Category: Quality test

Determination of total amount of cations in water

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Different types of metal salt are dissolved in natural, industrial or any other water. Therefore, the water contains different type of cations. The cations in water can be determined by using cation exchange resin. They are electron donors and consequent positively charged. Some common cations are Na+, K+, Mg2+, Ca2+, Fe2+ or Fe3+, Mn2+, Al3+. On the other hand, cation exchange resin contains negatively charged group. The most common group is sulfonate group, -SO3–. If the water passes through a cation exchange resin in hydrogen form then the resin except the metal ion from the water and leave equivalent hydrogen ion. In other words leave an equivalent amount of acid. It is just a substitution reaction.

M+ + R-H → R-M + H+

This total amount of acid can be determined by titration with NaOH solution.
Determination of total amount of cations in water

Regeneration
Initially the cation exchanger resin may be regenerated to introduce hydrogen ion into the resin. To regenerate a column, you have to pass HCl through the cation exchange resin. Then the following reaction occurs which is revise process of previous reaction.
R-M + HCl → R-H + MCl
Additional acid and metal salt are removed from resin by passing cation free water (distilled water).

Apparatus Required:

  • Cation exchange resin column
  • 250ml volumetric flasks
  • 20ml, 25ml pipette
  • Beakers
  • Graduated cylinder
  • pH meter and pH electrode
  • Wash bottle

Chemicals:

  • 2N HCl
  • Methyl orange indicator
  • AgNO3 solution
  • distilled water
  • litmus paper

Procedure:

  1. Took a long glass tube (as like burette) with stopcock and make a 25-30 ml long column by keeping some glass wool at the end point of the glass tube.
  2. Pass 250 ml 2N HCl through the column so that 3-4 ml solution is passing per minutes.
  3. Then rinse the column with distilled water until the elution becomes neutral (no acidity or pH is greater than 5.8). You can cheek it by the methyl orange or pH meter. Moreover, you can also use AgNO3 solution to check for the presence of Cl– ion; it indicates the presence of HCl. It should be noticed that always some water exist on the column.
  4. Take about 40 ml sample water with the pipette and pass 3-4 ml water per minutes through the column. Exit the elution and mark the upper level of the resin column.
  5. Now take 20ml sample water, then pass it through the column at same rate and collect the elution in a conical flask. At the moment, it should be noticed that the upper level of the resin column remain equal.
  6. Collect two more at same process.
  7. This resulting H+ (the collected water) can be determined by titration with NaOH using methyl orange indicator. Then calculated the original concentration of cations in water using the formula.

You can direct use the sample water. It may require diluted the water in case of higher concentration of cations. To dilute take 25ml sample water in a 250ml volumetric flask and fill up to the mark with distilled water.

Calculation
Generally, the total amount of cation in water is expressed as equivalent mineral acidity (EMA). It is the amount of equivalent calcium carbonate of per liter solution. If the volume of sample water is V ml, normality of the NaOH is B and the volume of the NaOH is A ml, then
EMA = (AᵡBᵡ50ᵡ1000)/V

Determination of chloride in water by mohr method

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Mohr method is one of the significant methods for determination of chloride in water. It is also known as Argentometric method. Chloride ion is a negatively charged ion. This method is appropriate for neutral or slightly alkaline water. Water sample is titrating against standard AgNO3 solution by using potassium chromate indicator. It is a precipitation titration method.

Table of Contents:

Sources of chloride in water
Generally, chloride ions are present in water as a different form of salts. The most common salts are NaCl, KCl, MgCl2 and CaCl2. They are extremely soluble in water. The Sources of chloride in water may be natural or human beings. The natural sources are surrounding rock or soil or seawater intrusion in coastal areas. Whereas, various human sources are fertilizers, road salting, wastewater from industries, animal feeds, septic tank effluents etc.

Limitation
The Mohr method for determination of chloride in water is a pH sophisticated method. It must be perform between the pH levels 6.5-9.0. It is better to carry out between the pH ranges 7-8. At upper pH level, the silver ions react with hydroxide ions and precipitated as silver hydroxide. In contrast, at lower pH level, potassium chromate may be converted into potassium dichromate (K2Cr2O7) and mask the end point. Consequently, accurate result cannot be obtained. If the water sample is acidic, then gravimetric method or volhard’s method is appropriate.
Ag+(aq) + OH–(aq) → Ag(OH)(s)
CrO42-(aq) → Cr2O72-(aq)

Theory of determination of chloride in water
The amount of chloride in water can be simply determined by titrating the collected water sample with silver nitrate solution by using potassium chromate indicator. The reaction is quantitative. The AgNO3 reacts with chloride ion in a 1:1 ratio. The result is expressed as ppm.

When silver nitrate solution is gradually added into the flask, then silver ions react with chloride ions and forms silver chloride. It is precipitated in bottom of the flask. The precipitation is white in color.
Ag+(aq) + Cl–(aq) → AgCl(s)

The end point of the titration takes place when all the chloride ions reacts and precipitated. Then slightly extra silver ions react with the chromate ions and form a brownish-red precipitate of silver chromate. The solubility product of silver chromate exceeded in the presence of additional silver ions, and then the precipitation occurs.
2Ag+ + CrO42-(aq) → Ag2CrO4(s)
Determination of chloride in water

Apparatus:
Conical flask, burette with stand, pipette, measuring cylinder, volumetric flask, beakers, wash bottle.

Reagents:
Deionized water, water sample, standard N/50 silver nitrate solution, pH test paper, sodium hydroxide solution, nitric acid, Indicator potassium chromate solution.

Procedures:

  1. Measure the pH of the water sample. Adjust the pH with nitric acid or sodium hydroxide, if needed.
  2. Take a 25 ml collected water sample into a conical flask.
  3. Add 2-3 drops potassium chromate (K2CrO4) indicator. The color of the water sample is turn into light yellow.
  4. Add standard N/50 silver nitrate solution from the burette and shake well. Titrate until the light yellow color changes to permanent brownish-red color (bricks-red color) precipitate with white color precipitate.
  5. Note the volume of silver nitrate added.
  6. Repeat the titration for concordant values.
  7. Calculate chloride ion concentration

Chloride ion concentration (mg/l) = (VSN× NSN ×35.45) ×1000/Vw
Where: VSN = volume of titrant used, NSN is normality of silver nitrate, and Vw = volume of water sample used (ml)

NB: If the collected water contains massive amount of Chloride ions such as sea water. Then it needs to be dilute into a volumetric flask.

Observations and Calculations:

Serial No Volume of collected water sample (ml) Burette readings (ml) Volume of silver nitrate solution (ml)
Initial Final
1
2
3

Concordant Volume of silver nitrate solution, VSN = …. ml

Normality of standard silver nitrate solution, NSN = 0.02N
Volume of silver nitrate solution, VSN = ……… ml
Volume of collected water sample, Vw = ……. ml
Normality of collected water sample, Nw = ?
Now, Nw can be calculated from the following normality formula
Nw ×Vw = NSN × VSN
Or, Nw = NSN × VSN / Vw

Amount of Chloride ions = Nw × equivalent weight of chlorine
= Nw × 35.45 g/lit
= Nw × 35.45 × 1000 mg/lit or ppm

Result: The Amount of Chloride in water sample is ——- ppm

Water testing kits

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The water testing kits are used for monitoring the quality of drinking water and controlling the important operational parameters. The kit is not given high level accurate result but it given a warp idea. This kit can help us by providing the idea about what is the condition of our water or check out how the treatment working on. Although we are not get exact result but this result is very important for us. Water test kit is the best technique to test the water quality in our home. There are several type water testing kits are used such as test strip, color disc, digital titration, drop count titration etc.

The water
testing kits are used for different quality test such as bacteria, Alkalinity, Arsenic, iron, lead, pesticides, pH, hardness, nitrites/nitrates, chlorine, chloride, dissolved oxygen, silica, phosphorus etc. Water test kit provides professional lab results in your own home within a short time. No mixing or measuring required.

Water ought to be uncontaminated and free from pathogenic organisms and unsafe chemicals. Contaminants in your drinking water system can lead to the severe health troubles. Some of them are described below:Water testing kits

Bacteria: E. coli and coliform Bacteria can cause serious illness or health problems.

Lead: Contaminants through the old brass plumbing components. It is an extremely poisonous metal and responsible for serious health problems such as effects on brain development and red blood cell, neurological and kidney damage. The highest level for lead in drinking water is 0.015 mg/L.

Arsenic: It is responsible for increasing the risk of bladder, lung, or skin cancer and cardiovascular disease. The highest level for arsenic in drinking water is 0.01 mg/L.

Pesticides: Contaminants through agricultural uses and responsible for increasing cancer rates.

Nitrates/nitrites: Contaminants through the fertilizers and animal waste or septic systems. It is responsible for oxygen deficiency in the blood, developmental and cancer problems. The maximum level for nitrate in drinking water is 10.0 mg/L.

Chlorine: It is responsible for raising cancer risk, bad taste and odor.

Hardness: It is responsible for lime scale, plumbing fixtures block, and higher detergent use.

pH: The pH is very important for industries such as boiler feed water. It is responsible for plumbing damage.

Alkalinity: It is caused by the presence of hydroxides, carbonates, bicarbonates, and other dissolved salts in the water. It is very important for food and beverage process or boiler water.

Iron: It is an essential element and has positive health effects for certain amount of level but negative effects for laundry and plumbing fixtures purpose.

Where to buy water testing kits
You can buy a water test kit from your neighboring residence center or online.

Determination of hardness of water by EDTA method

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Determination of hardness of water by EDTA method is one of the three main methods for determination of hardness of water. EDTA means Ethylenediaminetetraacetic acid. This EDTA reagent can be forming edta-metal complexes by the reaction with metal ions except for alkali metal ions. This reagent can forms a stable complex with the alkaline earth metal like calcium ion and magnesium ion in alkaline condition pH above 9.0. Therefore the total hardness of water can be determination by edta titration method.

In this method buffer solution is used for attain suitable condition i.e pH level above 9 for the titration. Buffer solution preserve pH at a balanced position. In aqueous solution edta exist as H2Y2- form. Hence edta react with alkaline earth metals as 1:1. As a result for every mole of alkaline earth metal ion in water sample, one mole of EDTA will be consumed during titration.

Reaction: H2Y2- + M2+ → MY2- + 2H+

During titration Eriochrome Black T is used as indicator. The indicator is red in color when it is forms complexes with the metal ions and blue in color when it is free.

Reaction: MIn– + H2Y2- → HIn2- + MY2- + H+

Determination of hardness of water by EDTA method is father classified into four methods.
Determination of hardness of water-1971

  • Ammonia Buffer procedure
  • Borate Buffer procedure
  • Low hardness procedure
  • Calcium hardness procedure.

Ammonia Buffer procedure: This type determination of hardness of water by EDTA method is especially preferred for those water, where is unfamiliar composition, sewage water, alkalinity or acidity high and for industrial waste water. This method can also be used for normal water. A high capability buffer solution is used to conquer buffering substance in the sample. It has mainly three disadvantages;

  • Utilize of ammonia buffer solution may perhaps not be acceptable if Nessler ammonia determination are being carried out in the same room.
  • If the water sample contains high in calcium ion and bicarbonate ion, it is a affinity for calcium carbonate to be precipitated.
  • The existence of magnesium in the titrant.

Borate Buffer procedure: Borate buffer method is a simpler among the determination of hardness of water by EDTA method. This method is to overcome the limitation of ammonia buffer method. This method does not liberate any ammonia; somewhat calcium carbonate precipitated but not totally holds back. It is not suitable for those water; which is unfamiliar water sample, contains acidity or high alkalinity, industrial waste and sewage.

Low hardness procedure: This is another type of determination of hardness of water by EDTA method. This method is used for waters of low hardness less than 5 mg/l and also for ionexchange effluent or other conditioning water.


Calcium hardness procedure: This method is used for determination of calcium hardness, but it is not standard accurate method for calcium.