Chemistry 223: Experiment 6
IODOMETRIC DETERMINATION OF COPPER IN BRASS
1. C, Chap. 10 (especially pp. 263-264 and 267-272) and pp.583-584.
2. H7, Chapter 16, especially section 16-7.
3. S & W, Chaps. 11, 12 (especially pp. 312-17, 320-23), pp.593-96.
4. SWH, Chaps. 13, 14 (especially pp. 339-344), 31 (pp. 781-784).
This experimental procedure is mainly based on the lab. Iodometric determination of copper
in brass. Chem. 223- UIUC
Brass is an alloy consisting principally of copper, zinc, lead, and tin. In addition, several other
elements, iron and nickel, for example, may be present in minor amounts. The iodometric
method is convenient for estimating the copper content of such alloys.
A solid brass sample is dissolved in acid. The Cu
is reacted with I
to form CuI(s) and I
The iodine generated is determined by titration with standardized thiosulfate, thus allowing
calculation of the copper content of the brass.
In acid solution practically all oxidizing agents will oxidize iodide ion to iodine
quantitatively. The iodine formed in the reaction can then be titrated by means of a standard
sodium thiosulfate solution. This type of indirect titration is given the general name of
Iodometric methods of analysis have a wide applicability for the following reasons:
1. Potassium iodide, KI, is readily available in high purity.
2. A good indicator, starch, is available to signal the equivalence point in the reaction
between iodine and thiosulfate. Starch turns blue-black in the presence of iodine.
Therefore, when the blue-black color disappears, the iodine has been completely
reduced to the iodide ion.
3. Iodometric reactions are rapid and quantitative.
4. A precise and stable reducing agent, sodium thiosulfate (Na
), is available to react
with the iodine.
The amount of iodine liberated in the reaction between iodide ion and an oxidizing agent is a
measure of the quantity of oxidizing agent originally present in the solution. The amount of
standard sodium thiosulfate solution required to titrate the liberated iodine is then equivalent
-- Converted from Word to PDF for free by Fast PDF -- www.fastpdf.com --