Monograph pubs.acs.org/doi/book/10.1021/acsreagents
Sodium Fluoride 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 Sodium Fluoride provides, in addition to common physical constants, a general description including typical appearance, applications, change in state (approximate), and aqueous solubility. The monograph also details the following specifications and corresponding tests for verifying that a substance meets ACS Reagent Grade specifications including: Assay, Insoluble Matter, Loss on Drying, Chloride, Titrable Acid, Titrable Base, Sodium Fluosilicate, Sulfate, Sulfite, Heavy Metals, Iron, and Potassium.
NaF
Formula Wt 41.99
CAS No. 7681-49-4
GENERAL DESCRIPTION Typical appearance . . . . . . . . Applications . . . . . . . . . . . . . Change in state (approximate) . Aqueous solubility . . . . . . . . .
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white solid sequestering agent melting point, 990 °C 4.3 g in 100 mL at 25 °C
SPECIFICATIONS Assay . . . . . . . . . . . . . . . . . . . . . . . . . . . . ≥99% NaF
Insoluble matter . . . . . . . . Loss on drying . . . . . . . . . Chloride (Cl) . . . . . . . . . . Titrable acid . . . . . . . . . . Titrable base . . . . . . . . . . Sodium fluosilicate (Na2SiF6) Sulfate (SO4) . . . . . . . . . . Sulfite (SO2) . . . . . . . . . . .
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© 2017 American Chemical Society
Maximum Allowable 0.02% 0.3% 0.005% 0.03 meq/g 0.01 meq/g 0.1% 0.03% 0.005%
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DOI:10.1021/acsreagents.4347 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
Heavy metals (as Pb) . . . . . . . . . . . . . . . . . . 0.003% Iron (Fe) . . . . . . . . . . . . . . . . . . . . . . . . . . 0.003% Potassium (K) . . . . . . . . . . . . . . . . . . . . . . . 0.02%
TESTS Assay (By indirect acid–base titrimetry). Weigh, to the nearest 0.1 mg, about 1.6 g of sample into a 100 mL volumetric flask. Dissolve, and dilute to the mark with water. Dilute 10.0 mL of the diluted sample with water to 50 mL. Pass the solution through a cation-exchange column [Part 2: Titrimetric Methods; Ion-Exchange Column Assays; Method for Ion-Exchange Column Assays] at a rate of about 5 mL/min, and collect the eluate in a 500 mL titration flask. Then wash the resin in the column with water at a rate of about 10 mL/ min, and collect in the titration flask. Add 0.15 mL of phenolphthalein indicator solution to the flask, and titrate with 0.1 N sodium hydroxide. Continue the titration, as the washing proceeds, until 50 mL of eluate requires no further titration. One milliliter of 0.1 N sodium hydroxide corresponds to 0.004199 g of NaF.
Note: All water used in the assay must be carbon dioxide- and ammonia-free.
Insoluble Matter [Part 2: Gravimetric Methods; Insoluble Matter]. Use 3.5 g dissolved in 100 mL of warm water in a platinum dish.
Loss on Drying Weigh accurately about 1 g in a tared, preconditioned platinum dish or crucible, and dry to constant weight at 150 °C.
Chloride [Part 2: Colorimetry and Turbidimetry; Chloride]. Dissolve 1.0 g plus 1 g of boric acid in 80 mL of water, filter if necessary through a chloride-free filter, and dilute with water to 100 mL. Use 20 mL of this solution.
Titrable Acid Dissolve 2.0 g in 50 mL of water (free from carbon dioxide) in a platinum dish, add 10 mL of a saturated solution of potassium nitrate, cool the solution to 0 °C, and add 0.15 mL of phenolphthalein indicator solution. If a pink color is produced, omit the titration for free acid, and reserve the solution for the test for titrable base. If no pink color is produced, titrate with 0.01 N sodium hydroxide until the pink color persists for 15 s while the temperature of the solution is near 0 °C. Not more than 6.0 mL of the 0.01 N sodium hydroxide should be required. Reserve the solution for the test for sodium fluosilicate.
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4347 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
Titrable Base If a pink color was produced in the solution prepared in the test for titrable acid, add 0.01 N hydrochloric acid, stirring the liquid only gently, until the pink color is discharged. Not more than 2.0 mL of the acid should be required. Reserve the solution for the test for sodium fluosilicate.
Sodium Fluosilicate Heat the solution reserved from one of the preceding tests to boiling, and titrate while hot with 0.01 N sodium hydroxide until a permanent pink color is obtained. Not more than 4.3 mL of the sodium hydroxide should be required.
Sulfate [Part 2: Colorimetry and Turbidimetry; Sulfate; Procedure for Sulfate, Method 2]. Evaporate 0.17 g with 2 mL of hydrochloric acid in a platinum or Teflon dish. Repeat the evaporation four more times.
Sulfite Dissolve 8.0 g in 150 mL of water, and add 2 mL of hydrochloric acid and 0.25 mL of starch indicator solution. Titrate immediately with 0.01 N iodine. Not more than 1.0 mL of the 0.01 N iodine should be required to produce a blue color.
Heavy Metals [Part 2: Colorimetry and Turbidimetry; Heavy Metals (as Lead); Procedure for Heavy Metals, Method 1]. Dissolve 1.0 g in about 25 mL of water, and dilute with water to 30 mL. Use 25 mL to prepare the sample solution, and use the remaining 5.0 mL to prepare the control solution. Use pH paper to adjust the pH.
Iron Dissolve 0.50 g of sample in 20 mL of water in a 100 mL beaker. Prepare the standards containing 0.01 and 0.015 mg of iron ion (Fe), respectively, and dilute each to 25 mL with water. To each solution, add in the order specified, 15 mL of 4% boric acid, 3 mL of hydrochloric acid, 30–50 mg of ammonium persulfate, and 3 mL of ammonium thiocyanate reagent solution, mixing after each addition. Any red color in the sample must not exceed that of the 0.015 mg standard solution (0.003%).
Potassium (By flame AAS, [Part 2: Trace and Ultratrace Elemental Analysis; Atomic Absorption Spectroscopy; Analysis; Procedure for Flame AAS]).
For the Determination of Potassium
S a m p l e S t o c k S o l u t i o n . Dissolve 1.0 g of sample with water in a 100 mL volumetric flask, and dilute to the mark with water (1 mL = 0.01 g).
For the Determination of Potassium
Element
Wavelength (nm)
Sample Wt (g)
Standard Added (mg)
Flame Type*
Background Correction
K
766.5
0.10
0.02; 0.04
A/A
No
*A/A is air/acetylene.
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4347 ACS Reagent Chemicals, Part 4
