Monograph pubs.acs.org/doi/book/10.1021/acsreagents
Zinc Part 4, Monographs for Reagent Chemicals: General Descriptions, Specifications, and Tests eISBN: 9780841230460 Tom Tyner Chair, ACS Committee on Analytical Reagents James Francis Secretary, ACS Committee on Analytical Reagents
ABSTRACT This monograph for Zinc provides, in addition to common physical constants, a general description including typical appearance, applications, and change in state (approximate). The monograph also details the following specifications and corresponding tests for verifying that a substance meets ACS Reagent Grade specifications including: Assay, Suitability for Determination of Arsenic, Iron and Lead.
Zn
Atomic Wt 65.38
CAS No. 7440-66-6
GENERAL DESCRIPTION Typical appearance . . . . . . . . . . . . . . . . . . . silver-gray metal Applications . . . . . . . . . . . . . . . . . . . . . . . . reducing agent; determination of arsenic Change in state (approximate) . . . . . . . . . . . . melting point, 419 °C
SPECIFICATIONS Assay . . . . . . . . . . . . . . . . . . . . . . . . . . . . ≥99.8% Zn Suitability for determination of arsenic (As) . . . Passes test Maximum Allowable Iron (Fe) . . . . . . . . . . . . . . . . . . . . . . . . . . 0.01% Lead (Pb) . . . . . . . . . . . . . . . . . . . . . . . . . 0.01%
TESTS Assay (By complexometric titration for zinc). Weigh, to the nearest 0.1 mg, about 0.2 g of sample, and dissolve with 10 mL of (1:1) nitric acid. When completely dissolved, dilute with water to about 300 mL, and with the aid of magnetic stirring, neutralize with 10% sodium hydroxide to methyl red. Add a few milligrams of ascorbic acid, 15 mL of pH 10 ammoniacal buffer
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4425 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
solution, and about 50 mg of Eriochrome Black T indicator mixture. Titrate immediately with 0.1 M EDTA volumetric solution to a blue end point. One milliliter of 0.1 M EDTA corresponds to 0.006538 g of Zn.
Suitability for Determination of Arsenic The apparatus used for this test is described in the general method for arsenic in [Part 2: Colorimetry and Turbidimetry; Arsenic; Procedure for Arsenic]. Add 13 g of the sample to a generator flask containing a mixture of 35 mL of water, 10 mL of hydrochloric acid, 2 mL of 16.5% potassium iodide reagent solution, and 0.5 mL of 40% stannous chloride reagent solution. Immediately connect the scrubber–absorber assembly to the generator flask. When the gas evolution stops, disconnect the flask, and add successive 5 mL portions of hydrochloric acid. Immediately connect the scrubber–absorber assembly to the flask after each addition. After four or five portions of acid have been added, decant the spent acid, and add a mixture of 35 mL of water, 10 mL of hydrochloric acid, 2 mL of 16.5% potassium iodide reagent solution, and 0.5 mL of 40% stannous chloride reagent solution. Immediately reconnect the scrubber–absorber assembly to the flask. Continue the addition of 5 mL portions of hydrochloric acid and the decantations, if necessary, until all of the zinc sample is dissolved. Disconnect the tubing from the generator flask, and transfer the silver diethyldithiocarbamate solution to a suitable color-comparison tube. Any red color in the silver diethyldithiocarbamate solution of the sample should not exceed that in a control prepared with 3 g of the zinc sample and containing 0.001 mg of arsenic ion (As).
Iron and Lead (By flame AAS, [Part 2: Trace and Ultratrace Elemental Analysis; Atomic Absorption Spectroscopy; Analysis; Procedure for Flame AAS]).
For the Determination of Iron and Lead
S a m p l e S t o c k S o l u t i o n . Dissolve 10.0 g of sample in 75 mL of (1:1) nitric acid. When dissolution is nearly complete, add 5 mL of nitric acid, and heat to boiling, or until any residue from the zinc is dissolved. Cool, transfer with water to a 100 mL volumetric flask, and dilute to the mark with water (1 mL = 0.1 g).
For the Determination of Iron and Lead
Element
Wavelength (nm)
Sample Wt (g)
Standard Added (mg)
Flame Type*
Background Correction
Fe
248.3
1.0
0.05; 0.1
A/A
Yes
Pb
217.0
1.0
0.05; 0.1
A/A
Yes
*A/A is air/acetylene.
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4425 ACS Reagent Chemicals, Part 4
