Potassium sodium tartrate tetrahydrate, C4H4KNaO6·4H2O as weighed (Hill order), has a formula weight of 282.218 g/mol. 25.53 percent of that mass is water of crystallisation; the anhydrous formula, C4H4KNaO6, is 210.158 g/mol.
Weigh the form on your label, and if the label or certificate gives a formula weight, use that. A hydrate and its anhydrous form are not interchangeable: the same mass of each holds a different amount of substance.
Read the supplier's safety data sheet before you handle this reagent.
Molar mass is the SI name for this quantity; formula weight is the usual term for a salt or a hydrate, and labels and searches usually say molecular weight. On this page all three mean the mass of one mole of the formula as written, in grams per mole.
Atomic weights are the CIAAW standard values, with the conventional value for elements whose atomic weight varies in nature, such as hydrogen, carbon, sulfur, chlorine and lithium. The last decimal place is arithmetic, not measured precision: a real sample's formula weight can differ in the second decimal place, and by more for lithium salts.
The molarity calculator is open below in Drybench Calc with this reagent chosen; it shows the formula weight to two decimal places. Enter your concentration and volume there; nothing you do here is saved unless you save it.
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Potassium sodium tartrate tetrahydrate in the molarity calculator
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Not medical advice. For research and education only, and not medical advice: the stock, dilution and buffer calculations here are not for dosing or clinical preparation.
Element composition, as weighed
Element
Mass percent
C
17.02
H
4.29
K
13.85
Na
8.15
O
56.69
Making a solution
For a molar concentration, mass = concentration × volume × formula weight, assuming the reagent is pure; dissolve, then make up to the final volume. The calculator above uses this formula weight. The conversions below are arithmetic on this formula weight, not example stocks.
Mass for a concentration, by arithmetic
For Potassium sodium tartrate tetrahydrate as weighed (C4H4KNaO6·4H2O, 282.218 g/mol), the table converts between concentration and mass of solid per volume of final solution. It is arithmetic on the formula weight (mass = concentration × volume × formula weight), assuming a pure reagent made up to volume, and nothing else: it does not say whether Potassium sodium tartrate tetrahydrate dissolves at any of these concentrations, in what solvent, at what temperature, or what the pH would be. Whether a concentration can be made is a separate question, answered with a cited solubility; this page does not answer it.
Concentration
mg per mL (the same number in g per L)
1 mM
0.2822
10 mM
2.822
100 mM
28.22
1 mg/mL of Potassium sodium tartrate tetrahydrate is 3.543 mM.
Weigh the form on your label; if the label or certificate gives a formula weight, use that.
How this page was made
Computed when the site was built by the Drybench Calc formula-mass engine, version 1.0.0, from /data/lab-calculators/reagents.e8f6883588.json (built 2026-11-07) with CIAAW 2021 atomic weights. Every formula weight, percent and conversion on this page was compared with CIAAW 2021 sum in Python decimal (reference.py's transcription) (Python 3.13.18); a disagreement stops the build. PubChem's weight (read 2026-11-07) is shown as a cross-check, not as the source.