INTRODUCTION

Copper is one of the most used metals in the innovation history of man. Pure copper

metal is characterized as soft, ductile, unlimited capacity to cold-work and high corrosion-

resistivity. To improve its mechanical and corrosion-resistance properties, copper metals undergo

an alloying process where some particular metal elements are used as substitutional impurity.

(Callister W. Jr., 2007)

One type of copper alloy is brasses. Brasses are copper alloy which uses zinc as the

primary alloying component (Callister W. Jr., 2007) but some brasses uses small amounts of

other elements rather than zinc to make the desired characteristic and properties of a particular

brass(Avner S., 1974). Brasses are classified according to zinc concentration present: α- brass

and α + β brass. Alpha (α) brasses had up to 36% zinc concentration while alpha plus beta (α +

β) brass contains 38% - 46% zinc (Avner S., 1974).

Alpha brasses are characterized to have good quality corrosion resistance and mechanical

performance. Due to the amount of copper present in the homogenous solid solution, the colors

of alpha brasses differ. Alpha brasses are classified into two: the yellow alpha brass that has 20%

- 36% zinc concentration, and the red brass that has 5% - 20% zinc concentration. Yellow alpha

brasses have good mechanical properties and are applicable to undergo extreme cold-working

operation. While, red brasses had high corrosion resistance than yellow alpha brass. Alpha

brasses are used for automotive parts, electrical devices, hardware, coins and medals, and some

body accessories.

On the other hand, alpha plus beta brasses are characterized to have high strength,

excellent hot-working properties and are the perfect copper-zinc alloy to be introduced by

another metal element to improve and to get the desired properties of a particular brass. Alpha

plus beta brasses are used in architectural works, marine hardware, machine parts and in ship-

sheathing. (Avner S., 1974)

The concentration of solvent and solute present and the type of element introduced to

copper-zinc alloy may differ due to the particular desired properties and characteristic it were

made for but totally, the purpose is to develop, innovate and improve human living.

The experiment aims to determine the zinc content in the given brass sample and identify

the particular brass type it belongs. It gives information to the students about a particular process

in determining the amount of zinc present in the given brass sample and gives the idea of what

type of copper-zinc alloy it belongs. It limits only to the determination of zinc concentration

present in the sample and identification of brass classification.

METHODOLOGY

Materials and Equipment

The materials used in this experiment are as follows: brass sample, hot plate, digital

balance, funnel, 100-mL graduated cylinder, oven, H2S generator, burette, 600-mL and 250-mL

beakers, Gooch crucible, nitric acid, hydrochloric acid, sulfuric acid, diammonium hydrogen

phosphate, filter paper, pyrite, ammonia, litmus paper and phenolphthalein indicator.

Procedures

A. Preparation of (NH4)2HPO4 reagent:

Seven and four hundred four thousandths milliliters (7.484 mL) of phosphoric

acid was added to 15.73 mL of ammonia in a 250-mL beaker, and was diluted to 140 mL.

Litmus paper was put into the solution for checking the acidity.

B. Preparation of the H2S Generator:

The H2S generator was washed then dried. Pyrite and HCl were put inside the

generator (see Figure 1).

C. Zinc in Brass Determination:

A sample of brass was cut and weighed (see Figure 2). The brass sample was

dissolved in nitric acid and hydrochloric acid and was then evaporated to dryness (see

Figure 3). The dried sample was treated with 2.5 mL HCl and 50 mL water and was

saturated with H2S (see Figure 4). The solution was diluted to 100 mL and was saturated

again with H2S until the precipitate appeared. Precipitate was left to settle then the H2S

was swirled again until the solution would not react with H2S. Copper sulfide and other

sulfides was filtered off and washed (see Figure 5). The filtrate was then boiled to

eliminate H2S. The filtrate containing zinc was neutralized by drop wise addition of

ammonia. Litmus paper was put into the solution. The solution was heated nearly to

boiling and large excess of filtered (NH4)2HPO4 reagent was added slowly. The solution

was heated gently until the precipitate became crystalline. Then the solution was allowed

to cool. The precipitate was filtered off in a weighed Gooch crucible and then washed

with 1% (NH4)2HPO4 solution and 50 mL of 50% solution of alcohol (see Figure 6).

Finally, the precipitate was dried at 105ᵒC for an hour and weighed as Zn(NH4)PO4.

RESULTS AND DISCUSSION

In this activity, zinc content of a brass sample in grams was determined using the data in

the table below and guided with specified reactions. ____________________

Weight of sample (brass) 1.24 g

Volume of HNO3 added 7.00 mL

Volume of HCl added 9.50 mL

Gooch + Filter paper 28.58 g

Final weight 31.57 g

Weight of residue Zn(NH4)PO4 2.99 g

Table 1. Data obtained throughout the experiment

Using a strong oxidizing agent (HNO3), the brass sample was dissolved resulting to a

solution containing metal ions in their highest normally occurring oxidation states (Cu 2+, Zn2+,

Pb2+ and Ni2+). The reactions between nitric acid and the several metals in brass are shown

below.

Cu(s) + 4H+ + 2NO3 → Cu2+ + 2H2O + 2NO2 (g)

Zn(s) + 4H+ + 2NO3 → Zn2+ + 2H2O + 2NO2 (g)

Pb(s) + 4H+ + 2NO3 → Pb2+ + 2H2O + 2NO2 (g)

Ni(s) + 4H+ + 2NO3 → Ni2+ + 2H2O + 2NO2 (g)

Fe(s) + 6H+ + 3NO3 → Fe3+ + 3H2O + 3NO2 (g)

Sn(s) + 4H+ + 4NO3 → SnO2 (s) + 2H2O + 4NO2 (g)

NO2 gas and H2O are eliminated by evaporation during heating. The addition of HCl and

H2S, were used to get rid of the insoluble sulfides and nitrogen oxides that resulted from the

reactions of other metal ions with H2S. The white precipitates of PbSO4 caused by the addition

of water will be expelled upon filtering. On the other hand, Zinc reacts with HCl and forms into

zinc chloride (colorless or white) which is highly soluble in water.

Zn+2HCl → ZnCl2 + H2

Zn2+ + NH4+ + HPO4

2− ↔ Zn(NH4)PO4 + H+

Finally, Zinc content was calculated and obtained 1.20 g as shown below.

g Zn=2.99 g Zn (NH 4 ) PO 4 ( 1mole Zn ( NH 4 ) PO4178.43 g )( 1 mole Zn

1 mole Zn ( NH 4 ) PO 4 )( 65.41 g1mole Zn )=1. 10

CONLUSION

The study revealed that the brass sample contains approximately 1.1 grams or 89% Zn.

Clearly, a huge error was made during the experiment.The solutions were left unattended for

days which could trigger side reactions. Thus, the experimenters cannot give the possible

properties corresponding to the result sincethe theoretical composition of zinc in yellow brasses

ranges up to 20 to 36 percent only to obtain good strength with high ductility. Besides, the

concentration of copper must be greater than zinc. Furthermore, the best combination of strength

and ductility in brass is obtained at 30percent zinc.

REFERENCES

Avner, S. (1974). Introduction to Physical Metallurgy. 2nd Edition. New York. McGraw-Hill

Book Company

Callister, W. Jr. (2007). Materials Science and Engineering: An Introduction. 605 Third Avenue,

New York. John Wiley & Sons, Inc.

APPENDIX

Figure 1. Preparation of H2S generator (a) pyrite was put inside the generator, (b) HCl was added

(c) cork stopper was put into the generator.

Figure 2. Brass sample was cut and weighed.

(a) (b) (c)

(a)(b)

Figure 3. The brass sample was dissolved in nitric acid and hydrochloric acid.

Figure 4. The dried sample was treated with 2.5 mL HCl and 50 mL water and was saturated

with H2S.

Figure 5. Copper sulfide and other sulfides was filtered off and washed.

Figure 6. The precipitate was filtered off in a weighed Gooch crucible.