Monograph pubs.acs.org/doi/book/10.1021/acsreagents
Hydrofluoric Acid 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 Hydrofluoric Acid provides, in addition to common physical constants, a general description including typical appearance, applications, aqueous solubility, density, and pKa. The monograph also details the following specifications and corresponding tests for verifying that a substance meets ACS Reagent Grade specifications including: Assay, Fluosilicic Acid, Residue after Ignition, Chloride, Phosphate, Sulfate, Sulfite, Arsenic, Copper and Iron, and Heavy Metals.
HF
Formula Wt 20.01
CAS No. 7664-39-3
GENERAL DESCRIPTION Typical appearance Applications . . . . . Aqueous solubility . Density . . . . . . . . pKa . . . . . . . . . .
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clear liquid determination of silicon dioxide miscible 1.15 3.1
SPECIFICATIONS Assay . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48.0–51.0% HF Maximum Allowable Fluosilicic acid (H2SiF6). . . . . . . . . . . . . . . . . 0.01% Residue after ignition. . . . . . . . . . . . . . . . . . 5 ppm Chloride (Cl) . . . . . . . . . . . . . . . . . . . . . . . 5 ppm Phosphate (PO4) . . . . . . . . . . . . . . . . . . . . . 1 ppm Sulfate and sulfite (as SO4) . . . . . . . . . . . . . . 5 ppm Arsenic (As) . . . . . . . . . . . . . . . . . . . . . . . . 0.05 ppm Copper (Cu) . . . . . . . . . . . . . . . . . . . . . . . . 0.1 ppm Iron (Fe) . . . . . . . . . . . . . . . . . . . . . . . . . . 1 ppm Heavy metals (as Pb) . . . . . . . . . . . . . . . . . . 0.5 ppm
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4165 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
TESTS Assay (By acid–base titrimetry). Tare a stoppered plastic flask containing about 25 mL of water, and deliver about 1.5 mL of sample under the water surface, using a plastic pipette. Weigh accurately, wash down the sides, and dilute the solution to 50–60 mL with water. Add 0.15 mL of phenolphthalein indicator solution, and titrate with 1 N sodium hydroxide volumetric solution. One milliliter of 1 N sodium hydroxide corresponds to 0.02001 g of HF.
Fluosilicic Acid Weigh about 37.5 g (33 mL) into a large platinum dish. Add 2 g of potassium chloride and 3 mL of hydrochloric acid, and evaporate to dryness on a hot plate (~100 °C) in a fume hood. Wash down the sides of the dish with a small amount of water, add 3 mL of hydrochloric acid, and repeat the evaporation. Dissolve the residue in about 100 mL of water, cool to 0 °C, and add 0.15 mL of phenolphthalein indicator solution. Neutralize any free acid with 0.1 N sodium hydroxide solution to a colorless end point, keeping the temperature of the solution near 0 °C. Heat the solution to boiling, and titrate with 0.1 N sodium hydroxide solution. One milliliter of 0.1 N sodium hydroxide corresponds to 0.0036 g of fluosilicic acid.
The chemistry of this method involves the replacement of the six fluorides with four hydroxide ions. For additional information, see Welcher, F.J., 1963.
Residue after Ignition [Part 2: Gravimetric Methods; Residue after Ignition]. To 200 g (180 mL) in a tared, preconditioned platinum dish, add 0.05 mL of sulfuric acid, evaporate as far as possible on a hot plate (~100 °C) in the hood, heat gently to volatilize the excess sulfuric acid, and ignite.
Chloride Add 1.8 mL to 45 mL of water, filter if necessary through a chloride-free filter, and add 1 mL of nitric acid and 1 mL of silver nitrate reagent solution. Any turbidity should not exceed that produced by 0.01 mg of chloride ion (Cl) in an equal volume of solution containing the quantities of reagents used in the test.
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For the Determination of Phosphate, Sulfate and Sulfite, Arsenic, Copper and Iron, and Heavy Metals
S a m p l e S o l u t i o n A . In a fume hood, to 500.0 g (425 mL) sample in a platinum or Teflon dish, add 10 mg of sodium carbonate, and evaporate to dryness on a hot plate (~125 °C). Cool, add 5 mL of hydrochloric acid, evaporate to dryness. Cool, add 5 mL of water, evaporate to dryness. To the residue, add three 10 mL portions of (1:9) hydrochloric acid, transfer to a 50 mL volumetric flask, and dilute to the mark with water (1 mL = 10.0 g).
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4165 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
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Phosphate
To 2.0 mL (20.0 g) of sample solution A, add 25 mL of approximately 0.5 N sulfuric acid, 1 mL of ammonium molybdate–sulfuric acid reagent solution, and 1 mL of 4-(methylamino)phenol sulfate reagent solution. Allow to stand for 2 h at room temperature. Any blue color should not exceed that produced by 0.02 mg of phosphate ion (PO4) in an equal volume of solution containing the quantities of reagents used in the test.
Sulfate and Sulfite† To 1.0 mL (10.0 g) of sample solution A in a beaker, add 1 mL of 30% hydrogen peroxide. Evaporate to dryness on a hot plate (~100 °C) in a fume hood, wash down the sides of the dish with a small volume of water, and add 3 mL of perchloric acid. Evaporate to about 1 mL, dilute with about 15 mL of water, and add 0.15 mL of phenolphthalein indicator solution. Neutralize with ammonium hydroxide, dilute with water to 20 mL, and add 2 mL of dilute hydrochloric acid (1:19) and 2 mL of 12% barium chloride reagent solution. Any turbidity should not exceed that produced by 0.05 mg of sulfate ion (SO4) in an equal volume of solution containing the quantities of reagents used in the test. Compare 10 min after adding the barium chloride to the sample and standard solutions.
Arsenic† To 4.0 mL (40.0 g sample) of sample solution A in a dish, add 5 mL of sulfuric acid and 5 mL of hydrochloric acid, swirling the beaker gently after each addition. Allow to stand at room temperature for 5 min. Evaporate in a hood in a sand bath to dense fumes of sulfur trioxide. Cool, wash down the sides of the beaker with 15–20 mL of water, and evaporate again in a sand bath to dense fumes of sulfur trioxide. Cool, and transfer to a 125 mL generator flask, rinsing the beaker thoroughly with water. Place the flask on a hot plate, evaporate to dense fumes of sulfur trioxide, add sulfuric acid if necessary to make a volume of about 4 mL, and cool. Add 50 mL of water, 2 mL of 16.5% potassium iodide solution, and 0.5 mL of 40% stannous chloride reagent solution, and mix. Proceed as described in the general method for arsenic in [Part 2: Colorimetry and Turbidimetry; Arsenic; Procedure for Arsenic], starting with the second sentence, which begins “Allow the mixture to stand…” Any red color in the silver diethyldithiocarbamate solution of the sample should not exceed that in a standard containing 0.002 mg of arsenic ion (As).
Copper and Iron† (By flame AAS, [Part 2: Trace and Ultratrace Elemental Analysis; Atomic Absorption Spectroscopy; Analysis; Procedure for Flame AAS]). To three 10.0 mL portions of sample solution A (100.0 g sample) in a 25 mL volumetric flask, add 5 mL of (1:1) hydrochloric acid to each, and add standards as per the following table to second and third flasks, respectively. For the Determination of Copper and Iron
Element
Wavelength (nm)
Sample Wt (g)
Standard Added (mg)
Flame Type*
Background Correction
Cu
324.8
100.0
0.01; 0.02
A/A
Yes
Fe
248.3
100.0
0.10; 0.20
A/A
Yes
*A/A is air/acetylene.
Heavy Metals† [Part 2: Colorimetry and Turbidimetry; Heavy Metals (as Lead); Procedure for Heavy Metals, Method 1]. Take 4.0 mL (40.0 g) of sample solution A, and dilute to 25 mL with water. Solution color should not exceed the control solution of 0.02 mg of lead.
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4165 ACS Reagent Chemicals, Part 4
