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13 Dec 2019

What is the formula weight of sodium thiosulfate pentahydrate? What mass of this salt is required to prepare 100 mL of a 0.0250 M sodium thiosulfate solution?

3) Joe the chemist titrated 100 mL of a sample that was 1.0 mM in Ca2+ with a standard EDTA solution to the EBT endpoint. Jane the chemist titrated a 100 mL sample that was 0.50 mM in Ca2+ and 0.50 mM in Mg2+ with the same EDTA standard solution. Both required exactly the same volume of the standard. Why?

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A 100.00-mL water sample was adjusted to pH 10 and titrated to the calmagite endpoint with 10.87 mL of 0.0125 M EDTA solution. Then the pH of another 100.00-mL water sample was adjusted to pH 12 and titrated with EDTA to the calcon endpoint. In this second titration, 2.63 mL of titrant was required. Calculate the concentration of Mg2+ and Ca2+ in the water. Express your answers in mg/L of CaCO3 and MgCO3, respectively.

a corrosion technologist pipetted a 100. 00 mL hard water sample and titrated it with 37.64 mL of 0.01 M EDTA solution for a total hardness endpoint and 29.32 mL of 0.01 M EDTA solution for a calcium endpoint. Calculate the concentration of magnesium and calcium in ppm. Record your answers as ppm Mg2+, and Ca2+ respectively. For each answer indicate the ppm as CaCO3 also.

A student wishes to analyze a seawater sample to determine the amounts of Na+ , Ca2+ and Mg2+ present. She begins with 50.00 mL sample of seawater that she dilutes to 500.00 mL. She removes a 50.00 mL aliquot of the diluted solution, which she analyzes for total cations present by exchanging the cations for H+ on an ion exchange column and titrating the liberated acid with 0.5000 M NaOH. The amount of NaOH required to reach the endpoint was 22.48 mL.

The student then titrates another 50.00 mL aliquot of her diluted seawater solution with 15.31 mL of 0.0100 M EDTA solution at a pH of 10 to the Erio T endpoint.

The third titration, performed on a 50.00 mL aliquot of the diluted seawater solution involves precipitating Mg2+ as the hydroxide and titrating the Ca2+ remaining in solution with 0.010 M EDTA solution. Only 5.15 mL of EDTA were required to reach the end point.

Summary of titration data:

Original seawater = 50.00 mL; diluted seawater = 500.00 mL

Vol. of titration aliquot = 50.00 mL

First titration: [NaOH] = 0.5000 M; V NaOH = 22.48 mL

Second titration: [EDTA] = 0.0100 M; VEDTA = 15.31 mL

Third titration: [EDTA] = 0.0100 M; VEDTA = 5.15 mL

From the titration data, calculate the following (show work):

A). mmol of Ca2+ present in the third 50.00 mL titration aliquot - ans.__________

B). mmol of Ca2+ present in the original 50.00 mL seawater sample - ans.__________

C). mg of Ca2+ present in the original 50.00 mL seawater sample - ans.__________

D). mmol of Ca2+ and Mg2+ present in the second 50.00 mL titration aliquot - ans.__________

E). mmol of Mg2+ present in the 50.00 mL titration aliquot - ans.__________

F). mmol of Mg2+ present in in the original 50.00 mL seawater sample - ans.__________

G). mg of Mg2+ present in in the original 50.00 mL seawater sample - ans.__________

H). meq of Ca2+ and Mg2+ present in the 50.00 mL titration aliquot - ans.__________

I). total meq of Na+ , Ca2+ and Mg2+ present in the 50.00 mL titration aliquot - ans.__________

J). meq of Na+ in the 50.00 mL titration aliquot - ans.__________

K). meq of Na+ present in the original 50.00 mL seawater sample - ans.__________

L). mg of Na+ present in in the original 50.00 mL seawater sample - ans.__________

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