Water Chemistry Lab
Summary
Students get to analyze surface water (fres water) samples using a variety of techniques, and determine their hydrochemical facies.
Collapse
Context
Audience
Audience:
The lab is intended for Geology/ Environmental Science/ Chemistry majors who have some prior knowledge of college chemistry (typically sophomores or juniors).
The lab is intended for Geology/ Environmental Science/ Chemistry majors who have some prior knowledge of college chemistry (typically sophomores or juniors).
Skills and concepts that students must have mastered
The students have already been introduced to the theoretical background behind colorimetry, and ICP-AES analysis, and have used the ICP-AES for the analysis of aqueous solutions. They are also familiar with the preparation of standard solutions and the principles of dilution.
How the activity is situated in the course
Three hour lab in the 7th week of a semester long lab class.
Goals
Content/concepts goals for this activity
Learning Goals:
This lab is designed to teach the students practical methods of major element analysis of a water sample. Using a variety of techniques commonly used in industry, students will collect their own data on the concentrations of major cations and anions in previously filtered but unacidified water samples provided to them. They will then plot their results on a Piper diagram, and determine the hydrochemical facies of their samples. Specific learning objectives include: (i) introduction to the principles of colorimetry; (ii) electrical neutrality; (iii) units of concentration and expressing analytical results in meq./litre; TDS; (iv) charge balance error calculations; (v) titrations and end-points; (vi) hardness and alkalinity; (vii) pH and conductivity.
This lab is designed to teach the students practical methods of major element analysis of a water sample. Using a variety of techniques commonly used in industry, students will collect their own data on the concentrations of major cations and anions in previously filtered but unacidified water samples provided to them. They will then plot their results on a Piper diagram, and determine the hydrochemical facies of their samples. Specific learning objectives include: (i) introduction to the principles of colorimetry; (ii) electrical neutrality; (iii) units of concentration and expressing analytical results in meq./litre; TDS; (iv) charge balance error calculations; (v) titrations and end-points; (vi) hardness and alkalinity; (vii) pH and conductivity.
Higher order thinking skills goals for this activity
Data interpretation.
Other skills goals for this activity
Operating analytical equipment
Description of the activity/assignment
Activity:
The students are split into two groups. Each group is provided with the same set of water samples that are filtered, but unacidified (typically, I provide them with 2 different samples of surface waters; either stream or lake water). One of the groups is charged with determining the concentrations of Na, K, Mg, and Ca in solution using the ICP-AES after calibration, while the other group is charged with determining the concentrations of sulfate, chloride, carbonate and bicarbonate in the same solutions. I suggest providing the second group with at least 500 ml of each sample.
Group 1 (Cations):
This group is given the assignment of determining the pH and conductivity of their unknown samples using a pH meter, and then determining the concentrations of Na, K, Mg, and Ca in their solutions. Because students have already been exposed to ICP-AES analysis, they are basically on their own. They have to decide on which analytical lines (wavelengths) to use for each element (using the manuals provided with the instrument or its software), and whether they can analyze for the four cations simultaneously or separately. They also need to decide on the concentration ranges of standards to be used, knowing that they are provided with samples of "Fresh" water. They are also encouraged to do "standardless analysis" for their two samples using the ICP-AES to figure out concentration ranges/ necessary dilutions. Students will then prepare their standard solutions, create a calibration curve, and analyze their two samples. At the end of the lab period, this group will provide everyone in the lab with the following: (i) pH, (ii) conductivity in ïS and expressed as TDS, and (iii) the concentrations of Na, Ca, Mg, and K in ppm.
Group 2 (Anions):
This group will measure:
The students are split into two groups. Each group is provided with the same set of water samples that are filtered, but unacidified (typically, I provide them with 2 different samples of surface waters; either stream or lake water). One of the groups is charged with determining the concentrations of Na, K, Mg, and Ca in solution using the ICP-AES after calibration, while the other group is charged with determining the concentrations of sulfate, chloride, carbonate and bicarbonate in the same solutions. I suggest providing the second group with at least 500 ml of each sample.
Group 1 (Cations):
This group is given the assignment of determining the pH and conductivity of their unknown samples using a pH meter, and then determining the concentrations of Na, K, Mg, and Ca in their solutions. Because students have already been exposed to ICP-AES analysis, they are basically on their own. They have to decide on which analytical lines (wavelengths) to use for each element (using the manuals provided with the instrument or its software), and whether they can analyze for the four cations simultaneously or separately. They also need to decide on the concentration ranges of standards to be used, knowing that they are provided with samples of "Fresh" water. They are also encouraged to do "standardless analysis" for their two samples using the ICP-AES to figure out concentration ranges/ necessary dilutions. Students will then prepare their standard solutions, create a calibration curve, and analyze their two samples. At the end of the lab period, this group will provide everyone in the lab with the following: (i) pH, (ii) conductivity in ïS and expressed as TDS, and (iii) the concentrations of Na, Ca, Mg, and K in ppm.
Group 2 (Anions):
This group will measure:
- The sulfate concentration in mg/l (using the Hach spectrophotometer). They need to calibrate the spectrophotometer first using the standard solutions provided (I suggest having those standards pre-prepared for them), and then determine the concentrations using the calibration technique which uses the SulfaVer-4 method.
- The chloride concentration using the digital titrator (silver nitrate method).
- The hydroxide, carbonate, and bicarbonate alkalinity values using the digital titrator.
- The total Hardness of the sample using the digital titrator.
Determining whether students have met the goals
Assessment:
Assessment can be based in part on students providing a report with their analytical results and interpretations, as well as details of their analytical techniques. Good book-keeping skills should be rewarded.
More information about assessment tools and techniques.Assessment can be based in part on students providing a report with their analytical results and interpretations, as well as details of their analytical techniques. Good book-keeping skills should be rewarded.
Teaching materials and tips
Other Materials
- Supplementary Material (Acrobat (PDF) 55kB Jun10 10)
Supporting references/URLs
Supplementary Material/ Resources:
I suggest providing the students with a handout with the necessary definitions, as well as a copy of a Piper diagram. Students can also download the program: GW_chart from the USGS website for free and use it to plot their data. The program can be downloaded from: http://water.usgs.gov/nrp/gwsoftware/GW_Chart/GW_Chart.html.
Assigned readings can also be helpful.
I suggest providing the students with a handout with the necessary definitions, as well as a copy of a Piper diagram. Students can also download the program: GW_chart from the USGS website for free and use it to plot their data. The program can be downloaded from: http://water.usgs.gov/nrp/gwsoftware/GW_Chart/GW_Chart.html.
Assigned readings can also be helpful.