DETERMINACIÓN COMPLEXOMÉTRICA DE LA DUREZA DEL AGUA POTABLE (VOLUMETRÍAS DE FORMACIÓN DE COMPLEJOS)

New Section

This video is part of a series on analytical chemistry practices at the University of Valladolid. The objective is to determine the hardness of drinking water using complexometric volumetry.

Determining Water Hardness

• Water hardness is defined as the content of calcium and magnesium salts in water.

• The hardness of water affects its quality for domestic and industrial purposes.

• Precipitation of calcium carbonate can cause issues with pipes and appliances.

• In this video, two types of hardness will be determined: total hardness and calcium hardness.

Total Hardness Determination

• Burette is filled with standardized ethylenediaminetetraacetic acid (EDTA) solution.

• Burette measures the volume of known concentration reagent used in the titration.

• A sample of tap water is taken and transferred to a flask.

• Ammonia buffer solution is added to maintain pH 10 for indicator reaction.

• Indicator solution (net) forms complexes with magnesium ions, turning the solution red-violet.

• EDTA solution is slowly added from the burette until a color change occurs, indicating complete reaction with calcium and magnesium ions.

• The color changes from red-violet to blue when all magnesium and calcium ions are complexed by EDTA.

Calcium Hardness Determination

• Similar procedure as total hardness determination, but only calcium ions are targeted.

• Sodium hydroxide is added to achieve pH 12 for indicator reaction.

• Indicator solution (murexide) forms complexes with calcium ions, turning the solution pink.

• EDTA solution is titrated until a color change occurs, indicating complete reaction with calcium ions.

Calculation

• By knowing the average volume of EDTA used in each determination and stoichiometric relationships, total hardness (in millimoles) can be calculated for the first determination. Calcium hardness is determined by the millimoles of EDTA used in the second determination. Magnesium hardness is calculated as the difference between total and calcium hardness.

• Water hardness is often expressed in milligrams of calcium carbonate per liter or parts per million of calcium carbonate.

New Section

This video provides a practical guide for conducting the water hardness experiment in the laboratory.

Experimental Procedure

• Follow the steps outlined in the video to perform the total and calcium hardness determinations.

• Take triplicate measurements for each determination.

• Observe color changes during titration reactions to determine endpoint.

• Record volumes of EDTA solution used for calculations.

Importance of Water Hardness Determination

• Water hardness measurement helps assess water quality for domestic and industrial purposes.

• Understanding water hardness can prevent issues with pipes and appliances due to scale formation.

New Section

The video concludes by summarizing key points about water hardness determination.

Key Points

• Total hardness represents the combined content of calcium, magnesium, and other polyvalent ions in water.

• Calcium hardness specifically measures the concentration of calcium ions in water.

• Magnesium hardness is calculated as the difference between total and calcium hardness.

• Water hardness is commonly expressed in milligrams of calcium carbonate per liter or parts per million of calcium carbonate.

• This experiment provides a practical approach to determine water hardness using complexometric volumetry techniques.