What are the commonly used methods to determine the pH value of a solution?

It can usually be measured with pH test strips, pH meters, and pH indicators.

pH test paper: Put a piece of dry pH test paper on the glass plate, dip the test solution into the pH test paper with a glass rod, compare the test paper with the standard color card, and read out the pH of the solution.

pH meter: In the actual measurement, the electrode is immersed in the solution to be measured, and the H' ion concentration in the solution is converted into a MV-level voltage signal and sent to the electrometer. The electrometer amplifies this signal and converts it logarithmarily into a pH value, which is then displayed by a millivolt level display meter.

The hydrogen ion concentration index is the ratio of the total number of hydrogen ions in a solution to the amount of total substances. It is generally referred to as "pH", not "pH". Its value is colloquially known as the "pH value".

A numerical value that represents the pH of a solution, pH = -LG [H+] which is the negative value of the commonly used logarithm of the concentration of hydrogen ions contained in it.

pH value is sometimes called hydrogen ion index, because the value of hydrogen ion concentration is often very small, it is very inconvenient to apply, so the concept of pH value is used as a judgment index of acidity and alkalinity of aqueous solution. Moreover, the negative logarithmic value of hydrogen ion activity can represent the magnitude of the change in acidity and alkalinity by an order of magnitude, which is very convenient to apply, and thus obtained (under 25):

Neutral aqueous solution, pH=7;

Acidic aqueous solution, C(H)>C(OH), pH<7, the smaller the pH value, the stronger the acidity;

Alkaline aqueous solution, c(h)7, the higher the pH value, the stronger the alkalinity.

pH determination: There are many ways to determine the pH of a solution:

1.Use a pH indicator. Add a pH indicator to the solution to be measured, different indicators will change color according to different pH values, and the pH range can be determined according to the study of the indicator. During titration, a precise pH standard can be made.

2.Use pH test strips. pH test paper has a wide range of test strips and precision test strips, dip a glass rod into the test strip with a little solution to be measured, and then according to the color change of the test strip against the standard color card can get the solution of the test strip can not show the pH value of the oil, because the pH test paper uses hydrogen ions to measure the pH value of the solution to be measured, but the oil does not contain hydrogen ions, so the pH test paper can not show the pH value of the oil.

3.Use a pH meter. A pH meter is an instrument that determines the pH value of a solution, and it can be accurate to two decimal places by a pH selector electrode (such as a glass electrode).

The pH value is an important parameter of the plating bath solution, which has a great influence on the electroplating process, so it is necessary to check the pH value of the plating solution frequently. There are two methods commonly used in factories to determine the pH value of a solution. 1. Test strip method:

Take a pH test strip and drop a drop of the tested solution, the pH test paper will change color, and compare it with the color scale of the known pH value to determine the pH value of the solution. Its advantage is that it is convenient and simple, and the disadvantage is that the error is large. This is still the most widely used method for the day-to-day production of the plant.

To improve the accuracy of the test, a precision pH test strip can be used. 2. pH value tester: according to the concentration of hydrogen ions, the hydrogen electrode generates different potentials and the potential difference between a standard electrode, and displays the reading on the potentiometer.

The advantage is that the accuracy is high, and the disadvantage is that the test is more complicated. Hope.

Acidity meter, also known as pH meter, is a more commonly used instrument and equipment in the laboratory, mainly used to accurately measure the pH value of liquid media (such as Mettler pH meter).

In the day-to-day operation of the laboratory, the first thing we need to do is calibration. Adjust the slope regulator of the acidity meter to the 100 position, and then adjust the temperature regulator to this temperature value according to the temperature of the solution to be measured. Then position and insert the composite electrode into the instrument.

Secondly, the key is positioning. Select a buffer solution that is closest to the pH value of the sample, place the electrode in this buffer solution, and shake the beaker to homogeneous solution. Wait until the reading is stable to see the reading, which is the pH of the buffer solution.

If high-precision measurement is required, it is necessary to choose two buffer solutions, that is, the pH value of the measured sample is between or close to the pH value of the two buffer solutions, and the pH value can be read after the reading of the second buffer solution is stable, and if it is unstable, it is necessary to adjust the positioning regulator.

After that, it's time to measure. A pH-calibrated instrument can be used to determine the pH value of a sample. At this point, all regulators need to be left in their original position.

Then clean the electrode, insert the electrode into the beaker containing the sample to be measured, and gently shake the beaker until the reading is stable, and the pH value of the sample will be displayed. Here, it is important to note that the glass electrode must be soaked in distilled water for more than one day and night before being used for the first time, and it should also be soaked in distilled water when it is usually used, and it must be cleaned before use. In addition to this, there are a few points that we need to pay attention to:

1) The glass electrode should not be in contact with the strong absorbent solvent for too long, and should be operated as soon as possible when used in a strong alkali solution, and should be washed with water immediately after use;

2) Because the glass electrode bulb membrane is very thin, it cannot collide with the glass and hard objects;

3) When the glass film is stained with oil, it should be soaked with alcohol, then carbon tetrachloride or ether, and finally soaked in alcohol, and then washed with distilled water. Otherwise, when measuring protein-containing solutions, contamination of the electrode surface can lead to non-standard readings and large errors.

4) After cleaning the electrode, only gently blot it with filter paper, and never wipe it with fabric, as this will cause the electrode to generate an electrostatic charge and cause the reading to be wrong.

The correct way to use the acidity meter is to establish the care of the instrument during use. The Mettler acidity meter is easy to maintain and easy to operate. Good or bad instrument maintenance determines the results achieved in the experiment, so we must pay attention to details when using laboratory instruments and equipment such as acidity meters.

1. Indicator method.

2. PH test strip method.

3. The pH instrument can be directly detected.

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1. Add pH indicator to the solution to be measured, different indicators will change color according to different pH values, such as:

1) If the acidic solution is dropped into the litmus solution, the litmus solution will turn red; If the alkaline solution is dropped into the litmus solution, the litmus solution will turn blue (the litmus solution will not change color when it encounters a neutral liquid). Based on the study of the indicator, the pH range can be determined.

2) drop the colorless phenolphthalein solution into an acidic or neutral solution, and the color will not change; The colorless phenolphthalein solution was dropped into the alkaline solution, and the solution turned red.

Note: When adding a pH indicator to the colored solution to be measured, a pH indicator that can produce significant color difference should be selected.

2. When titrating, it can be used as an accurate pH standard.

Use pH test strips, pH test strips have a wide range of test strips and precision test strips, dip a glass rod into the test strip with a little solution to be measured, and then according to the color change of the test strip and compare the color card can also get the pH value of the solution. The ** above is equivalent to a colorimetric card.

3. Use a pH meter, a pH meter is an instrument that measures the pH of a solution, and it measures the solution through a pH selection electrode (such as a glass electrode) that can be accurate to two decimal places.

The pH value is an important parameter of the plating bath solution, which has a great influence on the electroplating process, so it is necessary to check the pH value of the plating solution frequently. There are two methods commonly used in factories to determine the pH value of a solution. 1. Test strip method:

Take a pH test strip and drop a drop of the tested solution, the pH test paper will change color, and compare it with the color scale of the known pH value to determine the pH value of the solution. Its advantage is that it is convenient and simple, and the disadvantage is that the error is large. This is still the most widely used method for the day-to-day production of the plant.

To improve the accuracy of the test, a precision pH test strip can be used. 2. pH value tester: according to the concentration of hydrogen ions, the hydrogen electrode generates different potentials and the potential difference between a standard electrode, and displays the reading on the potentiometer.

The advantage is that the accuracy is high, and the disadvantage is that the test is more complicated.

The pH range is usually between 0 and 14 Solutions with pH less than 7 are acidic, solutions with pH equal to 7 are neutral, and solutions with pH greater than 7 are alkaline The easiest way to determine pH is to use pH test strips.

Therefore, fill in: 0-14; Take it as a pH test strip

Answer] Guess quietly: C, D

The pH value of water is determined, and the sample is stored at 0 4 after the water sample is collected from the ear residue, and the test is carried out within 6 hours after sampling; Before use, the glass electrode is soaked in distilled water for 24 hours to bend it.

1. PH test strip. Open the pH test strip box and take out a pH test strip. Use a glue-tip pipette to drop the measured volume on the pH test paper, or you can immerse the pH test paper in the test solution.

After the test is completed, the test result is compared with the pH test strip color comparison card to determine the pH of the tested solution. The lower the pH, the more acidic the solution becomes. When the pH value is 7, it is neutral, and the higher the pH value, the stronger the alkalinity of the solution.

2. PH meter. Blot the excess water droplets on the electrode or rinse twice with the solution being measured. Turn on the machine and preheat it for 30 minutes, then immerse the electrode in the solution to be measured, and gently turn or shake the small beaker so that the solution evenly touches the electrode.

The temperature of the fissure solution to be measured should be the same as that of the standard buffer solution. Adjust the zero position, press the reading switch, and the value pointed by the pointer is the pH of the liquid to be measured. If the pointer reads more than the scale when measuring in the range of 0 to 7, the range switch should be placed at 7 to 14 and the measurement should be repeated.

After the measurement is completed, after releasing the reading switch, the pointer must point at pH7, otherwise it will be readjusted. Turn off the power, rinse the electrodes, and clean up the soak.

3. Acid-base neutralization titration. Inject hydrochloric acid of known concentration into an acid burette that has been rinsed with the hydrochloric acid solution in advance, until the scale is above 0, and fix the burette on the burette clamp. Gently turn the piston below so that the pointed nozzle portion of the tube is filled with solution and free of bubbles.

Then adjust the liquid level in the tube so that it stays at a certain scale below 0 or 0 and note down the accurate reading. Inject the NaOH solution at the desired concentration into a basic burette that has been previously rinsed with the solution and also attach it to the burette clamp. Gently squeeze the glass bead so that the tip portion of the tube is filled with solution and free of bubbles, then adjust the liquid level in the tube so that it remains at or below 0 at a certain scale and note the accurate reading.

Put a clean Erlenmeyer flask under the tube, release 25ml of NaOH solution from the basic burette, inject it into the Erlenmeyer flask, add 2 drops of phenolphthalein test solution, and the solution will immediately turn pink. Move the Erlenmeyer flask to the acid burette, adjust the piston with the left hand to add the hydrochloric acid of the known concentration of the substance drop by drop, and at the same time shake the Erlenmeyer flask clockwise with the right hand to make the solution fully mixed. As hydrochloric acid is added drop by drop, the concentration of OH- in the Erlenmeyer flask gradually decreases.

When 1 drop of hydrochloric acid is added, the solution fades into a colorless macro-closed, and a drop of NaOH solution turns back to red, indicating that the reaction is just complete. Stop the titration, accurately write down the scale of the burette solution level, and accurately calculate the volume of hydrochloric acid removed for titration. In order to ensure the accuracy of the determination, the above titration operation should be repeated two to three times, and the average volume of hydrochloric acid used for titration should be obtained.

Then, according to the relevant dosage relationship, the amount concentration of the substance in the NaOH solution to be measured is calculated.