CEE 350 Lab 05: Water Alkalinity Analysis

Environmental Engineering (CEE 350) Lab #05: Determination of Water Alkalinity

• Aim: To determine the alkalinity of a given water sample.
• Instructor: Dr. M. T. Amin
• Date: 10/29/2024

Theory

• Alkalinity measures water's capacity to neutralize acids or resist pH changes, maintaining stability.
• Alkalinity primarily originates from bicarbonate, carbonate, and hydroxide ions.
• Total alkalinity = (HCO₃^-) + (CO₃^2-) + (OH^-) - (H⁺)
• Alkalinity is expressed as mg/L of CaCO₃.

Significance

• Determines a stream/river's capacity to neutralize acid pollution (e.g., acid rain).
• Provides guidance for adjusting coagulant doses in water and wastewater treatment processes, especially in coagulation, softening, and anaerobic digestion operation control.
• Indicates the presence of acid impurities from industrial discharges.

Principle

• Alkalinity measurement involves titrating the water sample with standard acid (HCl or H₂SO₄).
• Phenolphthalein indicator decolorizes at pH 8.3, signifying complete hydroxide and half carbonate neutralization.
• A sharp color change (yellow to pink/orange) at pH 4.5 signals complete neutralization of total alkalinity (OH^-, CO₃^2-, HCO₃^-).

Ions Contributing to Alkalinity

• OH^- + H⁺ → H₂O
• CO₃^2- + H⁺ ↔ HCO₃^-
• HCO₃^- + H⁺ → CO₂ + H₂O

Alkalinity in Water (due to Ions)

• All three ions (OH^-, CO₃^2-, HCO₃^-) cannot coexist in water solutions.
• Multiple possibilities for alkalinity types exist, including those caused by hydroxide, carbonate, or combinations.

Identification of Ions and Acid Volume

• Tables provide different scenarios for determining the appropriate ions present.
• Measures (mL) of acid (P & M) consumed at various end-points for various scenarios.

Required Apparatus and Solutions

• 0.02 N HCl Solution
• 1% Phenolphthalein Indicator
• 1% Methyl Orange Indicator
• 50 mL Beaker
• Burette and stand
• Conical Flask
• Funnel
• Dropper
• Magnetic Stirrer
• Magnet Stir (bar)

Procedure (Partial/Phenolphthalein Alkalinity (P))

1. Measure 50 mL of the water sample.
2. Add 2-3 drops of Phenolphthalein indicator.
3. Titrate with 0.02 N HCl until the pink color disappears.
4. Record the volume of HCl used.

Procedure (Total/Methyl Orange Alkalinity (M))

1. Measure 50 mL of the water sample.
2. Add 2-3 drops of Methyl Orange indicator.
3. Titrate with 0.02 N HCl until a color change to orange/pink occurs.
4. Record the volume of HCl used.

Calculation

• Phenolphthalein Alkalinity (mg/L as CaCO₃): (V_AN/V_S) × 50000 , where V_A=acid volume (mL), N=normality of acid, V_s=sample volume
• Total Alkalinity (mg/L as CaCO₃) = (V_BN/V_S) x 50,000, where V_B is the volume of acid used.

Results

• Tables for P and M alkalinity results for various trials and samples (lab sample, tap water) are included, along with standard guidelines for acceptable drinking water alkalinity values (200 mg/L).

Calculation for Determining Ions Contributing to Alkalinity

• Formulas for calculating hydroxide and carbonate alkalinity based measured volumes are provided.

This lab aims to determine the alkalinity of a water sample, highlighting its importance in water quality management. Students will learn about the components contributing to alkalinity and its relevance in neutralizing acid pollution and guiding water treatment processes. Through titration techniques, participants will gain hands-on experience in measuring water alkalinity.