Monograph pubs.acs.org/doi/book/10.1021/acsreagents
Calcium Carbonate, Chelometric Standard 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 Calcium Carbonate, Chelometric Standard 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, corresponding tests for verifying that a substance meets ACS Reagent Grade specifications including: Assay, Insoluble in Dilute Hydrochloric Acid, Chloride, Fluoride, Sulfate, Ammonium, Heavy Metals, Iron, Barium, Magnesium, Potassium, Sodium, and Strontium.
CaCO3
Formula Wt 100.09
CAS No. 471-34-1
GENERAL DESCRIPTION Typical appearance . . . . . . . . Applications . . . . . . . . . . . . . Change in state (approximate) . Aqueous solubility . . . . . . . . .
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white solid chelometric standard decomposes, 825 °C insoluble
SPECIFICATIONS Assay (dried basis). . . . . . . . . . . . . . . . . . . . 99.95–100.05% CaCO3
Insoluble in dilute hydrochloric acid Chloride (Cl) . . . . . . . . . . . . . . . Fluoride (F) . . . . . . . . . . . . . . . . Sulfate (SO4) . . . . . . . . . . . . . . . Ammonium (NH4) . . . . . . . . . . . . Barium (Ba) . . . . . . . . . . . . . . . . Heavy metals (by ICP–OES) . . . . . . Iron (Fe) . . . . . . . . . . . . . . . . . .
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© 2017 American Chemical Society
Maximum Allowable 0.01% 0.001% 0.0015% 0.005% 0.003% 0.01% 0.001% 0.002%
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DOI:10.1021/acsreagents.4078 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
Magnesium (Mg) Potassium (K) . . Sodium (Na) . . . Strontium (Sr) .
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0.01% 0.01% 0.01% 0.01%
TESTS Assay (By complexometric titration for calcium). This method is a comparative procedure in which the calcium carbonate to be assayed is compared with NIST Standard Reference Material calcium carbonate (SRM 915). A minimum of two samples and two standards should be run according to this procedure.
Pr o c e d u r e . Dry the sample and NIST standard at 200 °C to 210 °C for 4 h. Weigh (to the nearest 0.1 mg) 0.4000 ± 0.0040 g of calcium carbonate, and place in a 400 mL beaker with a magnetic stirring bar and 50 mL of water. Cover with a watch glass, and add 12 mL of 10% hydrochloric acid with the pipette tip under the watch glass. Wash down the watch glass and the sides of the beaker. All of the sample must be dissolved. Weigh (to the nearest 0.1 mg) 1.4400 ± 0.0100 g of EDTA, disodium salt dihydrate (described below) (see Note 1). Add the EDTA directly to the calcium solution, dilute to about 125 mL, and add 15 mL of 5 M potassium hydroxide (described below). This addition should dissolve all the EDTA and leave a clear solution. Add 0.05–0.10 mL of 0.02% calcein indicator solution (described below), and titrate the excess calcium with 0.0200 M EDTA under UV illumination in a dark room or box (see Note 2). The end point is extremely sharp from a bright yellow-green fluorescence to black.
Note 1. This method is independent of the quality of the disodium EDTA used, but it is recommended that reagentquality material be selected, then crushed, and mixed thoroughly before use. Do not dry the EDTA, because water loss will change the proportions needed for the test. A disodium EDTA dihydrate having an assay of 99.9–100.1% is commercially available. ACS Reagent is 99–101% and suitable for this test.
Note 2. The UV lamp should have dark blue glass (little visible light) and should be placed at a right angle to the viewer, shielded from the viewer’s eyes. C a l c e i n I n d i c a t o r S o l u t i o n , 0 . 0 2 % . Dissolve 20 mg of calcein in 10 mL of water by addition of a few drops of 5 M potassium hydroxide (described below), and dilute with water to 100 mL. This solution is not stable at room temperature for more than 1 day. Frozen solutions are stable, so the indicator solution may be split into portions in plastic bottles and frozen, and a fresh bottle may be thawed as needed. E D TA , D i s o d i u m S a l t D i h y d r a t e , 0 . 0 2 M . Dissolve 7.446 g of reagent-quality (ethylenedinitrilo)tetraacetic acid disodium salt dihydrate in water, and dilute with water to 1 L. Standardize against a calcium solution prepared by dissolving 2.002 g (weighed to the nearest 0.1 mg) of NIST calcium carbonate in water by addition of 6 mL of concentrated hydrochloric acid, followed by dilution to exactly 1 L. The molarity of this solution should be calculated from the weight taken. The standardization of a 25 mL aliquot of the calcium solution will require 10 mL of 5 M potassium hydroxide (described below) and 0.05–0.10 mL of calcein indicator solution, as in the procedure cited.
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4078 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
Po t a s s i u m H y d r o x i d e , 5 M . Dissolve 56 g of potassium hydroxide in water, and dilute with water to 200 mL.
Insoluble in Dilute Hydrochloric Acid In a 400 mL beaker, add 20 g to about 200 mL of water, swirl, slowly and carefully add 40 mL of hydrochloric acid, and dilute ith water to 300 mL. Heat the solution to boiling, boil gently to expel the carbon dioxide, and digest in a covered beaker on a hot plate (~100 °C) for 1 h. Filter through a tared filtering crucible, wash thoroughly, and dry at 105 °C.
Chloride [Part 2: Colorimetry and Turbidimetry; Chloride]. Dissolve 1.0 g in 10 mL of water plus 2 mL of nitric acid, filter if necessary through a small chloride-free filter, wash with hot water, and dilute with water to 20 mL.
Fluoride Dissolve 1.0 g in 50 mL of water and 25 mL of 1 N hydrochloric acid in a 250 mL beaker. For the standards, add 1.0, 2.0, 3.0, 5.0, 10.0, and 15.0 mL of standard fluoride solution to 250 mL glass beakers containing 50 mL of water and 5 mL of 1 N hydrochloric acid. Boil the sample and six standard solutions for a few seconds, cool rapidly, and transfer to plastic beakers. To each solution, add 20 mL of 1 M sodium citrate reagent solution and 10 mL of 0.2 M (ethylenedinitrilo)tetraacetate, disodium salt dihydrate, reagent solution, and mix. If necessary, adjust the pH to 5.5 ± 0.1 with dilute hydrochloric acid (1:9) or dilute sodium hydroxide (1:9). Transfer to 100 mL volumetric flasks, dilute to the mark with water, mix, and pour into plastic beakers. For each solution, measure immediately the potential of a fluoride electrode versus a reference electrode using a pH meter with an expanded scale or an appropriate potentiometer. Plot a 2-cycle semilogarithmic calibration curve with micrograms of fluoride per 100 mL of solution on the logarithmic scale. Determine the concentration of fluoride from the calibration curve.
Sulfate Cautiously dissolve 2.0 g of sample with 15 mL of (1:1) hydrochloric acid in a 100 mL beaker. Add 0.05 mL of bromine water, and evaporate to dryness. Dissolve the residue in 5 mL of water, and evaporate to dryness. Dissolve the residue in 15 mL of water, add 1 mL of (1:19) hydrochloric acid, and filter through a small, washed filter paper. Add two 3 mL portions of water to the same filter. For the control, take 0.10 mg of sulfate ion (SO4) in 15 mL of water, and add 1 mL of (1:19) hydrochloric acid. Dilute both solutions to 25 mL, add 1 mL of 12% barium chloride reagent solution, and mix. Compare after 10 min. Sample turbidity should not exceed that of the control solution.
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For the Determination of Ammonium, Heavy Metals, and Iron
S a m p l e S o l u t i o n A . In a 400 mL beaker, cautiously dissolve 20 g in 100 mL of dilute hydrochloric acid (1:1), and evaporate on a hot plate (~100 °C) to dryness or a moist residue. Dissolve the residue in about 100 mL of water, filter, and dilute with water to 200 mL in a volumetric flask (1 mL = 0.10 g).
Ammonium† Dilute 10 mL (1 g sample) of sample solution A with water to 80 mL, add 20 mL of 10% sodium hydroxide reagent solution, stopper, mix well, and allow to stand for 1 h. Decant 50 mL through a filtering crucible that has been washed with 10% sodium hydroxide reagent solution, and add to the filtrate 2 mL of Nessler reagent. Any color should not exceed that produced by 0.015 mg of ammonium ion (NH4) in an equal volume of solution containing the quantities of reagents used in the test.
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4078 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
Heavy Metals
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([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 1.0 g sample.
Iron† [Part 2: Colorimetry and Turbidimetry; Iron; Procedure for Iron, Method 1 (Ammonium Thiocyanate)]. Use 5.0 mL of sample solution A (0.5 g sample).
Barium, Magnesium, Potassium, Sodium, and Strontium (By flame AAS, [Part 2: Trace and Ultratrace Elemental Analysis; Atomic Absorption Spectroscopy; Analysis; Procedure for Flame AAS]).
For the Determination of Barium, Magnesium, Potassium, Sodium, and Strontium
S a m p l e S t o c k S o l u t i o n B . Cautiously dissolve 10.0 g of sample in 50 mL of nitric acid (1:3), transfer to a 100 mL volumetric flask, and dilute to the mark with water (1 mL = 0.10 g). S a m p l e S t o c k S o l u t i o n C . Transfer 5.0 mL (0.50 g) of sample stock solution B to a 100 mL volumetric flask, and dilute to the mark with water (1 mL = 0.005 g).
For the Determination of Barium, Magnesium, Potassium, Sodium, and Strontium
Element
Wavelength (nm)
Sample Wt (g)
Standard Added (mg)
Flame Type*
Background Correction
Ba
553.6
2.0
0.10; 0.20
N/A
No
Mg
285.2
0.10
0.01; 0.02
A/A
Yes
K
766.5
0.50
0.05; 0.10
A/A
No
Na
589.0
0.10
0.01; 0.02
A/A
No
Sr
460.7
0.10
0.10; 0.20
N/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.4078 ACS Reagent Chemicals, Part 4
