Monograph pubs.acs.org/doi/book/10.1021/acsreagents
Potassium Carbonate Sesquihydrate 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 Potassium Carbonate Sesquihydrate provides, in addition to common physical constants, a general description including typical appearance and applications. The monograph also details the following specifications and corresponding tests for verifying that a substance meets ACS Reagent Grade specifications including: Assay, Loss on Heating at 285 °C, Insoluble Matter, Chloride, Phosphate, Silica, Sulfur Compounds, Heavy Metals, Iron, Calcium, Magnesium, and Sodium.
K2CO3•1.5H2O
Formula Wt 165.22
CAS No. 6381-79-9
GENERAL DESCRIPTION Typical appearance . . . . . . . . . . . . . . . . . . . white solid Applications . . . . . . . . . . . . . . . . . . . . . . . . invert sugar test; buffer
SPECIFICATIONS Assay . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98.5–101.0% K2CO3 · 1.5H2O Loss on heating at 285 °C . . . . . . . . . . . . . . . 14.0–16.5% Maximum Allowable Insoluble matter . . . . . . . . . . . . . . . . . . . . . 0.01% Chloride (as Cl). . . . . . . . . . . . . . . . . . . . . . 0.003% Phosphate (PO4) . . . . . . . . . . . . . . . . . . . . . 0.001% Silica (SiO2) . . . . . . . . . . . . . . . . . . . . . . . . 0.005% Sulfur compounds (as SO4). . . . . . . . . . . . . . . 0.004% Heavy metals (by ICP–OES) . . . . . . . . . . . . . . 5 ppm Iron (Fe) . . . . . . . . . . . . . . . . . . . . . . . . . . 5 ppm Calcium (Ca) . . . . . . . . . . . . . . . . . . . . . . . 0.005% Magnesium (Mg) . . . . . . . . . . . . . . . . . . . . . 0.002% Sodium (Na) . . . . . . . . . . . . . . . . . . . . . . . . 0.02%
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4281 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
TESTS Assay (By acidimetric titration of carbonate). Weigh accurately about 3.3 g, and dissolve in 50 mL of water. Add 0.15 mL of methyl orange indicator solution, and titrate with 1 N hydrochloric acid volumetric solution to the change from yellow to orange. One milliliter of 1 N hydrochloric acid corresponds to 0.08262 g of K2CO3 · 1.5H2O.
Loss on Heating at 285 °C Weigh accurately about 2.0 g, and heat in a tared, preconditioned container to constant weight at 270–300 °C.
Insoluble Matter [Part 2: Gravimetric Methods; Insoluble Matter]. Use 10.0 g dissolved in 100 mL of water.
Chloride Dissolve 1.0 g in about 40 mL of water plus 6 mL of nitric acid. Filter through a chloride-free filter, wash, and dilute the filtrate with water to 60 mL. To 20 mL, add 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.
Phosphate [Part 2: Colorimetry and Turbidimetry; Phosphate; Procedure for Phosphate, Method 2 (Extracted Molybdenum Blue)]. Dissolve 1.0 g in 50 mL of water in a platinum dish, and digest on a hot plate (~100 °C) for 30 min. Cool, neutralize with dilute sulfuric acid (1:19) to a pH of about 4, and dilute with water to about 75 mL. Add 0.5 g of ammonium molybdate to the solution, and when it is dissolved, adjust the pH to 1.8 (using a pH meter) with dilute hydrochloric acid (1:9). Heat the solution to boiling, cool to room temperature, add 10 mL of hydrochloric acid, and dilute with water to 100 mL. Proceed as described. Carry along a standard containing 0.01 mg of phosphate ion (PO4) and 0.05 mg of silica (SiO2) in about 75 mL of water treated as the 75 mL of sample solution. Reserve the aqueous phase for the determination of silica.
Silica Add 10 mL of hydrochloric acid to the solutions reserved from the determination of phosphate, and transfer to separatory funnels. Add 40 mL of butyl alcohol, shake vigorously, and allow to separate. Draw off and discard the aqueous phase. Wash the butyl alcohol three times with 20 mL portions of dilute hydrochloric acid (1:99), discarding the washings each time. Dilute the butyl alcohol solutions to 50 mL with butyl alcohol, take 10 mL of each, and dilute each to 50 mL with butyl alcohol. Add 0.2 mL of a freshly prepared 2% stannous chloride reagent solution. The blue color in the extract from the sample should not exceed that in the control. If the butyl alcohol extracts are turbid, wash them with 10 mL of dilute hydrochloric acid (1:99).
Sulfur Compounds [Part 2: Colorimetry and Turbidimetry; Sulfate; Procedure for Sulfate, Method 4]. Cautiously acidify with hydrochloric acid. Allow 30 min for turbidity to form.
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4281 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
Heavy Metals ([Part 2: Trace and Ultratrace Elemental Analysis; Inductively Coupled Plasma−Optical Emission Spectroscopy (ICP–OES); Calculation of Heavy Metals (by ICP–OES) Results], by ICP–OES). Use 2.0 g sample.
Iron [Part 2: Colorimetry and Turbidimetry; Iron; Procedure for Iron, Method 1 (Ammonium Thiocyanate)]. Dissolve 2.0 g in 20 mL of dilute hydrochloric acid (1:1), and evaporate to dryness on a hot plate (~100 °C). Dissolve the residue in 5 mL of dilute hydrochloric acid (1:1), and again evaporate to dryness. Dissolve the residue in 50 mL of dilute hydrochloric acid (1:24), and use the solution without further acidification. Use the residue from evaporation of 15 mL of hydrochloric acid to prepare the standard.
Calcium, Magnesium, and Sodium (By flame AAS, [Part 2: Trace and Ultratrace Elemental Analysis; Atomic Absorption Spectroscopy; Analysis; Procedure for Flame AAS]).
For the Determination of Calcium, Magnesium, and Sodium
S a m p l e S t o c k S o l u t i o n . Dissolve 5.0 g of sample with water in a 100 mL volumetric flask, and dilute to the mark with water (1 mL = 0.05 g).
For the Determination of Calcium, Magnesium, and Sodium
Element
Wavelength (nm)
Sample Wt (g)
Standard Added (mg)
Flame Type*
Background Correction
Ca
422.7
0.50
0.025; 0.05
N/A
No
Mg
285.2
0.50
0.01; 0.02
A/A
Yes
Na
589.0
0.05
0.01; 0.02
A/A
No
*A/A is air/acetylene; N/A is nitrous oxide/acetylene.
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4281 ACS Reagent Chemicals, Part 4
