Analysis (chemical, physico-chemical, physical and biological).
Requirements for reactions in quantitative analysis. Role
And the importance of quantitative analysis in pharmacy
Quantitative Analysis- a set of methods of analytical chemistry for determining the quantity (content) of elements (ions), radicals, functional groups, compounds or phases in the analyzed object.
Objectives of Quantitative Analysis
Quantitative analysis makes it possible to establish the elemental and molecular composition of the object under study or the content of its individual components.
Depending on the object of study, inorganic and organic analysis are distinguished. In turn, they are divided into elemental analysis, the task of which is to establish how many elements (ions) are contained in the analyzed object, into molecular and functional analyzes, which give an answer about the quantitative content of radicals, compounds, as well as functional groups of atoms in the analyzed object.
Along with qualitative analysis Quantitative Analysis is one of the main branches of analytical chemistry. Based on the amount of substance taken for analysis, macro-, semi-micro, micro- and ultra-micro methods are distinguished. Quantitative Analysis In macromethods, the sample weight is usually >100 mg, solution volume > 10 ml; in ultramicromethods - 1-10 -1, respectively mg and 10 -3 -10 -6 ml. Depending on the object of study, inorganic and organic are distinguished. Quantitative Analysis, divided, in turn, into elemental, functional and molecular analysis. Elemental analysis allows you to determine the content of elements (ions), functional analysis - the content of functional (reactive) atoms and groups in the analyzed object. Molecular Quantitative Analysis involves the analysis of individual chemical compounds characterized by a certain molecular weight. The so-called phase analysis is a set of methods for separating and analyzing individual structural (phase) components of heterogeneous systems. In addition to specificity and sensitivity, an important characteristic of the methods is Quantitative Analysis- accuracy, that is, the value of the relative error of determination; accuracy and sensitivity in Quantitative Analysis expressed as a percentage.
To classical chemical methods Quantitative Analysis include: gravimetric analysis, based on accurate measurement of the mass of the substance being determined, and volumetric analysis. The latter includes titrimetric volumetric analysis - methods for measuring the volume of a reagent solution consumed in a reaction with the analyte, and gas volumetric analysis - methods for measuring the volume of analyzed gaseous products.
Along with classical chemical methods, physical and physico-chemical (instrumental) methods are widely used Quantitative Analysis, based on the measurement of optical, electrical, adsorption, catalytic and other characteristics of the analyzed substances, depending on their quantity (concentration). Typically, these methods are divided into the following groups: electrochemical (conductometry, polarography, potentiometry, etc.); spectral or optical (emission and absorption spectral analysis, photometry, colorimetry, nephelometry, luminescent analysis, etc.); X-ray (absorption and emission X-ray spectral analysis, X-ray phase analysis, etc.); chromatographic (liquid, gas, gas-liquid chromatography, etc.); radiometric (activation analysis, etc.); mass spectrometric. The listed methods, while inferior to chemical methods in accuracy, are significantly superior to them in sensitivity, selectivity, and speed of execution. Accuracy of chemical methods Quantitative Analysis is usually in the range of 0.005-0.1%; errors in determination by instrumental methods are 5-10%, and sometimes significantly more.
CHEMICAL METHODS FOR QUANTITATIVE CHEMICAL ANALYSIS
Chemical methods of quantitative chemical analysis are based on the principle of conducting a chemical reaction with the determined component of the analyzed sample.
Chemical methods of chemical analysis are divided into titrimetric, gravimetric and volumetric methods.
1) titrimetry methods:
Titrimetric analysis (titration) - methods of quantitative analysis in analytical and pharmaceutical chemistry, based on measuring the volume of a reagent solution of precisely known concentration, consumed for the reaction with the substance being determined. Titration is the process of determining the titer of the test substance. Titration is carried out using a burette filled with titrant to the zero mark. It is not recommended to titrate starting from other marks, since the burette scale may be uneven. The burettes are filled with the working solution through a funnel or using special devices if the burette is semi-automatic. The end point of titration (equivalence point) is determined by indicators or physicochemical methods (electrical conductivity, light transmission, indicator electrode potential, etc.). The analysis results are calculated based on the amount of working solution used for titration.
Analytical chemistry deals with the study of experimental methods for determining the composition of substances. Determining the composition of substances includes identifying the nature of the components that make up the substance under study and establishing the quantitative relationships of these components.
First, the qualitative composition of the object under study is established, i.e. solve the question of what it consists of, and then proceed to determine the quantitative composition, i.e. find out in what quantitative ratios the detected components are found in the object of study.
Qualitative analysis substances can be carried out using chemical, physical, physicochemical methods.
Chemical methods of analysis are based on the use of characteristic chemical reactions to determine the composition of the analyte.
Chemical analysis of a substance is carried out in two ways: “dry way” or “wet way”. Dry analysis- these are chemical reactions that occur with substances during incandescence, fusion and coloring of the flame.
Wet analysis- These are chemical reactions that occur in electrolyte solutions. The analyzed substance is pre-dissolved in water or other solvents. Depending on the mass or volume of the substance taken for analysis, on the technique used, macro-, semi-micro- and micromethods are distinguished.
Macro method. To carry out the analysis, take 1-2 ml of a solution containing at least 0.1 g of the substance and add at least 1 ml of the reagent solution. The reactions are carried out in a test tube, the precipitate is separated by filtration. The filter cake is washed to remove impurities.
Semi-micromethod. For analysis, 10-20 times less substance is taken (up to 0.01 g). Since this method works with small quantities of a substance, microtubes, watch glasses or slides are used. Centrifugation is used to separate the precipitate from the solution.
Micromethod. When performing an analysis using this method, take one or two drops of the solution, and dry matter - within 0.001 g. Typical reactions are carried out on a watch glass or porcelain plate.
When carrying out the analysis, the following operations are used: heating and evaporation, sedimentation, centrifugation, checking the completeness of sedimentation, separation of the solution (centrifuge) from the sediment, washing and dissolving the sediment.
Heating solutions can be carried out directly with the flame of a gas burner, on an asbestos grid or in a water bath. A small amount of the solution is heated to a temperature not exceeding 100°C in a water bath, in which the water should boil evenly.
For concentration solutions use a water bath. Evaporation the solution to a dry residue is carried out in porcelain cups or crucibles, heating them on an asbestos mesh. If the dry residue after evaporation needs to be calcined to remove volatile salts, then the crucible is placed on a porcelain triangle and heated with the flame of a gas burner.
Precipitation. The precipitation reaction is carried out in conical flasks or cylindrical test tubes. The precipitating reagent is pipetted into the test solution. The precipitant is taken in excess. The mixture is thoroughly mixed with a glass rod and rubbed against the inner walls of the test tube, this accelerates the process of sediment formation. Precipitation is often carried out from hot solutions.
Centrifugation. The precipitate is separated from the solution by centrifugation using a manual or electric centrifuge. The test tube with the solution and sediment is placed in a sleeve. The centrifuge must be loaded evenly. With rapid rotation, the centrifugal force throws sediment particles to the bottom and compacts it, and the solution (centrifuge) becomes transparent. The rotation time ranges from 30 s to several minutes.
Checking the completeness of deposition. The test tube is carefully removed from the centrifuge and 1-2 drops of the precipitating reagent are added along the wall to the clear solution. If the solution does not become cloudy, the precipitation is complete. If cloudiness of the solution is observed, then a precipitant is added to the test tube, the contents are mixed, heated and centrifuged again, then the completeness of precipitation is checked again.
Separation of the solution (centrifugate) from the sediment. After making sure that precipitation is complete, separate the solution from the precipitate. The solution is separated from the precipitate using a drop pipette. The pipette is closed with the index finger and carefully removed from the test tube. If the selected solution is needed for analysis, then it is transferred to a clean test tube. For complete separation, the operation is repeated several times. During centrifugation, the precipitate may settle tightly to the bottom of the test tube, then the solution is separated by decantation (carefully drained).
Washing the sediment. The sediment (if it is examined) must be washed well; To do this, a washing liquid is added, most often distilled water. The contents are thoroughly mixed with a glass rod and centrifuged, then the washing liquid is separated. Sometimes in work this operation is repeated 2-3 times.
Dissolution of sediment. To dissolve the precipitate, add a solvent to the test tube, stirring with a glass rod. Often the precipitate is dissolved by heating in a water bath.
To determine quantitative composition substances or products, reactions of neutralization, precipitation, oxidation - reduction, and complexation are used. The amount of a substance can be determined by its mass or the volume of solution spent on interaction with it, as well as by the refractive index of the solution, its electrical conductivity or color intensity, etc.
According to the amount of substance taken for research, analytical methods of quantitative analysis are classified as follows: macroanalysis - 1-10 g of solid substance, 10-100 ml of the analyzed solution; semi-microanalysis - 0.05-0.5 solids, 1-10 ml of analyzed solution; microanalysis - 0.001-1-10-4 g of solid substance, 0.1-1 * 10-4 ml of the analyzed solution. In merchandising practice, gravimetric (weight) and titrimetric (volume) methods are often used.
Gravimetric (weight) analysis- one of the methods of quantitative analysis, which allows you to determine the composition of the analyte by measuring mass. Mass measurement (weighing) is performed on an analytical balance with an accuracy of 0.0002 g. This method is often used in food laboratories to determine moisture, ash content, and the content of individual elements or compounds. The analysis can be performed in one of the following ways.
1. The component to be determined is quantitatively (as completely as possible) isolated from the test substance and weighed. This is how the ash content of products is determined. The initial product (sample) weighed on an analytical balance is burned, the resulting ash is brought to a constant mass (calcined until the mass stops changing) and weighed.
The ash content of the product x (%) is calculated using the formula
where B is the mass of calcined ash, g;
A is the initial weight of the product, g.
2. The component to be determined is completely removed from the sample of the starting substance and the residue is weighed. This is how the moisture content of the products is determined, while a sample of the starting substance is dried in an oven to constant weight.
The moisture content of the product x (%) is calculated using the formula
where A is the initial sample of the product, g;
B is the mass of the sample after drying, g.
Volumetric analysis- a method of quantitative analysis, where the desired substance is determined by the volume of a reagent with a precisely known concentration spent on the reaction with this substance.
When determining by volumetric method, a reagent with a precisely known concentration is added in small portions (drop by drop) to a known volume of a solution of the analyte until its amount is equivalent to the amount of the analyte. A solution of a reagent with an accurately known concentration is called a titrated, working or standard solution.
The process of slowly adding a titrated solution to a solution of the analyte is called titration. The moment when the amount of the titrated solution is equivalent to the amount of the substance being determined is called the equivalence point or the theoretical end point of the titration. To determine the equivalence point, indicators are used that, near it, undergo visible changes, expressed in a change in the color of the solution, the appearance of turbidity or the formation of a precipitate.
The most important conditions for correct performance of volumetric analytical determinations: 1) the ability to accurately measure volumes of solutions; 2) the availability of standard solutions with precisely known concentrations; 3) the ability to accurately determine the moment of completion of the reaction (correct choice of indicator).
Depending on the reaction on which the determination is based, the following types of volumetric method are distinguished:
neutralization method
· oxidation-reduction method
· precipitation and complexation method.
At the core neutralization method lies the reaction of interaction between H + and OH - ions. The method is used to determine acids, bases and salts (that react with acids or bases) in solution. To determine acids, titrated solutions of alkalis KOH or NaOH are used, and to determine bases, solutions of acids HC1, H 2 SO 4 are used.
To determine, for example, the acid content in a solution, a precisely measured volume of an acid solution with a pipette in the presence of an indicator is titrated with an alkali solution of precisely known concentration. The equivalence point is determined by the change in color of the indicator. Based on the volume of alkali consumed for titration, the acid content in the solution is calculated.
Method oxidation - reduction is based on redox reactions occurring between a standard solution and the analyte. If the standard solution contains an oxidizing agent (reducing agent), then the substance to be determined must contain a corresponding reducing agent (oxidizing agent). The oxidation-reduction method is divided, depending on the standard solution used, into the permanganatometry method, the iodometry method, etc.
The basis of the method deposition there are reactions accompanied by precipitation. Unlike the gravimetric method, the sediment is not processed here; the mass of the substance under study is determined by the volume of the reagent consumed for the precipitation reaction.
Qualitative analysis of inorganic substances. Subject and tasks of qualitative analysis. Basic concepts.
Qualitative analysis is the discovery or discovery of constituent components in the system under study.
The purpose of qualitative analysis is definition; elemental or isotopic composition of a substance. When analyzing organic compounds, individual chemical elements, such as carbon, sulfur, phosphorus, nitrogen or functional groups, are directly found. When analyzing inorganic compounds, it is determined which ions, molecules, groups of atoms, and chemical elements make up the substance being analyzed.
Classification of methods of qualitative analysis. Analytical signal
Depending on the amount of sample used in the analysis, there are:
Macroanalysis (weight – more than 100 mg, solution volume – 10-100 ml)
Semi-microanalysis (weight – 10-100 mg, solution volume – 1-10 ml)
Microanalysis (weight – 1-10 mg, solution volume – 0.01-1 ml)
Submicroanalysis (weight – 0.1-1 mg, solution volume – 0.001-0.01 ml)
Ultramicroanalysis (weight – less than 0.1 mg, solution volume – less than 0.001 ml)
If it is necessary to detect any component, it is usually
The appearance of an analytical signal is recorded - the appearance of sediment, color, etc. The appearance of the analytical signal must be reliable
fixed. When determining the amount of a component, the value is measured
analytical signal - sediment mass, etc.
Fractional and systematic analysis. Group reagent.
Fractional analysis - detection of ions using specific reactions in individual portions of the test solution, performed in any sequence.
Systematic analysis is a specific sequence of reactions in which each ion is detected after all interfering ions have been removed.
During systematic analysis, ions are isolated from a complex mixture in whole groups, using the same relationship to certain reagents.
Reagents that make it possible to isolate a group of ions from a complex mixture are called group reagents.
Requirements:
* must precipitate ions almost completely
* the resulting precipitate should be easily dissolved in alkalis or acids for further research.
* its excess should not interfere with the detection of ions remaining in the solution.
Classification of cations into analytical groups.
Hydrogen sulfide (ammonium sulfide)
1 – Na+, K+, Pb+, Cs+, Fr+, NH4+, Mg+, (reagent group - no)
2 – Ca+2, Sr+2, Ba+2, Ra+2, (reagent group – (NH 4) 2 CO 3, pH=8-9)
3.1 – Fe (II and III), Mn+2, Zn+2, Co+2, Ni+2, (reagent group - (NH 4) 2 S, pH = 8-9) (precipitated in the form of sulfides)
3.2 – Al+3, Cr+3, Ti+4, Be+2 (reagent group - (NH 4) 2 S, pH = 8-9) (precipitated in the form of hydroxides)
4.1 – Cu+2, Hg+2, Bi+3, Cd+2, (reagent group – H 2 S) (do not dissolve in (NH 4) 2 S)
4.2 – Sn+2, Sn+4, Sb+3, Sb+5, As+3, As+5, (reagent group – HCl, pH=0.5)
5 – Ag+, Bb+2, Hg+4 (reagent group - HCl)
Classification of anions into analytical groups.
1.1 (not dissolved in HCl) – SO 4 -2, group reagent – BaCl.
1.2 (dissolved in HCl) – SO 3 -2, S2O3 -2, CO 3 -2, SiO 3 -2, PO 4 -3 group reagent – BaCl.
2 – I-, Cl-, S, Br-, group reagent – AgNO 3.
3 – NO 3 -, CH 3 COO- group reagent – no.
Subject and tasks of quantitative analysis. Classification of methods of quantitative chemical analysis.
Quantitative analysis - determines the quantitative content of components in the system under study.
Quantitative chemical analysis methods are used to determine the quantitative ratios of the constituent parts in the substance under study. Quantitative methods can be used to determine the compound of a chemical element or other component in a content, alloy, mixture, solution. In addition, quantitative methods make it possible to determine atomic, equivalent and molecular masses, equilibrium constants, solubility products, acidity or alkalinity of the medium.
Gravimetric (weight) methods – sediment is isolated and weighed.
Titrimetric (volumetric) methods - measurement of V standard solution required for the reaction.
Gas volumetric - Measurement of V gas released during a reaction.
The task of quantitative analysis is to determine quantitative
All methods of quantitative analysis are divided into chemical, physicochemical and physical. Chemical methods include gravimetric, titrimetric and gas analyses, physicochemical methods include photometry, electrochemical and chromatographic analyses, and physical methods include spectral analysis and luminescence.
1. Gravimetric analysis is based on determining the mass of a substance isolated in pure form or in the form of a compound of known composition. For example, to determine the amount of barium in its compounds, the Ba 2+ ion is precipitated using dilute sulfuric acid. The BaSO 4 precipitate is filtered, washed, calcined and accurately weighed. Based on the mass of BaSO 4 sediment and its formula, calculate how much it contains
barium The gravimetric method gives highly accurate results, but it is very labor-intensive.
2. Titrimetric analysis is based on accurate measurement of the volume of the reagent,
spent on a reaction with a certain component. The reagent is taken in the form of a solution of a certain concentration - a titrated (standard) solution. The moment when the reagent is added in an amount equivalent to the content of the substance being determined, i.e. the end of the reaction is determined in various ways. During titration, a reagent is added in an amount equivalent to the amount of the substance being tested. Knowing the volume and exact concentration of the solution that reacted with the substance being determined, its quantity is calculated.
Titrimetric analysis gives less accurate results than gravimetric analysis, but its important advantage is the greater speed of analysis. Depending on the type of reactions occurring during the titration process, titrimetric analysis includes acid-base titration methods, oxidimetric methods, and precipitation and complexation methods.
3. Photometric methods are based on measuring the absorption, transmission and scattering of light by a solution. For most photometric methods, so-called color reactions are used, i.e. chemical reactions accompanied by a change in the color of the solution. A method based on determining the content of a substance by color intensity is called colorimetry. The color intensity of the solution is assessed visually or using appropriate instruments.
Sometimes the component being determined is converted into a sparingly soluble compound and its content is judged by the intensity of turbidity of the solution. A method based on this principle is called nephelometry. Colorimetry and nephelometry methods are used to determine the components that make up the analyte in very small quantities. The accuracy of this method is lower than that of gravimetric or titrimetric methods.
4. Electrochemical methods. These methods include electrogravimetric analysis, conductometry, potentiometry and polarography. Electrogravimetric method used to determine the concentration of metals. The element to be determined is deposited by electrolysis on an electrode whose mass is known. Conductometry and potentiometry refer to electrotitrimetry. The completion of the reaction during titration is determined either by measuring the electrical conductivity of the solution or by measuring the potential of the electrode immersed in the test solution. The potentiometric method is also used to determine the pH of a solution. The determination is based on measuring the electromotive force of the solution (emf), which depends on the concentration of hydrogen ions. In the polarographic method The amount of the ion being determined is judged by the nature of the current-voltage curve (polarogram), obtained by electrolysis of the test solution with a dropping mercury cathode in a special device - a polarograph. This method is highly sensitive. Using the polarographic method, it is possible to qualitatively and quantitatively determine various elements in the same solution without resorting to chemical reactions.
QUANTITATIVE ANALYSIS
Chemical methods
Classical chemical methods of analysis
Gravimetry (weight analysis).
The method is based on measuring the mass (weight) of a poorly soluble compound (precipitate) formed as a result of a chemical reaction between determined component and reagent(precipitator). The measurement is carried out by weighing on a gravimetric analytical balance.
Determined component + precipitant = precipitate weighed form
(determinable form) (reagent, (precipitable (gravimetric)
reagent) form) form)
Titrimetry (titrimetric or volumetric analysis).
The method is based on accurate measurement of the volume of a solution of a known reagent that reacts with the component being determined. Used in titrimetry titrated solutions, the concentration of which is known. These solutions are called titrants (working solutions). The process of gradually pouring (adding dropwise) a titrant solution to a solution of the analyte is called titration. When titrating, add the amount of titrant substance equivalent quantity analyte.
The end of the reaction is called the point of stoichiometry or equivalence point.
Experimentally, the end of the titration is determined by the appearance or disappearance of the color of the solution, the cessation of precipitation, or using indicators. This point is called the titration end point
Requirements for reactions that form the basis of methods
Quantitative analysis
The interaction between the component being determined and the reagent must occur in certain stoichiometric ratios according to the reaction equation. The reaction should go almost to completion. The reaction product must have a certain exact composition and formula.
The reaction must proceed quickly, at high speed, which is especially important for direct titration. It is difficult to accurately fix the equivalence point for slow reactions. There should be a minimum of adverse or competing reactions.
There must be a satisfactory way of finding (determining) the equivalence point and the end of the titration.
Titrimetry
Classification of titrimetric analysis methods
By type of chemical reaction
1. Acid-base titration (neutralization method)
For example.
HCl + NaOH = NaCl + H 2 O
strong strong salt
acid base
indicator
HCl + NH 4 OH = NH 4 Cl + H 2 O
low salt
base
detectable titrant
component
2. Oxidation-reduction titration
For example.
2 KMnO 4 + 10 FeSO 4 + 8 H 2 SO 4 = 2 MnSO 4 + 5 Fe 2 (SO 4) 3 + K 2 SO 4 + 8 H 2 O
oxidizing agent reducing agent acidic medium
titrant detectable
substance
Titration methods
1. Direct titration method
The titrant is added to the solution of the component being determined in small portions (drop by drop) to the equivalence point.
Direct reverse titration method: a solution of the analyte from a burette is added in small portions (dropwise) to the exact volume of titrant contained in a conical flask.
2.Back titration method or residue titration
In this case, two titrants with known exact concentrations are used. In a conical flask, the exact volume of the first titrant V 1 with the exact concentration C 1 is added in excess quantity to the solution of the analyte. Since the first titrant is added in excess, part of it reacts with the substance being determined, and the unreacted part of the first titrant remains in solution and is titrated with the second titrant, and this consumes the volume V 2 of the second titrant with a concentration of C 2 .
If the titrant concentrations are equal to each other (C 1 = C 2), then the amount of the first titrant solution V that went into the reaction with the component being determined is determined by the difference between the added V 1 and the titrated volume V 2:
If the titrant concentrations are not equal, then calculate the number of mole equivalents (n) of the first titrant that reacted with the analyte, from the difference between the number of mole equivalents of the first titrant C 1 V 1 and the number of mole equivalents of the second titrant C 2 V 2:
n = C 1 V 1 - C 2 V 2
The back titration method is used when there is no suitable indicator or when the main reaction does not proceed very quickly.
For example. Determination of the amount of sodium chloride NaCl.
An excess volume of the first AgNO 3 titrant is added to the NaCl solution. Part of this titrant reacts with the analyte according to the equation
AgNO 3 + NaCl = AgCl + NaNO 3
Titrant 1 white
The remainder of titrant 1 (AgNO 3), which did not react with NaCl, is then titrated with the second titrant NH 4 SCN.
AgNO 3 + NH 4 SCN = AgSCN + NH 4 NO 3
Titrant 1 Titrant 2 red-brown
3. Substitution titration method
This method is used when for some reason it is difficult to determine the equivalence point, especially when working with unstable substances that are easily oxidized by atmospheric oxygen, etc., or substances that are difficult to determine by direct titration, or the reaction is slow.
The method consists in adding an auxiliary reagent to the substance being determined, upon interaction with which quantitatively the reaction product is released. This released reaction product is called deputy and then titrate with the appropriate titrant.
For example.
K 2 Cr 2 O 7 + 6 KI + 7 H 2 SO 4 = 3 I 2 + 4 K 2 SO 4 + Cr 2 (SO 4) 3 + 7 H 2 O
determined auxiliary acidic product
substance reagent reaction environment
deputy
I 2 + 2 Na 2 S 2 O 3 = 2 NaI + Na 2 S 4 O 6
substitute titrant indicator
Calculations in titrimetry
Law of equivalents: substances react with each other in equivalent quantities. In general, for any reacting substances according to the law of equivalents
where n is the number of moles of equivalents of reactants.
where C e is the molar concentration of the equivalent, mol/l.
C 1 V 1 = C 2 V 2
At the same concentration of solutions of reacting substances, reactions occur between their equal volumes.
For example. For 10.00 ml of acid solution, 10.00 ml of alkali solution is consumed if their concentrations are 0.1 mol/l.
Titer(T) of a solution is the mass of the substance contained in 1 ml of solution (or 1 cm3), dimension - g/ml.
T = m (substance) / V (solution)
T = C e M e / 1000
For example. T (HCl/HCl) = 0.0023 g/ml reads: the titer of hydrochloric acid (or hydrochloric acid) in HCl is 0.0023 g/ml. This means that every 1 ml of this hydrochloric acid solution contains 0.0023 g of HCl or 2.3 mg in 1 ml.
NEUTRALIZATION METHOD
Method of individual samples
For example. A certain sample is taken into a conical flask m(reagent grade) oxalic acid H 2 C 2 O 4 2H 2 O (weighed on an analytical balance with an accuracy of 0.0001 g). Dissolved in water and completely titrated with NaOH solution with methyl orange indicator. Volume consumed for titration V ml NaOH solution. Calculate the concentration of NaOH.
To calculate the NaOH concentration we use the formula:
m (H 2 C 2 O 4 2H 2 O) = C (NaOH) x V (NaOH) x M (1/2 H 2 C 2 O 4 2H 2 O)
From this formula we derive C (NaOH), all other data are known.
QUANTITATIVE ANALYSIS
METHODS of quantitative analysis
In quantitative analysis, chemical, physical and physicochemical methods are distinguished. The assignment of a method to one or another group depends on the extent to which the determination of the chemical composition of a substance by this method is based on the use of chemical or physical processes, or a combination of those and other processes.
Analytical methods have been developed that are based on the use of almost all known chemical and physical properties of atoms and molecules. It should be taken into account that the analytical technique, as a rule, consists of several stages, each of which is based on a particular property.
According to the three aggregate states of matter - solid, liquid, gaseous - quantitative measurements can be carried out by determining mass (by weighing) and by determining volumes of liquid or gaseous substances.
Chemical methods
Chemical methods are based on the following transformations: the formation of a precipitate or the dissolution of a precipitate, the formation of a colored compound or a change in the color of a solution, the formation of gaseous substances.
Chemical methods are used in analyzes that are called “classical”. They are well tested, consist of several stages, each of which introduces its own error and requires attentiveness, accuracy, and great patience from the analyst.
