Example: dental hygienist

EDTA Titrations 2: Analysis of Calcium in a …

CHEMICAL, ENVIRONMENTAL, AND BIOTECHNOLOGY. DEPARTMENT. EDTA Titrations 2: Analysis of Calcium in a Supplement Tablet; Analysis of Magnesium in Epsom Salt; Hardness of Water by Professor David Cash September, 2008. Mohawk College is the author and owner of these materials (excluding copyright held by others) and all copyright and intellectual property rights contained therein. Use of these materials for teaching or other non-commercial purposes is allowed. Contact information for Mohawk College will be found on the following page. This Experiment is a 3 hour Analytical Chemistry laboratory exercise.

1 Experiment 6 Complexometric Titration (2): Use of an EDTA Solution to Analyse for Calcium and Magnesium and to Determine the Total Hardness of Tap Water

Tags:

  Date, Analysis, Titrations, Edta titrations 2, Analysis of calcium, Calcium

Information

Domain:

Source:

Link to this page:

Please notify us if you found a problem with this document:

Other abuse

Transcription of EDTA Titrations 2: Analysis of Calcium in a …

1 CHEMICAL, ENVIRONMENTAL, AND BIOTECHNOLOGY. DEPARTMENT. EDTA Titrations 2: Analysis of Calcium in a Supplement Tablet; Analysis of Magnesium in Epsom Salt; Hardness of Water by Professor David Cash September, 2008. Mohawk College is the author and owner of these materials (excluding copyright held by others) and all copyright and intellectual property rights contained therein. Use of these materials for teaching or other non-commercial purposes is allowed. Contact information for Mohawk College will be found on the following page. This Experiment is a 3 hour Analytical Chemistry laboratory exercise.

2 It is designed for students in a common second term course of a 2-year diploma program (Biotechnology, Environmental, or Health Technician). For Information or Assistance Contact: MOHAWK COLLEGE. CHEMICAL, ENVIRONMENTAL, AND. BIOTECHNOLOGY DEPARTMENT. Professor Cindy Mehlenbacher 905-575-1212 ext. 3122. Bill Rolfe (Chief Technologist). 905-575-2234. Experiment 6. Complexometric Titration (2): Use of an EDTA Solution to Analyse for Calcium and Magnesium and to Determine the Total Hardness of Tap Water OBJECTIVE. Complexometric volumetric Titrations with EDTA (ethylenediaminetetraacetic acid) will be performed.

3 The comprehension and skills learned will be transferable to other laboratory and workplace situations. A secondary standard EDTA solution will be employed to determine the Calcium ion content of a dietary supplement tablet. A secondary standard EDTA solution will be employed to determine the percent by mass of magnesium ion in a sample of Epsom Salt (nominally magnesium sulfate heptahydrate). A secondary standard EDTA solution will be employed to determine the total hardness of a tap water sample. REFERENCE. Harris, Chapter 3, pages 265-281. INTRODUCTION. Reaction of EDTA with Calcium Ions and Magnesium Ions In contrast with a metal such as zinc, the EDTA complexes of Calcium and magnesium are not as stable.

4 For the metal ions in water: Zn2+ (aq) + EDTA4- (aq) Zn(EDTA)2- (aq) Kf = 1016. Ca2+ (aq) + EDTA4- (aq) Ca(EDTA)2- (aq) Kf = 1010. Mg2+ (aq) + EDTA4- (aq) Mg(EDTA)2- (aq) Kf = 108. pH Requirement for Titration of Calcium and Magnesium with EDTA. Since EDTA is an acid substance with four weak acid dissociations, the reactions with metal ions are pH dependent. The metals that react strongly with EDTA can be titrated in acidic solution. Zinc is an example. The metals that react more weakly with EDTA must be titrated in alkaline solution. Calcium and magnesium are examples.

5 To ensure consistent results of Titrations , the pH of the solutions must be controlled by using buffer solutions. The minimum pH required for successful titration of Calcium ions with EDTA. is about 8, and that for magnesium ions is about 10. Both of these metals are difficult to titrate with EDTA, especially magnesium. 1. Epsom Salt Epsom salt is the common name for magnesium sulfate heptahydrate (MgSO4 7H2O). This substance is found as a mineral deposit in several places around the world. It has uses in the dyeing industry, as a plant growth fertilizer, and as a solution in water that can be used to draw excess water out of the feet by soaking the feet in the solution.

6 It is sold in the pharmacy and supermarket for consumer use. The mineral Kieserite is magnesium sulfate monohydrate (MgSO4 H2O), a second stable hydrate of magnesium sulfate. Anhydrous magnesium sulfate (MgSO4) absorbs water strongly. It is used in chemical synthesis as a means of removing traces of water from organic substances as part of a purification process. Measurement of Total Hardness of Water Samples Total hardness is usually measured in one of two ways. It is measured either by a titration using EDTA, or by a soap titration method. In the EDTA titration, it is assumed that the total hardness is due to the presence mainly of Calcium and magnesium ions.

7 A sample of the water buffered at pH 10 is titrated with a standard solution of EDTA. The calculation is based on an equation written as if all the hardness were due to Calcium carbonate. The reaction is 1 mol to 1 mol. CaCO3 + EDTA4 (aq) Ca(EDTA)2 (aq) + CO32 (aq). Calculation of Total Hardness The total hardness can be calculated from the titration values. The units of hardness are based on the fictional assumption that the hardness ions are all Calcium : Water Hardness = mg / L or ppm of CaCO3. Definition of the ppm Unit for a Dilute Aqueous Solution For very dilute solutions in water, since the mass of L of the solution is very close to that of L of pure water, the total mass is very close to kg = 1000 g = 1,000,000 mg.

8 On this assumption, the solute concentration of a dilute aqueous solution in units of mg / L is called parts per million, or ppm. Be Very Careful About the ppm Unit. There is a different definition of ppm for solid mixtures and yet another for gaseous mixtures. 2. Sample Calculations Analysis of a Calcium Supplement Tablet Example 1. A supplement tablet containing (nominally) about 300 mg of Calcium ion was dissolved, filtered, and diluted to 100 mL volume. Several mL samples of the total solution were titrated with M EDTA solution by the method of this experiment. The mean corrected titration volume was mL ( L).

9 Calculate the Calcium content of the supplement tablet in mg units. State the value to the nearest mg. Answer One way to calculate the result is shown: Mass of Volume Molarity 1 mol Calcium g Calcium 1000 mg Calcium = . EDTA (L) EDTA (mol / L) . (mg) 1 mol EDTA 1 mol Calcium 1g Calculates Converts to Converts to Converts to mol of EDTA mol of Calcium g of Calcium mg of Calcium in Sampled Volume 100 mL Total Volume . 2 mL Sampled Volume Converts to Total mg of Calcium Mass of 1 mol Calcium g Calcium Calcium = L mol / L . (mg) 1 mol EDTA 1 mol Calcium 1000 mg 100 mL Total Volume.

10 1g 2 mL Sampled Volume Mass of Calcium = 274 mg This Section Continues on the Next Page . 3. Sample Calculations (Cont.). Analysis of an Epsom Salt Sample Example 2. A sample of Epsom Salt of mass g was dissolved uniformly in distilled water in a 250. mL volumetric flask. Portions of the magnesium ion solution of volume 10 mL were titrated using a M solution of EDTA by the method of this experiment. The mean corrected titration volume was mL ( L). Calculate the percentage by mass (% w / w) of the magnesium in the Epsom Salt sample. State the value to two (2) places after the decimal point.


Related search queries