A buffer solution is a chemical reagent with a constant pH. Preparation of indicator solutions Preparation of buffer solutions for pH measurements

Standard electrode potentials in aqueous solutions at 25 o C

Electrode	Half-reaction	E 0 , V
Electrodes reversible with respect to the cation
Zn 2+, Zn	Zn 2+ + 2e – → Zn	–0,763
Cd2+, Cd	Cd 2+ + 2e – → Cd	–0,403
Ni2+,Ni	Ni 2+ + 2e – → Ni	–0,250
Pb 2+, Pb	Pb 2+ + 2e – → Pb	–0,126
H+, H2 (g)	H + + e – → ½ H 2	0,000
Cu 2+ , Cu	Cu 2+ + 2e – → Cu	0,337
Ag+, Ag	Ag + + e – → Ag	0,799
Anion reversible electrodes
Cl 2 (g), Cl –	½ Cl 2 + e – → Cl –	1,360
Electrodes of the second kind
AgCl, Cl – (saturated), Ag	AgCl + e – → Ag + Cl –	0,222
Hg, Hg 2 Cl 2, KCl(saturated)	Hg 2 Cl 2 + 2е – → 2Hg + 2Cl –	0,2415 = = E(n.k.e.)
Redox electrodes
Fe(CN) 6 3– , Fe(CN) 6 4– (Pt)	Fe(CN) 6 3– + e – → Fe(CN) 6 4–	0,360
MnO 4 – , MnO 4 2– (Pt)	MnO 4 – + e – → MnO 4 2–	0,564
Fe 3+ , Fe 2+ (Pt)	Fe 3+ + e – → Fe 2+	0,771
Br 2 , 2Br – (Pt)	Br 2 + 2e – → 2Br –	1,087
BrO 3 – , Br – (Pt)	BrO 3 – + 6H + + 6e – → Br – + 3H 2 O	1,450

Limit equivalent electrical conductivity of ions at 25 o C

Half-wave potentials ( E½) some ions

Electrode half-reaction	Wednesday (background)	E½ , V
Сr 3+ + 3e – = Cr	0.5 M NaClO 4 solution	–1,46
Сd 2+ + 2e – = Cd	1 M HCl solution	–0,64
Сu 2+ + e – = Cu +	0.1 M KSCN solution	–0,02
Сu + + e – = Cu	0.1 M KSCN solution	–0,39
Fe 2+ + 2e – = Fe	0.1 M KCl solution	–1,30
Fe 3+ + e – = Fe 2+	1 M solution (NH 4) 2 CO 3	–0,44
Mn 2+ + 2e – = Mn	1 M KCl solution	–1,51
Ni 2+ + 2e – = Ni	0.1 M KCl solution	–1,10
Pb 2+ + 2e – = Pb	0.1 M NaOH solution	–0,76
Zn 2+ + 2e – = Zn	1 M KCl solution	–1,02

Wavelengths of the visible part of the spectrum and their corresponding colors

Flame photometry

Appendix 6

Questions from the test colloquium on the Physics and Mathematics MA course

1. Sensitivity, accuracy, correctness of analysis methods. Calculation confidence interval for analysis results.

2. Emission spectral analysis. Excitation, observation and recording of spectrum lines. Spectral line intensity. Qualitative analysis. Dependence of radiation intensity on concentration. Lomakin–Shaibe formula. Quantitative analysis.

3. Flame photometry. Sources of radiation excitation. Processes in a flame. Suppression of ionization and taking into account the anion effect. Block diagram of the device. Calibration curve and addition methods. Areas of use. Advantages and disadvantages of the method.

4. Atomic absorption analysis. Resonant absorption of atoms. Block diagram of the device. Radiation sources and method of atomization of the analyzed substance. Dependence of optical density on the concentration of the substance. Sensitivity, selectivity, versatility, rapidity of the method.

5. Molecular absorption analysis. Origin of color of analytical forms. Spectrophotometric curve. Integral, average and maximum light absorption coefficients. Bouguer–Lambert–Beer law. Optical density and transmittance. Physical and chemical reasons for deviations from the law of light absorption. The influence of various factors on the optical density value. Selectivity of analysis, masking of impurities. Extraction photometric method.

6. Spectrophotometers and photocolorimeters. Methods of photometric analysis (equalization and comparison of light flux intensities). Calibration curve and addition methods. Differential photometry, its advantages.

7. Photometry of light-scattering systems. Turbidimetry and nephelometry. Photometric and turbidimetric titration.

8. Fluorimetric analysis. The essence of the fluorescence phenomenon. Fluorescence patterns. Stokes rule. Vavilov's law. Factors influencing fluorescence intensity, concentration quenching. Schematic diagram of fluorimetric measurements. Qualitative and quantitative analysis. Sensitivity and reproducibility of the analysis in fluorimetric measurements.

9. Vibrational spectroscopy. General ideas about the types of analytical problems solved in IR spectroscopy. Qualitative and quantitative analysis using IR spectra.

10. Conductometric methods. Dependence of the electrical conductivity of the solution on various factors. Direct conductometry. Method capabilities. Conductometric titration. Schematic diagram of the installation for conductometric analysis. High frequency titration. Essence and features of the method.

11. Potentiometric methods of analysis. Electrode systems. Membrane electrodes, their varieties. The structure of a glass electrode and the dependence of its potential on pH. Ion selective potentiometry. Potentiometric titration. Indicator electrodes. Integral and differential titration curves. Automatic potentiometric titration. Possibilities and disadvantages of potentiometry.

12. Voltammetric types of analysis. Polarography. Schematic diagram of a polarograph. Electrode system. Mercury drop and solid electrodes. Areas of use. Polarograms. Limiting diffusion current. Ilkovich equation. Polarographic wave equation. Half-wave potential. Heyrovsky's equation. Selection of polarographic background. Qualitative and quantitative analysis. Modern polarographic methods.

13. Amperometric titration. The essence of the method. Schematic diagram of an amperometric installation. Selecting an electrode system. Selecting the potential of the indicator electrode. Types of titration curves. Possibilities and disadvantages of the method. Examples of practical implementation of analysis.

14. Electrogravimetric analysis. general characteristics method. Processes on electrodes. Electrodeposition conditions. Requirements for precipitation. Internal electrolysis. Practical use of the electrogravimetry method.

15. Classification of chromatographic methods. Frontal, eluent and displacement methods for chromatographic separation. Chromatograms (output curves). Dependence of the shape of the output curves on the type of adsorption isotherms. Measurement of chromatograms. Absolute and corrected retention parameters. Efficiency of the chromatographic process.

16. Gas chromatography. Its varieties. Schematic diagram of a gas chromatograph. Detectors. Their classification. Stationary phase, the nature of the interaction of the analyte with the stationary phase. Optimal chromatography mode. Van Deemter equation. Identification in gas chromatography.

17. Qualitative analysis. Retention indices. Quantitative analysis. Methods of normalization, absolute calibration, internal standard. Correction factors. Possibilities of gas chromatography.

18. Liquid chromatography. Ion exchange column chromatography. Ion exchange equilibrium. Ion exchange constant, Nikolsky equation. Output sorption curve, dynamic exchange capacity of the ion exchanger. Classification of ion exchangers. Sorption series. Application of ion exchange for purification, concentration and separation in analysis.

19. Plane chromatography. Partition paper chromatography. Mobile phases. One-dimensional, two-dimensional, circular paper chromatography. Qualitative analysis. Motion coefficient R f. Efficiency of paper chromatography. Appearance of stains. Quantitative analysis. Thin layer chromatography. Types of stationary phase. Features of the process of separation, identification and determination of the amount of the analyte.

20. High performance liquid chromatography (HPLC). Schematic diagram of a high-pressure liquid chromatograph. Types of detectors. Stationary phases: normal and reversed. Eluents. Capacitance factor, its physical meaning. Separation efficiency. Snyder's equation. Gradient elution. Relationship between efficiency, selectivity and column capacity. Advantages and limitations of the method.

Vladimir Ivanovich Lutsik

Alexander Evgenievich Sobolev

Yuri Valentinovich Chursanov

PHYSICAL AND CHEMICAL METHODS OF ANALYSIS

Tutorial

First edition

Editor I.V. Shunkova

Corrector

Technical editor G.V. Komarova

Signed for seal

Format 64x80/16 Writing paper

Phys. oven l. Conditional oven l. Academic ed. l.

Circulation Order No. C–

________________________________________________________________

Editorial and Publishing Center

Tver State Technical University

170026 Tver, emb. A. Nikitina, 22

With pH probes.

For the preparation of the specified buffer solutions, it is allowed to use only standard titres of the 2nd category with permissible deviations from the nominal pH value equal to ±0.01 units. pH, confirmed by a certificate of conformity or verification certificate.

Distilled water should be used to prepare buffer solutions.

Method for transferring standard titers into measuring containers

Insert a glass funnel with a diameter of 8-10 cm into a volumetric flask with a capacity of 1 liter according to GOST 1770-74.

If the standard titer is in a bottle, then:

carefully remove the cap from the bottle over the funnel and pour its contents into the funnel;
Thoroughly rinse the inner surface of the bottle and lid several times over a funnel with distilled water until the substance is completely removed into a volumetric flask and bring the volume of liquid to 1 liter.

If the standard titer is in an ampoule, then:

remove the label from the ampoule and rinse it with distilled water;
use a glass striker to pierce the upper recess of the ampoule;
Carefully turn the ampoule over the funnel with the hole down, pierce the second end of the ampoule;
Without changing the position of the ampoule, rinse it from the inside with distilled water in the amount of six times the volume of the ampoule and bring the volume of liquid to 1 liter, shake until completely dissolved.

To ensure complete dissolution of the substance, heat the flask with the solution to t = 20°C and thermostat for 30 minutes.

Place a label on the container indicating the pH of the buffer solution and the date of manufacture.

DRAW YOUR ATTENTION TO!

For preparing and storing buffer solutions, it is better to use liter bottles made of dark glass.
For reliable complete dissolution of crystals of a buffer solution with pH = 1.65, it is recommended:

place the solution in a bottle with a tightly screwed cap;
heat the solution to a temperature of 40÷50° C;
Shaking the bottle periodically to ensure complete dissolution of the buffer solution crystals in the water.

It is NOT RECOMMENDED to store buffer solutions, especially a solution with pH=1.65, in the refrigerator!

To calibrate the acidogastrometer, pour the required portion (≈50 ml) of buffer solutions into glass test tubes with pasted labels indicating the pH of the solution so that the level of the solution is 20-40 mm below the upper edge of the test tube (see the operating manual for the calibration device KFBUYU 441521.003 RE) and heat them to 37°C.

Working solutions in test tubes can be used repeatedly (until cloudy) for 2-3 weeks. Between measurements, test tubes with solutions must be tightly closed with stoppers, preferably rubber or polymer (silicone, etc.).

Do not pour working solutions from test tubes back into containers with clean buffer solutions.

Note – The preparation of buffer solutions is described in more detail in the instructions of the standard titre manufacturer.

Buffer solutions must be protected from the access of carbon dioxide from the air, i.e. they should be stored in tightly closed glass or plastic (fluoroplastic, polypropylene, etc.) containers at a temperature not exceeding 25°C.
All buffer solutions should be protected from direct sunlight to prevent photochemical degradation. They should be stored in a dark (preferably cool) place, covering the vessels and test tubes with an opaque material, for example, dark cotton cloth.

To prepare standard buffer solutions according to GOST 10171-62, it is necessary to quantitatively transfer the contents of the ampoule into a liter volumetric flask and dissolve it in distilled water with a specific electrical conductivity of three temperatures at 20°C of no more than 2.10-6 sym./cm.

When preparing buffer solutions of phosphates and borax, distilled water free of carbon dioxide should be used. Prepared solutions of these substances must be protected from the access of carbon dioxide from the air. The remaining buffer solutions (potassium tetraoxalate, potassium tartrate and potassium phthalate) can be prepared using ordinary distilled water and not protected from carbonic acid air.

A sample buffer solution of potassium tartrate should be saturated at 25°C. When preparing it, it must be shaken for a long time and thermostated at 25°C. Then filter.

Method for transferring standard titer into a flask

Before using the standard titer, you must remove the label from the ampoule and rinse its outer surface with distilled water.

An ordinary funnel with a diameter of 9-10 cm is inserted into a 1000 ml volumetric flask. Then a thickened striker is inserted into the funnel. When transferring the contents into the flask, the ampoule is turned bottom down and slightly hits the tip of the striker with its indentation, then, without turning the ampoules over, the upper recess of the ampoule is pierced with the second striker and the contents are allowed to come out completely.

Without changing the position of the ampoule, the latter is thoroughly washed from the inside with distilled water in an amount of six times the volume of the ampoule.

After dissolving the contents of the ampoule, the volume of liquid is adjusted to the mark and the solution is thoroughly mixed.

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This standard applies to standard titers, which are precise weighed amounts of chemical substances in vials or ampoules, intended for the preparation of buffer solutions with certain pH values, and establishes technical and metrological characteristics and methods for their determination

Replaces GOST 8.135-74 “State system for ensuring uniformity of measurements. pH-metry. Standard titers for the preparation of standard 2nd grade buffer solutions. Technical specifications"

Reissue. December 2007

1 area of use

3 Technical and metrological characteristics

4 Methods for determining the characteristics of standard titers

Appendix A (mandatory) Procedure for the preparation of chemical substances for standard titers

Appendix B (informative) Dependence of pH values of buffer solutions on temperature

Appendix B (mandatory) Procedure for the preparation of buffer solutions - working pH standards of the 2nd (3rd) category from standard titers

This GOST is located in:

Organizations:

08.12.2004	Approved	Interstate Council for Standardization, Metrology and Certification	26
15.04.2005	Approved	Federal Agency for Technical Regulation and Metrology	84-st
	Published	Standardinform	2008
	Published	Standardinform	2005
	Designed by	FSUE VNIIFTRI Federal Agency for Technical Regulation and Metrology

State system for ensuring the uniformity of measurements. Weight amouhts of the standard materials for preparation of the buffer solutions - operational pH standards of 2-nd and 3-rd classes. The technical and the metrological characteristics. Methods of their determination

GOST 1.0-92Interstate standardization system. Basic provisions. Replaced by GOST 1.0-2015.
GOST 24104-2001Laboratory scales. General technical requirements
GOST 6709-72Distilled water. Specifications
GOST 1.2-97Interstate standardization system. Interstate standards, rules and recommendations for interstate standardization. Procedure for development, acceptance, application, updating and cancellation. Replaced by GOST 1.2-2009.
GOST 1770-74Laboratory glassware. Cylinders, beakers, flasks, test tubes. General technical conditions
GOST 18270-72Acetic acid of special purity. Specifications
GOST 199-78Reagents. Sodium acetate 3-water. Specifications
GOST 3885-73Reagents and highly pure substances. Acceptance rules, sampling, packaging, packaging, labeling, transportation and storage
GOST 4172-76Reagents. Sodium phosphate disubstituted 12-water. Specifications
GOST 4198-75Reagents. Potassium phosphate monosubstituted. Specifications
GOST 4199-76Reagents. Sodium tetraborate 10-water. Specifications
GOST 4201-79Reagents. Sodium carbon dioxide is acidic. Specifications
GOST 4530-76Reagents. Calcium carbonate. Specifications
GOST 6552-80Reagents. Phosphoric acid. Specifications
GOST 8.120-99State verification scheme for pH measuring instruments. Replaced by GOST 8.120-2014.
GOST 8.134-98State system for ensuring the uniformity of measurements. pH scale for aqueous solutions. Replaced by GOST 8.134-2014.
GOST 8.135-74State system for ensuring the uniformity of measurements. pH-metry. Standard titers for the preparation of standard 2nd grade buffer solutions. Specifications. Replaced by GOST 8.135-2004.
GOST 83-79Reagents. Sodium carbonate. Specifications

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INTERSTATE COUNCIL FOR STANDARDIZATION, METROLOGY AND CERTIFICATION
(MGS)

INTERSTATE COUNCIL FOR STANDARDIZATION, METROLOGY AND CERTIFICATION
(ISC)

Preface

The goals, basic principles and basic procedure for carrying out work on interstate standardization are established by GOST 1.0-92 “Interstate standardization system. Basic provisions" and GOST 1.2-97 "Interstate standardization system. Interstate standards, rules and recommendations for interstate standardization. Procedure for development, adoption, application, updating and cancellation"

Standard information

1 DEVELOPED by the Federal State Unitary Enterprise "All-Russian Scientific Research Institute of Physical, Technical and Radio Engineering Measurements" (FSUE "VNIIFTRI") of the Federal Agency for Technical Regulation and Metrology

2 INTRODUCED by the Federal Agency for Technical Regulation and Metrology

3 ADOPTED by the Interstate Council for Standardization, Metrology and Certification (Protocol No. 26 of December 8, 2004)

Short name of the country according to MK (ISO 3166) 004-97	Country code according to MK (ISO 3166) 004-97	Abbreviated name of the national standardization body
Azerbaijan		Azstandard
Belarus		State Standard of the Republic of Belarus
Kazakhstan		Gosstandart of the Republic of Kazakhstan
Kyrgyzstan		Kyrgyzstandard
		Moldova-Standard
Russian Federation		Federal Agency for Technical Regulation and Metrology
Tajikistan		Tajikstandard
Uzbekistan		Uzstandard

4 By Order of the Federal Agency for Technical Regulation and Metrology dated April 15, 2005 No. 84-st, the interstate standard GOST 8.135-2004 was put into effect directly as a national standard Russian Federation since August 1, 2005

6 REPUBLICATION. December 2007

Information on the entry into force (termination) of this standard and amendments to it is published in the index “ National standards».

Information about changes to this standard is published in the index (catalogue) “National Standards”, and the text of the changes is published in information signs “National Standards”. In case of revision or cancellation of this standard, the relevant information will be published in the information index “National Standards”

INTERSTATE STANDARD

Date of introduction - 2005-08-01

1 area of use

2 Normative references

This standard uses normative references to the following standards:

3.8 Requirements for packaging, packaging, labeling and transportation of standard titers - according to technical specifications for specific standard titers.

3.9 Operational documentation The standard titers must contain the following information:

Purpose: category (2nd or 3rd) of working pH standards - buffer solutions prepared from standard titres;

Nominal pH value of buffer solutions at 25 °C;

Volume of buffer solutions in cubic decimeters;

Methodology (instructions) for preparing buffer solutions from standard titers, developed in accordance with Appendix B of this standard;

Shelf life of standard titer.

4 Methods for determining the characteristics of standard titers

4.1 Number of samples n to determine the characteristics of each modification, standard titers are selected according to GOST 3885 depending on the volume of the batch of standard titers of this modification, but at least three samples of standard titers in ampoules (for determining pH) and at least six samples in bottles (3 for determining mass, 3 - to determine pH).

4.2 The measuring instruments used must have verification certificates (certificates) with a valid verification period.

4.3 Measurements are carried out under normal conditions:

ambient air temperature, °C 20 ± 5;

relative air humidity, % from 30 to 80;

atmospheric pressure, kPa (mm Hg) from 84 to 106 (from 630 to 795).

4.4 The mass of a sample of a chemical substance in a bottle 1) is determined by the difference in the mass of the bottle with the sample and the mass of an empty, clean bottle. Measurements of the mass of the sample and the mass of the bottle are carried out with an error of no more than 0.0005 g on an analytical balance (accuracy class not lower than 2 according to GOST 24104).

1) In a glass ampoule, the mass of a sample of the standard titer is not determined.

4.4.1 Deviation D i, %, weight of the sample from the nominal value of the weight for each of the samples is determined by the formula

Where m nom- nominal mass of a sample of the chemical substance included in the standard titer (see Table 1);

i- standard titer sample number;

m i- mass measurement result i th sample ( i = 1 ... n), G.

4.4.2 If for at least one of the samples the value D i will be more than 0.2% (and for standard titers for the preparation of saturated buffer solutions - more than 1%), then the batch of standard titers of this modification will be rejected.

4.5 From the standard titre samples selected according to 4.1, buffer solutions are prepared to determine the pH value according to the method given in Appendix B.

4.5.1 The pH value of the buffer solution - the working standard pH of the 2nd category, prepared from the standard titer, is determined using the working standard pH of the 1st category (GOST 8.120) at the temperature of the buffer solutions (25 ± 0.5) °C at in accordance with the pH measurement procedures included in regulations working pH standard of the 1st category.

4.5.1.1 Deviation of pH from the nominal value (D pH) i, determined by the formula

(D pH) i= |pH nom - pH i |,

Where i- standard titer sample number;

pH nom - nominal pH value of the buffer solution according to table 1;

pH i - the result of measuring the pH value i th sample ( i = 1 ... n).

4.5.1.2 If value (D pH) i for each of the buffer solutions is not more than 0.01 pH, then the standard titers of this batch are considered suitable for the preparation of a working pH standard of the 2nd category.

If the value (D pH) i for each of the buffer solutions is not more than 0.03 pH, then the standard titers of this batch are considered suitable for the preparation of a working pH standard of the 3rd category.

4.5.4 The pH value of the buffer solution - the working pH standard of the 3rd category, prepared from the standard titer, is determined by the standard pH meter of the 2nd category (GOST 8.120) in accordance with the operating instructions for the pH meter at the temperature of the buffer solutions (25 ± 0.5) °C.

4.5.2.1 Deviation of pH from the nominal value (D pH) i determined according to 4.5.1.1.

4.5.2.2 If value (D pH) i for each of the buffer solutions is not more than 0.03 pH, then the standard titers of this batch are considered suitable for the preparation of a working pH standard of the 3rd category.

If for at least one of the buffer solutions (D pH) i will be more than 0.03 pH, then the measurements are repeated on twice the number of samples.

The results of repeated measurements are final. If the results are negative, the batch of standard titers is rejected.

Appendix A
(required)

Method for preparing chemicals for standard titers

Chemicals for standard titers are obtained by additional purification of chemical reagents of at least analytical grade. Chemical reagents of special purity and chemical grade qualifications can be used without additional purification. However, the final criterion for their suitability for standard titers is the pH value of buffer solutions prepared from standard titers. To purify substances, it is necessary to use distilled water (hereinafter referred to as water) with a specific electrical conductivity of no more than 5 × 10 -4 Sm × m -1 at a temperature of 20 ° C according to GOST 6709.

A.1 Potassium tetraoxalate 2-aqueous KH 3 (C 2 O 4) 2 × 2H 2 O is purified by double recrystallization from aqueous solutions at a temperature of 50 °C. Dry in a drying cabinet with natural ventilation at a temperature of (55 ± 5) °C until constant weight.

A.2 Sodium hydrodiglycolate (oxydiacetate) C 4 H 5 O 5 Na is dried at a temperature of 110 ° C to constant weight. If the chemical reagent is not available, then sodium hydrodiglycolate is obtained by half-neutralizing the corresponding acid with sodium hydroxide. After crystallization, the crystals are filtered on a porous glass filter.

A.3 Potassium hydrogen tartrate (potassium tartrate) KNS 4 H 4 O 6 is purified by double recrystallization from aqueous solutions; dried in an oven at a temperature of (110 ± 5) °C until constant weight.

A.4 Potassium hydrophthalate (potassium phthalate acid) KNS 8 H 4 O 4 is purified by double recrystallization from hot aqueous solutions with the addition of potassium carbonate during the first recrystallization. Filter off the precipitated crystals at a temperature not lower than 36 °C. Dry in a drying cabinet with natural ventilation at a temperature of (110 ± 5) °C until constant weight.

A.5 Acetic acid CH 3 COOH (GOST 18270) is purified using one of the following methods:

a) distillation with the addition of a small amount of anhydrous sodium acetate;

b) double fractional freezing (after the completion of the crystallization process, the excess liquid phase is removed).

A.6 Sodium acetate 3-water (sodium acetate) CH 3 COONa×3H 2 O (GOST 199) is purified by double recrystallization from hot aqueous solutions, followed by calcination of the salt at a temperature of (120 ± 3) °C to constant weight.

A.7 Piperazine phosphate C 4 H 10 N 2 H 3 PO 4 × H 2 O is synthesized from piperazine and orthophosphoric acid (GOST 6552), purified by triple recrystallization from alcohol solutions. Dry over silica gel in the dark in a desiccator until constant weight.

A.8 Single-substituted potassium phosphate (potassium dihydrogen phosphate) KN 2 PO 4 (GOST 4198) is purified by double recrystallization from a water-ethanol mixture with a volume ratio of 1: 1 and subsequent drying in an oven at a temperature of (110 ± 5) ° C to constant weight .

A.9 Sodium phosphate disubstituted 12-water (sodium monohydrogen phosphate) Na 2 HPO 4 (anhydrous) is obtained from the 12-aqueous salt Na 2 HPO 4 × 12H 2 O (GOST 4172) by three-fold recrystallization from hot aqueous solutions. Dry (dehydrate) in a drying cabinet with natural ventilation in stages in the following modes:

At (30 ± 5) °С - to constant weight

At (50 ± 5) °С - » » »

At (120 ± 5)°С - » » »

A.10 Tris-(hydroxymethyl)-aminomethane (HOCH 2) 3 CNH 2 is dried at 80 °C in an oven to constant weight.

A.11 Tris-(hydroxymethyl)-aminomethane hydrochloride (HOCH 2) 3 CNH 2 HCl is dried at 40 °C in an oven to constant weight.

A.12 Sodium tetraborate 10-aqueous Na 2 B 4 O7 × 10H 2 O (GOST 4199) is purified by threefold recrystallization from aqueous solutions at a temperature of (50 ± 5) °C. Dry at room temperature for two to three days. The final preparation of sodium tetraborate is carried out by keeping the salt in a glass-graphite (quartz, platinum or fluoroplastic) cup in a desiccator over a saturated solution of a mixture of sodium chloride and sucrose or a saturated KBr solution at room temperature until constant weight.

A.13 Sodium carbonate Na 2 CO 3 (GOST 83) is purified by threefold recrystallization from aqueous solutions, followed by drying in an oven at a temperature of (275 ± 5) °C to constant weight.

A.14 Sodium carbonate NaHCO 3 (GOST 4201) is purified by threefold recrystallization from aqueous solutions with bubbling with carbon dioxide.

A.15 Calcium hydroxide Ca(OH) 2 is obtained by calcination of calcium carbonate CaCO 3 (GOST 4530) at a temperature of (1000 ± 10) °C for 1 hour. The resulting calcium oxide CaO is cooled in air at room temperature and slowly poured in small portions water with constant stirring until a suspension is obtained. The suspension is heated to a boil, cooled and filtered through a glass filter, then removed from the filter, dried in a vacuum desiccator to a constant weight and ground to a fine powder. Store in a desiccator.

Appendix B
(informative)

Dependence of pH values of buffer solutions on temperature

Standard title modification number

Chemical substances included in the standard titer (modifications according to Table 1)

pH of buffer solutions at temperature, °C

Potassium tetraoxalate 2-water

Sodium hydrodiglycolate

Potassium hydrogen tartrate

Potassium hydrophthalate

Acetic acid + sodium acetate

Piperazine phosphate

Sodium monohydrogen phosphate + potassium dihydrogen phosphate

Tris hydrochloride + tris

Sodium tetraborate

Sodium carbonate acid + sodium carbonate

Calcium hydroxide

Appendix B
(required)

Methods for preparing buffer solutions - working pH standards of the 2nd (3rd) category from standard titers

IN 1 Preparation of working standards

Working pH standards are prepared by dissolving the contents of standard titers in distilled water according to GOST 6709 (hereinafter referred to as water) with a specific electrical conductivity of no more than 5 × 10 -4 Sm × m -1 at a temperature of 20 ° C.

Note - To prepare solutions with a pH value > 6, distilled water must be boiled and cooled to a temperature of 25 - 30 °C. When preparing glassware, synthetic detergents should not be used.

B.1.1 The standard titer is transferred to a 2nd class volumetric flask according to GOST 1770 (hereinafter referred to as the flask).

B.1.2 Remove the bottle (ampoule) from the packaging.

B.1.3 Wash the surface of the bottle (ampoule) with water and dry it with filter paper.

B.1.4 Insert a funnel into the flask, open the bottle (ampoule) in accordance with the manufacturer’s instructions, allow the contents to pour completely into the flask, rinse the bottle (ampoule) from the inside with water until the substance is completely removed from the surfaces, pour the washing water into the flask.

B.1.5 Fill the flask with water to approximately two-thirds of the volume, shake until the contents are completely dissolved (with the exception of saturated solutions of potassium hydrogen tartrate and calcium hydroxide).

B.1.6 Fill the flask with water without adding water to the 5 - 10 cm 3 mark. The flask is thermostated for 30 minutes in a water thermostat at a temperature of 20 °C (flasks with saturated solutions of potassium hydrogen tartrate and calcium hydroxide are completely filled with water and thermostated for at least 4 hours at a temperature of 25 °C and 20 °C, respectively, periodically stirring the suspension in the flask by shaking ).

B.1.7 Fill the volume of the solution in the flask with water to the mark, close with a stopper and mix the contents thoroughly.

In samples taken from saturated solutions of potassium hydrogen tartrate and calcium hydroxide, the precipitate is removed by filtration or decantation.

AT 2 Storage of working pH standards

B.2.1 Working pH standards are stored in tightly closed glass or plastic (polyethylene) containers in a dark place at a temperature not exceeding 25 °C. The shelf life of working standards is 1 month from the date of preparation, with the exception of saturated solutions of potassium hydrogen tartrate and calcium hydroxide, which are prepared immediately before measuring pH and which cannot be stored.

Buffer solution – chemical reagent with constantpH

Laboratory glassware, laboratory equipment, instruments and chemical substances these are the four main components of any modern laboratory, regardless of its specialization. Depending on the purpose, laboratory products - glassware, equipment, instruments - are made from various materials: plastic, porcelain, quartz, borosilicate, laboratory glass, etc. It’s just a matter of price and quality. Chemical reagents occupy a special place in the list of laboratory equipment - without them it is impossible to carry out even the simplest analysis, research, or experiment.

In laboratory practice, employees often encounter chemical solutions that have or should have a certain pH value. It is for these purposes that special buffer solutions are made.

What is this solution?

Buffer solutions are chemical reagents with a certain stable concentration of hydrogen ions; a mixture of a weakly concentrated acid and its salt. These solutions practically do not change their structure when concentrated or diluted with other chemical reagents or when highly concentrated alkalis or acids are added to it in small quantities. To obtain a buffer solution with a different pH, it is necessary to change the concentration and ratio of the chemical solutions used.

This chemical reagent is capable of maintaining a certain pH value to a certain level, depending on the specific amount of aggressive media, alkalis and acids. Each buffer mixture has a certain buffer capacity - the equivalent ratio of the elements of alkali and acid.

Unfortunately, acids and alkalis themselves cannot be classified as buffer mixtures, since when they are diluted with water, the pH level of these aggressive media changes.

In laboratory practice, a calibration buffer mixture is also applicable. It is designed to adjust the accuracy of the indicators of instruments that are used to determine the acid level of liquid substances - activity in various environments of hydrogen ions.

For work both in laboratory conditions and in private practice, it is recommended to use highly stable buffer mixtures prepared in specialized laboratories using laboratory glassware on special laboratory equipment and instruments. Independent preparation of this chemical reagent can be obtained with a large error.

What does the buffer solution consist of?

The composition of this chemical reagent includes water - a solvent and equally dissolved ions or molecules of substances that make up an acid-base or alkaline-acid buffer system. A buffer system is the interaction of a weakly concentrated acid with one of its salts.

Such chemical reagents, together with modern laboratory equipment and instruments, have found wide application in research. analytical chemistry, biology and microbiology, genetics, medicine, pharmaceuticals, research centers and other scientific fields.

Importance of buffer solution for humans

A natural buffer mixture is also very important for the normal functioning of the body, since it helps maintain a constant pH level of biological fluids of tissues, organs, lymph and blood.

Storage conditions

This chemical must be stored in a hermetically sealed container (glass or plastic bottles).

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