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MindMap Gallery Summary of precipitation titration and titration analysis

Summary of precipitation titration and titration analysis

This is a mind map about the summary of precipitation titration and titration analysis. The main content includes: summary of titration analysis and precipitation titration. Precipitation titration is an important type of titration analysis, which uses precipitation reactions to determine the content of the substance being measured. Titration analysis is a broader chemical analysis method, including many types and application scenarios.

Edited at 2024-10-28 20:44:24

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Summary of precipitation titration and titration analysis

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Outline

Summary of precipitation titration and titration analysis

precipitation titration

Overview

Definition: A reaction based on the quantitative formation of precipitates or slightly soluble salts between a titrant and the substance to be measured, and the reaction can quickly reach equilibrium and have a suitable indicator to indicate the chemical reaction metering point

Application: Use silver nitrate as titrant for halogen ions and pseudohalogen anions...

Comply with the conditions of precipitation titration method

Has constant composition and low solubility

Rapid and quantitative response

Able to indicate the end point using appropriate indicators

Commonly used precipitation titration methods

Morfa

Overview

Using potassium chromate as indicator

Silver nitrate standard solution as titrant

Titration of chloride ions, etc. in neutral or weakly alkaline solutions

Influencing factors

Indicator dosage

Reason: The aqueous solution of potassium chromate is yellow, which makes the color change of the titration end point insensitive.

Too high: the end point is advanced

Too little: The end point appears too late

titrating acidity

Notice

Dosage: Chromate is generally controlled at 0.005

PH: Neutral or slightly alkaline

In acidic solution: chromate will be converted into hydrogen chromate or dichromate, which will reduce the chromate, and the silver chromate indicating the end point will appear late or not.

In strong alkali: silver hydroxide or silver oxide is generated

The reaction is easy to adsorb: shake vigorously to reduce adsorption. At the same time, excess sodium sulfate can be added to eliminate barium ion interference.

application

Can titrate bromide ions, iodide ions, and thiocyanate ions (the latter two precipitates have strong adsorption, so the error is large)

When testing silver ions, a certain excess of NaCl standard solution needs to be added, and then nitrate is used to backtitrate chloride ions.

Forhad method

Overview

Titration of silver ions with thiocyanate in the presence of iron ions

Using iron ammonium vanadium as indicator

Thiocyanate is prepared with ammonium thiocyanate

Titration conditions

Comprehensive consideration, the iron ion is controlled within 0.02

AgSCN is easily adsorbed, so the solution needs to be shaken thoroughly during titration.

in acidic environment

application

Direct titration of silver ions

Determination of halide ions by backtitration

Step (because it is in nitric acid, so the selectivity is better)

In the nitric acid medium containing halogen, first add a certain excess amount of silver nitrate standard solution

Add ferric ammonium vanadium indicator

Back titration of excess silver nitrate with potassium thiocyanate standard solution

Error reduction measures

When measuring chloride ion content, excess thiocyanate will replace chloride ions... causing a large error

Boil the solution to reduce adsorption, wash the precipitate with nitric acid, and then back-titrate with potassium thiocyanate.

Adding organic solvents (not recommended, harmful to humans)

When measuring bromide ions and iodide ions by back titration, the solubility of silver bromate and silver iodide is less than that of silver thiocyanate, and no displacement reaction occurs.

When titrating iodide ions, the indicator must be added after adding an excess of silver nitrate standard solution, otherwise the iron ions will oxidize the iodide ions.

When measuring iodide, you cannot add an indicator first.

According to Forhard's end point principle, increasing the concentration of iron ions can reduce the concentration of thiocyanate and reduce errors.

fayang justice

Definition: A silver method that uses an adsorption indicator to indicate the end point of a titration.

Applicable: This method can be used to titrate chloride ions with silver nitrate standard solution or silver ions with sodium chloride standard solution.

Principle: The adsorption indicator indicates the end point of the titration because the color adsorbed to the precipitate is different from its color in the solution.

Titration conditions

Precipitate particles should be small, and precipitate aggregation should be prevented during titration (dextrin is usually added)

The solution to be dropped should not be too dilute. If the concentration is too dilute, the color of the endpoint indicator will be difficult to observe during indication.

Avoid doing it under bright light

application

Determination of sodium chloride

Determination of silver in silver alloys

Summary of titration analysis

What the four titration methods have in common

The content of the tested substance is determined by consuming accurately measured standard substances (suitable for higher concentrations, high accuracy and simple method)

A sudden jump occurs near the stoichiometric point

Differences between the four titration methods

The reaction product of strong acid titration and strong base is water. From the beginning to the end of the titration, water is a constant, about 55.5

Coordination titration product [ML], the titration starts at 0, and increases linearly as the titration proceeds until the stoichiometric point

There are two titration products of the redox reaction, and the concentration changes are similar to the changes in the coordination titration products.

Precipitation titration produces heterogeneous phases