Testing Procedure of Total Hardness(as CaCO3) in Water Sample

Testing Procedure of Total Hardness(as CaCO3) in Water Sample in our Lab

Water hardness (as CaCO₃) testing measures the total concentration of calcium and magnesium ions in water, expressed as milligrams per liter (mg/l) of calcium carbonate (CaCO₃).Hardness is a critical water quality parameter, affecting domestic, industrial, and agricultural water use. Excess hardness can cause scale formation in boilers, pipes, and appliances, which may affect on their working efficiency.

We, ProResearch Testing & Laboratory, followed the most common testing method is EDTA titration, which provides accurate results for total hardness.

Instruments, Glassware, and Chemicals Used in Water Hardness (as CaCO₃) Test :

Instruments and Glassware:

Burette (50 ml)- For precise titration of EDTA solution.
Pipette (10 ml or 2 ml)- For accurate sample measurement.
Conical Flask (250 ml) – For mixing the sample with reagents during titration.
Beaker (500 ml)- For preparing solutions.
Measuring Cylinder (100 ml) – For measuring distilled water or buffer solutions.
Volumetric Flask (1000 ml) – To prepare reagents.
Spatula – To measure indicator.
4 digit Analytical Balance – To measure the weight of reagent.
pH-meter- To check whether the pH of the sample is 10 after mixed with buffer solution.

Chemicals :

Ethylenediaminetetraacetic acid(EDTA) Solution (0.01 N)– Complexing agent that reacts with Ca²⁺ and Mg²⁺ ions.EDTA binds with Ca²⁺ and Mg²⁺, breaking the indicator-metal complex.
Eriochrome Black T (EBT) Indicator – Forms a wine-red complex with Ca²⁺ and Mg²⁺, signaling that all hardness-causing ions have been complexed by EDTA.
Ammonia-Ammonium Chloride Buffer (pH 10) – Maintains pH at 10 for optimal EDTA reaction.To prepare this buffer solution dissolve 16.9 g ammonium chloride (NH₄Cl) in 143 ml concentrated ammonium hydroxide (NH₄OH) and add 15-20 ml ammonia solution.
Distilled Water –For solution preparation and dilution. The conductivity of distilled water should be <5 μS/cm to prevent contamination.
Calcium Carbonate & Hydrochloric Acid – Calcium carbonate (CaCO₃) is poorly soluble in water, so direct dissolution in water is not possible.Dilute hydrochloric acid (HCl) is added to dissolve CaCO₃ by converting it into soluble calcium chloride (CaCl₂), which is fully soluble in water, allowing accurate preparation of a standard calcium solution.

Procedure for Water Hardness (as CaCO₃) Test :

Preparation of Standard 0.01N EDTA Solution	Weigh 3.723 g of EDTA in a small amount of distilled water, dissolve the EDTA. Transfer the solution into a 1-liter volumetric flask. Make up the volume to 1000 mL with distilled water and mix well. Store in a polyethylene bottles as these are chemical resistance and does not impact strength.
2. Standardization of 0.01 N EDTA Solution	Prepare standard CaCO₃ solution by dissolving 1 g in 250 ml of distilled water (equals 0.01 N).Add 10 ml distilled water, 5-6 ml HCl.Boil until it become dissolved.After then volume make up to 1000 ml. 10.00 mL of the standard CaCO₃ solution should be pipetted into a conical flask. Add 2 ml of Ammonia-Ammonium Chloride buffer . Add few amount of EBT indicator to it & titrate against the EDTA solution. The color become blue. Calculate the exact normality using the formula: N1V1 = N2V2 N1= Normality of CaCO₃ (0.01 N) V1= Volume of CaCO₃ solution (10 ml) N2= Normality of EDTA V2= Volume of EDTA used in titration( 10 ml) N₁V₁= N₂V₂ N₂=0.01 (N)
Sample Preparation	Take 100 ml (according to sample type) of the water sample into a 250 ml conical flask.If the titre value of the sample came very less in 100 ml sample,it has chance to get error result then the sample should be taken 250 ml or more.
Add Buffer Solution	Add 2 ml of Ammonia-Ammonium Chloride buffer (pH 10) to maintain pH.
Add Indicator	Add few amounts of Eriochrome Black T (EBT) indicator. The solution will turn wine-red if hardness is present.
Titration	Fill the burette with standard 0.01 N EDTA solution. Titrate the sample while stirring until the color changes from wine-red to clear blue (endpoint).
Calculation	Note the burette reading (ml of EDTA used) at the endpoint.Use the formula Total Hardness (as CaCO₃ in mg/L) = (Volume of EDTA(V₁) × 100 x 1000 × Strength of EDTA) / Sample Volume (V)

Purpose of Water Hardness (as CaCO₃) Testing :

Assess Water Quality: To determine if water is soft, moderately hard, or hard for household or industrial use.Hard water forms scale deposits in pipelines, boilers, heaters, and appliances, reducing efficiency and causing damage.
Protect Health: While hardness is not a direct health hazard, excessive hardness may lead to digestive discomfort in sensitive individuals.
Industrial Applications: Required for industries where water purity affects production, such as textiles, pharmaceuticals, and food processing.
Compliance with Standards: Ensures water meets BIS or other regulatory limits for hardness in drinking and industrial water.
Monitor Environmental Impact: Helps in monitoring water bodies to prevent environmental issues related to hard water.

Handling Mistakes to Avoid During Water Hardness (as CaCO₃) Testing :

Proper handling, careful titration, accurate measurement, and fresh reagents are essential for precise and reliable hardness testing. Following points can make error result –

Not maintaining pH : The EDTA reaction with calcium and magnesium is pH-sensitive. Incorrect pH leads to incomplete reaction or wrong endpoint detection.
Using of pure distilled water – To avoid contamination use pure & good quality distilled water. The conductivity of distilled water should be <5 μS/cm.
Using old Eriochrome Black T indicator : The indicator may not show a clear color change, causing inaccurate endpoint detection.
Improper rinsing of burette and pipette: Residual water or chemicals can dilute the reagents, leading to incorrect titration volume readings.
Adding excess indicator: Excess indicator can form stable complexes with calcium or magnesium, leading to false readings or higher EDTA consumption.
Titrating too fast: Rapid titration can cause overshooting of the endpoint, resulting in low hardness values.
Not standardizing EDTA accurately: If EDTA concentration is not correct, all subsequent results will be inaccurate.
Using contaminated glassware: Contaminants may introduce extra ions, leading to false higher hardness readings.
Incorrect sample volume measurement: Wrong sample volume directly leads to calculation errors in the final hardness result.

Conclusion of Water Hardness (as CaCO₃) Testing:

Water hardness (as CaCO₃) testing is a crucial analysis for evaluating the concentration of calcium and magnesium ions in water. This test helps in classifying water quality and determining its suitability for domestic, industrial, and agricultural use. Regular monitoring prevents problems like scaling, corrosion, and reduced appliance efficiency.By following the above-mentioned method, you can easily test the Total Hardness at any laboratory or manufacturing industry with the availability of the equipments and chemicals.This testing process ensures accurate results, which are crucial for quality control in various applications. Furthermore, if you can’t understand the procedure, you can check our real-time photo attached with this writing, which visually guides you through each step and enhances your understanding. Additionally, for those who prefer professional assistance or require more advanced testing, you can also reach out to Pro Research & Testing Laboratory for testing purposes.

FAQ on Water Hardness (as CaCO₃) Testing :

Q1: Why is hardness expressed as CaCO₃?
Ans: Calcium carbonate (CaCO₃) is used as a standard because it simplifies comparison and calculation, regardless of the actual forms of calcium or magnesium present.

Q2: What is considered acceptable hardness in drinking water?
Ans: According to BIS( IS 10500: 2012 amendment 4) water with up to 200 mg/L as CaCO₃ is acceptable. Beyond 600 mg/L, water is considered very hard. We recommend that hardness value should be <100 mg/L for drinking water.

Q3: Can hardness affect health?
Ans: Hard water is not harmful to health, but it can cause digestive discomfort in some people and may lead to skin dryness,hair health.

Q4: What are the main problems caused by hard water?
Ans: Hard water can cause scaling in pipelines and appliances, reduce soap efficiency, and increase energy costs due to scale buildup in heaters.

Q5: How often should water hardness be tested?
Ans: It is recommended to test water hardness regularly (once in a month), especially in areas prone to hard water or in industrial settings where water quality is critical.

Q6: What is the role of EDTA in the test?
Ans: EDTA is a chelating agent that binds with calcium and magnesium ions during titration, allowing the measurement of total hardness.

Q7: Why is the pH adjusted to 10?
Ans: A pH of 10 ensures that both calcium and magnesium ions react completely with EDTA, ensuring accurate results.

Q.8 Why do we use 0.01 N EDTA as a titrant not more stronger than that?
A: Using 0.01 M EDTA allows for controlled titration, where the endpoint can be easily observed without risk of overshooting, which commonly occurs with stronger solutions due to rapid reactions.If a stronger EDTA solution were used, the titration volume would be too small, leading to handling errors, while a weaker solution would require excessive volume, making the procedure time-consuming and inefficient.

Q9: How many times testing should repeat to get accurate result?
Ans: Minimum 3 times testing should be repeated.Average result should be calculated in 10% variation among the results.

How We Verified This Testing/Research Procedure :

This testing is done under qualified analysts in our lab.Continually monitored by expertise.Repeatedly testing is always done to get accurate result.

Written by
Anwesha Das (M.Sc Microbiology,BU)
Designation – Microbiologist

Reviewed by
Riya Ghosh (M.Sc. Food Technology, MAKAUT)
Designation – Chemist

Verified By
Dr. Jyotirmoy Kumar Dey (Phd,Chemistry)
Designation – Senior/Chief Chemist
Experience – 25 Years +