Environmental Engineering Lab 06: Water Acidity

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Questions and Answers

What color change indicates that the titration with NaOH is complete for mineral acidity?

Colorless to faint orange

Pink to colorless

Faint orange to yellow (correct)

Colorless to pink

What is the volume of NaOH used in the mineral acidity calculation referred to as?

VA (correct)

Which equation correctly defines the total acidity in mg/L as CaCO3?

Total Acidity = (VA/VN) x 50000

Total Acidity = (VBN/VA) x 50000

Total Acidity = (VAN/VS) x 50000 (correct)

Total Acidity = (VB / VS) x 50000

What initial observation is made when phenolphthalein is added to the sample before titration?

The solution remains colorless Signup and view all the answers

In the formula for CO2 acidity as CaCO3, how is CO2 acidity determined?

CO2 Acidity = Total Acidity - Mineral Acidity Signup and view all the answers

When titrating for total acidity, which color indicates that the titration is complete?

Colorless to pink Signup and view all the answers

What is represented by VS in the acidity calculations?

Volume of sample Signup and view all the answers

What is the normality of the NaOH solution used in the titration procedures?

0.02N Signup and view all the answers

What is the primary component of acidity in unpolluted surface water?

Dissolved carbon dioxide Signup and view all the answers

What is the significance of measuring water acidity?

It influences chemical and biological processes. Signup and view all the answers

At what pH is mineral acidity generally measured using methyl orange?

4.5 Signup and view all the answers

What must be the pH level for biological treatment of wastewater?

6 to 9.5 Signup and view all the answers

Which indicator is used for measuring carbon dioxide acidity in water samples?

Phenolphthalein Signup and view all the answers

Why are waters with mineral acidity considered unacceptable?

They pose corrosion problems. Signup and view all the answers

When adding methyl orange indicator to a sample, what does a green/blue color indicate?

Absence of methyl orange acidity Signup and view all the answers

What is the effect of acidic waters on water treatment processes?

They interfere with treatment. Signup and view all the answers

Study Notes

Environmental Engineering Lab 06: Determination of Water Acidity

Aim: To determine the acidity of a given water sample.
Theory:
Water acidity is its capacity to neutralize a strong base to a specific pH.
It measures the amount of base needed to neutralize a sample to a specific pH.
Acidity depends on the end-point pH or indicator used.
Dissolved CO2 is often the major component of acidity in unpolluted water.
Acidity is important as it contributes to corrosiveness and influences chemical and biological processes.

Significance

Significance: Acidity from free carbon dioxide is not a significant public health concern, but mineral acidity in water is problematic.
Corrosion: Acidic water causes more corrosion issues.
Water Treatment: Acidic water interferes with water softening and treatment processes.
Biological Treatment: Biological wastewater treatment requires a pH between 6 and 9.5, thus highly acidic water needs pH adjustment before treatment.

Principle

Mineral Acidity: Measured by titration to a pH of approximately 4.5 using methyl orange as an indicator. Carbon dioxide acidity is neutralized completely to reach a pH of 8.3 using phenolphthalein as an endpoint. This measures both mineral and CO2 acidity.

Required Apparatus and Solutions

Solutions: 0.02 N NaOH, 1% phenolphthalein indicator, 1% methyl orange indicator,
Equipment: Conical flask, burette, burette stand, funnel, magnetic stirrer, magnetic bar, beaker (50 mL), dropper.

Procedure (Mineral Acidity)

Step 1: Take 50 mL of sample in a conical flask and add 2 drops of methyl orange indicator.
Step 2: If solution turns green/blue, no mineral acidity is present.
Step 3: If faint orange color, titrate with 0.02 N NaOH until the color changes to yellow.
Step 4: Record the volume of NaOH used (VA).
Mineral Acidity Calculation: Mineral Acidity (mg/L as CaCO3) = (VA × N × 50000)/Vs where: VA = volume of NaOH in mL, N = Normality of titrant, Vs = volume of sample

Procedure (Total Acidity)

Step 1: Take 50 mL of sample in a conical flask and add 2 drops of phenolphthalein indicator.
Step 2: Initially, the solution is colorless.
Step 3: Titrate with 0.02 N NaOH until the appearance of a pink color.
Step 4: Record the volume of NaOH used (VB).
Total Acidity Calculation: Total Acidity (mg/L as CaCO3) = (VB × N × 50000)/Vs where; VB = volume of NaOH, N=Normality of the titrant, Vs=volume of sample

Results

Results Table (Mineral Acidity): Includes trials, initial and final readings, and NaOH added for lab samples and tap water.
Results Table (Total Acidity): Includes trials, initial and final readings, and NaOH added for lab samples and tap water.
Calculated values: Total Acidity, Mineral Acidity, and CO2 Acidity for each sample type.

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Description

Explore the procedures and significance of determining water acidity in this quiz. Learn how acidity affects water quality, including its implications for corrosion and treatment processes. Test your knowledge on the theory and practical applications related to water acidity.