Gravimetric analysis

Gravimetry is a quantitative analysis method in which the measurement of quantities for the determination of the mass (weight ) is based. Once again the precipitation analysis, and thermogravimetry Electrogravimetry be distinguished.

• 2.1 Determination of iron content of Fe (III ) salt solution
• 2.2 Determination of sulfate
• 2.3 Determination of nickel (II )

• 3.1 Advantages
• 3.2 disadvantages
• 3.3 views

Method

Precipitation analysis

In this case, the ions or molecules are placed in a precipitation shape. The precipitated compound is filtered off. Filtration can be done in a porcelain filter crucible or glass filter crucible or in a filter paper either (Where special ashless filter papers are used ). The filter cake is washed and dried. Optionally filtered using a paper filter is it must be incinerated. In some cases, the precipitation form is converted by annealing into specially provided heaters ( muffle ) in a stoichiometric Wägeform for precipitation analysis, so that the quantitative determination of the ingredients can occur.

Sometimes precipitation and Wägeform are identical. This is particularly the case when the precipitate has a unique stoichiometry and, for example, no varying amounts of bound water of crystallization: the determination of sulfate ions as barium sulfate, precipitation of nickel with dimethylglyoxime, the determination of potassium with sodium tetraphenylborate. An example in which the form and the precipitation Wägeform are not identical, the below-mentioned provision of iron as iron ( III) oxide.

Electrogravimetry

The test substance is weighed and then deposited in the Electrogravimetry at an electrode.

Thermogravimetry

In the thermogravimetric analysis method, the change of mass as a function of temperature is examined. A simple example is the gravimetric method for the determination of humidity.

Examples

Determination of iron content of Fe (III ) salt solution

The iron salt solution is mixed with ammonia water, the precipitated hydroxide (precipitated form) is filtered and then converted into iron (III ) oxide by ignition to constant weight. The mass of the oxide is determined by weighing on an analytical balance.

Reaction equation:

( Alkaline reaction of ammonia )

(Precipitated form)

( Wägeform )

The required mass of a element to be determined ( in our example, iron) is proportional to the mass balance of A Wägeform (here). The proportionality factor ( gravimetric factor) indicates how much of the mass is contained in a balanced composition A.

From the balanced mass, the mass is given by the multiplication by a factor a of the element to be determined.

Contains on the one hand the ratio of the molar masses of the element to be determined, the molar mass of the Wägeform. In addition, however, must take into account " how often" a formula unit of the substance sought finally per formula unit finds itself in the Wägeform. In this example, two iron atoms per formula unit of the Wägeproduktes find. This is expressed by the stoichiometric coefficient k, where k = 2:

Where k is the stoichiometric coefficient, the molecular mass of this substance and the molecular mass of the Wägeform is.

In our example we assume that we have a balanced 1.25 g. How much iron originally contained our Fe (III ) salt solution?

Onset of

Results:

A = m ( Fe) = 0.874 g

This means our Fe (III ) salt solution contained 874 mg of iron.

Determination of sulfate

The sulfate-containing sample solution is acidified with hydrochloric acid. While stirring, a 0.1 M solution of barium chloride is added dropwise until no more precipitate forms on Eintropfpunkt. The precipitate is heated on a sand bath overnight ( for Ostwald ripening). It formed at the expense of small crystallites larger crystals, which can be filtered easily. The precipitate is filtered off, washed with water and ethanol and dried. Then the precipitate at 600 ° C is annealed to constant weight. This will take no longer than 2-3 hours as a rule.

Reaction equation

( Precipitation and Wägeform )

Determination of nickel (II)

The aqueous nickel (II )-containing sample solution is treated dropwise with an alcoholic solution of dimethylglyoxime until no further precipitate more reddish fails. The ethanol is then cooked. Then it is filtered through a glass frit. After washing the precipitate is dried in a drying oven to constant mass. with dimethylglyoxime is abbreviated as H [ DMG ]

Gravimetric methods for measuring moisture

The most commonly used method for measuring the water content of samples is the gravimetric method (also Darr weighing drying). The water content of the material sample is determined by the weight loss on drying.

The material sample is packed and weighed after collection. Subsequently, the sample is dried until constant weight in a drying oven set at about 105 ° C in successive weighings. The drying time and temperature is dependent on material and defined in appropriate standards. When drying is not chemically bound water may be released. Therefore, the drying temperature of gypsum is only 40 ° C. After drying, the material sample is weighed again. The difference between the weighings, the water content of the material sample can be determined.

The gravimetric water content results from the mass of the wet sample and the mass of the dry sample:

Benefits

The procedure for removing the sample and drying procedure is recognized as a reference method. Many other methods can be compared with this method or the indirect calibration methods. Advantages of this method are the relatively simple handling and generally good accuracy.

Disadvantages

A disadvantage of the gravimetric method is that during the drying of organic materials can use chemical transformations by oxidation processes. These may affect the subsequent weighing to higher values ​​due to oxygen removal. Similarly, it can also result in thermal decomposition with a resultant weight loss. So in colloid-containing soils such as clay or clay is the complete removal of the stored water only from the destruction of the colloid structure.

View

The gravimetric method is not recommended for long-term field measurements. For laboratory measurements, however, it is established as the reference method. The long drying times by a quick- drying by means of

• Infrared heaters,
• Electric plate,
• Gas burner or
• Microwave Oven

Be abbreviated.

Other direct measurement method for the determination of water content in soils have not prevailed. This is partially due to the complicated handling, the effort required or to the low accuracy.

Swell

• Copper, K. 1997 Material Moisture Measurement: Basics, measurement methods, applications, standards, Expert Publishing House
• Hübner, C. 1999, " Development of high-frequency measurement method for soil and snow moisture determination ", Scientific Reports, FZKA 6329, Forschungszentrum Karlsruhe
• Völkner, S. 2003, " On the influence spatially limited discontinuities on the time-dependent distribution of moisture in exterior walls ", Dissertation, Ruhr- University Bochum
• Technical University of Braunschweig, Collaborative Research Center 477, " ensuring the usability of buildings using innovative structural health monitoring ", 2000
• John Weber, Wolfram Köhler: Non-destructive examination methods of stone monuments
• Kaatze, U. 2007 "Aspects of electromagnetic Aquametry ionic conducting materials," in Technical Fairs, issue 5/2007, 261-267