GB/T 11896-1989 English PDF (GBT11896-1989)

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GB/T 11896-1989: [GB 11896-1989] Water quality. Determination of chloride. Silver nitrate titration method
GB/T 11896-1989 (GB 11896-1989)
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
Water Quality – Determination of
Chloride – Silver Nitrate Titration Method
APPROVED ON. DECEMBER 25, 1989
IMPLEMENTED ON. JULY 01, 1990
Approved by. State Bureau of Environmental Protection
Table of Contents
1 Theme Content and Applicable Range ... 3
2 Principle ... 3
3 Reagents ... 3
4 Instruments ... 5
5 Sample ... 5
6 Analytical Procedures ... 5
7 Result Expression ... 6
8 Precision and Accuracy ... 6
Appendix A Determination of the Highly Mineralized Salt Water and Seawater
(Supplement) ... 8
Additional Instructions ... 9
Water Quality – Determination of
Chloride – Silver Nitrate Titration Method
1 Theme Content and Applicable Range
This Standard specifies using the silver nitrate titration method to determine the
concentration of chloride in water.
This Standard is applicable to the determination of chloride in the natural water; it is
also applicable to the highly mineralized water that has been diluted, such as salt water,
seawater, etc.; as well as applicable to the domestic sewage and industrial wastewater
that has removed the interference through the pretreatment.
This Standard is applicable to the chloride with concentration of 10~500mg/L. The
water sample above such range can expand its determination range after dilution.
The bromide, iodide and cyanide can be titrated together with chloride. When the
orthophosphate and polyphosphate separately exceed 250mg/L and 25mg/L, they
have interference. When iron content exceeds 10 mg/L, the end-point is not obvious.
2 Principle
In the neutral or weak alkaline range (pH 6.5~10.5), take potassium chromate as an
indicator; when using silver nitrate to titrate the chloride, since the solubility of silver
chloride is less than that of the silver chromate, chloride ion is firstly precipitated fully;
then the chromate was precipitated in the form of silver chromate; generate brick red,
which indicates that the titration end-point is reached. The titration reaction of the
precipitation is as follows.
3 Reagents
Only use analytical reagent to prepare during the analyzing period; as well as distilled
water or deionized water.
Brick red
3.1 Potassium permanganate, C (1/5 KMnO4) =0.01mol/L.
3.2 Hydrogen peroxide (H2O2), 30%.
3.3 Ethanol (C6H5OH), 95%.
3.4 Sulfuric acid solution, C (1/2 H2SO4) = 0.05mol/L.
3.5 Sodium hydroxide solution, C (NaOH) = 0.05mol/L.
3.6 Aluminum hydroxide suspension. dissolve 125g of potassium aluminum sulfate
[KAl (SO4)2 • 12H2O] into 1L of distilled water; heating to 60°C; then slowly add 55mL
of stronger ammonia water as stir, stand for about 1h; then move to larger bottle; use
pouring method to repeatedly wash the precipitant till the eluate doesn’t contain the
chloride ions. Use water to dilute to about 300mL.
3.7 Sodium chloride standard solution, C (NaCl) = 0.0141mol/L, equivalent to
500mg/L chloride content. place the sodium chloride (NaCl) into a porcelain crucible
to burn for 40~50min at 500~600°C. After cooling off in the dryer, take 8.2400g,
dissolve into the distilled water; dilute to 1000mL in the volumetric flask. Pipette 10.0mL,
accurately dilute to 100mL in the volumetric flask.
1.00ml of such standard solution contains about 0.50mg of chloride (Cl-).
3.8 Silver nitrate standard solution, C (AgNO3) = 0.0141 mol/L. take 2.3950g of silver
nitrate (AgNO3); dry for half an hour at 105°C; dissolve into the distilled water; dilute to
1000mL in the volumetric flask; store in the brown bottle.
Use sodium chloride standard solution (3.7) to calibrate its concentration.
Accurately pipette 25.00mL of sodium chloride standard solution (3.7) into 250mL
conical flask; add 25mL of distilled water; take another conical flask to weigh 50mL of
distilled water as blank. Separately add 1mL of potassium chromate solution (3.9); use
the silver nitrate standard solution to titrate till the brick red precipitant just appears as
continuously stir, which is the end-point. Calculate the chloride amount equivalent to
the silver nitrate solution per milliliter; then calibrate its concentration; then do the final
calibration.
1.00ml of such standard solution is equivalent to 0.50mg of chloride (Cl-).
3.9 Potassium chromate solution, 50g/L. take 5g of potassium chromate (K2CrO4);
dissolve into little amount of distilled water; titrate silver nitrate solution (3.8) till red
precipitant is generated. Shake evenly, stand for 12h; then filter it, and use distilled
water to dilute the filtrate to 100mL.
3.10 Phenolphthalein indicator solution. take 0.5g of phenolphthalein; dissolve into
50mL of 95% ethanol (3.3). Add 50mL of distilled water; then titrate 0.05mol/L sodium
hydroxide solution (3.5), so that the slight red appears.
4 Instruments
4.1 Conical flask, 250mL.
4.2 Burette, 25mL, brown.
4.3 Pipette, 50mL, 25mL.
5 Sample
Take representative water sample, place into the clean and chemically stable glass or
polyethylene bottle. When storing, it is not necessary to add anti-corrosive agent.
6 Analytical Procedures
6.1 Interference exclusion
If there aren’t various interferences below, such section can be omitted.
6.1.1 If the water sample is turbid and has a color, then take 150mL or appropriate
amount of water sample to dilute to 150mL; then place into 250mL conical flask; add
2mL of aluminum hydroxide suspension (3.6); shake and filter; discard the 20mL of
initial filtrate; then use clean conical flask to receive filtrate for spare-use.
6.1.2 If the organic substance content is high or the chroma is high, use muffle
furnace ashing method to pre-treat the water sample. Take appropriate amount of
waste water sample into porcelain evaporating dish; adjust pH value to be 8~9; place
onto the water bath for dry; then place into muffle furnace to burn for 1h at 600°C; after
taking out, cool off; add 10mL of distilled water; move into 250mL conical flask; use
distilled water to wash for three times; then transfer them together into the conical flask;
adjust pH value to be about 7; dilute to 50mL.
6.1.3 For the lighter chroma generated by organic substance, add 2mL of 0.01mol/L
potassium permanganate (3.1), boil. Then titrate ethanol (3.3), so as to remove the
excessive potassium permanganate till water sample fades; filter; the filtrate shall be
stored in the conical flask for spare-use.
6.1.4 If the water sample contains sulfide, sulfite or thiosulfate, then add sodium
hydroxide solution (3.5) to adjust the water sample into neutral or weakly alkaline; add
1mL of 30% hydrogen peroxide (3.2), shake evenly. After 1 minute, heat to 70~80°C;
so as to remove the excessive hydrogen peroxide.