Prac 8 - Water chemistryII essays

Prac 8 - Water chemistryII essays Ø To determine water hardness of tap water and river water samples by means of titration with Ethylenediaminetetra-acetic acid (EDTA). Ø To compare the different hardness levels of water samples from various sources. Hardness is primarily the measure of calcium (Ca2+) and magnesium (Mg2+) ions in the water. Other polyvalent metal ions can contribute to the hardness, but their effects are usually insignificant and the other ions are difficult to measure. Hardness is generally reported as ppm or mg/L of CaCO3. EDTA is a tetrabasic acid, and it has the ability to form chelated complexes with some multivalent metal ions (including Ca2+ and Mg2+). EDTA has 6 donor electrons, each of which can displace a water molecule from a hydrated metal ion. At the same time EDTA becomes deprotonated. The reaction is as follows: Mn+ + HmY(4-m)- MY(4-n)- + mH+ (where m depends on pH of solution) Because protons are liberated, the solution must be buffered. Tap Water Sample: River Water Sample Initial Volume Reading (ml) 0 3.92 0 0 0 Final Volume Reading (ml) 3.92 7.58 6.48 6.46 6.45 Volume Delivered (ml) 3.92 3.66 6.48 6.46 6.45 [EDTA] = 0.01M Volume sample used: 100ml Hardness = {([EDTA] Ãâ€" Volume EDTA used)/Volume of water sample} With [EDTA] in mol/L, and the volumes in ml, gives us hardness in mol/L. Hardness = {(0.01 Ãâ€" 3.92)/100) = 3.92 Ãâ€" 10-4M Converting to mg/L: (3.92 Ãâ€" 10-4mol/L Ãâ€" 100g/mol) Ãâ€" 1000mg/g Utilising this method, we get the following results for hardness (mg CaCO3/L): Tap Water Sample: River Water Sample Run1 Run2 Average Run1 Run2 Run3 Average Sample mean for river water samples = = ...