Sodium dihydrogen phosphate

Structural formula
General
Surname	Sodium dihydrogen phosphate
other names	Monosodium monophosphate Acid monosodium monophosphate Monosodium orthophosphate Sodium bisphosphate prim sodium phosphate
Molecular formula	NaH 2 PO 4
Brief description	colorless and odorless crystalline solid
External identifiers / databases
CAS number 7558-80-7 ( anhydrate ) 10049-21-5 (monohydrate) 13472-35-0 (dihydrate) PubChem 23672064 Wikidata Q415877
properties
Molar mass	119.98 g mol −1 (anhydrous) 138.00 g mol −1 (monohydrate) 156.01 g mol −1 (dihydrate)
Physical state	firmly
density	2.04 g cm −3 (monohydrate) 1.92 g / cm 3 (dihydrate)
Melting point	Decomposition> 170 ° C 100 ° C (monohydrate) release of the crystal water 60 ° C (dihydrate)
pK s value	7.21
solubility	very good in water (850 g l −1 at 20 ° C)
safety instructions
GHS labeling of hazardous substances no GHS pictograms H and P phrases H: no H-phrases P: no P-phrases
Toxicological data	> 2000 mg kg −1 ( LD 50 ,  rat ,  oral )
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Sodium dihydrogen phosphate is a colorless and odorless salt made from the ions Na ⁺ and H ₂ PO ₄ ^- .

Extraction and presentation

Like other phosphates , sodium dihydrogen phosphate is obtained from ores such as apatite .

In the laboratory, the presentation, by the neutralization of sodium hydroxide with phosphoric done:

${\displaystyle \mathrm {NaOH\ +\ H_{3}PO_{4}\longrightarrow \ NaH_{2}PO_{4}\ +\ H_{2}O} }$

The dihydrate can be crystallized in pure form from a cold water / ethanol solution .

properties

In addition to the anhydrous compound nor the contact mono hydrate (NaH ₂ PO ₄ · H ₂ O) and the dihydrate (NaH ₂ PO ₄ · 2 H ₂ O) on.

Sodium dihydrogen phosphate reacts, dissolved in water, acidic (pH 4.5 at 12 g / l, 25 ° C).

use

laxative

Sodium dihydrogen phosphate is a pharmaceutically active component of laxatives .

Pharmaceutical excipient

As a pharmaceutical excipient, sodium dihydrogen phosphate is a component of drugs that are administered in aqueous form (e.g. nasal sprays ).

Food technology

Sodium dihydrogen phosphate is used as a complexing agent , acid regulator and melting salt in food technology. Together with disodium hydrogen phosphate and sodium phosphate, it is approved in the EU as a food additive under the common number E 339 ("sodium phosphate") for certain foods, each with different maximum quantity restrictions. According to the Additive Admissions Ordinance , these are - largely uniform for most of the approved phosphates - individual specifications for a wide range of numerous different types of food. The maximum permitted amounts vary from 0.5 to 50 grams per kilogram (in creamer for vending machines) or the lack of a fixed limit ( quantum satis - as required, for food supplements and sometimes for chewing gum). Phosphorus is suspected of causing hyperactivity , allergic reactions and osteoporosis . A permissible daily dose of 70 milligrams per kilogram of body weight was set for the total amount of phosphoric acid and phosphates ingested.

Phosphate buffer

Phosphate buffer

Sodium dihydrogen phosphate is used in biochemistry and molecular biology for the production of buffer solutions . By mixing sodium dihydrogen phosphate with disodium hydrogen phosphate solution or adding sodium hydroxide solution , a phosphate buffer with a specific pH value (pH 6–8) can be produced.

safety instructions

Sodium dihydrogen phosphate may cause slight irritation on contact with the eyes. It is not flammable, but can lead to the release of phosphorus oxides when it burns . The LD ₅₀ for rats after oral administration is 8290 mg / kg body weight. The dermal LD ₅₀ in rabbits is> 7940 mg / kg. Sodium dihydrogen phosphate is slightly hazardous to water: Water hazard class  1.

Individual evidence

1. ↑ ^{a b c d e f} Data sheet sodium dihydrogen phosphate (PDF) from Merck , accessed on December 25, 2019.
2. ↑ ^{a b c} Data sheet sodium dihydrogen phosphate (monohydrate) (PDF) from Merck , accessed on December 25, 2019.
3. ↑ ^{a b c} Data sheet sodium dihydrogen phosphate (dihydrate) (PDF) from Merck , accessed on December 25, 2019.
4. ↑ Entry on phosphoric acid. In: Römpp Online . Georg Thieme Verlag, accessed on May 29, 2014.
5. ↑ G. Brauer (Ed.), Handbook of Preparative Inorganic Chemistry 2nd ed., Vol. 1, Academic Press 1963, p. 544.