Water Analysis Experiment Following is an outline of an experiment on water mdysis which has been highly successful with students in the first year chemistry classes. The experiment involves testing tap water, water from a river, pond, detergent solution or similar source, and analyzing a sample prepared by the instructor for calcium, magnesium, iron(II), iron(III), mercury(II), chloride, nitrate and phosphateions. I t takes four to five 50-min periods far completion.
General Instructions When solid reagents are called for, add a few crystals from the tip of a spatula. Keep a beaker of boiling water a t the lab station for heating test tubes where directed. For all tests except CaP+and Mgr+, use 1-2 ml portions of water in small test tubes. Learning the tests. Use a solution containing all the ions to familiarize yourself with the tests. Run a blank sample of demineralized water along side it. Part I1 Tap water. Evaporate 70-100 ml of tap water to about one-third of the original volume. Analyze and indicate ionspresent in your notebook. If test isvery faint, you may indicate a trace. Part 111 Special sample. Analyze water taken from river, creek, pond, ocean, detergent solutions, etc. Identify source, location, type of sample or brand if a commercial product is used. (Sample may require concentration.) Part I V Unknown. Bring small, clean beaker snd obtain prepared water sample. Anelyae and turn in results.
Psrt I
Tests CaP+ To about 4 ml of water sample, add 1M NBIOH until blue to litmus. If a dark precipitate forms, filter i t off then add a. little NH4C1and (NH&Cn04. Place in water bath and warm for a minute. A white precipitate indicates calcium in the form af calcium oxalste. Mgrc Feat Fez+ Hg'+
c1No8-
phate, upon shaking, indicates magnesium. Add a few drops of 1 M HCl and a. little potassium ferrocyanide, KPe(CNX, to a fresh sample of water. A dark blue precipitate (Prussian blue) shows presence of Fe3+. Add HC1 and ~otassinmferricvanide. KsFeiCN)s, signifies iron in the . . . and a similar dark blue precidtate . . . ierrous form. Add some ahinv Cu t,urnines and let stand for 1-2 min. A silverv coatine of H e metal will form an the Cu
test anduse the regular Cas+procedure. Add 0.2 M AgNOasolution, Look for a cloudy white turbidity t o develop which will t a m purplish in sunlight. (A vellow nreeinitak here could indicate the Dresence of PO2-. This will dissolve in a drop of concentrated H~SO+, t h e ~ gwill ~ inot.) To a. 1 ml sample in a. test tube, add an equal itmount of conoentrated HJOI. (Use utmost caution with this reagent. Note that the bottle may NOT he picked up by its lid, and avoid tilting so acid goes up into rubber bulb.) Cool by holding under tap, then carefully, without mixing, pour 0.5 M FeS0, down the side of the tube. The formation of a brown ring where the two liquids join indicate nitrate. The ring may not form immediately, so let stand for a few minutes and view over a. white surface. (Where sample contains Brr, an
POP water bath andlook'for the formation of a. bright yellow precipitate.
Volume 49, Number 1 I
, November 1972
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749
