Finding the percentage of copper in brass alloy.
This is an investigation to find out how much copper is in a brass alloy. The brass alloy we are experimenting on is called Muntz Metal. Muntz metal is 60% copper, 40% zinc and a hint of copper [http://en.wikipedia.org/wiki/Muntz_metal] (accessed 4/10/12). Muntz metal was developed as an alternative to expensive, heavy copper. It is comprised of about 60% copper and about 40% zinc, with a small amount of iron. The finished product actually is considered a form of brass, but it has maintained its name of Muntz metal. [http://www.wisegeek.com/what-is-muntz-metal.htm] (Accessed 4/10/12) Explanation
The brass is dissolved in sulphuric acid to create the blue solution of copper. We put the blue solution of copper in the colorimeter and measured the absorbance of the solution 3 times then we found the average of the 3 different results we had gotten. We then diluted the blue solution of copper with water and put it into the colorimeter and measured the absorbance 3 times again and got the average again. A colorimeter is a light-sensitive instrument that measures how much colour is absorbed by an object or substance. It determines colour based on the red, blue, and green components of light absorbed by the object or sample, much as the human eye does. When light passes through a medium, part of the light is absorbed, and as a result, there is a decrease in how much of the light reflected by the medium. A colorimeter measures that change so users can analyse the concentration of a particular substance in that medium. The device works on the basis of Beer-Lambert's law, which states that the absorption of light transmitted through a medium is directly proportional to the concentration of the medium. [http://www.wisegeek.com/what-is-a-colorimeter.htm] (Accessed 5/10/12) Prediction
If it is Muntz metal it should be 60% copper and 40% zinc. There for if we measure the percentage of copper anything that isn’t 60% we know that it isn’t Muntz metal. However if it is 60% copper we still cannot be certain that it is Muntz metal. Method
We were provided with a sample of brass that has been filled with a sample that is believed to be the stolen Muntz metal. Afterwards using a flame cupboard we placed 30cm3 of distilled water into a 250cm3 conical flask and slowly added 15cm3 of concentrated nitric acid to it. Then we stirred the mixture using a glass rod. Subsequently we weighed out accurately known to 2dp about 1.5g of the brass filings. We slowly to the diluted nitric acid in the fume cupboard. Then you had to leave the mixture for some minutes until all the brass has ‘dissolved’. During this procedure poisonous nitrogen dioxide gas is given off and a blue solution containing copper (Cu2+) and zinc (Zn2+) ions is formed.
We have two separate equations for what is happening to the zinc and copper in the brass as we don’t have a formula for the brass alloy. These equations are:
Cu(s) + 2HNO3(i) Cu(NO3)2(i)+2H+(aq) Cu(s) Cu2+(aq) (Ionic equation) Zn(s) + 2HNO3(i) Zn(NO3)2(i)+2H+(aq) Zn(s) Zn2+(aq) (Ionic equation)
we were then provided with around 100cm3 of a copper sulphate solution. This solution contain1.6g of copper (as Cu2+ ions) in 250cm3 of solution. We then diluted this copper sulphate solution with distilled water to make the solutions labelled A to F in the table below. This dilution is to be done accurately using appropriate apparatus, with mixing. Solution
| Copper sulphate (aq) /cm3
| Water/ cm3
| Concentration of solution G Cu/250cm3
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