CO2 isolation burette/pipette device glass instrument

Carbon dioxide (CO2) mainly exists in the form of dissolved gas molecules in water, but a small portion also reacts with water to form carbon

Acid is usually referred to as the sum of the two as free carbon dioxide. The main sources of carbon dioxide in surface water are organic compounds in water and sediment

The decomposition of substances and the respiration of aquatic organisms can also be absorbed from the air, so the determination of their content can be carried out according to the instructions in water

The degree of organic pollution suffered by the body

The content of free carbon dioxide in surface water is generally less than 10mg/L. When the content exceeds 40mg/L, it indicates water pollution

Has affected the growth of fish

The content in groundwater is generally between 15~40mg/L, and some mineral water has a higher content

There are two commonly used methods, namely phenolphthalein indicator titration and potentiometric titration. Potentiometric titration is not affected by the turbidity color of water samples

The influence of degree is widely applicable, and the phenolphthalein indicator titration method is simple, fast, and suitable for on-site experimental control and routine inspection

In addition to work, there is also graphical method

It is advisable to avoid contact between water samples and air as much as possible. Siphon sampling should be used for sample determination, and special measures should be taken at the sampling site

When the sample contains hydrolyzable salts or oxidizable cations, it should be analyzed immediately. If on-site measurement is difficult, it should be taken

A full bottle of water sample should be stored properly at a temperature lower than the sampling temperature. Before analysis, the bottle stopper should not be opened and dilution or concentration cannot be filtered

Shrink and measure as soon as possible

1 CO2 isolation burette/pipette device glass instrumentscope

Phenolphthalein indicator titration method is suitable for general surface water and not suitable for acidic industrial and mining wastewater and acid regeneration cation exchange

The outlet of the device

The turbidity and color interference of water samples can be measured by potentiometric titration method instead. If the mineralization degree of the water sample is higher than 1000mg/L

When the content of ferrous ions or aluminum ions exceeds 10mg/L, it will interfere with the measurement. 1mL of 50% (m/V) can be added before titration

Potassium sodium tartrate solution to eliminate interference with chromium copper amine ammonium borate, nitrite phosphate silicate

Sulfides, inorganic acids, strong acid and weak base salts can all affect the determination

2 CO2 isolation burette/pipette device glass instrumentPrinciple

Due to the ability of free carbon dioxide (CO2 H2CO3) to quantitatively react with * as follows

CO2 NaOH NaHCO3

H2CO3 NaOH NaHCO3 十 H2O

When it reaches the endpoint, the pH value of the solution is about 8.3, so phenolphthalein can be used as an indicator according to the standard solution of *

Consumption can be calculated based on the amount of free carbon dioxide emitted during travel

3 reagents

3.1 Carbon dioxide free water

Boil distilled or deionized water for 15 minutes before use to cool to room temperature for the preparation of standard solutions and dilution water

The pH value should be greater than 6.0 and the conductivity should be less than 2 μ S/cm

3.2 Phenolphthalein indicator (10g/L)

Weigh 1g of phenolphthalein and dissolve it in 100mL of 95% ethanol, then drop it with a 0.1mol/L * solution until a light red color appears

Until the color

3.3 Endpoint standard colorimetric solution

The endpoint standard colorimetric solution refers to a 0.1mol/L sodium bicarbonate solution. Weigh 8.401g of sodium bicarbonate (NaHCO3) in a small amount

Transfer water into a 1000mL volumetric flask and dilute to the mark. When using, take 10mL of the above solution and add phenolphthalein indicator

Shake 4 drops of the reagent evenly as a comparison of the endpoint color during titration

3.4 Neutral Potassium Sodium Salicylate Solution

Weigh 50g of potassium sodium tartrate (KNaC4H4O6) and dissolve it in 100mL of water. Add 3 drops of phenolphthalein indicator at a concentration of 0.1mol/L

Drop hydrochloric acid solution until the red color of the solution has just disappeared

3.5 * Standard solution

Weigh 60g * and dissolve it in 50mL of water. After cooling, transfer it into a polyethylene fine mouthed bottle, cap it tightly, and let it stand for 4 days

Then take 1.4mL of the upper clear solution and dilute it with water to 1000mL. This solution is approximately 0.01mol/L, and its precise concentration can be determined

The calibration method using potassium hydrogen phthalate is as follows

Take reference reagent grade potassium hydrogen phthalate (KHC8H4O4) and bake it at 105~110 until constant weight. Accurately weigh three portions each

About 0.1g (accurate to 0.0001g) is placed in a 250mL conical flask, and 100mL of water is added and slightly heated to dissolve

Add 4 drops of phenolphthalein indicator and titrate with * standard solution until the light red color does not fade. Record the * standard solution

Measure the amount of liquid (mL) and calculate its concentration according to the following formula

c= G 1000/ V 204.22

In the formula, c * standard solution concentration (mol/L)

V drip timing * standard solution dosage (mL)

Weight of potassium hydrogen phthalate (g)

204.22 Potassium hydrogen phthalate (KH4C4H4O4) molar mass (g/mol)

4 Instruments

4.1 Basic burette 25mL burette needs to be installed according to Figure 1

4.2 Non graduated pipette 100mL In order to avoid loss of free carbon dioxide when measuring water samples, the pipette for measuring water samples can be used

The lower end is connected to the siphon tube inserted into the water sample bottle (see Figure 2). When measuring the water sample, first inhale from the upper end of the suction tube and wait for the water sample to be filled

When the straw is full and about 100mL overflows from the top, remove the straw and simultaneously hold the top of the straw with your fingers until the water sample is in the straw

Immediately inject water into the conical flask upon reaching the mark