Citric acid

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Citric acid
Chemical formula C6H8O7
OTP appearance white solid 
Molar Mass(g/mol) 192 
Melting Point(°C) 156 
Boiling Point(°C) 310 
Density(g/cc) 1.665 
Index of refraction 1.49-1.51 
Solubility in water(g/L) 1477 
Solubility in ethanol(g/L) 489
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Citric acid is the tangy component of citrus fruit juice. It is an important acid medicinally because most of its conjugate bases can be digested. The pKa of the first three hydrogens are 3.13, 4.76, and 6.4

Uses

Primary

Other

  • Prevents coagulation of stored blood.

Natural Occurrence

  • Occurs naturally in virtually all life on earth
  • High concentrations in citrus fruit such as lemons
  • Can be produced by aspergillus niger as well

Hazards

Production

Synthesis

  • Combine calcium citrate with Sulfuric acid
    Ca3(C6H5O7)2 + 3 H2SO4 2 C6H8O7 + 3 CaSO4
  • Would phosphoric acid work as well?
    3 Ca3(C6H5O7)2 + 9 H3PO4 6 C6H6O7 + 5 CaHPO4 + 4 CaH4PO4
  • Would carbon dioxide work as well?
    4 Ca3(C6H5O7)2 + 18 CO2 + 7 H2O 12 CaCO3 + 9 C6H6O7

Extraction

from citrus juice

  1. Prepare filtered citrus juice
  2. Add sodium hydroxide until pH is 9, producing sodium citrate along with some sodium ascorbate
  3. Filter and discard residue
  4. Add an appropriate amount of saturated calcium chloride solution to the filtrate
  5. Heat the solution. This starts the reaction and gives sodium chloride and a precipitate
  6. Filter and discard filtrate.
  7. Wash residue with hot water. The washed residue is of calcium citrate. along with some calcium ascorbate
  8. Get the mass the residue to estimate moles
  9. Add dilute sulfuric acid to the solution precipitating calcium sulfate and leaving a solution of citric acid and ascorbic acid
  10. Separate the acids by fractional crystallization.

Purification

from Ascorbic Acid

See Also

References