Devarda's alloy

• DeVarda
• Devardsche alloy

From the composition of 45% Al, 50 % Cu and 5% Zn ( mass percent) results in a ratio formula of AL21, 8Cu10, 3Zn or rounded about Al22Cu10Zn.

Gray, odorless powder

A composition of 45% Al, 50 % Cu and 5% Zn ( mass percent) corresponds to an average molecular weight of 39.5 g · mol -1.

Fixed

5.79 g · cm -3

490-560 ° C

906 ° C

Insoluble in water

Risk

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The Devardasche alloy and alloy according DeVarda or shortly called DeVarda, is one by the Italian chemist Arturo DeVarda (1859-1944) named alloy of 45 % aluminum, 50 % copper and 5 % zinc. The brittle gray metal mixture is used primarily in analytical chemistry as a strong reducing agent. The most important applications of the alloy belongs to the detection of the quantitative determination of nitrate and nitrates, for example, in fertilizers or in waste water.

Properties

The Devardasche alloy is so brittle that it can be pulverized in a mortar. She has characterized and their composition following advantages:

• It can be easily cut, what the use of small amounts, eg allows for analysis on a micro scale very relieved and adjusting the dose so that it allows a more flexible application compared to aluminum granules.
• The large surface area of the finely zermörserten alloy is a faster response.
• Fresh divided metal has the advantage not to be covered with a passivating oxide layer at the same rate over zinc or aluminum powder. Also, the high copper content of the alloy contributes to the fact that fewer such layers form than in pure Al or Zn
• The copper acts through the formation of a local cell catalytically, ie Reductions with Devardascher alloy run much faster than with the use of zinc or aluminum.
• Reductions with aluminum often require a strong alkaline solution. In contrast, reductions with Devardascher alloy are feasible even in weakly alkaline solution or even in neutral solution, even if the reaction takes much longer in neutral solution.

Often, the alloy is used in a strongly alkaline medium. The composition of commercially available alloys vary in the range 44-46 % aluminum, 49-51 % copper and 4-6 % zinc.

Reaction with acids or alkalis

In acids or alkalis the aluminum and zinc dissolve, which evolved hydrogen:

Or

And

In non-oxidizing, oxygen-free acids, most copper remains unsolved. The reducing effect during the application of the alloy is based on in many cases the reactivity of the resulting hydrogen.

Detection of nitrates

Devarda is used for the detection of nitrates. After treating a nitrate -containing sample with DeVarda and sodium hydroxide and the solution was heated gently so the nitrate is reduced to gaseous ammonia, which is easily identifiable by its characteristic odor:

Kjeldahl nitrogen determination

When Kjeldahlschen nitrogen determination of nitrogen present investments are initially determined by reaction with concentrated sulfuric acid only as amines, amides or heterocycles. To further determine nitrogen from azo or nitro groups have this - like nitrates - are first reduced, which can be done with Devardscher alloy.

Detection of chlorates

Chlorates be reduced by the Devardasche alloy in acid, neutral or alkaline solution to form chlorides. The reduction is even by boiling with zinc dust possible, the reaction proceeds but especially in neutral solution with zinc very slowly, which is why the Devardasche alloy is preferred. For the detection of chlorate is removed if present, chloride by precipitation with silver nitrate and silver sulfate. After precipitated silver chloride was removed by filtration, you are a little Devardasche alloy and to cook.

After having filtered off the copper in the filtrate is acidified with nitric acid and treated with silver nitrate. A precipitation of silver chloride is then that the initial sample has included chlorates.

Perchlorate does not interfere with the detection, since they are not reduced by the Devardasche alloy.