Question

a) A metal ion buffer was prepared from 0.022 M ML and 0.026 M L, where ML is a metal-ligand complex and L is free ligand. M + L equilibrium reaction arrow ML Kf = 3.7 ✕ 108 Calculate the concentration of free metal ion, M, in this buffer.

b) By how many volts will the potential of an ideal
Mg^{2+} ion-selective electrode change if the electrode is
removed from 2.55 ✕ 10^{−4}*M* MgCl_{2} and
placed in 2.05 ✕ 10^{−3}*M* MgCl_{2}at 25°C?
(Assume that the Nernst potential is 0.05916 V.)

Answer #1

1. Given: Concentration of ML = 0.022 M

Concentration of L= 0.026 M

Kf value (given) 3.7x10^{8 }

To find the concentration of free ion M.

Solution:

Kf = ML / [M^{+}] [L]

3.7 x 10^{8} = 0.022 / [M^{+}] [0.026]

[M^{+}] = 0.022/3.7 x 10^{8} x 0.026

[M^{+}] = 0.022/9620000

[M^{+}] = 2.28 x 10^{-9}

Therefore, concentration of free ion M in the buffer is 2.28 x
10^{-9}.

2. Given : concentration of Mg^{+2} (c_{1}) =
2.55 x 10^{-4} M

concentration of Mg^{+2} (c_{2}) = 2.05 x
10^{-3} M

Nernst Potential = 0.05916 V

To find = no. of volts change

Solution:

delta E = E_{2} - E_{1}

= -0.05916/n ( log C_{2} - log C_{1} )

= -0.05916/2 ( log 2.05x 10^{-3} - log 2.55 x
10^{-4} )

= - 0.02958 x (-2.6882 - (-3.5934))

= -0.02958 x (-2.6882 + 3.5934)

= -0.02958 x 0.9052

= - 0.02677 Volts

Therefore, by -0.02677 volts the potential of an ideal
Mg^{+2} ion selecttive electrode will change.

A solution containing 30.00 ml of 0.0500 M metal ion buffered to
pH = 10.00 was titrated with 0.0400 M EDTA. Answer the following
questions and enter your results with numerical value only.
Calculate the equivalence volume, Ve, in milliliters.
Calculate the concentration (M) of free metal ion at V = 1/2
Ve.
Calculate the fraction (αY4-) of free EDTA
in the form Y4-. Keep 2 significant figures.
If the formation constant (Kf) is 1012.00.
Calculate the value of the...

The
M^+n (100.0 mL of 0.050 M metal ion buffered to pH 9.00) was
titrated with 0.050 M EDTA.
a) Calculate the concentration of M^+n when one-half of the
equivalence volume of EDTA (V=1/2Ve) is added.
b) What fraction of free EDTA is in the form Y^-4 at pH of
9.00?
c) If the formation constant Kf is 10^12.00, calculate the
concentration of M^+n at V=Ve.
d) What is the concentration of M^+n at V=1.100 Ve?

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