Question

Experiment 9: Water Hardness Pre-Laboratory Questions Name Section 1. Part of a buret measuring in mL is shown below. Read the volume to the proper number of significant digits. Volume 2. Suppose it takes 33.69 mL of 0.005123 M EDTA to titrate 25.00 mL of a hard water solution. a) How many moles of EDTA were required to titrate to the endpoint? b) How many moles of hard water ions, expressed as moles of Ca?", are present in the hard water solution? c) What is the concentration, expressed as molarity of Ca, of hard water ions in the solution? d) If the metal ions in the hard water all came from Cacos, how many grams of Caco, would be in 1.000 L of the solution in other words, determine g CaCO3/L)? e) Convert g CaCOL calculated in (d) to mg CaCO L. (This is equivalent to ppm.) Expt 9 - Page 5

Answer 1

1 46.5 mL 2. Using the formula V,S, = V₂2 Hand Water. EDTA 7 33.69 mL 0.005123 (M) EDTA Das required. CH) . number of moles. 0.005123 x 33.69 mol 1000 = 1.73x10 9 mol 6) 1 mol EDTA = 1 mol cakt: So, moles of Ca2t in hard warten 11 al = 1.73x109 & moles. 1.73x 100 x 1000 na 25 ey 1.73x109 moles of Ca 2+ was in 25 mL of hard & water solution. so, 25 ml contains 1.73x109 mile 1000 mL & are = 619x103 (M) Molarity of Calt, ire, hard water ich = 609x 103 (M) d) Molecular weigh of CaCO₃= 100 g/mol 1000 ml solution contain 6.90x10 3 moles of Call = 1Litre = 6.9x103 4100 g Call - 0.69 og cao, CaCO3 = 0.69 g/L ex Calloz - 0.69 x 103 mgfe. - 690 mg/e