1. potassium permanganate, c (1/5kmno4) = 0.01mol/l.
2. Hydrogen peroxide (H2O2), 30%.
3. Ethanol (C6H5OH), 95%.
4. sulfuric acid solution, c (1/2h2so4) = 0.05mol/l.
5. Sodium hydroxide solution, C (NaOH) = 0.05 mol/L.
6. Aluminum hydroxide suspension.
7. Sodium chloride standard solution, c (NaCl) = 0.0141mol/L.
8. Silver nitrate standard solution, C (AgNO3) = 0.0141mol/L.
9. Potassium chromate solution, 50g/L.
10. Use phthalein indicator solution.
Instrument: 1. Conical flask, 250 ml.
2.25ml brown burette.
3. Pipette, 50 ml, 25 ml.
Material: water sample.
Experimental process:
1. Eliminate interference
This section can be omitted if there is no interference as follows.
1. 1 If the water sample is turbid and colored, take 150mL or take an appropriate amount of water sample and dilute it to 150mL, put it in a 250mL conical flask, add 2mL of aluminum hydroxide suspension (3.6), shake it evenly and filter it, discard the 20mL of the initial filtration, and use a dry and clean conical flask to take the filtrate for later use.
1.2 If the organic matter content is high or the chromaticity is high, the water sample can be pretreated by the ashing method of Maofu furnace. Take a proper amount of wastewater samples in a porcelain evaporating dish, adjust the pH value to 8-9, put them in a water bath to dry, then put them in a Muff furnace to burn at 600℃ for 65438+0h, take them out and cool them, add 65438±00ml distilled water, move them into a 250mL conical flask, wash them with distilled water for three times, then move them into the conical flask together, adjust the pH value to about 7, and dilute them to 50mL.
1.3 The lighter color produced by organic matter can be boiled by adding 2ml of 0.01mol/L/L potassium permanganate (3. 1). Then drop ethanol (3.3) to remove excess potassium permanganate until the water sample fades, filter and store the filtrate in a conical flask for later use.
1.4 If the water sample contains sulfide, sulfite or thiosulfate, add sodium hydroxide solution (3.5) to adjust the water sample to neutral or weakly alkaline, add 1 ml of 30% hydrogen peroxide (3.2) and shake well. After one minute, it was heated to 70-80℃ to remove excess hydrogen peroxide.
measure
2. 1 Suck 50mL water sample or pretreated water sample with a straw (if the chloride content is high, appropriate amount of water sample can be diluted to 50mL with distilled water) and put it in a conical flask. Add 50 ml distilled water into another conical flask for blank test.
2.2 If the pH value of the water sample is within the range of 6.5- 10.5, it can be directly titrated. If the water sample exceeds this range, phenolphthalein should be used as an indicator to adjust it to the red color that has just receded with dilute sulfuric acid (3.4) or sodium hydroxide solution (3.5).
2.3 Add 1mL potassium chromate (3.9) solution 1), and titrate with silver nitrate standard solution (3.8) until brick red precipitate just appears as the titration end point.
Do blank titration in the same way.
Calculation:
Chloride content c (mg/l) is calculated according to the following formula:
(V2-V2)×35.45×m× 1000 \u V
Where: v1-the amount of silver nitrate standard solution consumed by distilled water, ml;
V2—— the amount of silver nitrate standard solution consumed by the sample, milliliter (ml);
M—— concentration of silver nitrate standard solution, mol/l;
V-sample volume, milliliter (mL).
Note: The concentration of potassium chromate in water samples will affect the arrival of the end point sooner or later. Add 1ml 5% potassium chromate solution to 50- 100 ml titration solution, so that the concentration of CrO4 is 2.6×10-3 ~ 5.2×10-3 mol/L. At the end of titration, the addition of silver nitrate skips the end point, which can be passed through.
Drinking water containing a small amount of chloride ions does not affect human health, so it is unnecessary to put forward improvement measures. Therefore, the topic can be changed to "Investigation on Chloride Ion Content of Drinking Water in Our School".