The standard heat of dissociation of acetic acid, the degree of dissociation of acetic acid and the

Pipettes are used to calibrate the concentration of acetic acid solution (if the experimental time is not enough, it can be calibrated by the laboratory first).

Accurately measure ml hac (mol?DM-3) solution, each injected into two 50ml Erlenmeyer flasks, and 2 drops of phenolphthalein indicator were added to each. Titrate with standard NaOH solution until the solution is light red, and does not disappear after shaking, and write down the readings of the NaOH liquid level in the burette before titration and at the end of titration, respectively, and calculate the volume of NaOH solution used, so as to find the exact concentration of acetic acid.

2 Preparation of acetic acid solution of different concentrations and determination of pH in 4 dried 100 ml beakers.

medium, with an acid burette.

Add the calibrated acetic acid solution ml, ml, ml, ml respectively, and note that they should be added drop by drop when they are close to the scale to be made. Then, from the other contains deionized water.

Add ml, ml, and ml of deionized water to the next three beakers respectively (so that the volume of each solution is all, and mix evenly, and find the exact concentration of each acetic acid solution. The pH value of the above concentrations of acetic acid solution (from dilute to concentrated) was measured by pH meter, the pH value of each solution and the temperature of the experimental laboratory were recorded, and the ionization degree and ionization constant of acetic acid in each solution were calculated.

and included in the table below:3 Acetic acid vs. sodium acetate.

The pH of the buffer solution was determined using 25 ml of calibrated HAC (mol DM-3) solution and Naac (?) eachDM-3) solution, inject into a beaker and mix well, measure the pH value of this buffer solution with a pH meter, calculate the ionization degree of this solution, and then add ml HCl (mol?DM-3) solution, stirred and measured with a pH meter, and then added 1 ml NaOH (mol?

DM-3) solution, and the pH value was determined with a pH meter after stirring. The experimental and calculated values obtained above were compared.

The relationship between the degree of dissociation and the dissociation constant of acetic acid and its concentration: the dissociation constant is only related to temperature, not to the change of concentration. The dissociation process of weak electrolyte is an endothermic process, and the dissociation degree and dissociation constant increase when the temperature rises.

Concentration changes according toLe Chatre's principleJudging the dissociation of weak electrolytes, the concentration becomes smaller, and the degree of dissociation increases.

Strictly speaking, the ion concentration should be replaced by activity (in fact, the pH measured on the acidity meter reflects the activity value in the solution). In dilute solutions of weak acids, if no other strong electrolytes are present.

That is, the ionic strength in the solution is very small, the activity coefficient is close to 1, and the concentration can be used instead of the activity.

Significance. The dissociation constant (PKA) is a very important property of organic compounds, which determines the form of the compound in the medium and thus its solubility.

Lipophilic, bioagrichable, and toxic. For drug molecules, PKA also affects its pharmacokinetics.

and biochemical properties, the exact PKA value of organic compounds is of great significance in the fields of environmental chemistry, biochemistry, medicinal chemistry and drug development.

Acetic acid (CH3COOH or abbreviated as HAC) is a weak electrolyte with the following proton dissociation equilibrium in aqueous solution: HAC ==H+ +AC-

The [H3O+ AC-] in the solution can be calculated from pH== Lg[H3O+] by measuring the pH of the solution. [HAC] Chac H3O+ while ChaC can be measured by titration with NaOH standard solution. In this way, k a at this temperature can be calculated, and the degree of dissociation of acetic acid can also be obtained.

What about your degree of dissociation? What is asked is the degree of dissociation and the dissociation constant.

If there is a-b c the degree of dissociation is a, the initial concentration is c

Dissociation constants k criterion (1-) c criterion.

The determination of the standard dissociation constant and degree of dissociation of acetic acid is as follows:

First, the purpose of the experiment.

1.Learn and master the determination method of acetic acid ionization degree and ionization constant;

2.Further practice in titration and solution preparation;

3.Learn to use an acidity meter.

Second, the principle of experiment.

The following ionization equilibrium exists in acetic acid solution:

hac= h+ +ac-

The expression for its ionization constant is:

Let the initial concentration of acetic acid be c, and at equilibrium c (h+) c (ac-) x, substituting the above equation (1) can be obtained:

At a certain temperature, the pH value of a series of acetic acid of known concentration is measured with an acidity meter, and c(h+) is converted into c(h+) according to pH = -lg c(h+), and a series of correspondings can be obtained by substituting equation (2).

value, taken as the average value, is the ionization constant of acetic acid at that temperature.

3. Instruments and medicines.

Instruments: acidity meter, beaker, graduated cylinder, volumetric flask.

Drug: buffer, HAC (calibrated).

Fourth, the content of the experiment.

1 Prepare acetic acid solutions of different concentrations.

Measure the calibrated HAC solution with a 50 ml graduated cylinder and pour three dried 50 ml into ml, ml, and ml respectively

ml beaker, add ml, ml, respectively

ml distilled water, shake well, find the concentration of the above three HAC solutions, numbered 2 4, and the calibrated HAC solution is numbered 1.

2 Determination of pH value of acetic acid solution.

The above 1 and 4 cups were reduced from dilute to concentrated, and their pH values were measured with PHS-25 acidity meters, and the pH values of each solution and the temperature during the experiment were recorded. The ionization constant of acetic acid in each solution is calculated.

Acetic acid (CH3COOH or abbreviated as HAC) is a weak electrolyte with the following proton dissociation equilibrium in aqueous solution: HAC ==H+ +AC-

The [H3O+ AC-] in the solution can be calculated from pH== Lg[H3O+] by measuring the pH of the solution. [HAC] Chac H3O+ while ChaC can be measured by titration with NaOH standard solution. In this way, k a at this temperature can be calculated, and the degree of dissociation of acetic acid can also be obtained.

Number ph12

345 Unknown Weak Acid NaOH Dosage 19 degrees.

The degree of dissociation of acetic acid and the determination of the dissociation constant are as follows: Understand the principle and method of determining the dissociation constant of acetic acid with a pH meter. Learn how to use acid burettes and PHS-25 pH meters correctly.

Experimental principle Prepare a series of acetic acid solutions of known concentration, and carefully measure their pH value with a pH meter at a certain temperature, calculate C(H+) according to pH = -lg[c(h+) c0], substitute the equilibrium constant relation, and obtain a series of (hac) values, the average value of which is the dissociation constant at this temperature.

Instruments, Drugs & Materials Instruments: PHS-25 pH Meter, Composite Electrode, Beaker (50ml, 4 pcs), Acid Burette (50ml, 2 pcs) Drug: HAC ( Ingredients:

Shredded filter paper, standard buffer solution Experimental content and stepsPreparation of a series of acetic acid solutions of known concentration Take 5 dried 50 ml beakers, number them, and measure the acetic acid solution of known concentration (provided by the laboratory) with an acid burette according to the dosage in Table 5-1, and prepare acetic acid solutions of different concentrations.

Determination of pH value of acetic acid solution The pH value of No. 1 No. 5 HAC solution was determined according to the order of acetic acid concentration from dilute to concentrated with PHS-25 type pH meter, which was recorded in Table 5-1. .Data processing Calculate the values of each item in Table 5-1, calculate the dissociation constant of HAC at laboratory temperature, calculate the relative error, and analyze the cause.

Experimental purpose of the determination of acetic acid dissociation degree and dissociation constant:

1. Understand the principle and method of pH method for determining the dissociation degree and dissociation constant of weak acids.

2. Master the use of pH meter.

3. Proficient in basic operations such as pipettes, volumetric flasks and burettes.

Experimental Procedure:1Determination of acetic acid dissociation degree and dissociation constant.

1) Prepare acetic acid solutions of different concentrations. Use a pipette to measure the known concentration of HAC solution ml, ml, ml into three 50ml volumetric flasks, dilute to the scale with distilled water, and shake well. Take the matched in order.

Prepare about 40 ml of the solution in 3 dried 50 ml beakers, numbered 1, 2, 3. Take about 40 ml of undiluted HAC solution directly in a small beaker of 50 ml, numbered 4.

2) Determine the pH of the HAC solution. The pH of the four solutions was measured with a pH meter, and the room temperature and measured pH were recorded.

2.Determination of the dissociation constant of the standard for unknown weak acids.

Measure the unknown monolithic weak acid solution with a graduated pipette with a dried 50

ml in a small beaker (number 5), add 1 2 drops of phenolphthalein indicator, and titrate with the solution to the end point (reddish color, not fading for 30s) under the stirring of a magnetic stirrer.

Then use a graduated pipette to measure the weak acid solution and add it to the above-mentioned titration solution, stir evenly, and record the measured pH