General Knowledge - General Science - Discussion

Discussion Forum : General Science - Elements and Metals (Q.No. 1)
1.
Brass gets discoloured in air because of the presence of which of the following gases in air?
Oxygen
Hydrogen sulphide
Carbon dioxide
Nitrogen
Answer: Option
Explanation:
No answer description is available. Let's discuss.
Discussion:
248 comments Page 1 of 25.

Tejashwini said:   9 years ago
The normal brown coloration on brass which slowly forms is primarily due to the oxidation of the copper (which makes up about 70% or more of the Brass alloy) to copper oxide. The greenish patina that forms on brass (especially in inclement environments) can be a complex of copper carbonates and acetates (acetates come from naturally or artificially occurring contaminants or droppings in the atmosphere depending on the presence of Industry).

Vinegar (acetic acid) is capable of producing an intense green corrosion on brass (copper acetate) and copper alloys generally. Regions near industry may be exposed to Sulfur compounds such as Sulfur Dioxide, or Hydrogen Sulfide. Both of these are potent copper oxidizers, hence the use of 'Liver of Sulfur' by artisans to oxidize copper, bronze, and brass castings.

Additionally Hydrogen Sulfide as well as liquid polysulfide concentrates are a potent oxidizer for Silver alloys as well. For this reason, do not keep your brass and silverware in a cabinet that also contains matches!

Asawira Emaan Khan said:   9 years ago
The normal brown coloration on brass which slowly forms is primarily due to the oxidation of the copper (which makes up about 70% or more of the Brass alloy) to copper oxide. The greenish patina that forms on brass (especially in inclement environments) can be a complex of copper carbonates and acetates (acetates come from naturally or artificially occurring contaminants or droppings in the atmosphere depending on the presence of Industry).

Vinegar (acetic acid) is capable of producing an intense green corrosion on brass (copper acetate) and copper alloys generally. Regions near industry may be exposed to Sulfur compounds such as Sulfur Dioxide, or Hydrogen Sulfide. Both of these are potent copper oxidizers, hence the use of 'Liver of Sulfur' by artisans to oxidize copper, bronze, and brass castings.

Additionally Hydrogen Sulfide as well as liquid poly-sulfide concentrates are a potent oxidizer for Silver alloys as well. For this reason, do not keep your brass and silverware in a cabinet that also contains matches!

Ciel Phantomhive said:   9 years ago
Hydrogen sulfide is a chemical compound with the formula H2S. It is a colorless gas with the characteristic foul odor of rotten eggs; it is heavier than air, very poisonous, corrosive, flammable, and explosive.

Hydrogen sulfide often results from the bacterial breakdown of organic matter in the absence of oxygen gas, such as in swamps and sewers; this process is commonly known as anaerobic digestion H.

2S also occurs in volcanic gases, natural gas, and in some sources of well water. It is also present in natural halite type rock salts, most notably in Himalayan Black Salt, which is mostly harvested from the mineral-rich "Salt Range" mountains of Pakistan.

The human body produces small amounts of H2S and uses it as a signaling molecule.

Upender said:   10 years ago
The normal brown coloration on brass which slowly forms is primarily due to the oxidation of the copper (which makes up about 70% or more of the Brass alloy) to copper oxide.

The greenish patina that forms on brass (especially in inclement environments) can be a complex of copper carbonates and acetates (acetates come from naturally or artificially occurring contaminants or droppings in the atmosphere depending on the presence of Industry).

Vinegar (acetic acid) is capable of producing an intense green corrosion on brass (copper acetate) and copper alloys generally. Regions near industry may be exposed to Sulfur compounds such as Sulfur Dioxide, or Hydrogen Sulfide.

Angela said:   8 years ago
Hydrogen sulfide is a reducing agent and when brass comes in its contact reduction occurs and causes it discoloration being reactive and due to its acidic properties and oxygen and carbon dioxide can't do it. And it not present in dry air composition.

But you should not forget that some gases are present as pollutants and hydrogen sulphide is a primary pollutant and you cannot consider that the composition is always the same as it is described in books as pollutants are not considered while giving composition of dry air and more over moisture is there in air which helps in reduction of brass. As far as I understand and option B is the right option.

Ankur said:   7 years ago
This is called Tarnishing. It is a thin layer of corrosion that forms over copper, brass, silver, aluminium, magnesium and other similar metals as their outermost layer undergoes a chemical reaction. Tarnish does not always result from the sole effects of oxygen in the air. For example, silver needs hydrogen sulfide to tarnish, although it may tarnish with oxygen over time. It often appears as a dull, grey or black film or coating over metal. Tarnish is a surface phenomenon that is self-limiting, unlike rust. Only the top few layers of the metal react, and the layer of tarnish seals and protects the underlying layers from reacting the tarnishing.

Jerish Paul J said:   4 years ago
Brass is a copper alloy with the addition of zinc.

Copper is reactive with some materials in the atmosphere at different temperatures.

Exposure to air at normal temperatures results in discolouration (tarnish) due to reaction with sulfur and chlorine compounds and carbonates,

Exposure at high temperatures > 150° C. Results in reaction with oxygen producing red oxides (cuprous) at lower temperatures and brown or black oxides (cupric) at higher temperatures.

Pranjal Tripathi said:   2 years ago
Brass is a copper alloy with the addition of zinc.

Copper is reactive with some materials in the atmosphere at different temperatures.

Exposure to air at normal temperatures results in discolouration (tarnish) due to reaction with sulfur and chlorine compounds and carbonates,

Exposure at high temperatures > 150°C. Results in reaction with oxygen-producing red oxides (cuprous) at lower temperatures and brown or black oxides (cupric) at higher temperatures.
(3)

Jyoti Prakash Panda said:   1 decade ago
Safe corrosion will look reddish, black to brown or green to blue. Safe corrosion will occur if the brass has been kept clean and dry. If it is brownish or black this will be due to oxidization of the copper which occurs when exposed to air; this a natural phenomenon and is non-destructive. This is usually called "tarnish" and can be removed by careful cleaning and polishing. If the corrosion is green, continuous and non-flaky this again is safe corrosion.

Manik sambyal said:   9 years ago
Hydrogen sulfide:

Chemical Compound:
Hydrogen sulfide is a chemical compound with the formula H 2S. It is a colorless gas with the characteristic foul odor of rotten eggs; it is heavier than air, very poisonous, corrosive, flammable, and explosive.

Formula: H2S.
Molar mass: 34.0809 g/mol.
Density: 1.36 kg/m^3.
Boiling point: -60 °C.
Melting point: -82 deg;C.
Soluble in: Water.
Classification: Sulfide, Sulfur compounds.


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