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Chapter 12: Q24P (page 285)

List four methods for detecting the end point of an EDTA Titration

Short Answer

Expert verified

The four methods for detecting the end point of an EDTA titration are

a) With metal ion indicators

b) With a glass electrode

c) With a mercury electrode

d) With an ion selective electrode.

Step by step solution

01

EDTA

EDTA, also known as ethylenediaminetetraacetic acid forms strong complexes with metal ions and plays a major role in quantitative analysis. In industries it is used as a metal binding agent and used in production of detergents, cleaning agents, food additives etc

02

EDTA titration

In most of the cases little amount of indicator is induced at the beginning of the titration experiment. EDTA is then added to the colorless metalcomplex solution and reacts until all the free metal ions are consumed.

03

List of methods

The four methods for detecting the end point of an EDTA titration are

a) With metal ion indicators

b) With a glass electrode

c) With a mercury electrode

d) With an ion selective electrode.

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Most popular questions from this chapter

Calculate pCu²⁺ at each of the following points in the titration of 50.00 mL of 0.001 00 M Cu²⁺ with 0.00100 M EDTA at pH 11.00 in a solution with [NH₃] fixed at 1.00 M:

(a) 0 mL(b) 1.00 mL (c) 45.00 mL (d) 50.00 mL (e) 55.00 mL

Spreadsheet equation for auxiliary complexing agent. Consider the titration of metal M (initial concentration = C_M, initial volume = V_M) with EDTA (concentration = C_EDTA, volume added = V_EDTA) in the presence of an auxiliary complexing ligand (such as ammonia). Follow the derivation in Section 12-4 to show that the master equation for the titration is

$ϕ = \frac{C_{ETDA} V_{ETDA}}{C_{M} V_{M}} = \frac{1 + K_{f}^{"} {[M]}_{free} - \frac{{[M]}_{free} + K_{f}^{"} {[M]}_{free}}{C_{M}}}{K_{f}^{"} {[M]}_{free} + \frac{{[M]}_{free} + K_{f}^{"} {[M]}_{free}^{2}}{C_{ETDA}}}$

where role="math"> is the conditional formation constant in the presence of auxiliary complexing agent at the fixed pH of the titration (Equation 12-18) and [M]_free is the total concentration of metal not bound to EDTA. [M]free is the same as [M] in Equation 12-15. The result is equivalent to Equation 12-11, with [M] replaced by [M]_free and K_f replaced by $K_{f}^{"}$ .

Calculate pCu2+ at each of the following points in the titration of 50.00 mL of 0.001 00 M Cu2+ with 0.00100 M EDTA at pH 11.00 in a solution with [NH3] fixed at 1.00 M:

(a) 0 mL(b) 1.00 mL (c) 45.00 mL (d) 50.00 mL (e) 55.00 mL

What is the predominant form of arginine atpH11? What is the second major species?

Spreadsheet equation for formation of the complexes ML and ML₂.Consider the titration of metal M (initial concentration = C_M, initial volume = V_M) with ligand L (concentration = C_L, volume added = V_L), which can form 1:1 and 2 : 1 complexes:

$\begin{array}{clc} M + L 𝆏 & ML & β_{1} = \frac{[ML]}{[M] [L]} \\ M + 2 L 𝆏 & {ML}_{2} & β_{2} = \frac{[{ML}_{2}]}{[M] [L]^{2}} \end{array}$

Let αM be the fraction of metal in the form M, α_ML be the fraction in the form ML, and $α_{{ML}_{2}}$ be the fraction in the form ML2. Following the derivation in Section 12-5, you could show that these fractions are given by

role="math" localid="1667801924683" $\begin{aligned} α_{M 1} = \frac{1}{1 + β_{1} [L] + β_{2} [L]^{2}} \\ α_{ML} = \frac{β_{1} [L]}{1 + β_{1} [L] + β_{2} [L]^{2}} \\ α_{{ML}_{2}} = \frac{β_{2} [L]^{2}}{1 + β_{1} [L] + β_{2} [L]^{2}} \end{aligned}$

The concentrations of ML and ML2are

$[ML] = α_{ML} \frac{C_{M} V_{M}}{V_{M} + V_{L}} [{ML}_{2}] = α_{{ML}_{2}} \frac{C_{M} V_{M}}{V_{M} + V_{L}}$

because $\frac{C_{M} V_{M}}{V_{M} + V_{L}}$ is the total concentration of all metal in the solution. The mass balance for ligand is

$[L] + [ML] + 2 [{ML}_{2}] = \frac{C_{M} V_{M}}{V_{M} + V_{L}}$

By substituting expressions for [ML] and [ML₂] into the mass balance, show that the master equation for a titration of metal by ligand is

$ϕ = \frac{C_{L} V_{L}}{V_{M} + V_{M}} = \frac{α_{ML} + 2 α_{{ML}_{2}} + \frac{L}{C_{M}}}{1 - \frac{L}{C_{L}}}$

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