Method for measuring content of free acid in inorganic acid solution

Abstract

The invention relates to the technical field of chemical engineering, and discloses a method for measuring the content of free acids in an inorganic acid solution, which comprises the following steps: (1) adding an alkaline standard titration solution into the inorganic acid solution for first potentiometric titration to obtain an equivalent point; (2) taking a solvent with the same amount as the inorganic acid solution as a blank solution, adding the alkaline standard titration solution, and carrying out second potentiometric titration to obtain a blank titration end point; and (3) calculating the mass percentage W of H < + > in the inorganic acid solution according to the equivalent point and the blank titration end point. The method is simple and convenient to operate, high in accuracy and high in detection efficiency, is used in all weak-acid and dark-color solution systems, and can be used for rapidly and accurately determining the H < + > content.

Description

Technical Field

[0001] The present invention relates to the field of chemical engineering technology, and particularly relates to a method for determining the content of free acid in an inorganic acid solution. Background Art

[0002] Solutions of chloropalladic acid and chloroauric acid are commonly used raw materials for the preparation of noble metal catalysts. The content of free acid in the solutions of chloropalladic acid and chloroauric acid will directly affect the activity of the catalyst. Therefore, accurately determining the content of free acid is of great significance for the preparation of noble metal catalysts.

[0003] The prior art generally uses acid-base titration to determine the content of free acid. Since the solutions of chloropalladic acid and chloroauric acid have a relatively dark color, it has a great influence on the color change during the titration jump of the indicator, making it impossible to accurately judge the titration end point. In order to eliminate the error caused by the color, it is necessary to derivatize the solution. In addition, when using acid-base titration to determine the free acid in the solutions of chloropalladic acid and chloroauric acid, when the acid in the solution is a weak acid or a low-concentration acid, the result deviation will become larger. If a pH meter is used to determine the pH change during the titration to determine the titration end point, although the error can be reduced, the operation is troublesome and time-consuming.

[0004] Therefore, there is an urgent need to provide a method that is simple to operate, has high precision, and can quickly determine the content of free acid in the solutions of chloropalladic acid and chloroauric acid. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problems of large errors and troublesome operations (derivatization treatment is required before titration) in the existing methods for determining the content of free acid in chloropalladic acid or chloroauric acid, and to provide a method for determining the content of free acid in an inorganic acid solution.

[0006] To achieve the above purpose, the present invention provides a method for determining the content of free acid in an inorganic acid solution, wherein the method includes:

[0007] (1) Adding a basic standard titration solution to the inorganic acid solution for the first potentiometric titration to obtain the equivalence point;

[0008] (2) Using a solvent equivalent to that in the inorganic acid solution as a blank solution, adding the basic standard titration solution for the second potentiometric titration to obtain the blank titration end point;

[0009] (3) Calculating the mass percentage content W of H + in the inorganic acid solution according to the equivalence point and the blank titration end point.

[0010] Through the above technical solutions, the present invention achieves the following beneficial technical effects:

[0011] The present invention uses potentiometric titration. An alkaline standard titration solution is used to titrate a weak acid solution with a relatively dark color. The change in pH in the solution will cause a change in the potential of the solution. The titration endpoint of the chemical reaction is determined by the change in potential. This method does not require derivatization of the weak acid solution, does not require the use of indicators, does not require the use of complex instruments or reagents, eliminates the influence of the indicator color on the titration result, is easy to operate, has high precision, and high detection efficiency. It is used in all solution systems of weak acids with dark colors and can quickly and accurately determine the content of H + . BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a device for determining the free acid content by potentiometric titration.

[0013] DESCRIPTION OF THE REFERENCE NUMERALS

[0014] 1 - Magnetic stirrer 2 - Inorganic acid solution 3 - Beaker

[0015] 4 - Alkaline standard titration solution 5 - Working electrode 6 - Potentiometric titrator DETAILED DESCRIPTION OF THE INVENTION

[0016] The endpoints and any values in the ranges disclosed herein are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed herein.

[0017] The present invention provides a method for determining the free acid content in an inorganic acid solution, wherein the method includes:

[0018] (1) Adding an alkaline standard titration solution to the inorganic acid solution for the first potentiometric titration to obtain an equivalence point;

[0019] (2) Using a solvent equivalent to that in the inorganic acid solution as a blank solution, adding the alkaline standard titration solution for the second potentiometric titration to obtain a blank titration endpoint;

[0020] (3) Calculating the mass percentage content W of H + in the inorganic acid solution based on the equivalence point and the blank titration endpoint.

[0021] In the present invention, the potentiometric titration method refers to a method of determining the titration end point by measuring the potential change during the titration. Before and after the titration reaches the end point, the concentration of the analyte ions in the solution often changes by n orders of magnitude continuously. The titration end point (equivalence point) is determined based on the sudden jump of the electrode potential, and then the content of the analyte is calculated by the amount of the titrant consumed.

[0022] In the present invention, as long as the inorganic acid solution does not contain a precipitate or a suspension, the method of the present invention can be used to determine the free acid content. Preferably, the inorganic acid solution in the present invention is a weak acid solution with a color.

[0023] In the present invention, the depth of the color of the inorganic acid solution is represented by the chromaticity value, and the determination method of the chromaticity value is carried out according to "GB / T5750.4 - Platinum - cobalt standard colorimetric method". Taking the chromaticity value of deionized water (filtered through a 0.2μm filter membrane) as the reference standard, the chromaticity value of the inorganic acid solution only needs to be higher than that of deionized water. Preferably, the chromaticity value of the inorganic acid solution is 5 - 500 degrees.

[0024] Preferably, according to some embodiments of the present invention, wherein the inorganic acid solution is selected from chloropalladic acid solution and / or chloroauric acid solution.

[0025] In the present invention, the inorganic acid solution is a pre - prepared chloropalladic acid or chloroauric acid solution in industrial dissolution. There is no particular limitation on the preparation method of the chloropalladic acid or chloroauric acid solution. For example, a certain amount of chloropalladic acid / chloroauric acid can be accurately weighed and dissolved in a solvent to prepare a solution. The solvent can be ethanol or water. Preferably, the solvent in the inorganic acid solution is water.

[0026] In the present invention, "equal amount" in step (2) means that the volume of the solvent in the inorganic acid solution is equal to the volume of the solvent in the blank solution. The difference between the blank solution and the inorganic acid solution is only that the blank solution does not contain inorganic acid salts, and the others are the same.

[0027] In the present invention, the purpose of the blank titration is to eliminate the interference brought by the solvent in the inorganic solution to the potentiometric titration, so as to further improve the accuracy of the potentiometric titration.

[0028] In the present invention, the equivalence point refers to that in the titration process, when the inorganic acid solution is titrated with a standard alkaline solution, when the titrant and the titrand react exactly completely, the two react in equivalent amounts, and this point is called the equivalence point. The equivalence point is a calculated value, the theoretical end point calculated according to the equivalent amount of acid and base, and this value has no connection with the actual determination method, indicator, etc.

[0029] In the present invention, there is no particular limitation on the method for determining the equivalence point. For example, the equivalence point can be determined by measuring the change in the electrode potential, as follows: Place the solution to be analyzed in a beaker, start the magnetic stirrer, and add a standard alkaline titrant for titration. Add a certain volume of the standard titrant from the burette, measure the potential (E) of the solution, and then measure the potential every time 1 mL or an appropriate amount of the standard titrant is added. Before and after the stoichiometric point (equivalence point), measure the potential every time 0.1 mL of the standard titrant is added, and continue titrating until the potential change is small. Plot the titration curve with the volume of the titrant as the abscissa and the potential (E, mV) of the indicating electrode as the ordinate. Draw two tangents to the titration curve that form a 45° angle with the abscissa, and draw a parallel line between the two tangents at an equal distance from the two tangents. The intersection point of this line and the titration curve is the titration end point, which is the equivalence point. The abscissa of the intersection point is the volume of the alkaline standard titrant consumed at the titration end point, and the ordinate corresponding to the intersection point is the potential at the titration end point.

[0030] According to some embodiments of the present invention, wherein, the calculation method of the mass percentage content W of H + in the inorganic acid solution includes: calculating the mass X of H + in the inorganic acid solution according to the equivalence point and the blank titration end point; and then calculating the mass percentage content W of H + in the inorganic acid solution according to the mass X of H + in the inorganic acid solution and the mass m of the solute in the inorganic acid solution.

[0031] According to some embodiments of the present invention, wherein, the mass percentage content W of H + in the inorganic acid solution satisfies the following formula:

[0032] W = X ÷ m × 100% (I);

[0033] wherein, X is the mass of H + in the inorganic acid solution, with the unit of mg;

[0034] wherein, m is the mass of the solute in the inorganic acid solution, with the unit of mg.

[0035] According to some embodiments of the present invention, wherein, the calculation method of the mass X of H + in the inorganic acid solution includes: obtaining the parameters V and V 0 according to the equivalence point and the blank titration end point, and constructing the relationship formula -1 between the mass X of H + in the inorganic acid solution and V, V 0 ;

[0036] wherein, V 0V is the volume of the basic standard titrant consumed when reaching the blank titration end point, in mL;

[0037] Wherein, V is the volume of the basic standard titrant consumed when reaching the equivalence point, in mL.

[0038] According to some embodiments of the present invention, the relational expression -1 satisfies the following formula:

[0039] X = C×(V - V 0 )÷n×M 1 (II);

[0040] Wherein, C is the molar concentration of the basic standard titrant, in mol / L;

[0041] Wherein, n is the number ratio of the acidic reaction groups of the inorganic acid solution to the basic reaction groups of the basic standard titrant;

[0042] Wherein, M 1 is the relative molecular mass of the solute in the inorganic acid solution.

[0043] In the present invention, the "acidic reaction groups" of the inorganic acid solution refer to the sum of the free H + in the inorganic acid solution and the H + combined with the solute in the inorganic acid solution; the "basic groups" of the basic standard titrant refer to the free OH - in the basic standard titrant.

[0044] In the present invention, during the laboratory test process, the inventor believes that the H 4 in chloropalladic acid ((NH 2 ) 6 ·PdCl + ) is combined with Cl - . For the convenience of calculation, when calculating the mass percentage content of H + in the inorganic acid solution, M 1 in the formula is calculated based on the relative molecular mass of hydrogen chloride.

[0045] In the present invention, the potential of the solution is monitored through a working electrode, and one end of the working electrode is equipped with a probe. In order to more accurately monitor the potential change in the solution, the probe of the working electrode needs to be completely immersed in the inorganic acid solution. In the present invention, potentiometric titration is carried out in a glass beaker, and the volume of the inorganic acid solution can be adjusted accordingly according to the capacity of the selected beaker. Taking a beaker with a capacity of 100 mL as an example, the mass ratio of the solute to the solvent in the inorganic acid solution is 1:(25 - 100), such as 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, 1:55, 1:60, 1:70, 1:80, 1:90, 1:100, and any value within the range formed between any two values.

[0046] In the present invention, the molar concentration of the inorganic acid solution affects the test results of potentiometric titration. In order to further improve the accuracy and precision of potentiometric titration, the molar concentration of the inorganic acid solution needs to be controlled within a certain range. Preferably, the molar concentration of the inorganic acid solution is 0.05 mol / L - 5 mol / L.

[0047] In the present invention, when the concentration of the inorganic acid solution is too high and exceeds the measurement range, or when the concentration of the inorganic acid solution is too low and is lower than the detection limit of the potentiometric titrator, the titration result has a large deviation, and the accuracy and precision of potentiometric titration are poor.

[0048] According to some embodiments of the present invention, the alkaline standard titration solution is sodium hydroxide standard titration solution and / or potassium hydroxide standard titration solution.

[0049] In the present invention, the molar concentration of the alkaline standard titration solution affects the sensitivity and accuracy of potentiometric titration. In order to further improve the accuracy of potentiometric titration, according to some embodiments of the present invention, the molar concentration of the alkaline standard titration solution is 0.1 - 0.5 mol / L, such as 0.1, 0.2, 0.3, 0.4, 0.5, and any value within the range formed between any two values.

[0050] In the present invention, when the molar concentration of the alkaline standard titration solution is too high or too low, the titration error is large, and when the molar concentration of the alkaline standard titration solution meets the above-defined range, the accuracy and precision of the potentiometric titration result are high.

[0051] In the present invention, there is no particular limitation on the instrument for potential measurement, as long as it can achieve potential detection. For example, an automatic potentiometric titrator with the instrument model of Metrohm - 888 from Metrohm Switzerland can be used for potential detection, such as Figure 1As shown, weigh a certain mass of chloropalladic acid / chloroauric acid into beaker 3 (with a capacity of 100 mL), add an appropriate volume of deionized water, and configure it into inorganic acid solution 2 by stirring with magnetic stirrer 1. Before the titration starts, immerse the probe of working electrode 5 into inorganic acid solution 2. As the basic standard titration solution 4 is continuously added, the pH of the solution continuously changes, which causes a change in the solution potential. The potential value is directly read through potentiometric titrator 6, and the end point of this chemical reaction is determined by setting the pH of the solution at the titration end point, and pH = -lgC(H + ), at this time, the magnitude of the potential in the solution is only related to the concentration of H + in the test solution, and can be expressed by the Nernst formula: E 膜 = K - 0.059pH (K is a constant, which is determined by the membrane electrode itself). The above formula shows that at a certain temperature, the solution potential has a linear relationship with the pH of the test solution.

[0052] The present invention will be described in detail below through embodiments.

[0053] The potentiometric titrator is an automatic potentiometric titrator of Metrohm - 888 from Metrohm, Switzerland.

[0054] Unless otherwise specified, the reagents used in the following examples are all commercially available products.

[0055] Preparation Example 1

[0056] (1) Preparation of 0.5 mol / L sodium hydroxide standard solution

[0057] Weigh 100 g of sodium hydroxide and dissolve it in 100 mL of deionized water, shake well, pour it into a polyethylene container, and keep it airtight until the solution is clear. Measure 26 mL of the supernatant with a plastic tube and dilute it to 1000 mL with carbon dioxide - free water, shake well;

[0058] (2) Standardization of 0.5 mol / L sodium hydroxide standard solution

[0059] Accurately weigh 3.0001 g of working reference reagent potassium hydrogen phthalate dried to constant weight at 105 °C, add 80 mL of carbon dioxide - free deionized water, add 2 drops of phenolphthalein indicator solution (10 g / L), and titrate with the prepared sodium hydroxide solution until the solution turns pink and remains so for 30 s, while performing a blank test at the same time;

[0060] (3) Calculation

[0061] The actual concentration of the sodium hydroxide standard solution is calculated according to the following formula (a):

[0062]

[0063] In formula (a),

[0064] C(NaOH) is the molar concentration of the sodium hydroxide solution, with the unit of mol / L;

[0065] V1 is the amount of sodium hydroxide used at the titration end point, which is 28.95 mL;

[0066] V 2 is the amount of sodium hydroxide used at the titration end point of the blank test, which is 0.00 mL;

[0067] m is the mass of potassium hydrogen phthalate, which is 3.0001 g;

[0068] M is the molar mass of potassium hydrogen phthalate, which is 204.22 g / mol;

[0069] The actual concentration of the standard titration solution of sodium hydroxide is calculated to be 0.5074 mol / L.

[0070] Preparation Example 2

[0071] (1) Preparation of 0.1 mol / L standard sodium hydroxide solution

[0072] Weigh 100 g of sodium hydroxide and dissolve it in 100 mL of deionized water. Shake well and pour it into a polyethylene container. Close it and let the solution stand until it is clear. Pipette 5 mL of the supernatant and pour it into 1000 mL of water free of carbon dioxide. Shake well to obtain a sodium hydroxide solution with a theoretical concentration of 0.1 mol / L;

[0073] (2) Standardization of 0.1 mol / L standard sodium hydroxide solution

[0074] Accurately weigh 0.5995 g of primary standard potassium hydrogen phthalate dried to constant weight at 105 °C, add 50 mL of deionized water free of carbon dioxide, add 2 drops of phenolphthalein indicator solution (10 g / L), and titrate with the prepared sodium hydroxide solution until the solution turns pink. The amount of sodium hydroxide used at the titration end point is V 1 (27.93 mL), and at the same time, perform a blank test (the amount of sodium hydroxide used at the titration end point of the blank test is V 2 (0.00 mL);

[0075] (3) The actual concentration of the standard titration solution of sodium hydroxide is calculated to be 0.1051 mol / L according to formula (a).

[0076] Preparation Example 3

[0077] (1) Preparation of 1 mol / L standard sodium hydroxide solution

[0078] Weigh 100 g of sodium hydroxide and dissolve it in 100 mL of deionized water. Shake well and pour it into a polyethylene container. Seal it and let the solution stand until it is clear. Pipette 52 mL of the supernatant and pour it into 1000 mL of water free from carbon dioxide. Shake well to obtain a sodium hydroxide solution with a theoretical concentration of 0.1 mol / L.

[0079] (2) Standardization of 1 mol / L sodium hydroxide standard solution

[0080] Accurately weigh 6.00007 g of potassium hydrogen phthalate dried to constant weight at 105 °C. Add 80 mL of deionized water free from carbon dioxide and 2 drops of phenolphthalein indicator solution (10 g / L). Titrate with the prepared sodium hydroxide solution until the solution turns pink. The volume of sodium hydroxide used at the titration end point is V 1 (26.81 mL), and at the same time, perform a blank test. (The volume of sodium hydroxide used at the titration end point of the blank test is V 2 (0.00 mL);

[0081] (3) Calculate the actual concentration of the sodium hydroxide standard titration solution according to formula (a) to be 1.0960 mol / L.

[0082] Example 1

[0083] (1) Accurately weigh 2.0175 g, 2.0034 g, and 2.0236 g of chloropalladic acid ((NH 4 ) 2 ·PdCl 6 ) into 3 clean and dry beakers respectively. Accurately add 50 mL of deionized water to each beaker to dissolve and prepare chloropalladic acid solutions;

[0084] (2) Use the 0.5074 mol / L sodium hydroxide standard titration solution (Preparation Example 1) to perform potentiometric titration on the above chloropalladic acid solutions. The potentiometric titrator automatically records the consumption volume of the sodium hydroxide standard titration solution at the equivalence point. The specific data is shown in Table 1;

[0085] (3) Use the same amount of solvent in the chloropalladic acid solution in step (1) as the blank solution, add the 0.5074 mol / L sodium hydroxide standard titration solution to perform potentiometric titration, and obtain the consumption volume of the sodium hydroxide standard titration solution at the blank titration end point. The specific data is shown in Table 1;

[0086] (4) Calculate the mass percentage content of H + in the chloropalladic acid solution according to the following formulas (b) and (c):

[0087] W = X ÷ m × 100% (b)

[0088] X = C × (V - V 0 ) ÷ n × M1 (c)

[0089] Wherein, m is the mass of chloropalladic acid, in mg;

[0090] Wherein, X is the mass of H + in the chloropalladic acid solution, in mg;

[0091] Wherein, C is the molar concentration of the sodium hydroxide standard titration solution, in mol / L;

[0092] Wherein, V is the volume of the basic standard titration solution consumed when reaching the equivalence point, in mL;

[0093] Wherein, V 0 is the volume of the basic standard titration solution consumed when reaching the blank titration end point, in mL;

[0094] Wherein, n = 1;

[0095] Wherein, M 1 is the relative molecular mass of hydrogen chloride.

[0096] Example 2

[0097] (1) Accurately weigh 2.0043 g, 2.0041 g, and 2.0372 g of chloropalladic acid ((NH 4 ) 2 ·PdCl 6 ) into 3 clean and dry beakers, and accurately add 50 mL of deionized water to each beaker to dissolve, preparing chloropalladic acid solutions;

[0098] (2) Use the sodium hydroxide standard titration solution (Preparation Example 2) with a concentration of 0.1051 mol / L to perform potentiometric titration on the above chloropalladic acid solutions. The potentiometric titrator automatically records the consumption volume of the sodium hydroxide standard titration solution at the equivalence point. The specific data is shown in Table 1;

[0099] (3) Use the same amount of solvent in the chloropalladic acid solution in step (1) as the blank solution, add the sodium hydroxide standard titration solution for potentiometric titration, and obtain the consumption volume of the sodium hydroxide standard titration solution at the blank titration end point. The specific data is shown in Table 1;

[0100] (4) The mass percentage content of H + in the chloropalladic acid solution is calculated according to formulas (b) and (c). The specific results are shown in Table 1.

[0101] Example 3

[0102] (1) Accurately weigh 2.0152 g, 2.0032 g, and 2.0061 g of chloropalladic acid ((NH 4 )2 ·PdCl 6 (1) In three clean and dry beakers, accurately add 50 mL of deionized water for dissolution respectively to prepare chloropalladic acid solutions;

[0103] (2) Use the sodium hydroxide standard titration solution with a concentration of 1.0960 mol / L (Preparation Example 3) to conduct potentiometric titration on the above chloropalladic acid solution. The potentiometric titrator automatically records the consumption volume of the sodium hydroxide standard titration solution at the equivalence point. The specific data is shown in Table 1;

[0104] (3) Use the same amount of solvent in the chloropalladic acid solution in step (1) as the blank solution, add the sodium hydroxide standard titration solution for potentiometric titration, and obtain the consumption volume of the sodium hydroxide standard titration solution at the blank titration end point. The specific data is shown in Table 1;

[0105] (4) The mass percentage content of H + in the chloropalladic acid solution is calculated according to formulas (b) and (c), and the specific results are shown in Table 1.

[0106] Comparative Example 1

[0107] (1) Accurately weigh 2.0175 g, 2.0034 g, and 2.0236 g of chloropalladic acid ((NH 4 ) 2 ·PdCl 6 ) into three clean and dry beakers respectively, accurately add 50 mL of deionized water for dissolution respectively to prepare chloropalladic acid solutions;

[0108] (2) Use the sodium hydroxide standard titration solution with a concentration of 0.5074 mol / L (Preparation Example 1) to titrate the chloropalladic acid solution, and use a pH meter to record the consumption volume of the sodium hydroxide standard titration solution at the titration end point. The specific data is shown in Table 1;

[0109] (3) Use the same amount of solvent in the chloropalladic acid solution in step (1) as the blank solution, add the basic standard titration solution for potentiometric titration, and obtain the consumption volume of the sodium hydroxide standard titration solution at the blank titration end point. The specific data is shown in Table 1;

[0110] (4) The mass percentage content of H + in the chloropalladic acid solution is calculated according to formulas (b) and (c), and the specific results are shown in Table 1.

[0111] Test Example 1

[0112] Accuracy test:

[0113] (1) Accurately weigh 2.0171 g, 2.0049 g, and 2.0034 g of chloropalladic acid ((NH 4 ) 2 ·PdCl6 ) In three clean and dry beakers, accurately add 5.03 mL, 5.00 mL, and 5.01 mL of hydrochloric acid solution (the molar concentration of the hydrochloric acid solution is 0.1538 mol / L) to dissolve and prepare a chloropalladic acid solution. Among them, the mass percentage content (theoretical content) of H + in the chloropalladic acid solution is shown in Table 2;

[0114] (2) Use the 0.5074 mol / L sodium hydroxide standard titration solution (Preparation Example 1) to carry out potentiometric titration on the above chloropalladic acid solution. The potentiometric titrator automatically records the consumption volume of the sodium hydroxide standard titration solution at the equivalence point. The specific data is shown in Table 2;

[0115] (3) Take the solvent equivalent to that in the chloropalladic acid solution in step (1) as the blank solution, add the 0.5074 mol / L sodium hydroxide standard titration solution for potentiometric titration, and obtain the consumption volume of the sodium hydroxide standard titration solution at the blank titration end point. The specific data is shown in Table 2;

[0116] (4) The measured mass percentage content of H + in the chloropalladic acid solution is calculated according to the above formulas (b) and (c), and the results are shown in Table 2.

[0117] Test Example 2

[0118] (1) Accurately measure 5.00 mL, 5.01 mL, and 4.98 mL of hydrochloric acid solution (the molar concentration of the hydrochloric acid solution is 0.1538 mol / L) into three clean and dry beakers respectively. Add 50 mL of deionized water to each beaker to prepare hydrochloric acid solutions respectively. Among them, the content (theoretical content) of H + in the hydrochloric acid solution is shown in Table 2;

[0119] (2) Use the 0.5074 mol / L sodium hydroxide standard titration solution (Preparation Example 1) to carry out potentiometric titration on the above hydrochloric acid solution. The potentiometric titrator automatically records the consumption volume of the sodium hydroxide standard titration solution at the equivalence point. The specific data is shown in Table 2;

[0120] (3) Take the solvent equivalent to that in the hydrochloric acid solution in step (1) as the blank solution, add the 0.5074 mol / L sodium hydroxide standard titration solution, and obtain the consumption volume of the sodium hydroxide standard titration solution at the blank titration end point. The specific data is shown in Table 2;

[0121] (4) The content of H + in the hydrochloric acid solution is calculated according to the above formulas (b) and (c), and the results are shown in Table 2.

[0122] Test Example 3

[0123] Using the hydrochloric acid solution in Test Example 2 as the system to be measured, the content of H in the hydrochloric acid solution was determined by the method of Comparative Example 1. + The results are shown in Table 2.

[0124] Table 1

[0125]

[0126] Table 2

[0127]

[0128]

[0129] It can be seen from the data of Examples 1-3, Test Examples 1-3, Comparative Example 1 and Table 2 that the potentiometric titration method of the present invention for determining the content of free acid in inorganic acids has the advantages of simple operation, rapidity, high accuracy and precision.

[0130] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for determining the content of free acid in an inorganic acid solution, characterized in that, the method comprises: (1) Adding an alkaline standard titration solution to the inorganic acid solution for a first potentiometric titration to obtain an equivalence point; (2) Using a solvent equivalent to that in the inorganic acid solution as a blank solution, adding the alkaline standard titration solution for a second potentiometric titration to obtain a blank titration end point; (3) Calculate the mass percentage content W of H in the inorganic acid solution based on the equivalence point and the blank titration end point. + in it.

2. The method according to claim 1, wherein, The calculation method of the mass percentage W of H in the inorganic acid solution includes: calculating the mass X of H in the inorganic acid solution according to the equivalence point and the blank titration end point; then calculating the mass percentage W of H in the inorganic acid solution according to the mass X of H in the inorganic acid solution and the mass m of the solute in the inorganic acid solution. + The calculation method of the mass percentage W of H in the inorganic acid solution includes: calculating the mass X of H in the inorganic acid solution according to the equivalence point and the blank titration end point; then calculating the mass percentage W of H in the inorganic acid solution according to the mass X of H in the inorganic acid solution and the mass m of the solute in the inorganic acid solution. + The calculation method of the mass percentage W of H in the inorganic acid solution includes: calculating the mass X of H in the inorganic acid solution according to the equivalence point and the blank titration end point; then calculating the mass percentage W of H in the inorganic acid solution according to the mass X of H in the inorganic acid solution and the mass m of the solute in the inorganic acid solution. + The calculation method of the mass percentage W of H in the inorganic acid solution includes: calculating the mass X of H in the inorganic acid solution according to the equivalence point and the blank titration end point; then calculating the mass percentage W of H in the inorganic acid solution according to the mass X of H in the inorganic acid solution and the mass m of the solute in the inorganic acid solution. + The calculation method of the mass percentage W of H in the inorganic acid solution includes: calculating the mass X of H in the inorganic acid solution according to the equivalence point and the blank titration end point; then calculating the mass percentage W of H in the inorganic acid solution according to the mass X of H in the inorganic acid solution and the mass m of the solute in the inorganic acid solution.

3. The method according to claim 2, wherein, The mass percentage content W of H + in the inorganic acid solution satisfies the following formula: W = X ÷ m × 100% (I); Wherein, X is the mass of H + in the inorganic acid solution, with the unit of mg; wherein, m is the mass of the solute in the inorganic acid solution, with the unit of mg.

4. The method according to claim 2 or 3, wherein, The calculation method of the mass X of H in the inorganic acid solution includes: according to the equivalence point and the blank titration end point, obtaining parameters V and V + , constructing the relationship formula -1 between the mass X of H in the inorganic acid solution and V, V 0 , + , 0 ; Wherein, V 0 is the volume of the basic standard titrant consumed when reaching the blank titration end point, with the unit of mL; wherein, V is the volume of the alkaline standard titration solution consumed when reaching the equivalence point, with the unit of mL.

5. The method according to claim 4, wherein, the relational expression -1 satisfies the following formula: X = C×(V - V 0 )÷n×M 1 (II); wherein, C is the molar concentration of the alkaline standard titration solution, with the unit of mol / L; wherein, n is the number ratio of the acidic reaction groups in the inorganic acid solution and the basic reaction groups in the alkaline standard titration solution; Among them, M 1 is the relative molecular mass of the solute in the inorganic acid solution.

6. The method according to claim 1, wherein, the inorganic acid solution is selected from chloropalladic acid solution and / or chloroauric acid solution.

7. The method according to any one of claims 1-6, wherein, the solvent in the inorganic acid solution is selected from ethanol and / or water, preferably water.

8. The method according to any one of claims 1-7, wherein, in the inorganic acid solution, the mass ratio of the solute to the solvent is 1:(25-100); and / or, the molar concentration of the inorganic acid solution is 0.05 mol / L - 5 mol / L.

9. The method according to any one of claims 1-8, wherein, the alkaline standard titration solution is sodium hydroxide standard titration solution and / or potassium hydroxide standard titration solution.

10. The method according to any one of claims 1-9, wherein, the molar concentration of the alkaline standard titration solution is 0.1 - 0.5 mol / L.

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