TIÊu chuẩn xây dựng tcxd 81: 1981

2.7.1. Scope of application

This method is meant for determination of overall hardness of every kind of water.

2.7.2. Nature of the method

At pH - 10, calcium ions and magnesium ions react with eriochrome black T and create a dark red solution. When titrating with komplexon III, the compound of calcium and komplexon III is more stable, thus calcium and magnesium ions are detached from the initial compounds to combine with komplexon III. Anion of the indicator is released and the color of the solution turns from dark red to a distinctive blue at the equivalence point.

2.7.3. Chemicals

Komplexon III, 0.05 M solution: dissolve 18.613 g of komplexon III in distilled water (boiled and cooled twice); then filter the solution and add more distilled water until the volume reaches 1 l.

The titer of komplexon III is determined as follows: dissolve 5.005 g of analytical grade (a.g.) calcium carbonate dried at 105 ⁰C in dilute hydrochloric acid (1 + 1) using a 1-liter volumetric flask. Add hydrochloric acid slowly until no more carbon dioxide bubbles are seen. Boil the solution for a few minutes, leave it to cool down, add more distilled water until the volume reaches 1 l and gently shake the flask. Add distilled water to 20 ml of calcium chloride until the volume reaches 100 ml; add 10% sodium hydroxide until pH = 12 (test with paper indicator) and titrate with komplexon III with murexide indicator. Take the average value after three titrations.

The titer of komplexon III solution according to CaO is expressed as g/ml and calculated as follows:

Where:

V₂ - Volume of komplexon III used for titrating 20 ml of calcium chloride, expressed as ml.

The titer of komplexon III solution shall be determined every week.

+ Powdered calcium carbonate, analytical grade.

+ Sodium hydroxide, 10% solution

+ Murexide, in a mixture with sodium chloride (1 +50) in a brown glass jar.

+ Eriochrome black T, in a mixture with sodium chloride (1 +50).

+ Buffer solution pH = 10; mix 65 g of analytical grade ammonium chloride (NH₄Cl) with distilled water in a 1-liter volumetric flask. Add 350 ml of 25% ammonia solution and add more distilled water until the volume reaches 1 l.

2.7.4. Running the test

Pour 100 ml (if overall hardness reaches 15 German degrees), 50 ml (if overall hardness reaches 30 German degrees), 25 ml (if overall hardness exceeds 30 German degrees) of water sample into a 250-ml conical flask; add distilled water until the volume reaches 100 ml. Neutralize alkalinity of the water sample with 0.1 N hydrochloric acid (the amount of acid used for titration of total alkalinity); add 5 ml of buffer solution and 0.1 - 0.2 g of eriochrome black T; titrate the solution with komplexon III until the color red turns blue.

2.7.5. Result calculation:

Overall hardness (expressed as German degree) is calculated as follows:

Where:

T - Titer of komplexon III according to CaO, expressed as g/ml;

V - Volume of water sample, expressed as ml.

2.8. Hardness without carbonate.

The hardness without carbonate (expressed as Germany degree) is calculated as follows:

X₇= X₆ - X₅

Where:

X₆ - Overall hardness, expressed as German degree;

2.9 Bicarbonate (HCO^-₃) and carbonate (CO₂^-)

The amount of bicarbonate and carbonate ions is calculated according to total alkalinity and free alkalinity according to Table 3.

Table 3 - Calculation of concentration of bicarbonate and carbonate ions

Ratio of free alkalinity to total alkalinity	Bicarbonate (HCO3- )		Carbonate (CO2-3 )
	mg- dl/l	mg/l	mg-dl/l	mg/l
1	2	3	4	5
X1 =0 2X1 2 2X1= X2 2X1 > X2 X1= X2	X2 X2- 2X1 0 0 0	X2.61 (X2-2X1).61 0 0 0	0 2X1 2X1 2(X2-X1) 0	0 2X1.30 2X1.30 2(X2-X1).30 0

Where:

X₁ - Free alkalinity, expressed as mg – dl/l (see 2.3);

X₂ - Total alkalinity, expressed as mg – dl/l (see 2.3);

61 - Equivalent amount of HCO₃^-;

30 - Equivalent amount of CO^2-₃;

TCXD 81 : 1981

2.10. Calcium (Ca²⁺)

2.10.1. Scope of application

This method is meant for determination of calcium ions in water, common cations such as Mg²⁺, K⁺, Na⁺ and when the concentration of Fe³⁺, Al³⁺, Mn²⁺ , Cu²⁺ is low (iron < 20 mg/l, aluminum < 5 mg/l, manganese < 10 mg/l, copper < 2 mg/l).

2.10.2. Nature of the method

In an alkaline environment (pH = 12), calcium ion reacts with murexide and create a compound that makes the solution turn into a dark red color. When titrating with komplexon III, the compound between calcium and komplexon III is more stable that the compound between calcium and murexide, thus the calcium ions are released from the initial compound and combine with komplexon III. The solution then turns into a distinctive violet-blue color at the equivalence point, which is the color of murexide anions released.

2.10.3. Chemicals

+ Komplexon III, 0.05 M solution. See preparation in 2.7.3.

+ Sodium hydroxide, 10% solution

+ Murexide, in a mixture with sodium chloride (1 +50) in a brown glass jar.

2.10.4. Running the test

Pour 100 ml (if calcium concentration reaches 300 mg/l), 50 ml (if calcium concentration reaches > 300 to 500 mg/l), 25 ml (if calcium concentration exceeds 500 mg/l) of water sample into a 250-ml conical flask; add distilled water until the volume reaches 100 ml.

Notes: If the total alkalinity of the water sample exceeds 6mg dl/l, it shall be neutralized with 0.1 N hydrochloric acid. Boil the solution for one minute, then leave it to cool down to determine calcium.

2.10.5. Result calculation

The concentration of calcium ion (Ca²⁺) (mg/l) is calculated as follows:

Where:

V₁ – Volume of komplexon III solution, expressed as ml;

T - Titer of komplexon III according to CaO, expressed as g/ml;

(V₂ is the volume of komplexon III, use .0.0020 to titrate 20 ml of calcium chloride solution, expressed as ml, according to 2.7.3);

V - Volume of water sample, expressed as ml.

2.11. Magnesium (Mg²⁺)

2.11.1. Scope of application

This method is meant for determination of magnesium ion in natural water where concentration of Fe³⁺, Al³⁺, Mn²⁺, Cu²⁺ is low (according to 2.10.1)

2.11.2. Nature of the method

At pH = 10, calcium ions and magnesium ions react with eriochrome black T and create a dark red solution. When titrating with komplexon III, the calcium and magnesium ions are released from the initial compounds and combine with komplexon III to create a more stable compound. The solution turns into a blue color at the equivalence point, which is the color of the indicator anion at pH = 10. Since calcium ions do not produce an obvious change in color, the titer can only be determined in this condition if magnesium ions are also present. Therefore, the quantity of magnesium ions is the difference between this titration and the titration of calcium ions when pH = 12.

2.11.3. Chemicals

Komplexon III, 0.05 M solution. See preparation in 2.7.3.

The titer of komplexon III solution according to magnesium (Mg²⁺) is determined as follows: Dissolve 6.0180g of anhydrous magnesium sulfate in 1 liter of distilled water; pour 20 ml of this solution in a 250-ml conical flask; add distilled water until the volume reaches 100 ml, add 3 - 5 ml of ammonia buffer solution until pH reaches 10 and titrate with komplexon III and eriochrome black T indicator three times, then calculate the average value.

The titer of komplexon III solution according to magnesium (Mg²⁺) is calculated as follows:

Where:

V₃ - Volume of komplexon III used for titrating 20 ml of magnesium sulfate, expressed as ml.

- Anhydrous magnesium sulfate, analytical grade.

- Buffer solution pH = 10. See preparation in 2.7.3.

- Eriochrome black T, in a mixture with sodium chloride (1 + 50).

- Triethanolamine hydrochloride, crystals, analytical grade

- Hydroxylamine hydrochloride, crystals, analytical grade

2.11.4. Running the test

Pour 100 ml (if total calcium and magnesium concentration reaches 300 mg/l), 50 ml (if total calcium and magnesium concentration reaches 300 - 800 mg/l), 25 ml (if total calcium and magnesium concentration exceeds 800 mg/l) of water sample into a 250-ml conical flask; add distilled water until the volume reaches 100 ml. The amount of water sample must be equal to the amount of water sample for calcium test.

Add 0.5 g of triethanolamine hydrochloride and 0.1 g of Hydroxylamine hydrochloride if concentration of Fe³⁺, Al³⁺,Mn²⁺ in the water sample is high.

Add buffer solution until pH reaches 10 and heat the solution to 40 - 50 ⁰C. Add an amount of 0.05 M komplexon III that is equal to the amount of komplexon III used or titrating calcium, then add 0.02 g of eriochrome black T and keep titrating with 0.05 komplexon III until the solution turns from dark red into blue. In this condition, calcium and magnesium have been titrated.

2.11.5. Result calculation

The concentration of magnesium ion (Mg²⁺) is expressed as mg/l and calculated as follows:

Where:

V₁- Volume of 0.05 M komplexon III used for titrating calcium, expressed as ml (see 2.10.4);

T - Titer of komplexon III solution according to magnesium (Mg²⁺), expressed as g/cm³

v - Volume of water sample, expressed as ml

2.12. Chloride (Cl^-)

2.12.1. Scope of application

This method is meant for determination of concentration of chlorine ions in water if exceeding 2 mg/l. With accuracy from 1 to 3 mg/l, up to 100mg/l of chlorine ion concentration may be determined. To accurately determine the concentration of chlorine ion that is below 10 mg/l, leave 250 - 300 ml of water sample to evaporate until the volume is 100 ml, then run the test.

Determination of chlorine is difficult if concentration of Hg²⁺, Pb²⁺, H₂S, H₂S, Fe³⁺ exceeds 10 mg/l and concentration of phosphate exceeds 25 mg/l.

2.12.2. Nature of the method

The determination of chlorine is based on precipitation of silver chloride from silver nitrate. When all chloride ions are reacted with, the solution will turn red at the equivalence point because of the precipitation of silver chromate. The reactions occur at pH = 10 y 10

2.12.3. Chemicals

Silver nitrate, 0.05 N solution. Dissolve 8.4945g of a.g. AgNO3 in distilled water using a 1-l volumetric flask and add more distilled water until the volume reaches 1 liter.

potassium chromate 5% solution;

2.12.4. Running the test

Pour 100 ml of filtered water sample in a 250-ml conical flask, add 1 ml of 5% potassium chromate and titrate with 0.05N silver nitrate until stable reddish orange precipitates are seen. If the concentration of chloride is small, titration shall be carried on until reddish brown sediment is seen. Run the test twice and calculate the average value.

Notes: To remove H₂S and HS^-, take an amount of water sample, acidize it with dilute nitric acid (1 + 5), boil the solution for 8 - 10 minutes, adjust until the pH reaches the initial level and then run the test. Remove organic substances by evaporate the water sample until it dry, heat it at 200 ⁰C, dissolve the dreg in dissolved water until the solution reaches the initial volume, and then run the test. When pH of the water sample is below 6, neutralize it with sodium bicarbonate. If pH of the water sample is above 10, neutralize it with dilute nitric acid (1 + 5).

2.12.5. Result calculation:

The concentration of chloride ion (Cl^-) is expressed as mg/l and calculated as follows:

Where:

N - Equivalent concentration of silver nitrate;

0.03546 - miliequivalent weight of chlorine;

V - Volume of water sample, expressed as ml.

2.13. Sulfate (SO^4-)

2.13.1. Scope of application

This method is meant for determination of concentration of sulfate ions in water.

Determination of sulfate is obstructed by impurities, high concentration of silicate and iron.

2.13.2. Nature of the method

In dilute hydrochloric acid, sulfate ions form a precipitate in the form of barium sulfate (BaSO₄) with barium chloride solution (BaCl₂)

2.13.3. Chemicals

+ Dilute hydrochloric acid (1 + 1).

+ Dilute hydrochloric acid (1 + 99).

+ Barium chloride, 10% solution.

Silver nitrate solution: dissolve 1g of a.g. AgNO₃ in distilled water; add 5ml of concentrated nitric acid, then add more distilled water until the volume reaches 100 ml.

+ Methyl orange, 1% solution.

2.13.4. Running the test

Pour 500 ml (if concentration of SO^2-₄ reaches 50 mg/l), 250 ml (if concentration of SO^2-₄ reaches > 50 - 200 mg/l), 250 ml (if concentration of SO^2-₄ reaches > 200 - 500 mg/l), or 50 ml (if concentration of SO^2-₄ exceeds 500 mg/l) of filtered water sample into a beaker; leave it to evaporate or dilute it until the volume reaches 100 ml; add 3 - 4 drops of methyl orange and hydrochloric acid (1 + 1) until the solution turns pink.

Boil the solution; add 10 ml of 10% barium chloride drop by drop while stirring. Boil the solution for 5 more minutes; cover the beaker with a plate of glass and put it on a double boiler for 2 - 4 hours to form barium sulfate precipitate; filter with ashless filter paper; rinse the precipitate on the filter paper with hot dilute hydrochloric acid (1 + 99), then rinse again with hot distilled water until chloride ions are no longer present in the rising water (no precipitates are formed in the rinsing water when more silver nitrate is added). Put the filter paper that contain barium sulfate precipitate in a beaker with a known weight; dry it at 105⁰C, burn and heat at 800⁰C for 30 - 40 minutes; stabilize the temperature in the desiccator and weigh it until its weight remains unchanged.

2.13.5. Result calculation

The concentration of sulfate ion (SO^2-₄), is expressed as mg/l and calculated as follows:

Where:

0.₄115 - coefficient for converting the weight of barium sulfate into SO^2-₄

V - Volume of water sample, expressed as ml.

2.14. Oxidization number

2.14.1. Scope of application

This method is meant for determination of oxidization number of water in which concentration of chloride does not exceed 300 mg/l.

2.14.2. Nature of the method

In sulfuric acid, potassium permanganate oxidizes the reducing agents in water. After boiling, add oxalic acid to reduce the amount of potassium permanganate that remains after reaction. Titrate the remainder of oxalic acid with potassium permanganate solution.

2.14.3. Chemicals

+ Potassium permanganate, 0.01N solution;

+ Dilute sulfuric acid (1 + 3).

+ Oxalic acid, 0.01N solution.

2.14.4. Running the test

Pour 100 ml of water sample in a 250-ml conical flask; add 5 ml of dilute sulfuric acid (l + 3); use a burette to add exactly 10 ml of 0.01N potassium permanganate. Boil the solution for 10 minutes. If the pink color of the solution is not vibrant, run the test again with less water sample and dilute it until the volume reaches 100 ml.

Add exactly 10 ml of 0.01N oxalic acid to the hot solution and titrate immediately with 0.01N potassium permanganate until the solution turns into a stable pink.

The temperature of the solution during the titration must not fall below 50⁰C.

Make a counterpart sample by replacing water sample with distilled water and follow the steps above.

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2.14.5. Result calculation

Oxidization number is calculated as follows:

Where:

V₁ - volume of 0.01 N potassium permanganate solution used for titrating the counterpart sample, expressed as ml;

N - Equivalent concentration of potassium permanganate;

8 - Equivalent amount of oxygen;

V - Volume of water sample, expressed as ml

2.15. Hydrogen sulfide and sulfides

2.15.1. Scope of application

This method is meant for determination hydrogen, sulfides, and various forms of sulfide ions in water with concentration of 10 mg/l.

2.15.2. Nature of the method

This method is based on direct titration of hydrogen sulfide and various forms of sulfide ions using iodine solution.

2.15.3. Chemicals

+ Iodine, 0.01N solution.

+ Starch, 0.5% solution.

+ Concentrated acetic acid.

2.15.4. Running the test

Add 200 ml of filtered water sample into a 500-ml flask; add 3 - 4 drops of acetic acid, 2 - 3 drops of starch solution, and titrate with 0.01N iodine solution until it turns into a light blue.

The test is repeated in the following order:

Pour an amount of 0.01N iodine solution that is equal to the amount used for the first titration, then pour 200 ml of water sample into the flask and add some drops of 0.5% starch solution. Then keep titrating with 0.01N iodine solution until the solution turns into a light blue.

Calculate the average value after two titrations.

2.15.5. Result calculation

The concentration of hydro sulfide and sulfide ions is expressed as mg/l and calculated as follows:

Where:

N - Equivalent concentration of iodine solution;

0.017 - Miliequivalent of H2S;

V - Volume of water sample, expressed as ml.

2.16.1. Scope of application

This method is meant for determination of nitrite in water that does not contain strong oxidizing and reducing agents. Determination of nitrite is obstructed by opaque and colored water, Fe³⁺, Hg²⁺ , Ag⁺, Bi²⁺, pb²⁺, Au³⁺, chlorplatinate, and metavanadate ions Cu²⁺ _­makes the result lower than actuality.

The influencing factors can be eliminated by diluting the water sample.

2.16.2. Nature of the method

The method is based on the diazotization reaction in acid between nitrite and a mixture of sulfanilic acid and - naphthylamine, which forms a pink dye.

2.16.3. Chemicals

- Sulfanilic acid, 0.6 % solution: Dissolve 6.0 g of a.g. sulfanilic acid in 750 ml of boiled distilled water; add 250 ml of acetic acid,

- Naphthylamine, 0.6% solution: Dissolve 1.2 g of a.g. naphthylamine in distilled water; add 250 ml of acetic acid and add more distilled water until the volume reaches 250 ml.

This solution can be used for 2 - 3 months.

- Sodium nitrite, solution I: Dissolve 0.1497g of a.g. NaNO₂ , which has been dried at 105⁰C, in distilled water; then add more distilled water until the volume reaches 1 liter. Add 1 ml of chloroform. Preserve the solution at a low temperature and it can be used for one month. A liter of solution I contains 0.100ml of NO₂^-

Solution II: dilute 100 ml of solution I by adding distilled water until the volume reaches 1 liter. Every ml of this solution contains 0.010mg of NO₂. Only prepare this solution before use.

Solution III: dilute 50 ml of solution II by adding distilled water until the volume reaches 1 liter. Every ml of this solution contains 0.0005mg NO₂. Only prepare this solution before use.

2.16.4. Drawing standard graph

Use distilled water to successively dilute 0; 0.5; 1; 1.5; 2; 2.5; 3 ml of solution II until the volume reaches 50 ml. The concentration of the new solution is 0; 0.1; 0.2; 0.3; 0.4; 0.5; 0.6 mg/l NO₂ respectively. Test each of them in the same way as testing the water sample. Measure color intensity of each solution using a photoelectric colorimeter

Draw a standard graph based on the measured optical density of the solutions. The vertical axis indicates optical density, the horizontal axis indicates corresponding concentration (mg/l).

2.16.5. Standardized color chart

Pour 0; 0.2; 0.5; 1.00; 1.500; 2.00; 2.50 ml of solution III in netle cylinders; successively dilute them with distilled water until the volume reaches 50 ml. Test the solutions successively in the same way as testing water sample. Respective concentrations of the new solutions are 0.000; 0.002; 0.003; 0.01; 0.015; 0.020; 0.025 mg/l NO₂.

2.16.6. Running the test

Pour 50 ml of water sample into a conical flask. If the initial volume is below 50 ml, dilute it with distilled water until the volume reaches 50ml. Add 1 ml of sulfanilic acid and shake gently. Leave the solution for five minutes, then add 1 ml of a-naphthylamine and shake gently. Measure the intensity of the solution using the photoelectric colorimeter after 40 minutes from the addition of a-naphthylamine; use a green filter glass (O = 520mm, cuvet thickness = 1 - 5 cm), or compare the color with the standard color chart with bare eyes.

2.16.7. Result calculation

The concentration of nitrite ion (NO₂) is expressed as mg/l and calculated as follows:

Where:

v - volume of water sample, expressed as ml

50 - Volume of diluted water sample, expressed as ml.

2.17. Nitrate (NO₃)

2.17.1. Scope of application

This method is meant for determination of nitrate with concentration of up to 1 mg/l in water where concentration of chloride does not exceed 200 mg/l, iron 5 mg/l, and nitrite 2 mg/l.

2.17.2. Nature of the method

This method is based on the reaction between nitrate and sodium salicylate in sulfuric acid, which creates a yellow salt of nitrosalicylic acid.

2.17.3. Chemicals.

+ Sodium salicylate, 0.5%.

+ Concentrated sulfuric acid.

+ Sodium hydroxide 10N: Dissolve 400g of a.g. NaOH in dissolved water. Add more distilled water until the volume reaches 1 liter when it has cooled down.

Potassium nitrate, solution I: Dissolve 0.1631g of a.g. KNO₃, which has been dried at 105⁰C, in distilled water; then add more distilled water until the volume reaches 1 liter.

Thus 1 ml of solution I contains 0.100mg of NO₃

Solution II: dilute 10 ml of solution I by adding distilled water until the volume reaches 100 ml. Every ml of solution II contains 0.010 mg of NO₃. Only prepare this solution before use.

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2.17.4. Drawing standard graph

Successively add distilled water to dilute 0, 0.5; 1; 2; 5; 10ml of solution II until the volume reaches 10 ml. Leave them to evaporate in ceramic bowls on double boilers until they dry out, and test each of them the same way as water sample. Respective concentrations of the new solutions are 0; 0.1; 0.2; 0.4; 1.0; 2.0 mg/l NO -. Measure color intensity of each solution using a photoelectric colorimeter

Draw a standard graph based on the measured optical density of the solutions. The vertical axis indicates optical density, the horizontal axis indicates corresponding concentration (mg/l).

2.17.5. Standardized color chart.

Successively add distilled water to dilute 0; 0.2; 0.5 , 1.0; 2.0; 4.0; 6.0; 8.0; 10.0 ml of solution III until the volume reaches 10 ml. Leave them to evaporate in ceramic bowls on double boilers until they dry out, and test each of them the same way as water sample. Add distilled water to dilute colored solutions in netle cylinders Respective concentrations of the new solutions are 0; 0.04; 0.1; 0.2; 0.4; 0.8; 1.2; 1.6; 2.0 mg/l NO₃.

2.17.6. Running the test

Take 10 ml of water sample, add 1 ml sodium salicylate and leave it to evaporate in a ceramic bowl on a double boiler until it dries out. Add 1 liter of sulfuric acid when it has cooled down. Use a glass stick to stir the solution against the side and the bottom of the bowl to make sure all dregs are dissolved, then leave it for 10 minutes.

Pour distilled water into the bowl, stir gently and pour it into a 50-ml flask. Rinse the bowl many times with distilled water; pour the rinsing water into a flask. Add 7 ml of 10N sodium hydroxide, then add distilled water until the volumetric mark is reached and gently shake the flask. After 10 minutes from the addition of sodium hydroxide, the color of the solution must not change. Measure the color intensity of the solution using the photoelectric colorimeter, use a green filter glass (O = 410 mm, cuvet thickness = 1 - 5 cm), or compare the color with the standard color chart with bare eyes.