#1. So the sample answer I got from #1 is 2.6. My initial volume(ml) for EDTA wa

Question

#1.
So the sample answer I got from #1 is 2.6.

My initial volume(ml) for EDTA waa 8.8. My final EDTA was 6.2 making my EDTA used 2.6

#2.

So I used 10ml of water and when I solve the equation in #2 I get 0.0026.

#3.

I am confused how to solve. I don't understand what its asking.

Equations for analysis 1-3 1. Calculate the volume of EDTA ed for each trial using the following equation Record each value in the results table Initial volume of EDTA Final volume of EDTA volume of EDTA used 2. Calculate the concentration of Ca+2 ns per liter of water using the following equation. Record each value in the results table. The molarity of EDTA is o.01M. Recall that molarity moles/L. moles Ca molarity EDTA) x (mL EDTA) mL of water sample 3. Calculate the water hardness using your results from part 2 and the following equation. Record each value in the results table. ppm CaCO3 moles Ca x 1 mol CaCO3 x 100.06 g CaCO3 x 1000 mg 1 L 1 mol Ca 1 mol CaCO3

Explanation / Answer

1 mole of Ca2+ reacts with 1 mole of EDTA

so,

moles of EDTA = molarity of EDTA (mol/L) x volume of EDTA (L)

                         = moles of Ca2+

molarity = moles/L of solution

Volume of water sample = 10 ml

So,

molarity (moles/L) of Ca2+ in 10 ml water sample = moles of Ca2+ (which is equal to moles of EDTA)/0.01 L of water sample

                                                                                = 0.0026 mol/L

For water hardness in terms of CaCO3

1 mole of CaCO3 has 1 mole of Ca2+ in it.

1 mole of CaCO3 = molar mass of CaCO3 = 100.06 g

ppm of CaCO3 = mg of CaCO3 in solution/L of solution

                         = moles Ca2+ x molar mass CaCO3 x 1000/L of solution

So with 0.0026 mol/L of Ca2+

Water hardness = 0.0026 x 100.06 x 1000 = 260.156 ppm (mg/L CaCO3)

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