data
Observations
Procedure Development

18. Data collection and computation
Show all math for Questions 1 and 2
Express water hardness as mg/L as CaCO3
You know the mass of precipitate and the volume of the water sample…stoichiometry! Just don’t forget that the volume of the water samples have been reduced by 200 times (use this: 1mL sample/200mL original solution)
Data collection and computation

19. Lab Report Requirements
Include all parts of the lab report as usual in the usual order
Materials will include the items needed for the Practice with I and P as well as the Investigation
Specifics for the Procedures
Write a brief procedure for the Practice with Instrumentation and Procedure
Include a data table and observations after it
Answer the Practice with Instrumentation and Procedure Questions after the data table (show all work)
Include your procedure for the Investigation
Include the data table and observations after it
Answer the Data Collection and Computation Questions after it (show all work)
Determine your Percent Error for the Calcium Carbonate produced
Answer the Post Lab Assessment Questions as your Post Lab Questions
Lab Report is due by 3:20PM on Thursday, 3/17/16 via
Lab Report Requirements

20. Argumentation and documentation requirements
the following to me by 3:20 on Thursday, 3/10/16:
Sample #, hardness (in mg/L as CaCO3)
Write a letter to your client regarding your findings. One letter per group is due by 3:20 PM on Tuesday, 3/22 (use proper letter form)
What you did to determine water hardness
What you found
Which area you would recommend as having the lowest water hardness (remember, he’s hoping to find a location where a water softener will not be needed)
Make a recommendation for a type of water softener to use (if one is required)
Re-read the Explanation to Strengthen Student Understanding for additional information
Argumentation and documentation requirements