Gravimetric Analysis of Water Hardness Lab
In this lab you will determine how hard our tap water is by analyzing the calcium chloride content and comparing that content to a
water hardness scale. To accomplish this, gravimetric technique will be performed for a standard solution containing calcium
chloride and the results will be used to analyze the tap water, containing an unknown amount of calcium chloride.
Goggles and apron should be worn at all times in lab.
Suggested Materials:
Vacuum Filtration Setups
Filter Paper
1.0 M Sodium Carbonate
250 mL Beaker
25 mL Graduated Cylinder
100 mL Graduated Cylinder
Wash Bottle with Deionized Water
Stir Rod
Balance
Introduction to guided inquire lab.
For this lab you will not be given step by step procedures to follow. It is your task to work with your partner to determine your
own procedure for obtaining the necessary data that will enable you to determine the hardness of tap water.
To get you started, a list of suggest materials is above, and a chart showing the necessary data that needs to be collected or
calculate is below.
Requirements of Your Procedures:
1. Must address the reaction of tap water mixed with sodium carbonate in such a way as to obtain the mass of the precipitate that
is caught on the filter. 200.0 mL of tap water should be used with 20.0 mL of sodium carbonate.
2. Must address cleaning up the lab equipment as you proceed and the final disposal of the chemicals in the proper manner.
3. You should write your procedures in pencil, and must get it checked by Mr. Belland before you may begin.
Mass of “tap” filter paper
Mass of “tap” filter paper and solid
Calculated mass of “tap” solid
Lab Report Requirement:
In a neat, well written, grammatically correct report that is written in ink or typed include the following:
1. The purpose of this lab, in detail
2. The procedures you followed, step by step
3. The data table and the data to complete it.
4. Detailed completion of the Calculations and Analysis questions.
Calculations and Analysis:
1. Assume the source of calcium in the tap water is calcium chloride, which you then reacted with sodium carbonate. Write
a balanced equation for this reaction.
2. How many moles of calcium chloride were originally in the tap water?
3. What is the concentration, in Molarity, of the calcium chloride in the tap water?
4. Your calculation from calculation #3 expresses the hardness of the tap water, but in molarity. Most water hardness scales
are expressed in parts per million, ppm. To convert the molarity of calcium ion into parts per million, the ratio is 1 M =
40,000 ppm. What is the hardness of the tap water in ppm?
5. Below is a water hardness scale. What is the classification of our tap water?
PPM
Classification
< 17.1
Soft
17.1-60
Slightly Hard
60-120
Moderately Hard
120-180
Hard
>180
Very Hard