METTLER TOLEDO

Complexometric Titration of Lead in Alloy
Lead is determined by complexometric titration with EDTA using xylenol orange and hexamethylene tetramine as colour indicator. The titration is monitored with a DP550 phototrode. Sample
Lead-tin-antimony alloy, 10 mL aliquots of a solution of the alloy
Preparation and Procedures
1) Dissolve 1.5 g of pulverized alloy in a 250mL beaker. 2) Add 20 mL 1:1 HCl and heat. 3) Add 10 mL 1:1 HNO3 , heat until complete dissolution. 4) Add 20 mL of 4% KCl, 50 mL of 1:1 HCl, 50 mL deion. water and 20 mL 20% tartaric acid solution. 5) Boil 2 minutes and then cool to room temperature. 6) Add 5 drops of 0.2% aqueous solution of xylenol orange and 30% hexamethylene tetramine until the solution turns red (ca. 35 mL for this sample size). 7) Dilute to 200 mL with 1:1 HCl since no precipitate is formed at high HCl concentration. 8) Take aliquots of 10 mL. 9) This procedure is only suitable for the determination of Pb in Pb/Sn/Sb alloy. The alloy is dissolved due to the formation in a strong acid medium of a soluble chloro-plumbate complex. 10) Sn and Sb are masked by tartaric acid. Pb can be directly determined by titration with EDTA: Pb2+ + H2-EDTA2- = Pb-EDTA2- + 2H+ The colour change at the equivalence point turns from red to yellow.

Substance Chemicals

Lead, Pb2+ M = 207.2, z = mL deion. water, 20 mL 1:1 HCl, 10 mL 1:1 HNO3 , 20 mL 4% KCl, 20 mL 20% Tartaric acid EDTA c(EDTA) = 0.1 mol/L

Titrant

Standard Instruments
Zinc sulphate, ZnSO4 (see M528) DL53,DL50 Graphix, DL55/DL58, DL70ES, DL77, Rondo 60 sample changer, Olivetti ArtJet 20 Glass titration beakers ME-101446

Accessories

Remarks Indication Chemistry
DP550 Phototrode with DIN-Lemo adapter ME-89600 Pb2+ + H2-EDTA2- = Pb-EDTA2- + 2H+
The method was developed on the DL40 titrator and has been adapted for the DL5x- and DL7x-titrators. The Pb(II) content is detemined by complexometric titration with EDTA.
Literature: 1. DL40 application no. 406

Calculation

R=Q*C/(m*20) C=M/(10*z) Pb content in %
2. Application no. M528 in Application brochure18, "Standardization of Titrants", 2000.

Results

Waste disposal

Special waste.

Author
MT Analytical, Application Laboratory
Pb2+ Mean value n Comments DL40 application no. 406

45.49 % 5

Rel. standard deviation srel Consumption:

0.34 % 1.7 mL

Mean value

98.13 % 5

DL40 application no. 403
Rel. standard deviation srel

0.21 %

Test with Pb((NO3)2 standard Preparation: 1. use buffer solution pH 5.4 2. Indicator: xylenol orange 3. Sensor: DP550 4. Titrant: 0.1 ml/L EDTA Buffer pH 4.5: Hexamethylene tetramine: 400 g Hydrochloric acid:100 mL Dilute with deion. water to 1 L

Table of measured values

Titration curve

Method

Method 40007 Version Pb2+ 22-01-2001 10:47. 40007. Pb2+. 22-01-2001. Title Method ID. Title. Date/time. Sample Sample ID. Entry type. Lower limit [g]. Upper limit [g]. Molar mass M. Equivalent number z. Titration stand. Pump. Rinse. Solvent. Volume. Conditioning. Temperature sensor. Stir Speed [%]. Time [s]. EQP titration Titrant/Sensor Titrant. Concentration [mol/L]. Sensor. Unit of meas. Predispensing. Titrant addition. dV [mL]. Measure mode. dE [mV]. dt [s]. t(min) [s]. t(max) [s]. Recognition Threshold. Steepest jump only. Range. Tendency. Termination at maximum volume [mL]. at potential. at slope. after number EQPs. n =. comb. termination criteria Evaluation Procedure. Potential 1. Potential 2. Stop for reevaluation. Condition. Calculation Formula. Constant. Decimal places. Result unit. Result name. Statistics. Calculation Formula. Constant. Decimal places. Result unit. Result name. Statistics. Calculation Formula. Constant. Decimal places. Result unit. Result name. Statistics. Report Output. Printer Results. No All results. Yes Raw results. No Table of measured values. Yes Sample data. No E - V curve. Yes dE/dV - V curve. Yes d2E/dV2 - V curve. No log dE/dV - V curve. No E - t curve. No V - t curve. No dV/dt - t curve. No
Pb/Sn/Sb alloy Weight 1.4 1.6 207.ST20A No Yes H2O 20.0 No Manual
. 50. 10. EDTA 0.1 DP550 mV No Incremental 0.05 Equilibrium controlled 0.5 2.0 5.0 30.No No Positive 5.0 No No Yes 1 No Standard No No Yes neq=0 R=Q*C/(m*20) C=M/(10*z) 2 % Pb content Yes R2=VEQ 3 mL Consumption Yes