Potassium tetroxalate

For the secondary pH reference standards, the buffer value is 0.070 for potassium tetroxalate and 0.09 for calcium hydroxide. 

To prepare the standard pH buffer solutions recommended by the National Bureau of Standards (U.S.), the indicated weights of the pure materials in Table 8.15 should be dissolved in water of specific conductivity not greater than 5 micromhos. The tartrate, phthalate, and phosphates can be dried for 2 h at 100°C before use. Potassium tetroxalate and calcium hydroxide need not be dried. Fresh-looking crystals of borax should be used. Before use, excess solid potassium hydrogen tartrate and calcium hydroxide must be removed. Buffer solutions pH 6 or above should be stored in plastic containers and should be protected from carbon doxide with soda-lime traps. The solutions should be replaced within 2 to 3 weeks, or sooner if formation of mold is noticed. A crystal of thymol may be added as a preservative. 

Potassium tetroxalate (2H2O) [127-96-8] M 358.3. Crystd from water below 50°. Dried below 60° at atmospheric pressure. 

M Potassium Tetroxalate Potassium Hydrogen Tartrate" 0.01 M Potassium Tartrate 0.05 M Potassium Hydrogen Phthalate 0.025 M k2hpo4+ 0.02 M NaH2P04 0.01 M Na2B407 Ca(OH)2"... 

Potassium Tetroxalate, KOOC—COOH HOOC—COOH 2H2O.— This salt is also known commercially as salt of sorrel. The salts of oxalic acid with the alkali metals are more soluble in water than the free acid itself. Both the salts and the free acid dissolve iron rust and iron inks and are often used for the purpose of removing such substances from cloth. 

Table 18. Some dimensions in ammonium tetroxalate neutron eUffracfion results). Some dimensions in potassium tetroxalate (By X-rays) are added for comparison...

Potassium tetroxalate. See Potassium tetraoxalate Potassium thiocyanate CAS 333-20-0 EINECS/ELINCS 206-370-1 Synonyms Potassium isothiocyanate Potassium rhodanate Potassium rhodanide Potassium sulfocyanate Potassium thiocyanide... 

Sodium tetraborate, Na2B407, dissociates to form an equimolar concentration of metaboric acid, HBO2, and metaborate ion, B02, estabhshing such a reproducible hydrogen ion concentration in the solution that this material is used as a primary standard in pH measurement. (This interpretation is oversimplified account should also be taken of the tendency of boric acid and borate ion to form concentration-dependent polymers.) Another example is potassium tetroxalate which is an equimolar mixture of potassium hydrogen oxalate and oxalic acid. 

A practical limitation of a different kind arises in measurements when the pH is less than 3 or more than 11. The hquid junction potential of the common pH cell shows a great variability under these conditions, preventing, for example, the use of potassium tetroxalate (pH = 1.675 at 20°C) as a primary pH standard. 

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