What is the essence of the neutralization method? Neutralization reaction, essence of the method and practical application

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Neutralization method used for quantification acids, bases, as well as salts having an acid-base environment (sodium carbonate and bicarbonate, ammonium chloride).

The method is based on the neutralization reaction: H+ + OH- = H2O

There are:

• Alkalimetry, for determination of acids, titrant - alkali

Installation substances:

Fixanal hydrochloric acid

Oxalic acid Н2С2О4*2Н2О

Succinic acid H2C4H4O4 (less often)

• Acidometry, to determine base, titrant - acid

Installation substances:

Borax Na2B4O7*10H2O

Sodium carbonate fixing solution

To determine the equivalence point, acid-base indicators are used, which are given in reference books. The most commonly used are phenolphthalein, methyl orange, and litmus.

Indicators- substances that change their structure and physical properties when the properties of the environment change.

The change in color of indicators is explained by two theories: Ostwald (ionic theory) and Hantzsch (chromophoric).

Ostwald's theory.

According to it, indicators are weak organic acids or bases. According to the theory, when the pH of the medium changes, the equilibrium during dissociation of the indicator shifts to the left and right according to Le Chatelier's principle. In this case, the concentration of the colored or colorless form of the indicator changes and we record changes in the color of the indicator

The theory does not explain the change in color of the indicator during the titration process. To clarify this point, the chromophore theory was formulated.

Ganch's theory.

According to this theory, color is imparted by special groups - chromophores, which contain conjugated bonds. It has been established that organic compounds contain groups that enhance color while remaining colorless; these are auxochromes.

For accurate quantitative determination, it is necessary to know the transition interval of the indicator, i.e. pH within which the color of the indicator changes.

However, a more accurate characteristic than the color transition interval is the pH of the indicator - this is the pH at which titration using this indicator ends.

As a rule, pT lies in the middle of the indicator transition interval and is conventionally assumed to be equal to pK of the indicator.

The permissible error using a specific indicator in this system is 0.2%.

Types of indicator errors:

H+ - error, there is an excess of strong acid in the solution

OH- - error, there is an excess of a strong base in the solution

HA - error, excess of weak acid

MeOH - error, excess of weak base

Titration curves.

The titration curve is the dependence of pH on the volume of titrant added.

Calculation of titration curves is necessary for selecting an indicator and reducing titration errors.

The titration jump is calculated for the points when the solution is 0.1 ml short and when it is overtitrated by 0.1 ml.

Application of the neutralization method:

• Determination of carbonate hardness of water. It is caused by the presence of salts of carbonates and bicarbonates of calcium and magnesium.

F = St*Vt*100 / Vwater

Mol/dm3

• Temporary and permanent water hardness is determined.

Temporary hardness is removed by boiling.

By determining the permanent hardness and knowing the carbonate hardness, you can determine the temporary hardness.

Constant hardness is determined by back titration. The essence: an excess of a standard Na2O3 solution is added to the analyzed water sample, the solution is evaporated, then distilled water is added to the resulting dry residue, and the solution is titrated with hydrochloric acid.

F = (Cst*Vst - St*Vt)*1000 / Vwater

• Determine the acidity of bread and milk (lactic and acetic acids).

The acidity of milk is determined in degrees Turner.

Precipitation titration

• Classification of deposition methods:

Argentometry - this method uses ra-r nitrate silver (secondary standard). Installation materials - chemically pure NaCl or KCl.

Argentometry is divided into:

The method of enlightenment - the essence of the method is that i.e. is fixed when, upon addition of the titrant, the titrated solution clears.

Equal turbidity method - i.e. in the method is determined by selecting 2 small samples of the analyzed sample. Silver nitrate is added to one sample and sodium chloride to the other. If the turbidity is equal, the titration is completed. Method without indicator.

Mohr's method - direct titration, K2CrO4 indicator. This method is used to determine chlorides and bromides. They are not used for the determination of iodides, because iodide ion is sorbed on the surface of potassium chromate, etc. difficult to install.

Process chemistry:

Cl- + Ag+ => AgCl (white precipitate)

i.e. CrO4 2- + 2Ag+ => Ag2CrO4 (brick sediment)

Chemistry is based on different PR values. According to the PR and the condition for the formation of a precipitate, silver halide precipitates at the beginning, and at i.e. When all the halide has precipitated, the condition for the formation of a silver chromate precipitate is reached.

Conditions of applicability:

Use only in neutral and slightly alkaline environments. Titration is impossible in an alkaline environment, because The titrant is destroyed:

Ag+ + OH- =>AgOH

2AgOH => Ag2O + H2O

In acidic environments, the Ag precipitate dissolves.

The following cations interfere with the determination: Ba, Pd, Bi anions: CO3 2-; PO4 2- .

Volgaard method - back titration.

Cl- + excess AgNO3 => AgCl (precipitate) + AgNO3 (remaining)

(remaining) AgNO3 + KSCN => AgSCN (white precipitate) + KNO3

i.e. Fe3+ (indicator) + SCN- =>Fe(SCN)3 (red)

iron-amonyl alum NH4Fe(SO4)4x12H2O is used as an indicator

Conditions of applicability:

It must be used in an acidic environment - alum will hydrolyze (acidification is necessary to suppress iron in alum).

Determination is interfered with by mercury salts and strong oxidizing agents.

Mercurimetry - use standard size Hg(NO3)2 - secondary standard. Installation materials - chemically pure NaCl and NaBr. The indicator is sodium nitropruside Na2 x 2H2O.

This method is used to determine Hal, cyanide ions, and thiocyanate ions.

In i.e. observe the precipitation of a white precipitate of mercury nitropruside

Na x 2H2O => Hg x 2H2O (white precipitate).

Mercurometry - use the standard solution Hg2 (NO3)2. The settings are the same as in Mercurymetry.

Iron thiocyanate III is used as an indicator (ra-p is red - i.e. discoloration of ra-ra) => formation of mercury thiocyanate I.

Fe (SCN)3 red => Hg2 (SCN)2

Adsorption indicator method (faience method).

The bottom line is that all processes take place on the surface of the sediment; in this method, the standard solution is silver nitrate; special adsorption indicators are used as indicators: eosin, dichlorofluorescein.

The color transition depends on the amount of adsorbed indicator and the surface area of ​​the sediment. Titration is carried out without heating and without shaking.

at the beginning of the titration:

X- (determining ion) + Ag+ => AgX (precipitate)

AgX (nucleus) x X- (potential-determining ions) => Repel Ind-

there is an indicator in the screen:

HInd => H+ Ind-

in i.e. the colloidal particle is recharged, because a slight excess of titrant appears

AgX (nucleus) x Ag+ (potential determining ion)<= притягивает Ind- следовательно появляется окраска.

• Titration curves

Curve will besiege titration is plotted in coordinates рХ = f (Vт).

• Application of precipitation titration in chemical analysis

Mohr's method is used in the analysis of food products, the determination of NaCl in sausages, cheeses, and fish.

The Volgaard method is used in clinical studies to determine chlorides in the blood.

The adsorption indicator method is used to determine iodides in the presence of chlorides.

Complexometric titration

• Characteristics of the method, complexons, their structure

The method is based on the formation reactions of complexes, cations with complexones. Derivatives of aminocarboxylic acids are used as complexes. These complexons are polydentate chylates, the dentation depends on the structure of the complexons.

As the method develops, it is distinguished:

Complexon I:

: N(CH2COOH)3 can form 4 bonds, 1 by a donor-acceptor mechanism, 3 by an exchange mechanism.

Complexon II:

(CH2COOH)2-N-CH2-CH2-N-(CH2COOH)2 EDTA (ethylenediaminetetraacetate)

Complexon III:

Na2EDTA (trilon B)

(CH2COOH/Na)2-N-CH2-CH2-N-(CH2COOH/Na)2

Complexons, when interacting with Me, give stable chylate compounds, and H+ protons are released. This fact must be taken into account when performing chemical tests. analysis and maintain a certain pH value using buffer systems. Me (EDTA) = 186 g/mol x eq.

To standardize the solution of Trilon B, a setting substance is used - a fixed solution of MgSO4 or a solution of metallic Zn in sulfuric acid.

• Methods of fixation i.e. and indicators of complexometric titration, mechanism of action of indicators
  1. use of acid-base indicators
  2. use of physicochemical methods of analysis (potentiometry, conductometry)
  3. the use of specific indicators aimed at determining Fe3+; potassium thiocyanate or sulfosalicylic acid are used as indicators. Before the start of titration, the solution is red or yellow; during the titration process, as EDTA is added, a complex of Fe3+ with EDTA is formed (colorless). In i.e. ra-r becomes discolored, because Fe3+ complexes with thiocyanate or salicylic acid are completely destroyed.
  4. application of special metalochromic indicators (weak organic compounds).

Let us consider the mechanism of action of the Me-chrome indicator using the example of the eriochrome black T indicator.

It is a weak 3-basic acid H3Ind.

Depending on the pH, Ind dissociates differently and the dissociated form has a certain color.

H3Ind<=>H+ + H2Ind-<=>H+ + HInd2-<=>H+ + Ind3-

pH 0-2 2-7 7-11.5 >11.5

used color red blue orange

mechanism of action of eriochrome black T (pH 8-10)

Me2+ + HInd2- (blue) => MeInd- (red) + H+

MeInd- + H2I2- + OH- => MeI2- (b/color) + Hind2- (blue) + H2O

• Classification of methods and conditions for complexometric titration

Direct titration - used when suitable indicators are available and complexation of the ion being determined with Trilon B occurs quickly. Be sure to use a buffer ra-r.

Back titration - performed when equilibrium is slowly established, there are a large number of parallel reactions (hydrolysis), and there is no suitable Me-indicator.

Chemical analysis is performed as follows: excess EDTA is added to the test solution and boiled, cooled, and the excess EDTA is titrated with magnesium sulfate in the presence of a specific indicator, magnesone (this is how Al is determined in solution).

Titration of the substituent - The method is based on the peculiarity of the Trilon B complex with Mg: the most unstable complex.

Rare earth metals are determined by indirect titration method

Mg2+ + H2I2- => (pH=10) MgI2- + 2H+

Acid-base titration - The equivalent amount of H+ released during complexation is titrated using acid-base indicators.

• Application of complexometry in chemical analysis

Used to determine the total hardness of water (mol/dm3) and to determine Ca and Mg in solution when present together.

Chemistry. Olovyannikova R.Ya.

Guidelines for laboratory lesson No. 2

for extracurricular work of students.

Neutralization method

The neutralization method is one of the types of titrimetric analysis, which is widely used in laboratories of various medical and environmental profiles: clinical, diagnostic, sanitary and hygienic, forensic, environmental monitoring, standardization and control of dosage forms.

The neutralization method is based on neutralization reaction . It is a reaction between an acid and a base, one or both of which are strong , For example,

H 2 SO 4 +2 NaOH → 2H 2 O+Na 2 SO 4 (1)

H + +OH − →H 2 O (in short ionic form, reflecting the essence of the process)

H2C2O4+ 2 NaOH → 2H 2 O+Na 2 C 2 O 4 (2)

H2C2O4+ 2 OH − → 2H 2 O+ (in short ionic form)

HCl +NH 3 ∙H 2 O→H 2 O+NH 4 Cl(3)

H + + NH 3 → + NH 4 (in short ionic form)

HCl +NaHCO 3 →H 2 CO 3 +NaCl(4)

H + + →H 2 CO 3 (in short ionic form)

NH4Cl+ NaOH → NH 3 ∙ H 2 O + NaCl (5)

NH4+ − OH →NH 3 ∙H 2 O (in short ionic form)

# In the technical execution of the method, a solution of a strong component (acid or base) is poured into a burette and serves as a titrant.

From examples 1 – 5, shown in molecular and brief ionic form, it can be noted that neutralization reactions do not always lead to the formation of water. Neutralization may simply involve the binding of a strong acid to a weak one (example 4) or a strong base to a weak one (example 5).

Examples 1 – 5 also show that neutralization method can be determined both strong and weak acids and bases, as well as salts, which, from the point of view of the Bronsted theory, act as acids or bases.

Thus, working solutions in the neutralization method, strong acids or strong bases are used as titrants, as well as standard salt solutions, which are used to establish the exact concentration of the titrants. Standard solutions - These are solutions of known concentration. Titrants, the concentration of which was established using standard solutions, are called titrated solutions .

Titration is the process of adding a titrant (titrated solution) drop by drop until the equivalence point (end of the reaction).

Equivalence point - this is the moment of the reaction when substances react with each other in equivalent quantities. Only in this case, the parameters of the substance being determined (its mass, concentration, quantity or volume) can be calculated based on the law of equivalents. The equivalence point is established using acid-base type indicators.

Indicator in the neutralization method, it is a weak acid or weak base of organic nature, the molecular and ionic forms of which differ in color. From the perspective of Brønsted's protolytic theory, the indicator is a conjugated acid-base pair, the components of which differ in color:

HInd ⇄ H + +Ind −

colorI colorII

Therefore, each indicator is characterized by a certain value pK a, or the so-called titration index pT=pK a =−. Let us remember that pK a is the pH value of the medium at which the content of the acidic and conjugate basic forms are the same. This means that at the pT point the color of the indicator solution will be mixed. But the human eye notices a mixed color even when one of the indicator forms predominates over the other by a factor of 10. In this case, we get a transition zone of the indicator color pT ± 1 . With values pH < pT ± 1 (i.e. to the left of the color transition zone) the indicator will be mainly in its acidic form Hind . And with values pH > pT ± 1 (i.e. to the right of the color transition zone) its conjugate basic form will significantly predominate I nd − . Table 1 provides examples of indicators and their characteristics.

Table 1. Indicators

When selecting an indicator are guided by the rule: the pH value at the equivalence point (pH e) must fall within the color transition zone of the indicator (i.e. pH e ∋pT±1). The pH value is determined by the reaction products, when the starting substance in the titration flask has already been consumed, but there is still no excess titrant (and there are only reaction products).

# In the neutralization method, not only direct titration can be used, but also reverse titration (or titration by excess). Its essence: a fixed excess of a standard auxiliary solution is added to the substance being determined, which is then titrated with another solution that acts as a titrant. Back titration is used when, for example, the necessary indicator for direct titration is not available or the substance being determined is too volatile.

Application of the neutralization method (acid-base titration) to determine the acidity of gastric juice.

Introduction. Gastric juice in the lumen of the stomach has an acidic pH: on an empty stomach the normal pH is ~1.5-2 in an adult and pH~3-4 in newborns. After eating, the pH is even lower. The main inorganic component of gastric juice is hydrochloric acid, which is produced by the parietal cells of the stomach and is found in the lumen of the stomach in a free and bound state (mainly with proteins). However, in addition to proteins, gastric juice also contains other weak acids: bicarbonates, hydrosulfates, dihydrogen and hydrophosphates, phosphoric acid itself, acetic, lactic, pyruvic, butyric, malic and some others. Therefore, they distinguish three types of acidity: total, free (due to the concentration of free H +) and bound (due to the presence of undissociated weak acids).

Determination of gastric juice acidity. In the laboratory, the acidity of gastric juice is determined by titrating it with a titrated working solution of NaOH in the presence of indicators. Results are given in titrimetric units (i.e.).

One titrimetric unit – this is the volume of 0.1 e NaOH solution that must be spent on titrating 100 ml of gastric juice.

Since the study takes not 100 ml of gastric juice, but 5-10 ml, and titrates not with 0.1 e NaOH, but usually with a lower concentration (for example, 0.089 e), then when calculating the acidity of gastric juice in titrimetric units, two corrections must be made: on the volume of gastric juice and on the concentration of an ideal (0.1 e) NaOH solution. Taking these amendments into account, it is not difficult to derive a general formula for calculating the acidity of gastric juice (in titre units):

where are the NaOH parameters according to the definition of the titrimetric unit; - the volume of NaOH spent on titrating the gastric juice sample taken for research (5 - 10 ml, for example); - the concentration of the titrated NaOH working solution.

# If the working solution NaOH turns out to be ideal - C e (NaOH) = 0.1 mol/l, and the volume of gastric juice taken for research V (liquid juice) = 5 ml, then the formula for calculating acidity is simplified:

Acidity juice = , titer . units

The following formulas are used to determine any type of gastric acidity: free acidity (in the presence of methyl orange indicator; aka sodium 4-(4-dimelaminophenylazo)benzenesulfonate) or total acidity (in the presence of phenolphthalein). In this case associated acidity determined by the difference between total and free acidity.

Rationale for selecting indicators. As already noted, in order to determine two fractions of acidity in gastric juice (free and bound), it is necessary to titrate in the presence of two indicators. The first indicator sets the equivalence point for the 1st reaction, when free hydrochloric acid is titrated:

HCl+NaOH=H 2 O+NaCl, or in short ionic form H + +OH − =H 2 O

If it were not gastric juice that was titrated, but an aqueous solution of HCl, then pH e1 = 7. Gastric juice also contains weak acids, which should not be affected during titration in the first reaction. That's why end of titration for the first reaction (when allHClwill already be titrated) is dictated not by the reaction product, but by the pH value created by dilute solutions of weak acids (for example, acetic acid gives a pH of ~3.5). Thus, pH e1 = 3,5 . The indicator whose color transition zone includes the pH point e1 3.5 is methyl orange (sodium 4-(4-dimelaminophenylazo)benzenesulfonate).

# From here, the 1st stage of titration: titrate a portion of gastric juice until the red color of the solution changes to orange (methyl orange will work), and note the volume of alkali used for titration. And if we introduce it into the formula for calculating acidity, we get free acidity gastric juice in titrimetric units.

Following free hydrochloric acid, weak acids (organic and inorganic) are titrated. Reaction using acetic acid as an example:

CH 3 COOH + NaOH = H 2 O + CH 3 COONa

CH 3 COOH + OH − = H 2 O + CH 3 COO −

The pH at the equivalence point for the second reaction is the pH value that is determined by the reaction product - a salt that undergoes hydrolysis at the anion. It can be calculated using the formula already discussed (we get pH e2 ~ 8,7 ). The indicator whose color transition zone includes the pH point e2 8.7 is phenolphthalein.

# From here, the 2nd stage of titration: we continue to titrate until the orange color of the solution changes to bright crimson (phenolphthalein will work). We note the volume of alkali used for titration in the second stage. And if we introduce it into the formula for calculating acidity, we get associated acidity gastric juice in titrimetric units. In this case total acidity Let's calculate it as the sum of free and bound.

Situational and educational-cognitive tasks.

The titration of 15 ml of sodium carbonate solution required 13.4 ml of 0.15 M sulfuric acid solution. Calculate the percentage concentration of sodium carbonate if its density is 1.15 g/ml. What indicator should you titrate with?

Brief summary of the task:

V(Na 2 CO 3) = 15 ml

V(H 2 SO 4) = 13.4 ml

indicator−?

Solution:

We select the indicator with the condition pH e = pT ± 1. Therefore, we pay attention to the reaction products:

Na 2 CO 3 + H 2 SO 4 ⇄ H 2 CO 3 + Na 2 SO 4 pH e<7

The Na 2 SO 4 salt does not undergo hydrolysis, and the acidity of the medium at the equivalence point is due only to carbonic acid:

=

The found pH value of 3.8 falls within the color transition zone of the methyl orange indicator (see Table 1).

Answer: ; indicator – methyl orange.

Working solutions used in the neutralization method as titrants

1. weak bases NH 3 ∙H 2 O

   weak acids CH 3 COOH, H 2 CO 3

   strong reasonsNaOH, KOH

To set the titer of acids, use

1. Na 2 CO 3 ,Na 2 B 4 O 7 ∙10H 2 O

   H 2 C 2 O 4 ∙2H 2 O

To set the alkali titer, use

1. Na 2 CO 3 , Na 2 B 4 O 7 ∙10H 2 O

   H 2 C 2 O 4 ∙2H 2 O

Titrate with KOH hydrochloric acid. The pH value at the equivalence point and, accordingly, the indicator used will be

1. 7 – litmus, bromothymol blue

   7 – thymol blue

   <7– лакмус, метиловый красный, метилоранж

Titrate an aqueous solution of ammonia with hydrochloric acid. The pH value at the equivalence point and, accordingly, the indicator used will be

1. >7 – thymolphthalein, phenolphthalein

   7 – thymolphthalein, phenolphthalein

   <7 – methyl orange, methyl red

   >7 – methyl orange, methyl red

Titrate boric acid H 3 BO 3 with KOH solution. The pH value at the equivalence point and, accordingly, the indicator used will be

1. 7 – litmus, phenol red

   >7 – thymolphthalein, phenolphthalein

   >7– methyl orange, methyl red

   <7– метилоранж, метиловый красный

To determine nitrous acid by neutralization, you can use a working reagent

1. oxalic acid

   sodium hydroxide

   aqueous ammonia

   sulfuric acid

To titrate 2 ml of nitrous acid solution, 4 ml of titrant solution with an equivalent concentration of 0.03 mol/l was used. The equivalent concentration of nitrous acid and its titer turned out to be equal

1. 0.06 mol/l; 2.82∙10 -3 g/ml

   0.06 g/ml; 2.82∙10 -3 mol/l

   0.15 mol/l; 1.41∙10 -3 g/ml

   0.06 mol/l; 2.82∙10 -3 g/l

A 25 ml sample of household ammonia cleaning solution was diluted with water to exactly 250 ml in a volumetric flask. The titration of 5 ml of a diluted solution required 4 ml of 0.025 M HCl solution. Assuming that the alkalinity of the sample is determined only by ammonia, we calculated the mass of ammonia per 1 liter of solution and obtained the value

1. 85∙10 -3 g/l

   1.7∙10 -3 g/l

   3,4∙10 -3 g/l

   34∙10 -3 g/l

In the Reaction NH 3 +H 2 PO 4 - →NH 4 + +HPO 4 2- dihydrogen phosphate behaves as

1. acid

   base

   oxidizer

   reducing agent

Indicators in the neutralization method are

1. complexing agents

   weak organic acids or bases

   the working solutions themselves act as inductors

   eriochrome black

To determine the equivalence point in the neutralization method, use

2. reactions that form a precipitate

   solutions that change color at the equivalence point

   acid-base indicators

To select an indicator in the neutralization method, you need to know

1. concentration of the indicator and its рТ

   titrant concentration and pH of the medium

   pH of the medium at the equivalence point

   PR of sediment and pH of the environment

An indicator for clarifying the concentration of NAOH for oxalic acid is

2. eriochrome

3. phenolphthalein

The active acidity in a 0.1 m solution of HC1 (in pH units) is equal to

1. When determining the free (active) acidity of gastric juice using the neutralization method, an indicator is used

   1. phenolphthalein

   2. methyl orange

      phenolrot (phenol red)

      methylrot

When determining the associated acidity of gastric juice using the neutralization method, an indicator is used

1. phenolphthalein

2. methyl orange

   phenolrot (phenol red)

   methylrot

When titrating gastric juice with a NaOH working solution, the first equivalence point corresponds to the pH value

2. When titrating gastric juice with a NaOH working solution, titrate to the first equivalence point

   1. total acidity

      free acidity (actuallyHCl)

      associated acidity

      lactic acid

When titrating gastric juice with a NaOH working solution, the second equivalence point corresponds to the pH value

3. When titrating gastric juice with a NaOH working solution, the equivalence point is titrated from the first to the second

   1. total acidity

      free acidity (actually HCl)

      associated acidity

      acetic acid only

If you titrate gastric juice with a working solution of NaOH in the presence of only one indicator - phenolphthalein, you can determine

1. total acidity

   associated acidity

   only hydrochloric acid

   only acetic acid

If you titrate gastric juice with a working solution of NaOH in the presence of only one indicator - methyl orange, you can determine

1. total acidity

   associated acidity

   only hydrochloric acid

   only acetic acid

In a healthy adult, the free acidity of gastric juice is (i.e.)

1. 20 – 40

In an adult healthy person, the total acidity of gastric juice is (i.e.)

1. 40 – 60

The titration of 5 ml of filtered gastric juice in the presence of phenolphthalein required 2.8 ml of 0.095 e NaOH solution. The total acidity of gastric juice is equal to (i.e.)

4. To titrate 10 ml of gastric juice with methyl yellow (dimethylaminoazobenzene), 3.1 ml of 0.098 e NaOH solution was used, and with phenolphthalein - 6.0 ml of NaOH. The hydrochloric acid content and total acidity were (i.e.)

   1. 30.4 and 58.8

NEUTRALIZATION METHOD(syn. acid-base titrimetry) is a titrimetric method for determining the concentration of acids (acidimetry) and alkalis (alkalimetry) in solutions, based on the neutralization reaction, i.e., the reaction of an acid with a base, which occurs with the formation of water and salt.

N. m. is used in clinical biochemical and sanitary hygiene. laboratories, as well as in control and analytical pharmaceutical laboratories. This method in clinical and biochemical laboratories determines the total acidity of the gastric contents, i.e. free and bound hydrochloric acid, organic acids and acid-reacting phosphates, titrating the fresh test material with 0.1 N. solution of caustic soda (see Gastric juice). N. m. is also used to determine the titration acidity and alkalinity of urine, the pH value of intestinal juice, blood, and certain foods.

In aqueous solutions, the neutralization reaction comes down to the combination of hydrogen ions (H +), formed by it, with hydroxyl ions (OH -), formed by an alkali, into water molecules: H + + OH - -> H 2 O.

When determining the concentration of a solution, gradually add it from a burette to a precisely measured volume of the analyzed solution. working solution alkali (for example, caustic soda solution) of a known concentration until the equivalence point is reached, i.e., until such a volume of the working solution (titrant) is added, which contains the amount of alkali equivalent to the amount of acid present in the test volume of the solution taken for titration. Determination of alkali concentration is carried out in a similar way. In this case, a worker is used as a titrant. acid solution, for example, hydrochloric acid, of known concentration.

The concentration of acid or alkali in the analyzed solutions is calculated using the equation:

H = (H 0 V 0)/V,

where V and V 0 are the corresponding volumes of the analyzed solution and titrant, and H and H 0 are the normal concentrations of the analyzed solution and titrant.

Having determined the normal concentration (H) of the analyzed solution, calculate, if necessary, the titer of the solution (T), i.e., the content of acid or alkali in grams in 1 ml of solution, according to the equation:

T = (N*E)/1000

where E is the equivalent of acid or alkali.

To determine the end of titration, acid-base indicators are used (see). Indicator size(1-2 drops) are first added to the solution being analyzed and the titration is completed at the moment of a sharp change in the color of the indicator. Indicators are usually used as indicators in N. m., the color of which is different in an acidic and alkaline environment, for example, bromothymol blue, the zone of color change of which from yellow to blue is in the pH range of 6.0- 7.6; phenol red, changing color from yellow to red at pH 6.8-8.4; phenolphthalein with a zone of color change from colorless to crimson-violet at pH 8.3-10.0, etc. There are also indicator-free methods for determining the equivalent point (see.

the most important methods of titrimetric analysis (See Titrimetric analysis). Based on a neutralization reaction (See Neutralization) , which is simply written in the form H + + OH - = H 2 O. N. m. make it possible to determine the acid content by titrating with a solution of a base (for example, NaOH, KOH) of a known concentration and the base content by titrating with an acid solution of a known concentration (for example, HCl). To establish the titration end point, various chemical indicators are usually used. , clearly changing their color. In the case of cloudy or colored test solutions, use instrumental methods establishing the titration end point (potentiometric, conductometric and other methods).

Titration of acids and bases is usually performed in an aqueous environment. In some cases, it is advisable to titrate in organic solvents, where the strength of acids and bases may be different than in an aqueous environment (see also Acids and Bases). N. m. are widely used in the chemical control of many industries, with scientific research and etc.

Lit.: Kolthof I.M., Stenger V.A., Volumetric analysis, trans. from English, vol. 1-2, M., 1950-52.

A. I. Busev.

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  Dictionary of microbiology

• - surveys in agriculture, a set of methods for collecting, processing and using materials from aero- and space...

  Agricultural Encyclopedic Dictionary

• - Rice. 1. Van Slyke apparatus for determining the alkaline reserve of blood plasma. Rice. 1. Van Slyke apparatus for determining the alkaline reserve of blood plasma...
• - neutralization reaction in microbiology, serological reaction for determining the immunological specificity of antigens and antibodies by the phenomenon of loss of their biological activity after interaction...

  Veterinary encyclopedic dictionary

• - 1) methods for studying the gas composition of blood, based on the principle of physical and chemical displacement of blood gases, absorption of released gases by chemical reagents and measurement of pressure in closed system before and...

  Big medical dictionary

• - a set of techniques that make it possible to study and predict the development of natural objects by comparing the inflow and outflow of matter, energy and other flows...

  Ecological dictionary

• - plant protection, a set of techniques for reducing the number of unwanted organisms with the help of other living beings and biological products...

  Ecological dictionary

• - a method for solving boundary value problems of mathematical physics, which boils down to minimizing functionals - scalar variables that depend on the choice of one or more functions...

  encyclopedic Dictionary in metallurgy

• - "..."exhaust gas aftertreatment system" - a set of components that ensure a reduction in emissions of pollutants from exhaust gases during engine operation;.....

  Official terminology

• - ways, techniques, means of ensuring the necessary control influence of executive authorities, local government bodies carrying out executive activities, their officials...

  Administrative law. Dictionary-reference book

• - I Van Slyke methods, gasometric methods for the quantitative determination of amine nitrogen, oxygen and carbon dioxide in the blood - see Nitrogen. II Van Slyke methods 1) methods for studying the gas composition of blood,...

  Medical encyclopedia

• - methods for identifying histiocytes in preparations nerve tissue and various organs using ammonia silver or pyridine-soda solutions of silver...

  Large medical dictionary

• - methods for neutralizing waste containing organic substances, based on their heating as a result of the vital activity of thermophilic aerobic microorganisms...

  Large medical dictionary

• - a method of identifying a virus based on the phenomenon of its loss of infectivity as a result of interaction with specific antibodies...

  Large medical dictionary

• - interaction of a toxin with a specific antitoxin, leading to the formation of a non-toxic complex...

  Large medical dictionary

• - adj., number of synonyms: 1 neutralized...

  Synonym dictionary

"Neutralization methods" in books

16. The mechanism of the neutralization reaction

16. The mechanism of the neutralization reaction This article should be prefaced with the following statement, which, undoubtedly, should preface all articles on chemistry and nuclear physics - everything where we are talking about chemical elements and their structure. It is necessary to repeat until this fact is not

5.14. About neutralizing Love