Disodium phosphate

• Sodium hydrogen phosphate
• Di - sodium phosphate
• Disodium hydrogen orthophosphate

Colorless crystalline substance

Fixed

1.52 g · cm -3 ( at 20 ° C)

> 250 ° C (decomposition, anhydrous) 93 ° C (crystal dehydration, dihydrate) 48 ° C (crystal dehydration, heptahydrate ) 35 ° C (crystal dehydration, dodecahydrate )

Poorly in water ( 77 g · l-1 at 20 ° C)

17,000 mg · kg -1 ( LD50, rat, oral)

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Disodium hydrogen phosphate is a sodium salt of phosphoric acid. It is also referred to as secondary sodium phosphate.

Properties

Anhydrous disodium hydrogen phosphate is a colorless, crystalline, hygroscopic compound. Addition of the anhydrous compound three hydrates are known:

• Dihydrate ( Na2HPO4 · 2 H2O)
• Heptahydrate ( Na2HPO4 · 7 H2O)
• Dodecahydrate ( Na2HPO4 · 12 H2O)

One mole of anhydrous disodium hydrogen phosphate takes from the air on 2 moles of water, and bind them as water of crystallization. The higher hydrates, however weather on air for the dihydrate. This stability of the dihydrate is also the reason for its choice as a buffer substance. When heating is first surrendered everything crystal water ( dodecahydrate at 35 ° C, heptahydrate at 48 ° C and dihydrate at 92.5 ° C), then ( at about 250 ° C) but also - of two molecules - another water molecule, whereby a pyrophosphate is formed.

Synthesis

Laboratory sodium hydrogen phosphate can be prepared from sodium hydroxide and phosphoric acid.

Use

Disodium hydrogen phosphate is in molecular biology and biochemistry, for the preparation of the buffer solutions used. Can be prepared with disodium hydrogen phosphate - sodium dihydrogen phosphate buffer solution, a certain pH 5-8 by mixing. Furthermore, it is a component of some drugs as a pH buffer.

In the food industry, disodium hydrogen phosphate is used as a complexing agent, acidity regulator and melting salt. It is approved together with sodium dihydrogen phosphate and sodium phosphate in the EU as a food additive under the joint number E 339 ( " sodium phosphates " ) for certain foods, each with different maximum quantity restrictions. After the additive approval regulations are the - for most approved phosphates largely uniform - individual specifications for a wide range with many different types of food. The approved maximum amounts vary from 0.5 to 50 grams per kilogram ( in creamer for ATM), or even the lack of a fixed restriction ( quantum satis - as necessary nutritional supplements and partly in chewing gum ). Phosphorus is in hyperactivity suspected of causing allergic reactions and osteoporosis. It was determined an allowable daily dose of 70 milligrams per kilogram of body weight for the total amount of recorded phosphoric acid and phosphates.