WHAT MAKES HARD WATER HARD A gravimetric analysis

WHAT MAKES HARD WATER HARD? A gravimetric analysis with a purpose

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

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)

Who lives in a house that has it? What is done to treat it? HARD WATER

7 questions Outside resources Question 5: Select an ion: Mg+2 , Ca+2 , Fe PRE LAB QUESTIONS +2

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

Metallic ions Causes soaps to lather poorly Formation of soap scum PRE LAB QUESTION 2

Insoluble precipitate that forms because of the presence of metal ions Example: Ca+2 (aq) + 2 C 17 H 35 COONa(aq) Ca(C 17 H 35 COO)2(s) + 2 Na+ PRE LAB QUESTION 3 (aq)

Ion exchange Magnetic Salt-free PRE LAB QUESTION 4

Mole ratio Molarity = mol/L Remove impurities PRE LAB QUESTION 5

A small Ksp value indicates a salt that is not very soluble Easier to precipitate out of solution PRE LAB QUESTION 6

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

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

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?

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

Mix solutions Collect Vacuum filtration Allow to dry over night precipitate 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 0. 001 g INSTRUMENTATION AND PROCEDURE

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. 5 M Na 2 CO 3 and Ca. Cl 2 (the water sample) 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 m. L of each solution (conserve the lab materials) You must use vacuum filtration Data table Data Observations PROCEDURE DEVELOPMENT

Show all math for Questions 1 and 2 Express water hardness as mg/L as Ca. CO 3 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: 1 m. L sample/200 m. L original solution) DATA COLLECTION AND COMPUTATION

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) Answer the Post Lab Assessment Questions as your Post Lab Questions Lab Report is due by 3: 20 PM on Wednesday, 3/25/15 via email LAB REPORT REQUIREMENTS

Email the following to me by 3: 20 on Tuesday: Sample #, hardness (in mg/L as Ca. CO 3) Write a letter to your client regarding your findings. One letter per group is due by 3: 20 PM on Friday, 3/27 (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