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Qualitatively Analyze the Chemical Composition of two Alloys: Brass and Bronze


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INTRODUCTION

An alloy is a homogeneous mixture of two or more metals or a metal and non-metal. They are generally harder than their components with reduced malleability and ductility. Alloys are prepared to enhance certain characteristics of the constituent metals, as per requirement. In this project, we shall qualitatively analyze the chemical composition of two alloys: Brass and Bronze

AIM OF THE EXPERIMENT

General objective: This project is being carried out with a view to increase the appreciation of alloy- analysis as an important branch of chemistry. The hands-on laboratory experience gained is highly beneficial in understanding the general procedure of qualitative analysis of an unknown sample. Specific objective: In this project, we shall be analyzing the constituents of Brass and Bronze.

Materials Required

1) Brass and Bronze pieces
2) China dishes
3) Filtration apparatus
4) Nitric acid
5) Hydrogen sulphide gas
6) Ammonium hydroxide
7) Ammonium chloride
8) Potassium ferrocyanide
9) Ammonium sulphide
10) Dil. hydrochloric acid
11) Mercuric chloride

THEORY

BRASS:

Brass contains Cu and Zn . Both dissolve in nitric acid. 4Zn+ 10 HNO3 → 4Zn(NO3)2 + N2O + 5H2O 3Cu + 8HNO3 → 3Cu(NO3)2 + 4H2O+2NO
Further analysis is carried out for respective ions.
Cu dissolves in H2S to give black ppt. of CuS. It is filtered to get the solution of Zinc Sulphide. It precipitates out in the form of ZnCl2 in an ammoniacal soln. of Ammonium chloride. The precipitate is dissolved in dilute HCl and then treated with Potassium ferrocyanide to get a bluish - white ppt. of Zn2[Fe(CN)6].

BRONZE:

Bronze contains Cu and Sn. Their nitrates are obtained by dissolving the sample in conc. Nitric acid. The nitrates are precipitated as sulphides by passing H2S through their solution in dil. HCl.
The CuS is insoluble in yellow ammonium sulphide, while SnS is soluble. The ppt. is separated by filtration.
The ppt. is dissolved in conc. HNO3 and then Ammonium hydroxide solution is passed through it. Blue colouration confirms the presence of Cu.

PROCEDURE:

Brass:

A small piece of brass was placed in a china dish and dissolved in minimum quantity of 50%conc.HNO3.
The soln. was heated to obtain a dry residue. The residue was dissolved in Dilute HCl.
H2S gas was passed and a black.ppt. was observed. The soln. was filtered and the ppt. was dissolved in NH4OH soln. A blue coloration observed indicates the presence of Cu.
The filtrate was tested for presence of Zn. Ammonium hydroxide and chloride solutions were added and then H2S gas was passed. A dull grey ppt. was separated and dissolved in dil. HCl followed by addition of Potassium ferrocyanide. A bluish white ppt. confirms the presence of Zn.

BRONZE:

1. The sample was dissolved in 50% HNO3 and then heated to obtain nitrates.
2. The nitrates were dissolved in dil. HCl and then precipitated as sulphides by passing H2S gas.
3. The precipitates were treated with yellow ammonium sulphide when a part of it dissolves. The soln. was filtered.
4. The ppt. was tested for Cu as in the case of brass.
5. The filtrate was treated with conc. HCl followed by Fe dust.
6. Then HgCl2 soln. was added. Formation of a slate-coloured ppt. confirmed the presence of Sn.

CONCLUSION

Brass contains Copper and Zinc. Bronze contains Copper and Tin.

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Abstract

Aim is To Analyze a Sample of Brass Qualitatively.

Brass is an alloy of copper and zinc. Small amount of iron and lead are also present. This dissolves in 50%nitric acid and generates the ions of the constituting metals in solutions. Presence of these ions in the solution can be conformed by qualitative inorganic analysis scheme. An alloy is a homogeneous mixture of two or more metals or metals and non-metals. In other words a solid solution of two or more metals or a metal and a non-metal. It is prepared by first melting the main metal, and then, dissolving the other elements in it in a definite proportion. It is then cooled to the room temperature. If one of the metals is mercury, then the alloy is known as amalgam. The electrical conductivity of an alloy is less than that of pure metals. More than ten thousands alloys have been prepared so far and about hundred of them are in common use, for example, stainless steel, brass, bronze, duralumin, soldering metal, gun metal, etc. So large numbers of alloys have been prepared because the properties of the parent metals constituting the alloy are modified a lot by alloy formation. For example, pure copper metal is soft and ductile, but when it is alloyed with small amount of zinc, becomes hard.