using Eriochrome Black T as the indicator. e a true blue color after the addton

Question

using Eriochrome Black T as the indicator. e a true blue color after the addton of 5.22 mof 0.010 M EDTA. Calculate 2. A 250 mL sample of water was titrated wit the following: a. molarity of Cain the sample (Hint: See Equation 7 in Scientific Background,) b. hardness of the water in ppm CaCo, c. Would this sample of water be classified as hard or soft? During the determination of ppm CaCO, in the unknown, 10 mL of unknown was diluted with 40 mL of distilled water. If tap water was mistakenly used in place of distilled water, how would this procedural error affect the calculated value of ppm CaCO, in the unknown? 3. 4. Write a balanced equation for the reaction of the soap potassium stearate (G, H, CO, with magnesium sulfate.

Explanation / Answer

Q2.

[Ca+2] --> from EDTA

EDTA + Ca2+ = EDTACA2+

mmol of EDTA = MV = 5.72*0.01 = 0.0572 mmol

then

mmol of C a2+ = 0.0572

[Ca2+] =) mmol/V = 0.0572/25 = 0.002288 M

b)

hardness of water in ppm

ppm = mg of Ca / L solution

0.002288 mol of Ca --> mass = mol*MW = 0.002288*40 = 0.09152 g = 91.52 mg

then

ppm = 91.52 mg/L = 91.52 ppm

c)

40-80 ppm --> recommended Ca2+ concentration

therefore, this is greater than that, so this msut be hard water

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